Pondering buying a forged 355 setup from a guy here. Eagle crank and rods, 3.48 stroke and 5.7 rods. Piston appears to be -22 cc dish JE but he thought it was -31cc. Question that I have is basically about the quench and suggestions for head gaskets to get a decent compression ratio to run about 10 psi boost and about 100-150 shot on rare ocassions. I have read you want between .035-.045 but I only see a few gaskets available for LT1 and that limits me there. What is the downfall of a quench higher than .045 and how much higher would you go because I was going to keep the deck up some to lower compression but from what ive read thats not a good idea in a supercharged application. The heads I plan on using are stock CNC ported with 54 cc chambers. Ive played with the calculator and the best I could see with the fel pro gaskets decking to .005 and assuming from the part numbers the guy gave me that the pistons are in fact -22 cc,....I could only come up with 9.5:1. Is this low enough for what I want to do? Suggestions are welcome as this is my first boosted/N2O engine and I dont want to do this twice!

 

Run Race Gas When Using N2O. You can cc your pistons when they are installed.

 

as far as gaskets...cometics mls head gasket seems to be the popular choice for FI, pretty reasonable price too...

 

I prefer a lower CR, but with 10psi you should be ok. The MLS type gaskets (Cometic, etc.) are a good choice, but the block and head deck need to be smooth, flat, and true if you are avoid seepage when using them. Not as bad as copper though, for sure. Quench is less of an issue on a blower motor. As long as it's not more than 0.050" or so, don't worry about it. N2O plus boost plus pump gas is going to be problematic - I'd be careful with the nitrous. I only use the nitrous when using 104 octane unleaded, but my combo is a lot higher boost and maybe with 10psi you will be ok, I can't tell you for sure. Run a VERY cold plug when using nitrous and boost, keep it rich, and don't expect it to last forever.

Good luck.

Rich

 

Why is quench less of an issue in an F.I. application? Is it because under boost you are already incurring significant turbulance (fuel atomization) and reducing the potential for detonation, negating the necessety for a tight quench? I was most curious about this as well.

Yet again, I called upon the almightly SEARCH functionand came up with this thread. It has some intersting points for both sides of the argument, but no definitive answer:
http://web.camaross.com/forums/showt...ghlight=quench

 

The idea about the relative unimprtance of quench with a boosted motor is an empirical one - I have seen boosted motors do fine with 50 thousanths clearance. As to why, I'd guess the same as you about turbulence, but though that's logical I have no way to prove or dispute it.

Rich

 

Correlation does not equal causation.


One question, and although it is going to SOUND like a wise@$$ question it is actually meant to be serious...

If you were building an engine, boosted or not; would you use a .050 quench?

 

Some hypothesize that with a boosted motor, quench is less important, since atomization (turbulence) is created with the introduction of positive pressure. Other s theorize that the flame front still has too far to travel under these increased compresion ratios, therefore increasing detonation potential. Adefinative answer with asupporting evidence has yet to be presented (based on my very limited research).

Let me futher complicate this quandrum. If you had to decide between .050 quench/ 9.4 to 1 compression or .035 quench/ 9.8 to 1 compression with a typical D shaped forged piston; which would you choose and why?

 

I would choose the .050 quench and 9.4:1 compression because the lower compression is better for FI and .035 quench is cutting it too close.

 

OK, did some more research and with 5.7 rods on a 3.48 crank with -24cc pistons, deck to .010 with .030 overbore and the 54 cc heads with a .039 head gasket I can get down to 9.2 to 1. More realistically I am probably only going to run about 8 .lbs of boost, most likely XE 224/236 114lsa cam. Will I be ok with a 100 shot on top of this, for track or serious a$$ whoopin' power on the street on 93 octane? Im going to either run an I/C or H2O/meth injection kit or both. Suggestions? Ive heard tuning a SC car with N2O can be a nightmare, any thoughts on that? Do I need 2 tunes and flip back and forth, or could I just run a MSD BTM and pull a few degrees extra out?

 

My advise is to eventually run more boost (10-12 pounds). Not too much nitrous, maybe a 50 shot.

 

Ok, since starting a new job that kicks ***, I have decided to go with a 383 setup instead of the 355. The place I work has connections and im going to get most of this done at a great price so, im opting for the 383. That being said, its going to be forged eagle crank and 5.7 rods, decked to .010 with -31 cc JE/srp pistons. Ive got the heads mentiond above, 54 cc cnc ported flow around the same as LE2's and im going to have the exhaust chambers cleaned up a little more. This setup should put me about 9.2 to 1 if im not mistaken, please verify. I know the powerdyne is a small unit but this is what I have already and I will probably upgrade to a procharger later since my boss has a hookup with them. For now though, im going to spin about 8 psi out of the PD unit but on a 383 will most likely read less. Question now is, im not sure what cam to go with. I was going to use the xe 224/236/114 (cc503 i think?) in the 355 but now since im going bigger cubes, is this still going to be a good choice of cams? Im looking to keep this setup streetable and on 93 octane. Will this setup be able to run a little N20? Thanks

 

If you run a wet N20 system you can tune the engine for the blown setup, then size your jets to provide the right fuel mixture for the combo. Like Rich, I only add the nitrous when I'm running race gas to manage detonation. I also pull another half degree of timing per lb of boost with my ignition system (dial in the cockpit) when running nitrous.

 

This guy has it down! I have two programs and when using more than a minimal amount of nitrous, I take a bit of timing out. Mine is so far retarded anyway (24 degrees) that I don't have to take much out. FWIW, it makes max hp with 24 degrees under boost and 22 degress with a 100hp nitrous shot. I assume that means the combustion is efficient.



Rich

 

9.8:1 with the .035 quench.

Because your not close enough to pushing the compression boost to me, and I'd probably run more cam than most guys.

Bret