V's Vette

Since I've done a couple of searches to find this info and had no luck, what is the max CR I can aim for w/my '89's engine? I'm planning to do a rebuild w/a 383 stroker and don't know which style of pistons to use.

Any help/tips appreciated!

8388

If your gonna keep the stock heads, the pistons are gonna be dished between 28 and 30cc yielding around 9.0:1 comp. Perfect for boosting

12cc dish will be closer to 10.75:1

Pete K

On pump gas, fuel injected,aluminum head cars I shoot for 10.5-10.75 to 1. This makes me happy. I am also carful to keep the quench at a minimal amount. This makes a more efficient package that is less octane sensitive and more powerful.

8388

With the quality of gas I'm seeing at the pump these days, I would have to think twice.

Pete K

Thanks for the tip.

V's Vette

Good point about the quality of gas...I forgot to mention that here in Nor. Calif. the top octane at the pumps is 91, and I'll be using my stock aluminum heads. So, given these additional factors, what is the top CR I should aim for?

8388

I would go about 9.5:1
Back in 91 I built a 383 with only 9.0:1 and this engine surprised every body in how well it ran. I used an old trick (special cam) the cam made the engine think it had more compression than it actually had. The 3500 lbs + car had a best run of 121 mph in the 1/4. It would pull factory vacuum and had all the manners of a stock factory car. Idled like a stocker too.

V's Vette

Hey 8388, what cam was this...how can I get one really similar?

8388

The cam is made by Wolverine Cams. Wolverine is or was a sister company of Crane cams. The specs : Billet roller 224/232 @.50 lift was .490/.510 lobe sep. 115. Cam did real well between 2000-6500 rpms, on the 383.

2manyfuncars

I'm running a real 11/1 with .040 quench and JE flat tops. Combustion chamber design and cam specs will have a huge impact on how much compression you can handle with pump gas. In my application it works. I just use 100 octane unleaded at the road race track for insurance. It's only a couple of times a year so I can afford it. On the street I haven't had any issues.

Good luck

information junkie

the cam has a large affect on how high of a CR you can run. ive run a iron head 350 with 11:1 on 91 octane gas and had no problems. but i would rather keep it around 9-10 and not risk having problems. i cant remember what cam it was but i do know they quit making it a few years back. the quality of pump gas these days seem to have gone down like 8388 said so thats another factor to look at. personally i would try to stay down below 10:1

ZD1

10.8 is a good mark with a good quench

I was running 11.1 compression ration with a lot of ping...I used a fat head gasket 0.051 to lower CR.

I am now running 11.6 compression ratio with no ping using a .039 gasket with 0.005 piston out of head clearance...mind you with upwards of 39 of advance (still tuning!)

quench hieght is definitely important...I say let whatever reasonable CR using a forged piston (hyper are nice, but tend to melt/crack/explode under more extreme circumstances like over heating)

p.s. I am using cryo treated and coated pistons and rods