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I am getting new pistons for a 350 block w/ 76cc heads that I am rebuilding with a friend and this block has a edelbrock performer-plus cam in it. I don't know which pistons to get? flat top or dished? which will give a higher compression ratio? and also will the valves clear the pistons? thanks for any help...
 

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MaitlandTron said:
I am getting new pistons for a 350 block w/ 76cc heads that I am rebuilding with a friend and this block has a edelbrock performer-plus cam in it. I don't know which pistons to get? flat top or dished? which will give a higher compression ratio? and also will the valves clear the pistons? thanks for any help...

Well a flat top piston will give you higher compression when you compare it to a dished piston. And personally, of course depending on cam lift, in my opinion both should clear without any problem. I have ran a .536/.554 lift 112 degree lobe center cam with flat tops and had no problems at all.
 

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There's some faulty logic going on here. First of all the top of the piston has nothing to do with piston to valve clearance. If you look at most pistons they have valve relief pockets. It's the depth of the pocket that you need to be concerned with. A domed piston could have more valve clearance than a stock flat top.

Next is the faulty assumption that maximum valve lift is the variable that causes insufficient Piston to valve clearance.
The point where the valve comes closest to the piston is not TDC or maximum valve lift. The valve is not fully opened when the piston is closest.
It's closest during overlap about 7-14 degrees ATDC for the Intake and 7-14 degrees BTDC on Exhaust. Usually the Intake valve is the problem because it's bigger, but never assume.

It's a good idea to check valve to piston clearance with clay before you bar the engine over. You don't need the cam to do this. You can mock it up with one piston and rod, and old gasket of the right compressed thickness and a dial indicator. Use a light checking spring to make it easy.
If your valve clears the pocket by .100" at TDC and maximum lift it's ok. If not you need to do further checking with the degree wheel.

Don't ever assume you have adequate valve to piston clearance!
I have a stock lift rule cam that interferes with a stock piston because of a tight LSA and a minimum quench dimension.
Read more:
Crane Cams FAQ
Isky VOTC
 

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Hi Paul

I was just curious about the stock rule cam engine you mentioned. Is it a chevy? What quench specs. are you using? Have the heads been milled?

Just curious, all of the stock rule type stuff interests me.


Thanks
Jeff
 

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Yes. I run a 4th gen Chevy Nova at the local circle track and the class requires "stock" engines with a claimer rule.
The cam was made by Howards Cams and has a real tight LSA. I wound up not using it because of the clearance issue.
 
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