Highest possible SAFE CR on pump gas?

[2M6]

I am building a 3400 for my '88 Fiero GT and still haven't decided whether to go FI or NA. I am leaning towards NA but am wondering what others with performance built NA 60V6 are doing as far as CR. While I'm at it, I might as well ask about cams/valves/rockers... Thanks

[1QUICKHATCH]

well their are a few people running 11:1 no problem on pump gas, but I don't know how much higher you can go!

[robby1870]

Brian's going to have like 11.3 or something. Im planning on the same. I think 92 octane should do the trick

[2M6]

So 11:1...thanks for the help guys. Much appreciated.

[SappySE107]

12:1 has been ran. Cam profile will make a difference as well.

[Rhedalert]

Brian's going to have like 11.3 or something. Im planning on the same. I think 92 octane should do the trick

More like 12:1...but if you have a low profile cam then even 10:1 would need premium

[robby1870]

Brian's going to have like 11.3 or something. Im planning on the same. I think 92 octane should do the trick

More like 12:1...but if you have a low profile cam then even 10:1 would need premium

Using the Iron head head gaskets?

[Rhedalert]

Brian's going to have like 11.3 or something. Im planning on the same. I think 92 octane should do the trick

More like 12:1...but if you have a low profile cam then even 10:1 would need premium

Using the Iron head head gaskets?

Buhh? ok fine!!! 11.7:1 Deal?

[Fierofiend]

Out of curiosity, are you using the fiero intake system, or the 3400 aluminum heads?

[2M6]

I am using the complete 3400 engine. I will be using forged pistons and possibly some Trick Flow forged con-rods out of the SBC in my garage. I am open to suggestions as far as performance and reliability as this will be primarily a DD but also will see some autocross and the occasional drag strip pass. I am hoping for 250 at the crank on 91 pump gas.

[DEI37]

It all depends on the supporting modifications. I would think that with the right timing, cam profile, and intake/exhaust setup, 93 octane would support upwards of 13.0:1. You'd be pushing your luck, but with a little "home made" octane booster, you could probably run 110+ octane unleaded, and be just fine.

[Fierofiend]

Just wanted to chime in and say nice car.... white GTs rock.. just 85 vs 88, lol.

[quaddriver]

Re: Highest possible SAFE CR on pump gas?

I am building a 3400 for my '88 Fiero GT and still haven't decided whether to go FI or NA. I am leaning towards NA but am wondering what others with performance built NA 60V6 are doing as far as CR. While I'm at it, I might as well ask about cams/valves/rockers... Thanks

short answer: as high as u can go until detonation occurs.

long answer: consider if you will, the chevy LT1/LS1 motors

to get 10.5:1, they use aluminum heads, reverse cooling and very sophisticated managment/flow changes.

aluminum heads will reject far more heat from the combustion chamber - needed.

the coolant flow of the 660 motors is going to hurt you, there is no way to reverse it, so everything must come up thru the block - the transfer ports suck and cannot be fixed with stock parts. the block at teh very least will require plugs in the deck to even the flow 'front to back' (actually side to side in a transverse)

the chevy v8s use finely tuned intakes and sfi fel metering to make sure all cylinders are alike, there exists no such intake for a 660, sfi does exist so you will need that, but there is also no beast like optispark which you will need.

there is a KS on the 660 motors, but you will need to change the stock programming, stock GM programming makes the timing/fule changes effective for a number of rpms, the LT1/LS1 motors make them effective nearly as granular as fire to fire for that hole.

in short, I dont think it safely can be done past 10:1

[2M6]

So 10.5:1 then?

This has turned into a very informative (but slightly confusing to me) thread. I don't understand some of the things being discussed but I am definately willing to learn. All this talk about different ECU/M's has got me thinking. Should I use the factory ECU for the 3400, an aftermarket ECu for the 3400, the stock Fiero ECU, or an aftermarket Fiero ECU? I didn't think the Fiero EDU would work as I plan on using the entire 3400 engine complete with DIS. Any advice on this is appreciated.

[bszopi]

Since the conversation was turning into a computer tuning topic, those posts have been moved to a new thread in the COMPUTER TUNING area of the forum. Please feel free to continue on with the conversation in that thread.