Thread: 64cc heads, 383 kit, what pistons for 8:1 CR? Need -35cc!

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So far I have come to find that the shop now claims my 193 heads are actually 64cc and that all the pistons out there will be to much compression to use regular unleaded, most will be boarderline with super unleaded. He says that with a zero deck and forged pistons we need to be at -30cc minimum and -35cc would be ideal. Whats the opinion from you guys on this? I need to do some CR math and check him....maybe after I get back from taking my family to the mall. If you guys know of a piston that will work for me with a 5.7" rod in a 383 combo please chime in. The machinist is now telling me that this plan is a no-go and that we need to stop and admit that this needs to be a .030" over 350 and leave it at that. I hate to settle for something after I have planned and dreamed about the outcome for 3 months.

8:1, that's lower than the low. 8.5 was standard for smog 350's in the 70's. 9:1 at least. 10:1 is no problem on 91 octane. I am planning on building a 9.5-9.8:1 engine, but that is because it's in a truck and I need a little safety margine for hot days with lots of dirt bikes in the back and all of my buddies in the front.

Try JE pistons, they make a lot of different pistons for all kinds of applications.

Speed Pro makes a hypereutectic piston for a 383. With a flat top piston (zero deck) and 64cc heads you would be in the ball park of 10.0 compression. You could fill up at any pump. I have had my 64cc head milled to 60cc and one terrible afternoon I realizing I had forgotten my fuel jugs at home. I stopped at the gas station and fueled up my race car with 93 octane. I had no choice. It ran just fine. I race a small block chevy that can turn 8000 rpm's but usually runs at 7400 most of the nights. I run Speed Pro pistons. They cost an 1/8 Of JE's and I have never had one fail. Use this info as use wish.

Jason

Don't forget about Wiseco, they make pistons that last over 25 hours in engines running 13,500 rpms. That's amazing.

All Speed Pro hypereutectic 383 pistons are advertised to have 10.0 compression from Speed Pro. Other piston brands vary from this.

Jason

I understand how everything is measured. I was only going off of the paper I got from Speed Pro. Again, they claim their 383 piston (don't have their part # in front of me) with 64cc heads and zero deck will produce 10.0 compression ratio. It does not mention head gasket thickness so I would assume that's with an oem gasket. I was just mentioning the information I have to try and help. If you feel this info is not correct, do not attempt to try it. Like I said I was just trying to help a guy out with information I feel was legit. I will read those two links in their entirety as time is available. Seems they may be quite valuable.

Jason

Originally posted by techinspector1
Jason, the piston alone is not what determines compression ratio. You must factor in combustion chamber volume, head gasket volume, deck height volume and volume in the piston crown, whether it be dished or eyebrowed.
Read these 2 threads....
http://www.clubhotrod.com/forums/sho...n+ratio+101%2A
http://www.clubhotrod.com/forums/sho...n+ratio+101%2A

Tech, how about dynamic compression ratio ? It stands to reason that the longer the duration on the intake valve and the longer the intake valve is open the higher the piston rises inthe bore befor actual compression takes place.

Tech, Im going with the origanal plan on parts, as in Scat crank, Eagle SIR rods, and KB 26cc dished pistons. The pistons are going to be hyperss rather than forged, I hope that does not bite me in the behind. It will be 8.77:1. He is ordering the parts today and when I get home again Ill go get the bored block and the rotating assembly and I'll do a mock-up fit, grind for clearance, and take it all back for ballance. I hope to get this in the box truck by mid january to late jan at the worst.

Question, I need a anti-balloning tq convertor, should I junkyard hunt for a factory 1-ton part or get a new ATI/B&M unit on the cheap? I dont think a stall is required with the 2040 cam, do you agree?

If I remember right I had to run a larger top ring gap with hyper pistons too. Check with the piston and ring mfgr to be sure you have the right ring gap for your combo.

Tom