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Original Message
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| Be aware... |
| By Dave Shoe - 09/08/2002 3:21:03 PM; IP 67.4.133.30 |
...the exhaust port positioning on the head surface is 5/16" different vertically between the two heads you have. If you plan to install headers, be sure to select a header which is compatible with the port position, otherwise you'll lose some performance to the port mismatch, and you'll have chronic exhaust leaks because one surface of the header gasket cannot be crushed by the header weld bead because there is no head underneath that segment.
The later small "velocity" runners are an excellent flowbenched design which apparently perform great in smaller displacement performance FEs. They were standard in 1968-later 428PI engines, and I know these engines ran great. Most 1966-67 428PI engines also got the small runner "emissions era" or "velocity" heads.
As horsepower climbs over 400-450, there may come a point where the small runner heads reach an efficiency limit and larger runner heads become easier to work with. Porting can resolve the limit with the velocity heads, but it's often easier to find a set of large runner heads.
If you don't plan to push more than 400 horsepower, the velocity heads will likely perform better, and will be notably stronger in the low to medium RPM ranges.
JMO,
Shoe. |
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