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Hey all.
I'm doing the research to build a 302 for my X-33.
Wondering if I should use a flat top piston (4 x 3. bore x stroke) in this assembly.? 302 pistons are sure fun to try to find huh?! Anyway, I see I have the option of going flattop vs .430 domes. A friend who is a machinist and has a pulling truck sez the flat top way is more efficient in the combustion chamber, instead of the TALL dome, then just deck the block and heads to get the 11 to 1 compression.

Anyone have some good advice here?? Should I go with domes? Or flat tops? Will just be a weekend fun machine.

PLUS, how much, with a flat top piston, would I have to remove from head/block to get the 11 to 1 compression?? How much can you get by with taking off?

thanks :confused:
 

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In a 3" stroke motor, you will struggle to get decent compression. A flat top is almost out of the question. I had a set of original 302 pistons, sold them about 5 years ago. They had a GM number and if I remember, a TRW logo too? Even a huge dome piston won't hurt too much in a 3" stoke motor, I ran a Speed Pro 12.5 setup in a .020" over 302. Just be sure the plug is not shrouded. You can roll back the edge of the dome and put in a small notch at the plug location, be sure to radius it gently with no sharp edges to cause detonation. Sometimes flame travel is better for overall power than just a high compression ratio. You see this as a nice even coloration on the dome and deck of the piston in a race motor when you pull the heads.
 

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A flat top piston with a .040 quench height and 58cc chambers makes 9.7:1 compression. That's decent, but may not work too well with the factory 30-30 cam.

IMO It would be OK though with a cam that has less advertised duration (like 270* at .004 for example) but you will probably be way off the factory power numbers with less cam and over a point less compression.

If I had to guess, to take a 64cc head down to 58cc you are talking about milling somewhere around .050-.060" off (I think) Definately talk to a machine shop about this, because when you start cutting that much off heads, you start creating other problems, like valve geometry (pushrods "act" too long), intake manifold fit, exhaust fit (probably not a big deal), etc.

What about using longer conn rods and a 383 type small dome piston? Like a 6.125" rod and a 1.420" compression height piston? You'd have to use a thick headgasket, but it might be cheaper and a better setup than factory rods and pistons.

I was thinking about the Wiseco #K237A3 (.350 hollow dome, 1/16" rings, +12cc piston). The piston would be .020 out of the hole on a 9.025" deck block which would mean you need a head gasket that is .055 - .060" thick. You could keep your factory stamp on the pad and still get a tight quench without decking the block or using a steel shim gasket.

Just an idea.
 

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You need a dome. If you are going to run the "30-30" cam, you need 10.5 or 11:1 to get it to run based on empircal evidence. Dynamic compression calculators will not help you here as the rules of thumb will not apply to this slow ramp profile. The factory cam duration figures will throw you off.

Consider the small duntov cam or maybe the Comp 282 solid. If you do run the CC 282, you should run the dynamic compression calculator and back into a target compression ratio. This profile will probably work just fine with the DCR calculator and rules of thumb. The rules of thumb are based on experience with modern cam profiles.

Just one man's opinon.

-Mark.
 

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Isn't all that a lot of trouble to go through. Just order new 302 pistons and make it like it shoud be.
 
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