Reher-Morrison Racing Engines' David Reher and Darin Morgan answer your questions about cylinder heads or anything else concerning your racing engine building problems. Remember who you're are dealing with so no soft-ball questions.
6/8/06
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Sal,
Well, first off I would like to congratulate you on the good choice you made in regards to cylinder head size. You will find that not only will you make more torque you will also make more top end power. There is somewhat of a fallacy that has hung around for decades but never seems go away. That fallacy is that large ports will make more top end power than ones that are properly sized. I think this is one of the reasons people still choose heads that are far to large for there engine and its intended rpm range. The final thing you asked was how bad would it hurt you to put that head on a 496. Well let’s look at the data and see.
The mean inlet velocity for the 310cc port on a 468 at 7500rpm is 363ft/sec and the engine is well suited to 7700rpm for max power.
With the 496cid engine however, the mean velocity at 7500rpm is 387ft/sec, which is a little fast for that RPM so that makes this engine well suited for max power at 7325rpm. So what does all this mean? Well, the 310 heads on the 468cid want to make peak power at 7700rpm and the 496cid will want to make peak power at 7325rpm. Of course this is all based on the premise the engine is cammed and has an intake manifold and bottom end capable of supporting that RPM range.
The 310cc heads will be ever so slightly small for a 496 but I wouldn’t panic because there is no change in port size that will make either situation perfect although both situations are livable and both engines will accelerate well. Neither engine is “ out of tune” from a cylinder head perspective so don’t worry. Use the 310s on the 496. As far as consistency goes, the 496 for all intensive purposes will probably be a bit more consistent than the 468.
I would like to give you a projected power output for the engines but without knowing the specific Camshaft, manifold, header and carburetion specifications, I can’t be accurate. I can tell you that the 496 will probably make about 50 more Horsepower and than the 468.
David Reher asked Darin Morgan to answer this question because it is his area of expertise.
Reher-Morrison Racing Engines
1120 Enterprise Place
Arlington Texas 76001
817-467-7171
FAX-468-3147
Visit our web site at http://www.rehermorrison.com
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