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Old 06-12-2010, 10:38 PM
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4 valve relief vs 2

On flat top pistons, whats the difference in 4 valve relief vs 2?
I'm getting a set of Hypereutectic flat top 4 eyebrows.
What kind of performace difference am i going to look at? Its not a crazy motor, just a .030 over small block 350 with a little cam and carb for my camaro
Thanks,
-Scott

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Old 06-12-2010, 10:51 PM
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2-relief pistons are left/right bank specific. The eyebrows go toward the intake manifold. 4-relief pistons can be used on either bank, with the indicator toward the front of the motor of course.

In my experience, 4-relief pistons are a little less money, but they are also rebuilder specials sometimes, meaning that the compression distance is shorter from the crown to the axis of the wrist pin. A shorter CD will add piston deck height and reduce squish. Not the sort of thing you want to do if you are building a performance motor. The other thing I've noticed about 4-relief pistons is that they have a recess across the entire crown, with a narrow raised band of material at the very edge of the piston. This will not aid in the generation of squish. You need a nice flat area on the crown to mate up with the underside of the cylinder head.

Here are a couple of examples of little or no squish area on the crown....
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Old 06-13-2010, 07:40 AM
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The ones i'm getting are flat tops, with no dish like these,


So, i should be good.
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Old 06-13-2010, 03:35 PM
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Quote:
Originally Posted by MrPhotographer06
On flat top pistons, whats the difference in 4 valve relief vs 2?
I'm getting a set of Hypereutectic flat top 4 eyebrows.
What kind of performace difference am i going to look at? Its not a crazy motor, just a .030 over small block 350 with a little cam and carb for my camaro
Thanks,
-Scott
A piston w/just one trough across the piston is thought to be a better design from a racing standpoint than the 4 relief-type pistons. But if your engine is a street driven performance build, the pistons you've chosen will work fine. Those pistons have been used successfully in countless builds, and are as good as they need to be.

Pay attention to the compression height of the pistons. Some will have a smaller CH of 1.540" instead of 1.560", this is to account for decking that's often done on rebuilt engines. Whichever piston you use, be sure the quench is as near to 0.040" as you can get it.
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Old 06-15-2010, 09:13 PM
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I'm taking them to the machinist tomorrow, so he can finish the block.




speed pro h345np30.

i'm only gonna get 8.34 compression with my stock heads, but i'll have heads on it before long
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Old 06-15-2010, 09:42 PM
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also, i got a full set, brand new, in excellent condition, for 50 bucks
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