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Old 03-02-2011, 07:31 PM
bobdmac bobdmac is offline
Older than old school
Location: Oaksterdam, Yay Area
Join Date: Feb 2011
Posts: 4,414
Mein Auto: 2001 540i/6, '90 k75s
Originally Posted by franka View Post

...One of the items that you might be interested in doing, while you have complete access to your valves, is to have your valves back-cut (I quote the full article below) to p/u 5-15 hp by picking-up 5-10 cfm between 0.100 to 0.500" of lift. Those numbers are right from the article and a picture with the article. And, like I already said, apply to any V8.

Quoting right from the article... "This is one of those small tricks that is worth way more than the paltry sum it usually costs for this extra step. If you have the heads apart to lap the valves, or you have them at a shop, the easiest thing to do is mark the face of the valves with layout fluid or even a Sharpie, lap the valves in, then just have your machinist gives the valves a standard 30 degree back-cut up to the edge of the lap mark - simple and worth an average of 5-10 cfm, 5-15 hp. It's worth more power than most gasket-match jobs!".
When I was stationed in Germany in the late 60's, we raced a '67 Mini-Cooper that was prepared by a former Downton (works) mechanic. He ground down the backs of the valves and polished them to the point that they looked like delicate jewelry. This not only allowed tremendous airflow, it lightened the valve train enough that the racing redline in the pushrod, long-stroke 1275cc engine was 7600 rpm.
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