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NHRA Stock class valve job

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NHRA Stock class valve job

Postby Greg Gessler » Tue Oct 18, 2005 12:04 pm

Has anyone had experience with 'legal' NHRA valve jobs? How strict are they and what do they actually check at teardown?

Can the topcut angle include a radius to open up chamber wall, as long as its not larger than valve size + .250"? (.125" per side)

The rules state bottom cut not to exceed 70 degrees. Can there be multiple machined bottom cuts?

Thanks in advance for any help.
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Postby SupStk » Tue Oct 18, 2005 1:06 pm

Greg,
The rule book is very specific on what is acceptable. I have been fudging on the rules and my engines have been passing tear-down. I'm not going to give instructions on cheating but will tell you to keep the original valve angle and go easy on opening up chambers. They have been measuring chamber wall thickness even on heads that appear not to have been machined.
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Postby airflowdevelop » Tue Oct 18, 2005 1:17 pm

Greg,
Stock class work (unless grandfather) Has a little more to do with "fracturing" of the rules and not breaking them. Most concerns today involve "undercover" work, that looks good, but certainly isn't. Of course, pay close attention to your angle and diameter as supstk pointed out. And most of all , be creative!

good luck
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Postby Greg Gessler » Wed Oct 19, 2005 8:07 am

I understand about the 'undercover' work to the ports, bottom angles, blending and chamber work. But I was curious about the actual (visable) machined cuts. Is only one (machined visable cut) bottom angle allowed?


Thanks
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Postby SupStk » Wed Oct 19, 2005 8:39 am

Greg,
Most heads have a machined cut below the seat from the factory. This is a grey spot but I work that area on most heads. If you try to put in several angles under the seat, i'm sure it would never fly in tear down.

The certification crew is getting very good at spotting worked ports, especially in common engines. Given the fact they have maximum CC specs for ports, the first tip-off is when the intake surface is machined back to the valve cover bolt holes.

I've heard it more than once, "stock class is where guys spend $5,000 to hide a $250 port job"
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Postby Greg Gessler » Wed Oct 19, 2005 7:31 pm

Thanks for the clarification!
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