Quote:
Originally Posted by Henry Schmidt
The springs we use are Aasco. Randy had them designed back in the early IMSA days to provide the seat and over the nose pressures required for the 8000+ rpm 2.5 GTU engines.
We've used them successfully for 35 years with zero failures from breakage and good results post over-rev. I believe part of the success lives in the lowest over-the-nose pressure possible for high lift applications. Most of the after markets [racing] springs we've tested have stupid high pressures. Silly numbers like 400+lb @ .500" lift. Things change, engineering and materials evolve over time but to date, we've have never seen a better spring for two valve 911 engines. .
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Yes we have installed these before when customers have them shipped to us to fit.
A couple of observations we made. Wire diameter and the number of active coils. They seem to offer a wider range of possibilities in pressures.
As our cam designs have become more "modern", so too has our springs designs.
Even our stuff is nonsense if the correct way to assemble is not followed. Cam designs today have come along way since the 70"s. We are now down in the high 50's for Intake seat pressure and in the mid 70"s - 80"s for the Exhaust. When you get this "light" you have to know what you have and be accurate.
As best as we can, there is a limit to the amount of air you can pass through these ports. High RPM's should always be limited to the air flow capabilities, not because it sounds good. You just wear out parts making less torque.
Running high RPM's has to be because the heads flow enough to allow. The flow has to be measured with all of the Intake attached. These heads suffer from some weird reversion effect when you start lifting the valve too much. Its a function of large port opening and slowing down the air speed in the Intake. The air does some odd turns and tumbling between the Intake and Exhaust. Keeping the percentage between the two is extremely important in any head but these 2V Porsche heads its critical.
Having good control over the valves is a huge part of controlling this phenonium. Cams and springs become your friend or your enemy.