915 trans 7:31 R&P

[Mixed76]

I was just reading a thread in which the 915 7:31 ring and pinion combination was referred to as weaker than the later 8:32.

Is that true? Elsewhere I read changing to the shorter ratio gives better torque to the ground, without no mention of durability concerns other than those associated with a mag-case 915.

Which is correct/ can both be correct?

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[H-viken]

Both are correct. The 7/31 ratio is weaker from a longevity perspective and it accelerates the car faster

[Matt Monson]

There’s threads on it here, but going from memory I want to say 16% less strength for 7:31. I still sell quite a few of them because they do offer better acceleration. Both are true.

[Bill Verburg]

As mentioned both are true

there is a trade off for better acceleration

the higher numerical ratio of the 7:31 also shortens the useful range of speeds and time in a given gear

[targa72e]

I believe you can also do a 8:35 for lower ratio but stronger than 7:31.

john

[Mixed76]

Thanks y'all.

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[Walt Fricke]

John - I've never seen reference to an 8:35 for an OEM Porsche with a 915. Maybe a 901 or a Sporto (both of whose gear sets aren't interchangeable with the 915 due to different shaft separation if I remember right)? I seem to recall a 6:something as a hill climb gear for the 901?

[Matt Monson]

Originally Posted by Walt Fricke

John - I've never seen reference to an 8:35 for an OEM Porsche with a 915. Maybe a 901 or a Sporto (both of whose gear sets aren't interchangeable with the 915 due to different shaft separation if I remember right)? I seem to recall a 6:something as a hill climb gear for the 901?

I used to make them (with Ricardo). Tandler and Albins both make them now, but they aren’t OEM quality for quietness and lifespan. They are more Motorsports parts.

[Helix8]

Originally Posted by Matt Monson

I used to make them (with Ricardo). Tandler and Albins both make them now, but they aren’t OEM quality for quietness and lifespan. They are more Motorsports parts.

Thank you Matt your input is always appreciated -

[Matt Monson]

Originally Posted by Helix8

Thank you Matt your input is always appreciated -

You’re welcome. Happy to help when I can.

[stephers]

Hi Chris

Trying to send you a PM but your box is full, need to clear some out

Thanks, Rick