i have a 89 gta with a 350, i have installed new pistons and want to know what the stock cc of the compression chamber is?

 

What cylinder heads? If they are the the 083 L98 heads, then they are 64cc +/- (casting imperfections).

 

they are the stock ones. the jegs book said if the heads are 64 i would have 10.2 to 1

 

What pistons are they? 10.2 is borderline for as high as i would go on 92/93 octane.

 

I have run 93 since i have has the car. the pistons are speed pro jegs number 844-345npstd. i also installed a comp cam 450 lift and 480 exhaust. 112 lobe sep. adjustable fuel reg and flow masters and hollowed cat 5 years ago. the rebuilt engine has i think 300 miles now. i just ordered a msd coil and new balancer msd box too. the crank is also new. after all the mods i expected more power. but it has yet to reach 1st oil change

 

What cam is that? 262HR-12? That cam profile doesn't exactly compliment the compression ratio, if want to get technical, not that many people do.

Do you have headers? What have you done to the cylinder heads. Im assuming the factory TPI is still on there?

 

08-300-8 only cam that would be able to run with stock computer. i started the rebuilt with a 3rd cylinder rod spin. the heads where lapped and new valve seals nothing else. the exhaust was done 5 years ago. the engine and tranny were done 3 weeks ago.

 

Ok, you've got a start. If you don't have headers, I would go that route as your next mod. From there, how handy are you with tools and is this your DD? from the looks of the picture you posted, I'm going to guess not. If you have the time, i would look into porting/polishing your own heads. They can be made to flow on par with Vortecs with the right work. Look up a guy named Sitting Bull. He's got some excellent instructions as to how to go about it. It's a lot easier than it would seem. By working the combustion chamber over, you also reduce the compression a bit, which, with those pistons, wouldn't be the worst thing in the world. Once you do up the cylinder heads, then you will really notice the added power.

 

seeing i just put engine together i am not to interested in taking it aparts again. most of the headers i have seen want them to be welded. i do not have a welder at home and hate to pay. I am very handy with my hands, seeing i have repaired cars for 15 years. 1 st time ever building one myself mostly stock repairs

 

What headers are you seeing that are requiring welding? My SLP's were bolt ons.

*edit* Most shorty headers are bolt ins, assuming they are chassis specific.

 

arent those the cheap rebuilder pistons that sit an extra 20 in the hole? if so its probably more like 9:1

yeah i looked them up, the 10.2:1 is only valid if the blocks been decked.

 

they said with a 64cc head they are 10.2to 1 so i dont think 9 to 1 would be right if i have 64 cc heads. it would be less if the heads are 74 cc. yes they are low priced piston. i think i paided 127 for all 8.

 

Speed-Pro Cast Pistons



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Product images may differ from actual product appearance.
These cast aluminum pistons are an excellent low-cost choice for most street and strip applications. Approximately 10.2:1 compression ratio with 64cc combustion chamber. Ring grooves are 5/64'', 5/64'', 3/16''. 1/pkg
(that was cut and pasted from the jegs site. i do not see anything about machining the head or block. if you found some where that said that let me know.)

 

89:

Thoses pistons do infact sit an extra .020" down in the bore at TDC as compared to the ones you took out.

The compression height is different. 1.54" rather than stock 1.56"
So the compression ratio will not be near as claimed on your motor.

On a .030" over 350 that has not been "decked"
You will have 9.30:1 with a .041" composite head gasket
or 9.89:1 if you use a thin .015" shim gasket.

If you had gotten your block "0 decked" for those pistons. (at least a .045" cut off each deck)
and used a .041" gasket then you would have a 10.3:1 cr.
it's all in the details Bud.....

 

yep, i infact have the exact same piston, though i did have my block decked after i found out.

i had that same ripped off feeling as you do right now, the money i saved on the pistons ended up going into machine work, oh well