bldgengineer

iTrader: (1)

I'm debating between buying a -11 dish or -3.2 dish piston set from Wiseco.

The -11 will bring me down around 9.3CR and -3.2 around 10.1CR

E85 is hard to come by around me but I'm more than open to going meth later on. Motor will be mostly ran on 93 octane and street driven(NOT street raced). Only drag raced for fun. Not competition.

Motors specs so far:

LQ9 Block 4.030 bore
Stock crank
317 heads
cam undecided
BW T6 S480 87/96 1.32

Tech advise and future upgrade explanations more than welcome!

Thanks!

HexenLord

You can do 10:1 on 93+meth and then run race gas in it at the track. With the 9.3:1 you could run pump gas at the track as well. Only when you really turn it up going for max peak numbers or best ET would you have to consider race gas.

bldgengineer

iTrader: (1)

So basically if I went for the higher CR i'd have go meth injection from the start? At that point I'd be better off starting with a lower CR and increasing it as I progress with the motor correct?

stevieturbo

Go with 9.3. It'll be safer and give you more scope all round.

It's a decent sized turbo, so you will have no problems making enough power to blow it to bits no matter what CR you have. There is absolutely no benefit in cases like these for wanting high compressions.

qqwqeqwrqwqtq

I prefer around 10-1 for street/strip turbo engine. Makes a big difference in throttle response and turbo response and the combo will make more power overall at any given boost level.

No you can't run as much boost on pump fuel but I would prefer to run a few lbs less boost on 93 for the previously mentioned benefits. Tuned conservatively on pump fuel and maxed out but tuned properly on race fuel it will be just as reliable as something with lower compression.

Just my opinion.

stevieturbo

At 10:1 you will be severely knock limited on pump fuel and never be able to run sensible timing, nevermind optimal timing.

It will only make more power per boost if timing is right. If you're stuck with heavily retarded timing due to knock...the lower CR setup will make more power, and it will do it far more safely.

If you have good fuel available, then by all means go high, or if it is only a very low boost setup

bldgengineer

iTrader: (1)

Yeah I'll be going lower compression pistons. If I want to go higher there are other means for me to raise it. Thanks!

qqwqeqwrqwqtq

Not at all true in my experience.

As long as it isn't a stock cam, high 11's or 12-1 a/f ratio, 17-18 degrees of timing and 10-12psi boost is conservative, will live forever and be a ton of power for the street on 93 octane.

An example.

Lets say you have a 10-1 engine making 700rwhp at 10psi, 93 octane.

Now with 9-1 compression you'll need more boost/timing to make that same number which means higher IAT's and limited max output if you do run it on race fuel. (and during normal driving throttle response and boost response is softer).

For a dual purpose car I would consider 11-1 aggressive, 10-1 perfect, 9-1 very conservative and anything less is just turning the combo into a slug for absolutely no reason at all.

Exidous

iTrader: (11)

I've been debating the exact same topic for how to build my motor. Intercooled A2A no meth 93 octane.

I'm building in stages.

Mild streetable forged short block 347. AFR205's with stock chambers.

I'm at a toss up between -3cc flat tops with .054 gasket(10:1) and -11cc dish with .040" gasket (9.5:1) on a 66cc chamber.

Not at all after a max effort setup. 600whp would be MORE than enough in a <3000lb car.

Can anyone reccommend a good turbo and whether they prefer 9.5 or 10:1? I'm going to have Martin spec me a mild cam. Smooth idle and able to pass the sniffer. I guess I'm just getting old but I don't consider teh setup I have below all that streetable. Mileage is poor and it feels soggy down low. After 3500 it's pretty damn fast.

The garret turbo program suggests a gt4508 which seems kinda big. I'd like full boost to carry to redline without too much head room. Read: fast spool.

The 10:1 would obviously feel a lot better while N/A.

I hope it's not too much of a thread jack. My goals seem pretty close inline with the OP. :-)

skinnies

iTrader: (33)

If you trust your tuner, I mean really trust him, the higher is fine, if not then go with the lower or you'll regret it.

NicD

iTrader: (7)

Mostly ran on 93 octane, street driven and raced every once in a while for fun... be conservative. I would shoot for 9.0-9.5 just because I've never seen a high compression boosted motor make more power than a lower compression one when octane limited.

Exidous

iTrader: (11)

Ya the 9.5 probably does provide a lot more safety margin.