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Old 10-21-2012, 03:08 PM
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Originally Posted by mustang 671 View Post
what your thoughts on exhaust header wraps ? always get mixed opinions on them. if you speak with exhaust guys they like them because they flow the wate gas better ? but others say not good as they kill headers ?

cheers shaun
Your engine control unit sounds like it should work fine once the other areas are covered.

Have you used a vacuum gauge to take a reading at the base of the carb yet? You could use one of the manifold vacuum ports for this if you wanted. I'm just curious- but this can wait until the guys at the dyno shop get tuning on it.

As you know the 1850-5 Holley was originally a 4160 and it had a secondary plate instead of a block until you converted it to a 4150-type set up. For reference, the original 134-9 secondary plate your carbs came with had a secondary orifice equivalent to a #64 jet. So if you are now using a 78 secondary jet, this should be plenty- it would prolly be enough even w/o the power valve. If you added the power valve to it, you'd have the equivalent of about an 85 jet in the secondaries!

Also for reference, here's a Holley numerical listing showing the factory specs, etc. And here's a chart showing the relationship between plates and jets.

Header wraps are OK, if you were to use stainless steel headers, the wrap wouldn't cause rust. If you use mild steel I'd prefer ceramic coating inside and out. But anything that'll keep the underhood temps down and the exhaust gas hot inside the header (and the gas velocity up) will be a good thing, overall.
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