I recently had a very dissapointing trip to the track and I am trying to narrow down what went wrong. I have an 89' IROC 350TPI, Edlebrock aluminum heads, Crane powermax cam, in a goodwrench short block and I was only able to run a 15.7 part of which was due to awful (2.77) gearing and my small cam. It looses everything above 4000rpm. It still seems as though it should have ran better anyway. I noticed that there was a lot more meat between the cylindars of the new motor as opposed to the old one. Someone told me it was because GM thinwalled the 80's motors to save weight. The problem being when I installed the new head gasket it appeared to be the perfect match for the old motor but there was 1/16" to 3/32" of open space between the egde of the gasket and the bore (gasket too big). I used it anyway. My concern is that the extra space could cause lower compression leading to an explaination on my poor times. Is this extra space negligable? Is there different size gaskets for small block 350's?

Thanks

 

Nicky,

If I understand your statement correctly, you compared a new head gasket to the bore on your old engine and to the bore on your new engine. The gasket fit closely to the bore on your old engine, but was larger than the bore on your new engine (by about 1/8-3/16"). If that is correct, the new engine sounds like a 305, not a 350. You'd better check your casting numbers to make sure you have what you think you have.

 

That would suck!

 

Bore center to center is the same on all SBC's, if your new engine has a lot more material between the bores then it has to be a smaller bore causing it and not anything to do with the thinness of the casting. 305's with a 3.736 bore have a lot of metal between the bores while 400's with a 4.125 bore are very thin there.

 

Yup sounds like ya got a 305.
If so the best cure other than replaceing the motor, would be to gear it 3.73's would be a start.

Your compression ratio may be in the toilet too.
Edelbrock heads are either 64 to 72cc's 305's are 58cc.

 

According to Mortec.com
"10243880...350...95-00...2 or 4...Vortec truck, Gen.I crate motors and "ZZ4", roller cam, one piece rear seal"
I am very confused does GM have like a tech line or somthing that I could ask?

 

The "standard" size gasket bore for the 350 is 4.166", this leaves a small area of "exposed" block/head and forms a kind of pocket, this adds to the quench area, you need/want quench area.
As to the blocks, GM made 2 different 350 blocks, one with siameased cylinders and one without. These blocks each have different pros and cons associated with them.

This article explains quench and whay you want it.

Quench, or squish area is typically the flat area on the top of the piston that's almost level with the top of the block deck. It must have a corresponding flat area on the deck surface of the head to qualify as quench.
If you look at a combustion chamber, you will usually see these flat areas, and they will have the volume of the actual combustion chamber between them. When the piston is compressing the mixture, as the piston nears the head, the flat areas on the head and piston come together and force the mixture from those areas to "squish" into the chamber, where the spark plug and burning mixture reside, so you achieve a more complete burn.
The quench area also runs cooler than the rest of the chamber / piston. These lower temperatures are where the "quench" comes from.
When properly designed, the quench areas can have a tremendous effect on the quality of combustion, and allow higher compression ratios, and due to this they are considered "artificial octane" by scientific types.
Bottom line is "properly designed, quench is good".

You can find the thread here. http://www.theoldone.com/archive/quench-area.htm