70 dart 470 ci drag car build.

92b said

This is from Jere Stahl's (of stahl headers) website. I don’t know if the site still exist. There was lots of helpful information about dynoing on his site. I copied it into my dyno book when researchinghow to build my dyno. Here is what he had to say about dyno exhaust. For what it's worth.

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We did some testing today again and besides having to find 40 HP that was lost, it was found again at 14 ° initial timing. We backed it up 2 degrees per test from 22. We made back to back 660 HP runs then before we made any changes we unhooked the Dyno exhaust and it picked up 15 HP and 10 ft lbs.
The Dyno exhaust is 5 inch by 12 feet long and big 5 inch semi truck mufflers ..