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Old 12-15-2018, 10:04 AM
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eschaider eschaider is offline
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Join Date: Feb 2006
Location: Gilroy, CA
Cobra Make, Engine: SPF 2291, Whipple Blown & Injected 4.6
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One of the challenges as you pursue higher engine speeds is obviously valve train control. The rockers and smaller diameter valve stems all contribute to the increased engine speed but eventually the need for higher spring rate / higher seat pressure valve springs becomes inescapable.

As we pushed the useful rpm range for the late model Hemi's higher and higher we needed increasingly robust valve springs and as was discovered with Spintron time, more rigid valvetrain components. Eventually springs with 450# of seat pressure (or more) and spring rates of 1000#/inch (or more) became available allowing us to substantially raise the engine's operating range. Predictably the next weak links began to appear and become the new front edge of the increased rpm range battle area. For the late model Hemi's those weak points became pushrod strength, integrity of rocker stand hardware geometry and not surprisingly pushrod end cup life.

At a 450# seat pressure and a 1.6 rocker ratio an intake spring puts 640# of pressure on the pushrod cup just to lift the spring off the seat! At max lift the spring has 1300+# of open pressure that translates to just over 2000# of open pressure on the push rods, their ends and the rocker stands. Stunning numbers by any standard. Without additives like Prolong and regular oiling of the pushrod ends before firing you quickly kill high dollar pushrods and rockers.

The FE rocker design is a lighter and a much simplified design compared to a late model Hemi however, it is still one of the gatekeepers to increased useful engine operating range as Brent has already so clearly demonstrated. The pregnant question quickly becomes is the build a street engine or a competition engine.

Although most of us are in street engine land, the challenge in building ultra high rpm engines can be entertaining even intoxicating. However, the question about what you do with the new found power you have in those upper rpm ranges, in an already overpowered steet vehicle, begs the question, why did you do this?

Extending the useful rpm range on the FE (for our type of applications) to 7500 or even 8500 (price and parts permitting) is probably useful if not entertaining. Much beyond that point however, the effort is going to take the kind of redesign and ongoing maintenance the Hemi guys went through / go through to raise their useful operating rpm range maybe not the proverbial screaming hot set up for the street.

BTW very impressive job Brent especially with such street friendly pieces!



Ed


p.s. We haven't even touched on the better flowing heads needed to benefit from the increased engine speeds possible ...
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