:::RHMT::: Real Home Made Turbo
General Category => Engine Management => Topic started by: TTC on August 18, 2010, 09:36:27 PM
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I'm having a discussion on an mr2 board about tuning and such. I wonder if there is much truth to a statement similar to this.
"I would be REALLY surprised to find out you could even get close to MBT on anything considered "pump gas". You are usually OK running as much timing as you can in the boosted areas of your map as long as you don't run into knock issues (assuming reasonable AFR). In fact, I would think that if trying to run "high" boost on pump gas you are usually more worried about high EGT from retarded timing that is necessary to run higher boost on pump."
I was stating how i wanted to view someone elses 300whp map to give me an idea of what kind of timing they got away with as a baseline for street tuning. My plan was to knock of a few degrees off there map and keep adding till the trap speeds stopped increasing. I assumed this was somewhere in and around MBT.
Anyway, turned into a bit of a flamewar lol.
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Let me preface my statement concerning why MR2 people are stupid by stating I tuned the car that holds stock 3S-GTE head power record @ 416 whp. There was more in the car but it the wastegate was a piece of shit.
Now, MR2 people are stupid because they believe everything they are told by 3-4 people who supposedly know everything MR2, and no one else in the world can fathom a piston going up and down because 3S are magically different. Some of these 3-4 people believe 3S oil pumps don't go bad, among other horseshit, and they all love Nemesis which is a self-corrupting non error checking pile of interface fail whose designer claims the firmware can't get corrupted by simply tuning the box despite it happening to me twice (although they run top notch if you can get through a tune without bricking the unit).
Now. Tom, if you have a question feel free to ask it or start a thread for debate, but leave MR2 never done it but I heard some guy who isn't known outside of the MR2 scene horseshit on the MR2 forums.
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Whats funny, is I got my answer. JD, I might toss you an email later regarding the tuning of my car by myself and brett. I've compared my maps to many others whom are dyno tuned and shit. Now I know its apples and oranges comparing tunes on different cars n shit, but I have fucktons more advance in my timing map than these guys and now that im externally gated im worried it will pop. Before it wasn't an an issue since it wouldnt hold boost to redline, but now i do. I wouldnt mind a critique on your part, but in the end we both need to split on dyno time for day. I'm slowly learning this shit, its a bit of a learning curve.
20lbs 4ag will turn u out.
Ninjaedit:
Maybe you can enlighten me a bit on MBT:
From my readings I've understood that the MBT curve is basically a depiction of how there is a point in timing where if you keep adding you wont make power. At this point you lose the cooling effects of pump gas and are nearing the knock threshold. Are there different MBTs for pump and race gas? Or is it more the fact that racegas lets you travel past the MBT point without knocking, thus creating more power?
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FYI, pump gas MBT is race gas MBT until you start running out of octane. Some people are just dumb.
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Ah, ok thx. Been a productive week. I thought there was more power to be had in AFR tuning, but apparantly its not as effective as I thought.
Second Question:
If you keep pumping the boost, and retarding timing up top how do you combat the increases in EGTs from retarding timing to add more boost. MBT stays the same, but you run out of octane so you gotta retard correct?
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you can lower and raise EGT's as well by changing the fueling. If you have to lower timing and the EGT's raise, add fuel to cool it off. The trade off will be "less" power as well as less heat.
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If you keep pumping the boost, and retarding timing up top how do you combat the increases in EGTs from retarding timing to add more boost. MBT stays the same, but you run out of octane so you gotta retard correct?
No.
Dumb faggots on HT who want to make 500-550 whp on pump gas with the net result of a 9K long block that lasts one oil change will tell you that you gotta retard, but the simple truth of the matter is that when you run out of octane the only solution is adding more octane.
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If you keep pumping the boost, and retarding timing up top how do you combat the increases in EGTs from retarding timing to add more boost. MBT stays the same, but you run out of octane so you gotta retard correct?
No.
Dumb faggots on HT who want to make 500-550 whp on pump gas with the net result of a 9K long block that lasts one oil change will tell you that you gotta retard, but the simple truth of the matter is that when you run out of octane the only solution is adding more octane.
Some cars will respond a lot different to fuel changes than others. 11.0 to 12.0 change in A/F was worth 75whp in my car ~ 8% increase in power.
Also I wholeheartedly agree on the 500 pump gas retarding timing thing. Been there done that, realized how retarded I was and decided to just put the car on a 117 octane diet.
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Sounds par for course, narfy. Past 11.5:1 indicated AFR, assuming that value is repeatable and consistent between vehicles/widebands/bunch of other shit which it is not, you're smothering the burn. At your power level the difference in fuel volume between 11.5:1 and 12:1, with an eye to the volume of your combustion chamber, is significant. Also, if the engine isn't fully loaded your indicated AFR is going to be leaner than the actual masses of air and fuel entering the chamber each cycle. Kinda hard to correctly load 700+ FWD whp across a tire interface, and it's not like most cars have the traction they should at that point on the track.
So yeah, lot of special case reasons why your car isn't going to act like a 200-350 whp one. Don't you feel special??
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very
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If you keep pumping the boost, and retarding timing up top how do you combat the increases in EGTs from retarding timing to add more boost. MBT stays the same, but you run out of octane so you gotta retard correct?
No.
Dumb faggots on HT who want to make 500-550 whp on pump gas with the net result of a 9K long block that lasts one oil change will tell you that you gotta retard, but the simple truth of the matter is that when you run out of octane the only solution is adding more octane.
So really, the limiting factor is mainly octaine. Regardless of rod and piston type and all that horseshit. If you want big numbers, it wont happen safely or for long on pump. Good thing I only want 300. I'm asssuming this isn't really an issue at such a low hp level.
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Maybe yes, maybe no. You have to look at what other people have done and apply common sense to that. If other people haven't done basic experimentation to determine limits (often resulting in broken shit) then you'll have to do so. After a couple times (tuner wise) you get pretty good at spotting some of those limits before they do any damage.
OK. Most imports have carbon drop forged rods, pretty good shit. When you exceed the power limit of a rod it will 90% likely S-bend. You see this a lot in the Miata crowd at the 330-ish whp level after a short duration at that power.
Cast pistons aren't "particularly" weak if you can limit their temps. Most imports come with a pretty decent piston, but they are efficiency AND emissions engines so they go together tight to limit blowby. Proceed to make power and shit gets hot, expands more than the piston's *clearances* are designed for, and the piston starts to scrape against to bore as opposed to transferring heat to the bore like it should, and temps go up. Hot aluminum is soft aluminum, shit breaks. If p2w and ring gap are correct most OEM pistons can handle more power than Dcommon forum knowledge" says they can. Look at Vitaras, those aren't even a well designed casting but STD size is loose in the bore and CR is way down so they run cooler, and they simply work.
My gut feeling is your (4A?) can do 300 just fine. If it's a 3S and hasn't cracked a crankshaft yet it can do more.
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So, this would be off topic without that last post.
JD, what do you think the odds of a "quiet" 75.5mm vitara block holding up to 400whp are? I am wanting to build a street car that doesn't sound like a diesel and makes 400whp on 93 octane.
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I'm certain the 4ag im using is fine. I can't remember what my p2w was but i do recall it was on the looser side. The pistons are "pft semiforged' which is toyota nonsese for a nice strong cast piston. The rods are liek 2-3x the wide of a D series lol. I'm sure it will be ok, even the headgasket is stout considering its not 100% MLS.
Whats strange is ive "heard" of people running unopened stock supercharged blocks at the 300 range, yet at times the "built" blocks always seem to explode lol. I don't know if its builder issues or what, but they seem to like to pop at 300 and its often ringlands iirc. From what I have read here, ringland damage is usually heat related or detonation no?
When your are talking heat, im assuming you mean egts more-so than lets say block heat. What can I do to limit these heat issues, from what i gathered adding more and more fuel stops working at 11.5ish give or take. So, keep from retarding crazy amounts of timing to try to make more power than what my octane has to offer and dont be stupid about it. Or is it as simple as ensuring decent airflowin the bay, a good rad and a better Tstat. I know in the miata motors like ours the 4th cylinder tends to go first. I planned on doing that weird coolant reroute thing they do.
Sidenote: What is considered extremely retarded? My motor is quite similar to a miata so would 12deg be far to retarded? Its more of a theory question, since there are often so many variables.
I need to get my hands on some meth.
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When I talk heat, I mean power. Power = heat.
EGTs are a furthest extent tuning issue, and frankly if I'm not operating an engine at it's extremest limit (with regards to octane) I could really give a fuck less about EGTs. For example, in the 1500+ whp domestics you see SBF a lot less than SBC, since the Chebby bits are 1/3rd cheaper to build they are built 10 times more often and therefore have ten times the R&D put into them. This has resulted in Chebby power being very reliable in the hardcore motherfucker power level (check www.yellowbullet.com (http://) for RMHTers with six digit incomes) whereas the Fords are *very* particular about individual cylinder EGTs. Honestly, if you don't tune SBF slightly rich the imbalance appears in the 600-700 range, just not as amplified.
Broken ring lands are either tune problems or clearance problems. To a lesser extent they are shitty piston problems. With 4A having paper headgaskets, if the ring land problems are greater than headgasket problems it's likely a shitty piston.
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I'm going to go with tune/clearance. Toyota guys are scared to make loose motors from what I can tell and generally do it on the cheap which is fine, but they dont do it smart.
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I've read many a internet forum, so I feel I am uniquely qualified to speak about tuning. ;)
75mm Vitaras are loose as fuck, and relatively so for "built" Honda motors too. I've also seen people use the Nippon LS pistons at a very high power level, so I'd agree with JD's p2w statement. I also know that no coolant + idle + .0035" Wisecos = rubbing when it overheats, so I can't imagine how bad a fresh OEM-spec motor can get when making big power. We all know a properly tuned stock GSR can make a lot of power, so the worn motor p2w clearances & squirters are staving off the 2 main issues with cast pistons.
As far as octane...I think I was talking to JD or sewell about that recently. Imagine starting with a conservative tune, you make a flat 140tq from idle to redline with perfect gas and a perfect [small] motor. Add 2* (or percentage, relative to piston speed) and it jumps to 145tq. Add another 2* and it jumps to 146tq. Add another 5* and it jumps to 147tq. You're finding the MBT of that motor, so you back it off a bit. Whoever it was said pump gas generally doesn't have enough octane to get MBT on most higher-boost Hondas. Instead you tend to get knock, which people think is MBT, so they don't back off enough (if at all) and eventually their shit fails. I'd surmise that's whats going on with the 'built' motors that pop at 300hp. People think their shit doesn't stink and get too greedy with timing.
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If you are wanting some good 3s info start hitting the old toyota boards, since the 3tc is starting to become harder to find quite a few are switching to the 3s. And the ricans listen to nobody, they crank the boost till it pops, rinse repeat till they have it down.
If I ever get sick of the 3tc my starlet will be getting a 3s or 4g63 swap (probably 4g since it's much cheaper and easier to get though :-[ ).
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Whats strange is this older fellow from the deuce forum has been doing this turbo 4ag shit since like the 80s. I'm not sure how he does it, but hes runnign almost 30degrees timing at redline, whille anyone else isnt running anything close to that. So I want to knjow how the fuck is he keeping the motor from knocking.
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Whats strange is this older fellow from the deuce forum has been doing this turbo 4ag shit since like the 80s. I'm not sure how he does it, but hes runnign almost 30degrees timing at redline, whille anyone else isnt running anything close to that. So I want to knjow how the fuck is he keeping the motor from knocking.
Who says he is keeping from knocking? Could be he fuckin' deaf. ;D
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I think hes put like 60 000kms on the motor at 300whp and that kind of timing
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I think hes put like 60 000kms on the motor at 300whp and that kind of timing
If the block or head has been shaved he could be compensating for mechanical timing with ignition timing. True up the cams to the crank and id bet this small bore motor wouldn't want as much timing.
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I think hes put like 60 000kms on the motor at 300whp and that kind of timing
Free race gas :P
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Whats strange is this older fellow from the deuce forum has been doing this turbo 4ag shit since like the 80s. I'm not sure how he does it, but hes runnign almost 30degrees timing at redline, whille anyone else isnt running anything close to that. So I want to knjow how the fuck is he keeping the motor from knocking.
Who says he is keeping from knocking? Could be he fuckin' deaf. ;D
Who says he is running that sort of timing? Could be another dude with a timing advance light and no clue of how to use one.
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I have nothing to really go on except his word, he posted a few bins of his timing map.
19.7,24.6,25.0,26.0,24.6,25.3,26.4,26.4,26.7,27.1, 26.7,27.8,28.8,28.9,29.2,29,4,29.4
4800 to redline at 240kpa
This is what he says he runs, who knows if hes compensating for errors in the mounting of his ign wheels ect.
I plan on just waiting till I get to the dyno and see how it goes.
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I'm having a discussion on an mr2 board about tuning and such. I wonder if there is much truth to a statement similar to this.
which MR2 board?
edit. nevermind, i found it. that squelch guy is a real ray of fucking sunshine.
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Yeah, so you have read the thread. See how im confused, I duno how hes running so much timing. All he gives are mixed elusive answers, hes more cryptic than JD.
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dunno for sure. that's about 10deg up on what i'm running at that MAP as well. probably has the static CR of the motor significantly lower than stock, which would want... er.. be more tolerant of more timing.
i do find it odd that he's only making 307whp at 20psi of boost though. must be a pretty small turbine..
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Yeah, so you have read the thread. See how im confused, I duno how hes running so much timing. All he gives are mixed elusive answers, hes more cryptic than JD.
Long time ago I put a trigger wheel on my car which makes the timing more consistant, and I noticed I could all-of-a-sudden run more timing everywhere. I knew it was the more accurate wheel. I ran more timing than most, and never had knock. Two years later when I redid my trigger wheel I discovered it was retarded about 8*. So I wasn't really running as much advance as i thought.
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There's an RB20 swapped '71 240Z wiring disaster at the shop that has a fresh engine, but has never run on it. Apparently the old motor died because the trigger wheel pickup was shaking all over the place. Open the tune for it and all the timing figures are 35-42 degrees. From -10 in/Hg to 30 psi, 35 degrees. Apparently it ran wellish before the old engine came apart. Only way that shit went down was if the trigger was never properly synced and was effectively retarded.
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You stumble upon a slut pile of RB's JD?
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When your are talking heat, im assuming you mean egts more-so than lets say block heat. What can I do to limit these heat issues, from what i gathered adding more and more fuel stops working at 11.5ish give or take. So, keep from retarding crazy amounts of timing to try to make more power than what my octane has to offer and dont be stupid about it. Or is it as simple as ensuring decent airflowin the bay, a good rad and a better Tstat. I know in the miata motors like ours the 4th cylinder tends to go first. I planned on doing that weird coolant reroute thing they do.
Sidenote: What is considered extremely retarded? My motor is quite similar to a miata so would 12deg be far to retarded? Its more of a theory question, since there are often so many variables.
I need to get my hands on some meth.
this has already been sort of covered and drifted away from in the thread but I'm posting anyway.
MBT simply stands for Minimum timing for best torque. You get the best torque when the Full burn is in affect After top dead center. Now heres the way to think about it. The timing is only changed to account for differant charge densities. A dense air charge in the combustion chamber like at 5500rpm at 30psi is a whole lot more packed together then a thin air charge in the cylinder in light cruise at 15nhg.
A thin charge burns slower because the air molocules are further apart so the burn has further to travel from molecule to molecule. it takes longer so if we lit it ATDC the piston would be way down the bore before the burn got fully started and we'd loose torque and have really bad gas milage because we wouldn't give the charge enough time to fully burn. SO at 30psi the cylinder charge is really packed together and it takes less time to fully burn so we take away timing if you light that fire at 30degrees theirs a good chance of breaking shit like rods ring lands and head gaskets a really dense charge in a small bore can get into negetive timing numbers.
And like others have said when your on the dyno add timing in small amounts until you stop gaining torque then pull a degree out. Then check your plugs to make sure everything your watching on the laptop or on the dyno screen are the truth. machines love to lie to humans.
And like Joseph said we don't give a fuck about egts.
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When your are talking heat, im assuming you mean egts more-so than lets say block heat. What can I do to limit these heat issues, from what i gathered adding more and more fuel stops working at 11.5ish give or take. So, keep from retarding crazy amounts of timing to try to make more power than what my octane has to offer and dont be stupid about it. Or is it as simple as ensuring decent airflowin the bay, a good rad and a better Tstat. I know in the miata motors like ours the 4th cylinder tends to go first. I planned on doing that weird coolant reroute thing they do.
Sidenote: What is considered extremely retarded? My motor is quite similar to a miata so would 12deg be far to retarded? Its more of a theory question, since there are often so many variables.
I need to get my hands on some meth.
this has already been sort of covered and drifted away from in the thread but I'm posting anyway.
MBT simply stands for Minimum timing for best torque. You get the best torque when the Full burn is in affect After top dead center. Now heres the way to think about it. The timing is only changed to account for differant charge densities. A dense air charge in the combustion chamber like at 5500rpm at 30psi is a whole lot more packed together then a thin air charge in the cylinder in light cruise at 15nhg.
A thin charge burns slower because the air molocules are further apart so the burn has further to travel from molecule to molecule. it takes longer so if we lit it ATDC the piston would be way down the bore before the burn got fully started and we'd loose torque and have really bad gas milage because we wouldn't give the charge enough time to fully burn. SO at 30psi the cylinder charge is really packed together and it takes less time to fully burn so we take away timing if you light that fire at 30degrees theirs a good chance of breaking shit like rods ring lands and head gaskets a really dense charge in a small bore can get into negetive timing numbers.
And like others have said when your on the dyno add timing in small amounts until you stop gaining torque then pull a degree out. Then check your plugs to make sure everything your watching on the laptop or on the dyno screen are the truth. machines love to lie to humans.
And like Joseph said we don't give a fuck about egts.
You forgot about the effect engine speed has on this though. If at a given density you have half the time to complete the burn, you need to start sooner( considering ignition delay and burn speed vs RPM) Which is the main reason MBT timing goes up with RPM after torque peak.
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When your are talking heat, im assuming you mean egts more-so than lets say block heat. What can I do to limit these heat issues, from what i gathered adding more and more fuel stops working at 11.5ish give or take. So, keep from retarding crazy amounts of timing to try to make more power than what my octane has to offer and dont be stupid about it. Or is it as simple as ensuring decent airflowin the bay, a good rad and a better Tstat. I know in the miata motors like ours the 4th cylinder tends to go first. I planned on doing that weird coolant reroute thing they do.
Sidenote: What is considered extremely retarded? My motor is quite similar to a miata so would 12deg be far to retarded? Its more of a theory question, since there are often so many variables.
I need to get my hands on some meth.
this has already been sort of covered and drifted away from in the thread but I'm posting anyway.
MBT simply stands for Minimum timing for best torque. You get the best torque when the Full burn is in affect After top dead center. Now heres the way to think about it. The timing is only changed to account for differant charge densities. A dense air charge in the combustion chamber like at 5500rpm at 30psi is a whole lot more packed together then a thin air charge in the cylinder in light cruise at 15nhg.
A thin charge burns slower because the air molocules are further apart so the burn has further to travel from molecule to molecule. it takes longer so if we lit it ATDC the piston would be way down the bore before the burn got fully started and we'd loose torque and have really bad gas milage because we wouldn't give the charge enough time to fully burn. SO at 30psi the cylinder charge is really packed together and it takes less time to fully burn so we take away timing if you light that fire at 30degrees theirs a good chance of breaking shit like rods ring lands and head gaskets a really dense charge in a small bore can get into negetive timing numbers.
And like others have said when your on the dyno add timing in small amounts until you stop gaining torque then pull a degree out. Then check your plugs to make sure everything your watching on the laptop or on the dyno screen are the truth. machines love to lie to humans.
And like Joseph said we don't give a fuck about egts.
You forgot about the effect engine speed has on this though. If at a given density you have half the time to complete the burn, you need to start sooner( considering ignition delay and burn speed vs RPM) Which is the main reason MBT timing goes up with RPM after torque peak.
No I didn't forget. It's an air pump dude it's all about charge density. If you spun an engine with an electric motor and just measured air flow out the exhuast you'd find peak torque by peak air flow. the reason you add timing back in after peak torue is because the engine isn't pumping as much air per cycle and that has to do with cam lift and duration valve stuff and other thingys.
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I'm a few beers deep so my explanation may be a bit weak and I should have mentioned the effect of VE(charge density) in my first post, however engine speed definitely is an integral part of MBT.
Examples:
#1
Typical timing at idle RPM is much lower that timing at cruise RPM in most cases even at the same manifold pressure. VE which is another term for air charge density in the cylinder basically is with any normal automotive engine is LOWER at idle than it is at cruise RPM, which is contradictory to your density is all post. With that theory, idle advance (1000rpm) at say 40KPA should be higher than advance at 40KPA at 3500rpm, since VE is higher at cruise, however it is the opposite.
#2
From your post, with a given charge density (or VE), it takes a certain amount of time for the full burn to happen, correct? ( I don't feel like doing math, but numbers are accurate relative to each other)
If it takes the engine 6ms to go from 15BTDC to 15ATDC at 1000rpm
then at 3000rpm it will only take 2ms to cover the same angle.
If VE increases like a normal engine then MBT should be lower at the higher RPM, but the reverse is true due to the time factor.
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Good info fellas thx.
So basically in a perfect world with no knock a timing map would kina go like this.
At 220kpa lets say, at redline you should have the most spark advance in those bins. Then Again, if motors didn't knock the timing curve would be kinda flat no?
so sorta like this : 20 25 30 35 40
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You stumble upon a slut pile of RB's JD?
Pretty much. This RB20's been sitting around for a minute because it's a bit of a wiring calamity and I've not had the patience for it. We managed to get rid of the one I was talking about to you yesterday, guy traded it for an 04 or 05 IS300 with a .60 trim T3/T04E on a Greddy piggyback, so of course it doesn't run right and my next paycheck is ensured. However, bossman is trading around for an R33 GTR SpecV and part of the deal is he has to pick up ALL of this guy's Nissan parts so a spare RB25 swap comes with it.
You forgot about the effect engine speed has on this though. If at a given density you have half the time to complete the burn, you need to start sooner( considering ignition delay and burn speed vs RPM) Which is the main reason MBT timing goes up with RPM after torque peak.
No. Burn rate for iso-octane based fuels remains proportional to engine speed, this is plainly stated in several engineering literatures. Some engines like more timing as the RPMS go up (before as well as after torque peak) like SR20 and KA24, but I've had no experience with that happening on a dyno as being anything that happens more often than very rarely. I hear people saying it, but they always seemed to have a dynojet so I just shrug and do something else more interesting than argue with them.
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Why is it that some people knock off a few degrees just before the torque peak and during?
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You stumble upon a slut pile of RB's JD?
Pretty much. This RB20's been sitting around for a minute because it's a bit of a wiring calamity and I've not had the patience for it. We managed to get rid of the one I was talking about to you yesterday, guy traded it for an 04 or 05 IS300 with a .60 trim T3/T04E on a Greddy piggyback, so of course it doesn't run right and my next paycheck is ensured. However, bossman is trading around for an R33 GTR SpecV and part of the deal is he has to pick up ALL of this guy's Nissan parts so a spare RB25 swap comes with it.
You forgot about the effect engine speed has on this though. If at a given density you have half the time to complete the burn, you need to start sooner( considering ignition delay and burn speed vs RPM) Which is the main reason MBT timing goes up with RPM after torque peak.
No. Burn rate for iso-octane based fuels remains proportional to engine speed, this is plainly stated in several engineering literatures. Some engines like more timing as the RPMS go up (before as well as after torque peak) like SR20 and KA24, but I've had no experience with that happening on a dyno as being anything that happens more often than very rarely. I hear people saying it, but they always seemed to have a dynojet so I just shrug and do something else more interesting than argue with them.
I guess I'm just used to looking at peoples DSM tunes then, almost all of them I see ramp up timing slowly as RPM rises. Usually its knock limit that they are up against, not sure if thats part of it.
Do you have a link to any of that engineering stuff. Sounds like something I'd like to read a bit of, always trying to learn.
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Why is it that some people knock off a few degrees just before the torque peak and during?
Safety margin.
If the vehicle is approaching any sort of limit - thermal, octane, what the internals can handle, the owner/operator is obviously dumb as shit or lacks common sense - you pull timing for safety. If the vehicle will be used in an abusive environment like roadracing then you really have to worry about shit like that, drag racing not so much because they are only in the pedal for a short period.
Also, some engines that are biased for low end and midrange powerband, like the traditional domestic small block V8 with a stock-ish cam meant to make 300 ft/lbs right off idle and torque peak at 2900 rpms, or horribly mis-built motors like my D16Y5 Type-R with way too much CR/stock cam/pumpgas, will continue to make power as you add in more timing until well after audible detonation has set in.
You stumble upon a slut pile of RB's JD?
Pretty much. This RB20's been sitting around for a minute because it's a bit of a wiring calamity and I've not had the patience for it. We managed to get rid of the one I was talking about to you yesterday, guy traded it for an 04 or 05 IS300 with a .60 trim T3/T04E on a Greddy piggyback, so of course it doesn't run right and my next paycheck is ensured. However, bossman is trading around for an R33 GTR SpecV and part of the deal is he has to pick up ALL of this guy's Nissan parts so a spare RB25 swap comes with it.
You forgot about the effect engine speed has on this though. If at a given density you have half the time to complete the burn, you need to start sooner( considering ignition delay and burn speed vs RPM) Which is the main reason MBT timing goes up with RPM after torque peak.
No. Burn rate for iso-octane based fuels remains proportional to engine speed, this is plainly stated in several engineering literatures. Some engines like more timing as the RPMS go up (before as well as after torque peak) like SR20 and KA24, but I've had no experience with that happening on a dyno as being anything that happens more often than very rarely. I hear people saying it, but they always seemed to have a dynojet so I just shrug and do something else more interesting than argue with them.
I guess I'm just used to looking at peoples DSM tunes then, almost all of them I see ramp up timing slowly as RPM rises. Usually its knock limit that they are up against, not sure if thats part of it.
Do you have a link to any of that engineering stuff. Sounds like something I'd like to read a bit of, always trying to learn.
MAF + a preference for internally gated turbos can result in weird ideas concerning how engines work. If you are dealing with a setup that tapers boost past torque peak, and is dealing with timing in terms of horsepower (airmass is directly related to horsepower), then it very much looks like the car wants more timing in the higher rpms.
Let me step back a bit from the concept at hand and give you a frame of reference as to how different shit works, and how that forms the way people "think" a thing works. It's pretty interesting, actually, as it makes some designs that start out looking fucking stupid turn into something that makes sense.
What I cut my teeth on, Hondas, you can view fuel maps in 2D format. Speed-density tunerboi adage, "fuel follows torque," and if there's nothing wrong with the vehicle your 2D fuel curve looks like your dyno torque curve. It is common practice to refer to 2D fuel maps while tuning as a sanity check, and people start thinking in these terms. With eCtune I commonly monitor AFR and MAP plotted out across an RPM axis in the same window that with a keystroke hosts the 2D fuel maps. With speed density eyes, boost is flat across a targeted scalar and timing is flat. When I tuned Robb's Integra with the internally gated 16G it would hit 24+ psi and taper to 12-14 with the boost controller on nig nog setting, and I chased his tune for that one boost setting across eight pressure scalars - at no point in time did I view it as requiring more timing past the (3800 rpm) torque peak... although it "did" due to boost taper.
MAF guys deal directly with airmass. Airmass is directly proportional to horsepower, ASSuming correct ignition timing. MAF guys could also view things as fuel follows torque as easily as speed density guys, but when dealing directly with airmass they have no reason to and therefore do not. The manner in which a MAF tune wanders across the scalars - or not depending on wastegate dynamics or appears not to due to a lack of resolution in the mappings - shapes the way a DSM or Ford or Nissan tuner thinks an engine operates. Dennis (DmC) is a couple Fords deep now, and has a similar Honda background, he'll attest to the number of "boost scalars" above 1.0 load axis on a 750 whp Ford aren't enough to correctly tune a 225 whp turbo Honda. On those same Fords the ignition map would look like timing goes up (slightly) with RPM, but not really. DSMs also have a similar lack of resolution, although not as pronounced, not that the average DSM tuner who uses SLIDERBARZZZ knows this or in truth has any real grasp of what's going on.
I've by no means tuned everything I need to in order to learn everything I feel I need to, but I have been through a LOT of stuff in the last two years and my perceptions have grown a lot. On top of the OEM ECUs mentioned previously, GM (MAF + MAP) and Chrysler (MAP expressed in terms of airmass a la MAF lolololol) are interesting things to poke at, as well as a rainbow assortment of standalones.
Also, keep in mind that the premise of a turbo 4 cyl is not to make huge peak torque, but to maintain whatever torque it makes as long as possible and then let high rpms spin it into higher horsepower. Given a traditional V8 engine that makes big midrange and then falls off suddenly, yes, the amount of airmass entering the engine falls off abruptly and would seem to require additional ignition timing. I've tuned slightly less than a dozen mod motor Fords and one SBF, none on a dyno, but this might be something Dennis or 79fairmont could chime in on. Something with exaggerated torque that falls off suddenly, like some of the redneck built 347 strokers that make 350 wtq right off idle and can't break 300 whp, that the owner thinks is fast because it wants to rip the tires free when trying to pull away gently from a traffic light, even though it runs a 14 at the strip.
As far as the particular reference in re: rate of burn for iso-octane based fuels, it's somewhere in the first 15-20 pages of the second volume of Taylor's ICE primer, a pretty vanilla read although his bibliography is a rewarding reading list that you can spend a lifetime trying to plow through.
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Okay, so that somewhat makes sense. thanks for the explanation. Hopefully my questions aren't too annoying, I appreciate the time. :noel:
I guess I'm also used to seeing the old timing curves from old distributor based ignition too, where its an upward curve with RPM, hard to get it out of my head.
My next question is, dumbing it down for me, since I don't have the background. I just like to know how stuff works a bit beyond it just does, if you know what I mean.
Why does timing not increase with RPM the way you would assume given the shorter window for initial ignition, and burn. What makes that burn happen faster at higher RPM to avoid that need? Is it higher in cylinder charge motion/speed/turbulence (that comes from higher RPM, piston speed etc) causing the flame to propagate through the charge faster? Or is there something else that causes what you see in this case that I'm completely missing?
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Well, the problem here is we are getting into territory no one really understands. There are thousands of books on the subject of combustion, energy released, end products, and theoretically what reactions and what dynamics take place in the chamber. You can generally get a feel for something being a property of a fuel, or the mixing action that is quench, etc, but at the end of the day there is no scientific proof. Lots of empirical evidence that shit works, but as to why? Meh.
My gut feeling is burn rate remains proportional to piston speed due to kinetic energy (stirring two chemicals while they react speeds the reaction) and the more sudden chamber temp rise from adiabatic heating of the charge during the compression stroke creates a bigger change in temp (which means quicker thermal transfer of heat into fuel) that partially offsets the lessened amount of time available to heat the charge. Also, temps are supposed to go up with rpm due to frictional losses, so the extra available heat as rpms go up help with that further. There are a couple other things I think it could be, too, all just pretty words coming out of my mouth. Again, while common sense is probably right no one really knows.
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Well, the problem here is we are getting into territory no one really understands. There are thousands of books on the subject of combustion, energy released, end products, and theoretically what reactions and what dynamics take place in the chamber. You can generally get a feel for something being a property of a fuel, or the mixing action that is quench, etc, but at the end of the day there is no scientific proof. Lots of empirical evidence that shit works, but as to why? Meh.
My gut feeling is burn rate remains proportional to piston speed due to kinetic energy (stirring two chemicals while they react speeds the reaction) and the more sudden chamber temp rise from adiabatic heating of the charge during the compression stroke creates a bigger change in temp (which means quicker thermal transfer of heat into fuel) that partially offsets the lessened amount of time available to heat the charge. Also, temps are supposed to go up with rpm due to frictional losses, so the extra available heat as rpms go up help with that further. There are a couple other things I think it could be, too, all just pretty words coming out of my mouth. Again, while common sense is probably right no one really knows.
I wondered about that, thanks.
Last thing for now. You referred to iso octane fuels several times. How do you feel about ethanol based fuels, do they behave appreciably different when it comes to timing and RPM? From your experience.
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Whew, I thought I was just stupid by not really getting the relationship of less timing for more rpm. This thread is cool though. I haven't gotten wrapped up in a tech thread in a long time.
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You referred to iso octane fuels several times. How do you feel about ethanol based fuels, do they behave appreciably different when it comes to timing and RPM? From your experience.
I've got a decent grasp on the nature of ethanol in small doses (E10 87 octane pumpgas) and how it curbs volatility especially at lower engine speeds, and acts like normal gasoline within a degree or two of normal gasoline timing in the higher rpms on a NA motor. I tried three different fuels on the dyno and 5-6 others on the street on top of the 0.4 octane fuel passed off as 93 during the gas shortage we had fall before last, on my 138 whp (140whp on 93, 142.5 whp on 93 while audibly knocking) all OEM internal 12.5:1 stock HX head SOHC. That was more than a casual tuning relationship where I spend 2-12 hours with the vehicle over a year, but it's still only one car.
I've exactly one E85 tune on an RB25 under my belt, car made great power, but I don't see much E85 as they don't sell it closer than an hour down the mountain. On that note, the same gas was converted to gasoline a few days ago for the convenience of it's new owner in GA. It had a history of smoking a little when idled for long periods, consensus was that it was the turbo. It started smoking when it first reached operating temp with the car sputtering as we'd just dumped some 93 on top of an empty and old tank of E85, within ten minutes it stopped and didn't do it again over the couple days it was driven until it was traded. This is a car that also had a bad history of condensation coming through the valvecover breather. I'm kind of wondering if this is a common quirk with the fuel, and what sort of fan temp switching points vs fuel ethanol content/PCV affairs OEM flex fuel vehicles run to combat this. Could have just been a fluke car though.
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I had some time to think about this thread today. Your right Aero Timing is proportional to rpm. Ive always known that, I just I guess I never really had to focus on it because the way honda roms and timing maps are setup with the advance in the background.
Check out this screen shot of the base timing advance table in crome. You'll find a table like this in almost all software so no shots at crome.
(https://realhomemadeturbo.com/forum/proxy.php?request=http%3A%2F%2Fi678.photobucket.com%2Falbums%2Fvv143%2FDmC_01%2Ftimingrpm.jpg%3Ft%3D1282695041&hash=f30744a47e4e68e0a5de88a6500aaac2868c30e6)
See what it's doing in a linear fashion in direct proportion to rpm.
It's advancing to account for the speed of increased rpm in order to hit the optimum crank burn angle.
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http://www.diracdelta.co.uk/science/source/e/n/engine%20excitation%20mechanisms/source.html (http://www.diracdelta.co.uk/science/source/e/n/engine%20excitation%20mechanisms/source.html)
Joseph I'd really like to see those technical manuels we need to track down the authors and check them for Khaki pants and collared shirts. they may be responsible for the dyno jet electronics designs
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I had some time to think about this thread today. Your right Aero Timing is proportional to rpm. Ive always known that, I just I guess I never really had to focus on it because the way honda roms and timing maps are setup with the advance in the background.
Check out this screen shot of the base timing advance table in crome. You'll find a table like this in almost all software so no shots at crome.
(https://realhomemadeturbo.com/forum/proxy.php?request=http%3A%2F%2Fi678.photobucket.com%2Falbums%2Fvv143%2FDmC_01%2Ftimingrpm.jpg%3Ft%3D1282695041&hash=f30744a47e4e68e0a5de88a6500aaac2868c30e6)
See what it's doing in a linear fashion in direct proportion to rpm.
It's advancing to account for the speed of increased rpm in order to hit the optimum crank burn angle.
Thats always how I understood it.
I've never worked with crome, MS is my only tuning experience so I don't have the same different perspectives.
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Cool now you need to show me how to do some trig to figure out the best torque angle in the crank rotation for peak torque.
But remember man what I posted at first about charge density is right. But their both peices of the bigger picture.
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Cool now you need to show me how to do some trig to figure out the best torque angle in the crank rotation for peak torque.
But remember man what I posted at first about charge density is right. But their both peices of the bigger picture.
Yes I was definitely not disagreeing with that. Wording was a bit off, due to the alcohol lol.
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I had some time to think about this thread today. Your right Aero Timing is proportional to rpm. Ive always known that, I just I guess I never really had to focus on it because the way honda roms and timing maps are setup with the advance in the background.
Check out this screen shot of the base timing advance table in crome. You'll find a table like this in almost all software so no shots at crome.
(https://realhomemadeturbo.com/forum/proxy.php?request=http%3A%2F%2Fi678.photobucket.com%2Falbums%2Fvv143%2FDmC_01%2Ftimingrpm.jpg%3Ft%3D1282695041&hash=f30744a47e4e68e0a5de88a6500aaac2868c30e6)
See what it's doing in a linear fashion in direct proportion to rpm.
It's advancing to account for the speed of increased rpm in order to hit the optimum crank burn angle.
careful. that table isn't what it's labeled as.
it's an adder for coil dwell, not base ignition timing. changing values in that table does nothing to the final ignition output value. it does, however, add more coil charge time. it took me a while to figure out why i was having misfires at 13psi on the honda ignition system (which is actually very powerful for what it is), and it was because at some point i had zero'd that table out thinking the table was what it was described as.
bumped the values back up and the misfire was completely gone. there was no change in the ignition values seen at the crank according to my timing gun.
it's actually a pretty neat feature, and one that not many aftermarket EMS have. even with motec, you have to do some skullduggery to get the dwell values to ramp as rpm increases.
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careful. that table isn't what it's labeled as.
it's an adder for coil dwell, not base ignition timing. changing values in that table does nothing to the final ignition output value. it does, however, add more coil charge time. it took me a while to figure out why i was having misfires at 13psi on the honda ignition system (which is actually very powerful for what it is), and it was because at some point i had zero'd that table out thinking the table was what it was described as.
bumped the values back up and the misfire was completely gone. there was no change in the ignition values seen at the crank according to my timing gun.
it's actually a pretty neat feature, and one that not many aftermarket EMS have. even with motec, you have to do some skullduggery to get the dwell values to ramp as rpm increases.
Um how about no it's not . Ive used this table many times to tune y8's add a degrees acrossed this table and watch crank timing fall into place.
Coil Dwell really?
(https://realhomemadeturbo.com/forum/proxy.php?request=http%3A%2F%2Fwww.wreckthetapedeck.com%2Fwp-content%2Fuploads%2F2009%2F10%2Fkanye-west-facepalm.jpg&hash=03c6d566191b3b5f19e2a86307c12a03aafe62ee)
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It is coil dwell. Compare the scalars and base values to Hdata, eCtune, neptune.
I have verified this on a 600whp lsvtec. Purposely induced misfire by nulling the table.
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i think the reason i never had issue with it when it was zero'd out before was because i was running the toyota igniter, which controls dwell time internally.
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Kanye west is a human facepalm.
That is all
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alright I'll check out tonight with a timing light again.
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In Ectune those timing values are base ignition timing value, not coil dwell. They were orginally thought to be coil dwell but they later found not to be.
Ectune and Neptune allow you to disable them.
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It is coil dwell. Compare the scalars and base values to Hdata, eCtune, neptune.
I have verified this on a 600whp lsvtec. Purposely induced misfire by nulling the table.
Well I checked this out with a timing light yesterday and I could swing timing either way. I talked to Master Sensie Blundell about this and he said that were both right and that table affects both and that some strange things are afoot in the honda code.
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Why does timing not increase with RPM the way you would assume given the shorter window for initial ignition, and burn. What makes that burn happen faster at higher RPM to avoid that need?
I don't have a degree in this BS, but I know you can't look at an individual burn as a static event. Many key factors are change as the piston moves from BDC to TDC and back.
The flame front speed isn't affected much by any variable, but the fuel's burn speed is. The flame front doesn't burn the fuel 100% as it touches it.
Burn speed is affected by pressure. The cylinder charge compresses 2x as fast at 2x the rpm (duh). That causes burn speed to accelerate (relative to time, not crank rotation), too, as burn speed increases with density. Imagine the flame front igniting a bunch of firecracker rolls. After the flame front rolls through lighting the last fuses, the first roll of firecrackers is still popping. As you increase charge density, each firecracker roll burns to it's end faster. So you meet peak cyl pressure in less time. That being the case, less time to burn is offset by reaching peak cyl pressure sooner, meaning you don't have to crank the timing.
http://www.spaceref.com/news/viewsr.html?pid=4051 (http://www.spaceref.com/news/viewsr.html?pid=4051)
The almost unchanging flame front speed does require some advance, though.
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Ive been working on my timing map, trying to get something close that I can dyno with and start tuning. I also made it conservative enough that we can for the most part safely road tune it with det cans. This is what ive come up with so far, let me know if you see any obvious holes in the map or anything that doesnt make sense.
One thing tho, is theres a big difference in spark angle from the cruise/vac area to the positive pressure area. Is that not ramped enough? What issues would I expect.
Ive retarded quite a bit, cause I havent put it on the dyno as of yet. A friend of mine with a similar build suggested 12deg as a good start but to me it seems retarded to much. Then again im going to tune for damn near 20lbs.
(https://realhomemadeturbo.com/forum/proxy.php?request=http%3A%2F%2Fi7.photobucket.com%2Falbums%2Fy270%2Fturbotincan%2Fnewmap.jpg&hash=e780fd9c68d8e72b958bddb33b84c27ec7bb35fd)
I have also retarded a bit of timing at the torque peak around 4-5k. Correction, dyno shows the peak around 5400, but its fairly flat from like 4k to 6k
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Arse brett helped me smooth it out some.
(https://realhomemadeturbo.com/forum/proxy.php?request=http%3A%2F%2Fi7.photobucket.com%2Falbums%2Fy270%2Fturbotincan%2Fthurstimignmap.jpg&hash=86819fe7f6ab83417cbb6e0275ab644b7e2f7eae)