justYncredible

iTrader: (1)

some of you may not know that i have dropped a valve in my motor making it useless. i havent opened it up but Turbo-LS and i came to that conclusion the night it happen at the race track. moving forward, i have sourced a fully built head and a 84mm sleeved blocked from my tuner that he has been sitting on for a few years. im seriously considering moving up compression from 9.1 to 10.1. my reason is to gain a little more low end and to be able to achieve the same hp with less boost. im not real sure if ill see any serious difference since im not moving up in compression like from 9.1 to 11.1 and up. my last setup

gsr motor
itr cam
9.1 Cp 81mm pistons with eagle rods
victor x manifold
ramhorn manifold
garrett t3/t4 57 trim .63ar
460/311 on 93 octane

so im wanting to move to 10.1 84mm pistons to improve the low end but i want to achieve similar whp gain on 93 octane. im wondering would it be worth it to move up or just stay where im at. ill be using the same parts on this motor as well until i decide i want to get a bigger turbo or shodan turbo down the line.

lastly, when i ran my car at the track my best 60 foot was a 1.7 on my last run before it blew on the top of 3rd gear on high boost. my low boost i was getting 1.8 (i believe) on my 60 foot and i was running consistent 12.0. honestly, i just want to run high to med 11's and i knew my last setup could do it. i just needed to prove it to myself but like i said earlier i dropped a valve due to a tired gsr valvetrain running itr cams. any input would be great so i can start my build thread with my opening pic

riceball777

It really depends on what type of fuel you plan on running most of the time.

Higher compression = more power per pound of boost but on pump fuel you have to run less boost than the lower compression engine

With race gas/e85 both a low compression and high compression engine can max out a certain turbo set up and both will make the same hp. The higher compression will use less boost and will have better off boost power and will have better low to mid rage power due to it making more power per pound of boost

On straight pump 91/93 octane the lower compression engine will make more power due to the fact that it can run more boost.

Example
My stock s2000 engine is at 11.0:1 compression. I make 442whp on 91 octane and over 600whp on e85/race gas. I know another s2000 with the same exact turbo set up as me but with a 9.0:1 compression motor. He make 540whp on 91 octane and the same over 600whp on e85/race gas. I can safely run 14 psi on 91 octane. Turbo gets maxed out at 19 psi on e85/ race gas. My buddy can safely run 22 psi on 91 octane and the turbo gets maxed out at 30 psi on e85/ race gas.

Moral of the story= run low compression for pump because it will make more power. Run high compression for race gas/e85.

Low compression has the advantage on low octane pump fuel. High compression had the advantage on high octane race gas/e85.

For myself I rather have low compression because I drive my car on the street and I am forced to run 91 octane fuel 99% of the time

justYncredible

iTrader: (1)

What you said is more or less exactly what my tuner told me. I like to drive my car and he knows that as well.

Turbo-LS

iTrader: (4)

Dude you can run 10:1 compression on 93 octane all day every day and boost no problem. Stock gsr motors are over 10:1 and do just fine and reliable

Rice ball your so far from the truth dude. Lower compression won't make more power. You'll make the same amount of power just takes less boost on higher compression. Higher compression the motor will have better throttle response in and out of boost. The turbo will respond better and it will be overall more efficient. Your not trying to run 13:1 on boost here it's 10:1.

Not to mention VP is located in San Antonio and you can get race gas easily for when you want to turn the power up to full tilt and being sleeved gives you more room for error. IMO if tuner is telling you that higher compression won't work. Find another tuner because it's done day in and day out. This isn't a crusty v8 American engine it's a very high efficient 4 cylinder honda.

OBRJosh

Just Go 9.5 if you can't make up ur mind lol

Turbo-LS

iTrader: (4)

There ya go half way in between hahaha

riceball777

Of course you can run 10.0:1 compression. I'm on a stock f20c and my compression is 11.0:1. All I'm saying is that with a turbo running Low octane pump fuel a low compression motor will make more power

blackeg

my motor is right at 10:1, 84.5mm. id have no regards against going 10:1. pistons/rods/sleeved block it will be strong. id think that you are about on the ragged edge of that turbo's efficiency and i might look for something larger if you increase the displacement of your motor

justYncredible

iTrader: (1)

yeah the turbo max is 475 but i dont want to push it anymore than what i have done already. my old setup was good and its the only setup ive done and know best.

TheShodan

iTrader: (14)

Agree with this. I'm at only 10.2:1 on 93 octane at 18psi on a GT30R-based turbocharger. the off boost response with "less boost needed" is really dependent upon what turbocharger you're using and the efficiency range of that turbocharger given a specific amount of boost. However, in your particular dilemna, going from 9.0:1 to 10.0:1 is not nearly as significant as say somethingin the 7.8:1 - 9.0:1 range that people associate with " old style" thinking.

I think 10.0:1 is fine. the more important thing is to make sure that with the equipment you decide to get that, like Muckman found, that you make sure that the wrist pins were designed to work with the increased cylinder pressures associated with turbocharging.

justYncredible

iTrader: (1)

I'll have to hit up Cp to find out but they should be fine but I'll still need a confirmation.

Turbo-LS

iTrader: (4)

Don't run the standard wrist pins always opt for the upgraded pins.

4genaccordfreak

Aside from the mechanical aspects of a static compression change, which you guys discussed above. The other aspect needing attention will be tuning. Increasing compression decreases the "room for error" so to speak in the tune. More on the IGNITION side, fuel trim will not change much. Ignition tuning will need to be "very good" especially when using pump fuel, which shouldn't be a problem in the Texas area. Lots of reputable/professional tuners around.

Avoiding the increased likelihood of detonation with static compression gains is probably the most important in your case, since your power level is still very "conservative/streetable" and most off-the-shelf engine internals will be fine under 500whp. Although upgraded wrist-pins are a no-brainer if you're planning to increase the power with a turbo upgrade.

justYncredible

iTrader: (1)

Is there an unknown issue with Cp wrist pin? They seem pretty beefy to me but I haven't compared them to anything else.

Oh ya, justin knows my end goal. I better be prepared for it if I decide to go that route.

wantboost

iTrader: (2)

that says it all. 11:1 is much more efficient than 9:1... you max out the same turbo at 19psi where it takes your buddy 30psi to make the same exact power

not to mention high compression motors are more efficient (3% for every full compression point increase) It's not only thermal efficiency but you'll get better fuel economy and better power off boost. just look at muckmans NA dyno of his 9:1 motor vs his 13.5 motor. the higher compression motor literally makes more power everywhere over the 9:1 motor

going from 9:1 to 10:1 won't be a drastic change but you will see moderately better power off boost, more mpg, and better midrange in boost

motoxxxman

if you take two identical engine/turbo setups, run them with the exact same pump fuel, but one engine is low compression and the other is high compression, the engine with higher compression will always make more power everywhere when comparing power levels at identical manifold pressures. for obvious reasons.

and like said above, higher compression requires less boost to make equal power, because the higher compression makes more power per psi of boost.

if you take the above setups, and max them out, if the lower compression engine makes more power it's ONLY because the tune is done much differently, and the low compression engine was probably tuned properly, whereas the higher compression motor with less power was probably tuned MUCH MUCH MUCH more conservatively in order to prevent engine damage, because of the smaller room for error in ignition timing with higher compression.
ie: if both engines are tuned for best power all in all, and are just below the knock limit, aka peak safe power for the overall setup; if something happens and ignition gets advanced 1 degree; the low compression engine will most likely survive with minimal damage whereas the high compression engine may go off like a grenade or become a pool of molten metal. (a bit of a drastic example, and slightly exhaggerated, but its still completely true)

moral of the story: peak power will be identical if the setups and fuel are identical and the tunes on both are absolutely flawless and ideal. the only difference will be the boost pressures, for obvious reasons. the problem however is that you can not measure what the absolute highest power level can be unless you keep going til it blows. cuz only then will you know that peak power was a hair lower than the amount that blew it up.