12.0 + CR?

[Kreb]

OK, entertaining the idea of the gen 3 head/intake on a 3.4. I'm told that'll give me a CR in the low 12s which seems like trouble with the stock bottom end. but...... What if I was to run something like Megasquirt with it, where I could enrich the A/F mixture and play with timing? Perhaps even knock sensing? Water injection? Or is that too much trouble where I'd be better off just getting good dished pistons?

Also, is there a simple formula for HP increase with higher CR levels?

[TurboGTU]

RE: 12.0 + CR?

The truble with high CR is the cylinder pressure. You can get away with it..My SHO is running 11:1 on a 3 liter on a 3600lbs car..and thats stock. MY 65 truck is also 11:1 on 4K lbs with a 327. Timming is everything. You have 3.4l on an fether weight..(awsome ride!)..so thats a walk in the park. CR won't kill the bottom end..rpm will. search for choosing the right cam on hotrod.com. That should give you good ideas. I know the MS system is easy to tune..but I don't know if it has ability for knock sensing.

[SappySE107]

RE: 12.0 + CR?

I have tuned a few cars in the 12:1 range, and surprisingly enough, its no big deal at all. Now, this is using the aluminum head programming. The iron head programming will not allow for this stock because iron heads need more spark advance to begin with. Use the gm computer 1227727 or 1227730 (same thing, one is water proof). If you are using a manual trans, either is fine. There is software to allow you to tune the engine and its cheaper overall than the mega squirt.

Oh, and if you tune it right, you can even run at least mid grade fuel. WIth headers on a gen 3 motor, we were able to get it to run good on the regular. I want to see if 16:1 has any way of working on just premium now. hahaha, BOOM!

[Froggx]

Re: RE: 12.0 + CR?

I have tuned a few cars in the 12:1 range, and surprisingly enough, its no big deal at all. Now, this is using the aluminum head programming. The iron head programming will not allow for this stock because iron heads need more spark advance to begin with. Use the gm computer 1227727 or 1227730 (same thing, one is water proof). If you are using a manual trans, either is fine. There is software to allow you to tune the engine and its cheaper overall than the mega squirt.

Oh, and if you tune it right, you can even run at least mid grade fuel. WIth headers on a gen 3 motor, we were able to get it to run good on the regular. I want to see if 16:1 has any way of working on just premium now. hahaha, BOOM!

Could you give a brief run down on why the iron heads need more spark advance, you just shot one over my head?

[Kreb]

I've been reading about water injection, and think that may be the ticket to control detonation and still allow plenty of advance with the 12 CR system.

I'd also like to convert to EFI for drivability reasons, and I'm vacilating on whether I want to dedicate the necissary time to learning megasquirt. Will e-manage or other piggyback engine management systems work with the stock 3400?

btw - isn't there a step-by-step data page on converting to the 3100/3400 top end somewhere on this site? Could I get a link?

Thanks guys.

[bszopi]

I don't think there is an actual step-by-step page for it, just a bunch of threads from the guys who have done it. One of these days I really am going to get all the data together and make the page, I just have to find the time to do it...

Well, wait... The above applies for putting a 3400 top end on an old style 3100. Lemme get the link for the Gen2 to Gen3 top end...

http://60degreev6.com/modules.php?op=modload&name=Pushrod&file=index&req=viewarticle&artid=35&page=1

And I think in your case, it will be different still because you are going onto a RWD block, correct? Probably need to put something together for that one as well. Again, there are several good threads about it, you just have to search for them.

[Kreb]

There is software to allow you to tune the engine and its cheaper overall than the mega squirt.

What software is that?

[GinoBeats]

I'm running close to 12:1 compression in this beast

[TurboZ24]

The iron heads run a much larger combustion chamber vs the aluminum, therefore need more spark advance. I believe the iron run a 52 CC combustion chamber while the aluninum run like a 24 CC.