Testing The Waters

[Jason@DSG]

Originally Posted by diss7

Thats why porn sites do so well.

They have discussions about rod compression in a different kind of cylinder

[wparsons]

Originally Posted by FreshFRS

i agree with most of the guys here, i mean my s2k went turbo (built motor but 11.5:1 comp) and i ran 15psi on pump gas through it with no problems and for lots of kms (<75,000) i drove it hard too and in winter. a better example in the Cobalt SS/TC 2.0 Ecotec, DI with 10.5:1 compression guys are running 400+whp out of 24Psi on the stock block with pump gas (94 here in canada), 9:1 is overkill and is going to kill off boost response. unless you want 40+psi with lots of lag anyway i really don't see anything less than 10.5:1 being viable for the street. this is all IMHO anyway.

Power on the s2k was 445whp/305tq @15psi is what we settled on, 18psi needed meth injection to be liveable. though we managed to make a couple runs without meth. This is on Engine without DI or VVT (VTEC kicked in at 4300 and only has 2 profiles) which would increase the boost threshold for sure. @Jason@DSG

Also food for thought, s2ks that had lowered compression(8.8-9:1) are running 5-7psi more than this car to produce the same power/torque. stock 11.3:1 compression blocks have generated 520+with 93+ meth at 17-18psi, 701/450 at 27psi on 116 and 740/470 on E85 at 30psi.

And that's without DI too! I see no reason why an FA20 with forged internals at 12.5:1 couldn't hold ~450whp on pump gas easily for a long life.

If you're after a lot more than 200hp/L, then sure you'll want lower compression but if everyone is being honest, how big of a market is that compared to the 350-450whp market in a 2800lb rwd car? Even 400whp is A LOT for these cars to put to the ground, what good would 600whp+ do you beyond bragging rights?

[ShadowSeraph]

No matter what route you go, it has already been shown that 700+hp can shred the gear box. $$$$$$$$$$$$ for anything >600

[w00t692]

Originally Posted by Jason@DSG

I guess the R35 has it wrong too at 9.0:1, maybe someone should let the guys making 1600-2000hp know that the experts here recommend 12.5:1 or higher to make big power, they're definitely missing out

http://en.m.wikipedia.org/wiki/Nissan_VR_engine

When you're making big power i agree with you. But are you really saying people should run 9:1 when their goals might only be 500 whp? Because i'm not ever going to agree with you on that.

[w00t692]

Originally Posted by Jason@DSG

It's not low tech...lol running high compression and high boost is asking for trouble tech. Any big power is also low compression. Please get me any engine build over 450-500whp with compression over 10, please (forced induction)...that is a daily driver on pump fuel (I'm aware of all our race setups on race fuel -- I'm talking every day cars running 91 or 93 oct)

http://www.8thcivic.com/forums/turbo...-si-build.html

Drives it every day on 91 pisswater. There's a dyno in there he's at 440 hp 330 tq i think.

11:1 compression stock motor. I'm sure he could add another .5 psi to hit 450 for you if you want.

His other civic is a ERL built bottom end with 10.5 or 10.8:1 compression (i forget which) wiseco pistons.

Massive turbo, only dyno of it is over 700 whp @ 20 psi i think?

[Jason@DSG]

Originally Posted by w00t692

When you're making big power i agree with you. But are you really saying people should run 9:1 when their goals might only be 500 whp? Because i'm not ever going to agree with you on that.

You need to read up. I was never saying that everyone should do 9.0:1 (aside from any big power builds for the safety aspect). I was using that as numbers from other engine platforms and theoretical numbers.

I think 10.5 would be a perfect spot but only time will tell. I can personally see it being lower IMO. There's a reason almost every factory 2.0L car is running in that range of 9 for high boost. Even on my car, I have lag at 1000-2800rpm but then boost is on and it's amazing. I also run 94 octane (lucky to have it here).

Even in my original post I mentioned it was just numbers for an exams showing that lowering the static compression will lower the full boost zone keeping things safer for pump fuel applications.

[w00t692]

Having the car be a dog out of boost sucks. You're gonna lose 2-3% torque every 1 point of compression you drop off along with adding 100 or so rpm of spool time to that turbo.

The focus st ecoboost 2.0L DI engine has a 10:1 compression ratio from the factory, the MS3 2.3 DISI turbo is 9.5:1

You're just talking old hat sir.

[nelsmar]

Originally Posted by w00t692

Having the car be a dog out of boost sucks. You're gonna lose 2-3% torque every 1 point of compression you drop off along with adding 100 or so rpm of spool time to that turbo.

The focus st ecoboost 2.0L DI engine has a 10:1 compression ratio from the factory, the MS3 2.3 DISI turbo is 9.5:1

You're just talking old hat sir.

The new wrx is 10.6:1. =x

[w00t692]

Originally Posted by nelsmar

The new wrx is 10.6:1. =x

You talking about the new 2.0L motor?

[Jason@DSG]

Yeah exactly, I think 10 range for this car boosted will be really potent.

[dave77]

Originally Posted by Jason@DSG

That's the whole point with these pistons. They lower the compression to allow much more boost or the same boost at safer levels.

Lol for sure. I think meant to post that in another thread, where people just throw on turbos on the stock engine. not sure why I missed your low compression pistons lol, my bad.

[Jason@DSG]

Originally Posted by dave77

Lol for sure. I think meant to post that in another thread, where people just throw on turbos on the stock engine. not sure why I missed your low compression pistons lol, my bad.

Ha! I think my original intent was misinterpreted. I might close this thread and post up a cleaner more concise thread with easier to find info for everyone. I appreciated all the input though. Hopefully this will help everyone make the best decision for their applications. Cheers man!