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Old 07-29-2020, 01:36 PM   #4
SSDiv6
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Default Re: NHRA Stock Replacement Piston Question

Quote:
Originally Posted by oldskool View Post
Here's a Pontiac 350 factory piston that was used to get a CP piston approved.

http://forums.maxperformanceinc.com/...8&postcount=77

As you can see, they're not EXACT duplicates. Main thing is that they are forged, & they are NHRA accepted & legal, for some Pontiac 350 engines.
Correct, they do not need to be exact duplicates, however, they must maintain the specifications I mentioned in my previous post.

It appears that some engine builders may have some close friends in piston companies because I have taken apart engines that although they have the approved part number stamped,they do not meet the approved spec sheet.

I have found the following discrepancies in some of the Stock Eliminator engines I have torn apart:

- Ring grooves that are thinner than spec.
- Shorter distance from top of piston to top ring land that shown in spec.
- Deeper valve reliefs than spec.
- Smaller domes than spec.
- Smaller dish volumes than spec.

During a teardown, does NHRA assume the piston was built and approved in that configuration or the engine owner blames the piston company?

I assume since there are less intrusive teardowns and less piston removals, that many are taking the risk by doing so.
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