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flat_black

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Re: MBT Discussion
« Reply #30 on: August 23, 2010, 10:50:38 PM »

You stumble upon a slut pile of RB's JD?
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DmC

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Re: MBT Discussion
« Reply #31 on: August 23, 2010, 11:02:29 PM »

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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Aero

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Re: MBT Discussion
« Reply #32 on: August 23, 2010, 11:08:08 PM »

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.

DmC

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Re: MBT Discussion
« Reply #33 on: August 23, 2010, 11:18:57 PM »

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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Aero

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Re: MBT Discussion
« Reply #34 on: August 23, 2010, 11:56:20 PM »

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.

TTC

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Re: MBT Discussion
« Reply #35 on: August 24, 2010, 07:35:32 AM »

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


Joseph Davis

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Re: MBT Discussion
« Reply #36 on: August 24, 2010, 07:51:16 AM »

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.
 
« Last Edit: August 24, 2010, 07:53:19 AM by Joseph Davis »
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TTC

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Re: MBT Discussion
« Reply #37 on: August 24, 2010, 08:09:57 AM »

Why is it that some people knock off a few degrees just before the torque peak and during?

Aero

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Re: MBT Discussion
« Reply #38 on: August 24, 2010, 08:16:33 AM »

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.

Joseph Davis

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Re: MBT Discussion
« Reply #39 on: August 24, 2010, 10:04:23 AM »

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. 

Aero

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Re: MBT Discussion
« Reply #40 on: August 24, 2010, 10:51:28 AM »

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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Re: MBT Discussion
« Reply #41 on: August 24, 2010, 11:07:53 AM »

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.

Aero

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Re: MBT Discussion
« Reply #42 on: August 24, 2010, 11:19:52 AM »

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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Re: MBT Discussion
« Reply #43 on: August 24, 2010, 11:46:34 AM »

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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 fucking box started smoking and i saw a flame start up so i grabbed a bucket of water and splashed it on the breaker box.

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Re: MBT Discussion
« Reply #44 on: August 24, 2010, 12:31:40 PM »

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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Re: MBT Discussion
« Reply #45 on: August 24, 2010, 08:17:09 PM »

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.

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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DmC

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Re: MBT Discussion
« Reply #46 on: August 24, 2010, 08:22:52 PM »

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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Aero

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Re: MBT Discussion
« Reply #47 on: August 24, 2010, 08:53:32 PM »

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.

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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Re: MBT Discussion
« Reply #48 on: August 24, 2010, 09:03:59 PM »

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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Re: MBT Discussion
« Reply #49 on: August 24, 2010, 09:08:58 PM »

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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Re: MBT Discussion
« Reply #50 on: August 26, 2010, 09:59:58 PM »


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.

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.
« Last Edit: August 26, 2010, 10:02:39 PM by kgx »
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DmC

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Re: MBT Discussion
« Reply #51 on: August 26, 2010, 10:35:40 PM »




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?
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leed

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Re: MBT Discussion
« Reply #52 on: August 27, 2010, 09:46:33 AM »

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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kgx

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Re: MBT Discussion
« Reply #53 on: August 27, 2010, 10:47:28 AM »

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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PhilStubbs

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Re: MBT Discussion
« Reply #54 on: August 27, 2010, 11:23:29 AM »

Kanye west is a human facepalm.

That is all
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Re: MBT Discussion
« Reply #55 on: August 27, 2010, 12:50:34 PM »

alright I'll check out tonight with a timing light again.
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sewell94

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Re: MBT Discussion
« Reply #56 on: August 27, 2010, 03:07:56 PM »

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.

« Last Edit: August 27, 2010, 03:17:54 PM by sewell94 »
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DmC

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Re: MBT Discussion
« Reply #57 on: August 31, 2010, 07:47:01 AM »

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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HiProfile

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Re: MBT Discussion
« Reply #58 on: September 02, 2010, 01:17:11 AM »

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

The almost unchanging flame front speed does require some advance, though.
« Last Edit: September 02, 2010, 01:23:37 AM by HiProfile »
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Re: MBT Discussion
« Reply #59 on: September 06, 2010, 11:12:47 AM »

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.



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
« Last Edit: September 06, 2010, 02:02:14 PM by TTC »
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