64 or 70 cc

by driveit Fri Oct 04, 2013 9:24 am

Trying to update my engine and make it perform, but with gas saving in mind.

New engine is to be 30 over, with flat top pistons.

Currently has a Weiand 7530 intake, Edelbrock 600 carb and headers.

looking at a Edelbrock Tokers Plus cam and Performer RPM head.

Which combustion chamber would I need to go with. The 70 would give less compression which should mean better mileage. Right?

by dynchel Fri Oct 04, 2013 10:25 am

Idk about mileage, but the higher the compression, the higher octane rating fuel you will have to run. I have 58 cc heads with flat top pistons and 92 is the absolute minimum octane it will run on.

by driveit Fri Oct 04, 2013 10:46 am

going with the 70s then. Now all I have to do if take up donations to buy the heads.

Penny for the poor?

by 77mali Fri Oct 04, 2013 12:13 pm

dynchel wrote:Idk about mileage, but the higher the compression, the higher octane rating fuel you will have to run. I have 58 cc heads with flat top pistons and 92 is the absolute minimum octane it will run on.

My Vortec's are 64cc with Flat-tops, running about 9.5:1 compression. Seems like it's plenty power-wise with the mild cam and standard 3.48 crank. Nothing outrageous but enough to make you happy. I plan to run 92/94 (or airport fuel when I can get some). The killer is the 10% ethynol Jacking

by dynchel Fri Oct 04, 2013 12:42 pm

i used to mix 3 gallons of cam 2 with a tank of 92 octane. that made it run good, plus it is old school leaded gas. GoFast

It was funny, you could only pump it directly in the car if it was on a trailer, otherwise they would shut off the pump and yell at you. Rolling Eyes

we can get plane fuel here also but i've always been taught to go with cam 2 if its available.

by dynchel Fri Oct 04, 2013 12:47 pm

driveit wrote:going with the 70s then. Now all I have to do if take up donations to buy the heads.

Penny for the poor?

I believe i read some where that if you are going with aluminum heads you want very small chambers as aluminum sheads heat quickly. heat = power. someone can correct me if i'm wrong.

by driveit Fri Oct 04, 2013 1:22 pm

I am thinking that the 64s would be fine. Everything I am reading tends to lead that way.

by bracketchev1221 Fri Oct 04, 2013 5:54 pm

Ok, before we go any further, what do you consider flat top pistons? 4 valve relief pistons, pistons with a ridge around 4 valve reliefs (semi dish), or a 2 valve relief flat top piston. You can be anywhere from 9 to 10.3-1 with these. With that being said, is there a specific gas you want to run? A 2 valve relief piston with a 64 cc head will get you 10.3-1 in a 350. But it will be pushing it on 93 octane and a steel head. A 2 valve relief and a 70 cc is like 9.7. Which is great on 93 with a steel head. A 4 valve relief flat top and a 64 cc head is good on 93 as well. A 4 valve relief with a ridge is good with a 64 cc and like 87-89 gas. If you are going for an aluminum head, go with the smallest chamber you can get. Aluminum dissipates heat and needs more compression. I have the SRP 2 valve relief pistons in the Nova with a 65cc AFR 195 head.

http://www.summitracing.com/parts/slp-l2403nf30/overview/make/chevrolet
http://www.summitracing.com/parts/slp-l2256f30/overview/make/chevrolet
http://www.summitracing.com/parts/srp-138093-8/overview/make/chevrolet

by driveit Sat Oct 05, 2013 8:19 am

bracketchev1221 wrote:Ok, before we go any further, what do you consider flat top pistons? 4 valve relief pistons, pistons with a ridge around 4 valve reliefs (semi dish), or a 2 valve relief flat top piston. You can be anywhere from 9 to 10.3-1 with these. With that being said, is there a specific gas you want to run? A 2 valve relief piston with a 64 cc head will get you 10.3-1 in a 350. But it will be pushing it on 93 octane and a steel head. A 2 valve relief and a 70 cc is like 9.7. Which is great on 93 with a steel head. A 4 valve relief flat top and a 64 cc head is good on 93 as well. A 4 valve relief with a ridge is good with a 64 cc and like 87-89 gas. If you are going for an aluminum head, go with the smallest chamber you can get. Aluminum dissipates heat and needs more compression. I have the SRP 2 valve relief pistons in the Nova with a 65cc AFR 195 head.

http://www.summitracing.com/parts/slp-l2403nf30/overview/make/chevrolet
http://www.summitracing.com/parts/slp-l2256f30/overview/make/chevrolet
http://www.summitracing.com/parts/srp-138093-8/overview/make/chevrolet

Thanks. I do not know what the actual piston is. I was just told they were flat tops. I'll check. Thanks for the info and recommendations.

by 77mali Sat Oct 05, 2013 9:34 am

Flat top vs "domed" or "dished"- this page has the other varieties too on it so you can see the types.

http://www.northernautoparts.com/ProductDetail.cfm?ProductId=2126

Mine are 4 valve relief as bracketchev mentioned. I think it's now a 355 or 360 I forget the new bore size but maybe 4.04 with the standard 348 crank.

by pila Sat Oct 05, 2013 9:50 pm

Some years ago, when I built my 400 to a 406, the pistons for using 350 rods in a 400 weren't available, so I bought stock 400 pistons. The 350 rods are 5.7 " long, and the 400 rods are 5.565 inches, so I milled .135" off of the tops of the 400 pistons, and milled valve reliefs on one side.
The compression ratio, using the CC method, came out to be 9.8:1. The engine had a lot of power & torque, but required premium gas.
In later years, after 76,000 more miles, I rebuilt it again, going to + .040 oversize, and used Keith Black pistons, which were for the 400 w/350 rod combo. These are 9.2:1 pistons.
The loss of power from the 9.8 to the 9.2 was noticable, but it's not as picky about fuel octane as it was at 9.8.
The point is, higher compression makes power differences that can be noticed.

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64 or 70 cc

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