I tried emailing Gary from TDR and he hasn't got back to me yet.. I have the 150mm crank overlay pulley and I was wondering what size nose pulley I need to be at around 15lbs of boost? Thanks

 

FormerDatsun510Man listed different boost setups on the 6-Rib hotsides. At 15psi, he required the 140mm/65mm combo which yields a pulley ratio of 2.15.

To approximately match that pulley ratio (2.14) with a 150mm Crank Pulley, you need something around the 70mm SC pulley.


As a counter point, Trikchop posted getting 14psi with the 150mm Overlay pulley and a 62.5mm SC pulley, yielding a ratio of 2.4. If you do the math on FormerDatsun510Man's table, you go up 1psi each time the pulley ratio goes up by an additional 0.07. So why did Trikchop's flatline at 14, when other MP62s have yielded more boost with lower ratios? Could be a number of factors (altitude/IC/TB restrictions), but the immediate issue that jumps out is anything smaller than a 65mm pulley, non-autotensioned, 4-rib typically is prone to belt slip.

 

Here's a link to the pulley ratio chart listed on the TDR site: TDR - Pulley RPM chart

He doesn't list expected psi readings, but it should help to infer from others reported ratios and corresponding psi.

 

Thanks guys, very helpful.