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[Urban Indian]

Since I and other noobs would like to know basic questions. I will ask them.


So I know most turbo guys go for a compression ratio of 8:1 or 8.5:1, what about if you were to go with a 9:1 ratio so that you would have a better power curve out of boost?


I have talked to a few high hp turbo V8 guys and they are comtemplating the 9:1 CR instead of their 8:1.



NOW I ask you

what are the limits to HP~CR~Octane?

Comparative to B-D-H-K ect. whatever

The reason I ask is because I get mixed results about asking different people for opinions of this. I want to run a 8.5:1 or 9:1 CR on my HX-52 build but some people tell me 8:1 is the only way to go.



Post up your knowledgeablitites 

[dvst8r]

Where octane is the limit, you will make more peak power, with less static compression and more added boost, then the opposite. I have a chart on one of my computers showing a test engine and the corresponding output. i will see if I can digg it up.

[patsmx5]

I can't wait to see what everyone's take on this is. Here's mine.

Higher compression makes for a more efficient cycle if you can do so and still reach minimum best timing for best torque without detonation, or without getting too close to detonating (IE- running 22* is MBT but 23 detonates, this is too aggressive for a street car IMO).

Adding a turbo essentially makes for a two stage compressor. The first stage you can aftercool to remove heat from the charge. The second stage you can't. So IMO I'd rather run less static compression (the engine's compression ratio) and run more boost. Net result is a lower dynamic compression ratio for the same power.  Burning fuel makes power. Dealing with heat is the problem. And I'd rather run 20 PSI and make 400whp and it be dead reliable vs. 19.1 PSI and it's tuned to the raged edge but has 0.913% higher thermal efficiency.

But I come from a mazda BP background where we have undersquare engines so maybe things are different in the honda world.

[dvst8r]

STOLEN FROM THE INTERNET, NOT MY INFO. DIDN'T BOTHER TO LOOK AT THE WEBSITE IT CAME FROM.

Consideration #1
Heat from compression by a supercharger or turbo can be removed (for the most part) through use of an intercooler. Heat from compression within the cylinder cannot. Also, the cylinder pressure at the end of the compression stroke (prior to ignition) goes up exponentially with an increase in static compression ratio, versus a linear increase with boost pressure. Therefore, increasing the static CR is going to unavoidably push you closer to the knock limit for a given fuel. In other words, the octane requirement goes up more by increasing the static CR than it does by increasing boost.

For example, increasing the static CR from 8.5 to 9.5 increases the temperature within the cylinder at the end of the compression stroke (but before ignition) by ~63°F, (assuming IAT2 = 130°F and ideal adiabatic compression with γ = Cp/Cv = 1.4. I won’t bore anyone with equations. The situation doesn’t change much even if IAT2 were only, say, 100°F. In that case, the increase in temp at the end of the compression stroke goes up by ~60°F for the same increase in static CR). Also, the pressure at the end of the compression stroke (before ignition) goes up by ~97 psi from 574 psi to 671 psi, assuming atmospheric and boost pressures of 14.7 and 14 psi, respectively. On the other hand, increasing the boost pressure from 14 to 15 psi increases the outlet temp of the compressor by only ~11°F, assuming AE=60% and IAT1 = 90°F. And by further assuming an intercooler efficiency of 80%, the increase in IAT2 is only ~2°F. Hence, the increase in temp at the end of the compression stroke will hardly change at all. Also, the increase in cylinder pressure at the end of the compression stroke only goes up by ~18 psi (from 516 to 534 psi) with this increase in boost pressure.

So summarizing the effects of increased temp and pressure at the end of the compression stroke for the two cases:
Increased CR from 8.5 to 9.5: ΔT = ~63°F and ΔP = ~97 psi
Increased boost from 14 to 15 psi: ΔT = ~2.4°F and ΔP = ~18 psi

A higher temp and pressure increase the likelihood of deadly preignition for a given octane fuel. And for those astute observers that know the physics I’ve applied, yes, although I’ve idealized things to keep it simple, (by not including effects such as heat loss thru the cylinder walls during the compression stroke or ignition and valve timing in the calculations), I’m sure they’ll also recognize that this doesn’t change the conclusion.

Consideration #2
Power is increased by two completely different mechanisms for the two approaches. Increasing the static compression ratio increases power via an increase in thermal-conversion efficiency. Increasing boost pressure increases power via an increase in mass-air flow rate. There’s less gain in thermal-conversion efficiency (and hence power) via an increased static CR compared to the power gain by increasing the mass-air flow rate via an increase in boost pressure. For example, increasing the static CR from 8.5 to 9.5 results in an increase in thermal-conversion efficiency (for an ideal Otto cycle) of about 3.2%. On the other hand, increasing the boost pressure from just 14 psi to 15 psi, increases the mass-air flow rate by about 3.5%. If boost pressure is increased by 2 psi, (from 14 to 16 psi), the increase in mass-air flow rate will now be more than twice that compared to the increase in thermal-conversion efficiency, (~7% vs ~3.2%), and ΔT and ΔP still won’t be as great as they are when increasing the static CR from 8.5 to 9.5. Therefore, not only can it be “safer” from the knock point of view, but a little more power is gained as well, (relatively speaking that is).

[stealthiskey]

stock civic has a compression ratio of 9.2:1.   At atmospheric pressure a compression test will yield 184 psi.

Atmospheric pressure (14.7) * 9.2 = 135 psi.  

184-135 = 49 psi unnacounted for.

This extra pressure increase is due to the heat generated by compressing a gas.  

Ideal gas law: PV=nrT
and we know that T (temperature) increases during compression, but does it increase enough to get an extra 50 psi?
300 Kelvin = 80* F
135*V=nr*300 or 135/300=nr/V, where nr/V remains constant
184*V=nr*T or 184/T=nr/V so 184/T=135/300
therefore T=408 Kelvin = 274 degrees F

so basically 9.2: C.R. at 14.7 psi will increase the temperature from 80 degrees F to 274 deg F.


Apply the same logic for 9.2 at (14.7 +whatever boost you want to run), to find out how much the temperature will increase when that amount of air is compressed.  This does not take into account the ambient temps of the cylinder walls etc.

Regular gasoline spontaneously combusts around 450 degrees F.  Higher octanes will be able to withstand higher temps.

[dvst8r]

Since I and other noobs would like to know basic questions. I will ask them.


So I know most turbo guys go for a compression ratio of 8:1 or 8.5:1, what about if you were to go with a 9:1 ratio so that you would have a better power curve out of boost?


I have talked to a few high hp turbo V8 guys and they are comtemplating the 9:1 CR instead of their 8:1.



NOW I ask you

what are the limits to HP~CR~Octane?

Comparative to B-D-H-K ect. whatever

The reason I ask is because I get mixed results about asking different people for opinions of this. I want to run a 8.5:1 or 9:1 CR on my HX-52 build but some people tell me 8:1 is the only way to go.



Post up your knowledgeablitites 

One last thing about your setup specifically. I would go with at least 9:1 as you want it to be a "Street" car first and a "Race" car second. Driveablity is therefore more important then every last hp. As you can only put down a very limited amount of HP on the street at the best of times, and shouldn't push an engine to near the edge of the octane rating. At the track you can run VP import or c16 or whatever and never have to worry about the octane rating and can push the turbo's limits, and have a chance at putting the power down.

[jdmhatchracer94]

One last thing about your setup specifically. I would go with at least 9:1 as you want it to be a "Street" car first and a "Race" car second. Driveablity is therefore more important then every last hp. As you can only put down a very limited amount of HP on the street at the best of times, and shouldn't push an engine to near the edge of the octane rating. At the track you can run VP import or c16 or whatever and never have to worry about the octane rating and can push the turbo's limits, and have a chance at putting the power down.



Dude do u even know what ur doing? 8.5 is fine to drive daily even n/a status buddy been doin it for three years not one prob and not even that much power los at all. my setup has a 8.1-8.3 comp so I can run 93 on higher boost. but in the end will make less power than a 9.1 setup but I can do it safer. When I wanna go nutz 35psi with 114oc should survive.





















or not

[dvst8r]

Dude do u even know what ur doing? 8.5 is fine to drive daily even n/a status buddy been doin it for three years not one prob and not even that much power los at all. my setup has a 8.1-8.3 comp so I can run 93 on higher boost. but in the end will make less power than a 9.1 setup but I can do it safer. When I wanna go nutz 35psi with 114oc should survive.

or not

This is a built 2.0L GSR with a GT4094 sized turbo. Meaningful boost doesn't happen till vtec. I have driven vitara setups in that 8:1 range or possibly lower, and while they are perfectly drivable, they are not as enjoyable pre boost, as my stock d16y8. Now a vitara build is all about budget. You happily give up some pre boost power for a ton of mid and top end power. In Urban's case it is not about budget so he can have as close to the best of both worlds as you can get, I guarantee he will notice going from 10:1 (stock GSR CR) to 8:1.

So lets read carefully. With a fully built motor (sleeves, rods, pistons, ported head, cams ect...) on race fuel, even at 10:1 CR he will run out of turbo before he runs out of motor. This is why I said in his specific application, he should be at least 9:1 as it will make it more enjoyable when driving around town out of boost, and will not have any detrimental effects on overall power at the track, and there is still no reason that it would not make a safe 350whp+ on pump 94.



Cliffs: Yeah I have a pretty good idea what I am talking about in this case.

[fysh]

I went 9.4:1 on my build to compensate for turbo lag. All motor is easier to launch as well. When it reaches full boost, the vehicle is already rolling off of mostly N/A power, same concept of "roll-racing" on the street. FWD has more traction when moving than standing still... just my idea about it all.  nothing based in fact, just assumptions.

[dive_miguel]

Many of the is300 guys run up to 10 psi on 10.5:1 cr.  but to make big powa most bring it down to 9.0:1.   The toronado (series 1 3800) that was turbocharged had 8.5:1 CR with a T3 .60 cold, .48 hot and drivability was not an issue...(nasty low to mid range torque)  Gearing, engine configuration and turbine size will most likely play an equal or bigger part.     I have read that you have less margin for error on the higher CR setups though. 

[Urban Indian]

so here is the delima

CP Pistons? JE Pistons?

at 9:1 CR makes 400whp? and max the turbo on the track for race gas........ what teh fuck

[dvst8r]

Many of the is300 guys run up to 10 psi on 10.5:1 cr.  but to make big powa most bring it down to 9.0:1.   The toronado (series 1 3800) that was turbocharged had 8.5:1 CR with a T3 .60 cold, .48 hot and drivability was not an issue...(nasty low to mid range torque)  Gearing, engine configuration and turbine size will most likely play an equal or bigger part.     I have read that you have less margin for error on the higher CR setups though. 

Not really a valid comparison at all. We are talking about a Honda, and a turbo capable of making over 700whp. Not about a series 1 3800 and a tiny turbo.

[dvst8r]

so here is the delima

CP Pistons? JE Pistons?

Ask your engine builder what he prefers.

at 9:1 CR makes 400whp? and max the turbo on the track for race gas........ what teh fuck

WTF are talking about? There is no set power for any specific CR each motor is different.

You should probably just trust your engine builder to build the engine, and your tuner to tune it. Or be prepared to spend a lot more time reading and researching. So you can be confident in why you chose what ever setup it is that you choose.

[dive_miguel]

I wasn't trying to compare or reference a honda at all. 

"Gearing, engine configuration and turbine size will most likely play an equal or bigger part."

Just a generalization, thats all.

[dive_miguel]

never mind, I forgot he was refering to a B, D,H, K ect. 

[Urban Indian]

I think I am going to run 9:1  :somb:

[dvst8r]

I think I am going to run 9:1  :somb:

Why?

[danz]

14:1 or go home.

[widebody93]

I think I am going to run 9:1  :somb:

CP's are the shit
Also Aries


ARE WE BOTH BUILDING AT THE "caps shit" same time

[Urban Indian]

I am going to run 9:1 mainly because everyone else seems to do good with that.

I was talking to mike laskey........ and i actually doubt he builds his own motors........


I was trying to ask him about differences between 9:1 and 9.5:1 or 10:1 CR. He basically said use 9:1 and he doesnt know about anything else and to ask my tooner because he doesnt know.


I couldnt reply..... I didnt know what to reply with. Depending on tranny, if Josh can get that thing back together that is at spikers. I want my tranny to hold. If it cant at 700whp I wont use it

[trevor72]

in all honesty i skipped over lots so forgive me if this is mentioned

when i think of the part that matters in compression ratio i think compression area on TDC compression stroke and chamber design. In essence the 'squish'.  In the case where you don't change the stroke of the motor the only 'real' area you're changing is how close to the head the piston gets in its travels.   like in my mustang motor for example a minimum .040 quench for the closed chamber iron head is ideal, more gap and it is detonation prone, i guess my point is it has lots to do with where the fire happens/ 

Cylinder pressure is cylinder pressure though no matter how you toss it, whether you get there with CR or with loads of boost i don't see the difference as long as you are talking "in boost WOT" and rod stretch is out of the equation.  Out of boost drivablility, well i think that has been pretty covered...but i think....

Low compression, low RPM, big bore would make for a lazy dog out of boost on the street.  The additional displacement of the bigger bore might have some effect compensating for the loss in CR. 

[Logan76]

This plays into my build before, Ive only ever worked on my nissan's (CA18DET, KA24DET) and they came from factory with a lower compression ratio than my current B16, The b16 doesnt mean much to me, So I will probably blow her up trying. With a .57 trim, water/meth injection, is it possible for me to break 350whp on stock internals? If you need more info Ill gladly give you it, I just want to know what the limits on the stock internals of a B16a are.

[ratcityrex]

If high compression is so great, then why do all the vit. pistons in the d's do so well with such little compression?


Fuck it run what ya brung Low comp for TeH WhhhHiiiInnnzzzzZ

[HiProfile]

The problem is everyone is trying to do the WRONG thing with their turbo setup.

People 8:1 setups are trying to race at 2000 rpm, people with 11:1 setups are trying for high boost. Then their's the people with 57trims on the street running just 10psi, and whining about off-boost power. None of them even have an idea of where peak cylinder pressure should be with timing, let lone where it ACTUALLY IS with their tune (for low RPM). Rarely do people push the limits of off-boost timing, despite their changed static compression REQUIRING it.

If you want street power, get a turbo that actually spools sometime the same day, and run higher boost. That entails getting a better MAP and at most 9:1 CR if you want to run pump gas. As fun as a the power from a big, laggy turbo can be, its not intended to feel fast at all RPM's. Or better yet, get Roger Mcdaniels to hurry up on his B-series M90 kit.

[bigdaddyvtec]

I am going to run 9:1 mainly because everyone else seems to do good with that.

I was talking to mike laskey........ and i actually doubt he builds his own motors........


I was trying to ask him about differences between 9:1 and 9.5:1 or 10:1 CR. He basically said use 9:1 and he doesnt know about anything else and to ask my tooner because he doesnt know.


I couldnt reply..... I didnt know what to reply with. Depending on tranny, if Josh can get that thing back together that is at spikers. I want my tranny to hold. If it cant at 700whp I wont use it

You WILL break that tranny Levi. Maybe not on the first few PASSES, BUT IF YOU DRIVE THAT pile of shit half as hard as Id drivew your cousin... It WILL fail... Its not even debatable. YOU NEED a gearset for your power goals.

[Urban Indian]

yeah i guess


Just spending another 3-5 G notes on my shit pile this year will most likely not be feasable


So the plan is to get it tuned on a street tune(have that money) and then go for gold with the tranny thats at your place


and when it blows the fuck up Its not like I didnt think it wasnt going to.


I am going to just run the street tune with my virgin SIR tranny until I can get the money to run a liberty or something the like and go back to maxing my turbo.


Balls to the wall, or nothing

[Conceptz-X]

CP's are the shit

+1

14:1 and go home on the trailer

fixed


Also look into rod ratio and quench area, they play a role in pre-ignition and detonation.  I have my preferences, but not going to elaborate too much, basicly I like a lower ratio rod (keeps the piston from dwelling at the ends of the stroke)  and as much quench as possible (dish in piston to match head), and .035-.045" piston to head clearance

[BoostForLife]

Seen a civic at BOTI last year.
Spiker probably knows this dude.
4dr maroon eg made over 600whp on 10:1 pistons.

[danz]

14:1 and go home to the trailer

fixed

fixed squared.