65mm Charger pully power gains

[JonnieG40]

Hi im new to the forum and purchased my first G40 yesturday it has a simple spec....Full 2.5" stainless exhaust, 4-2-1 stainless manifold. JabbaSport Induction it, 65mm charger pully, jabba chip, lightened flywheel.....bla bla bla. Whats interested me is the Smaller 65mm charger pully. Ive been informed this is smaller than the standard one which enables the charger to spin faster.

Does anyone know the gains this pully gives of hand?

Can anyone guestimate the power my engine is producing from my simple spec? I havnt thought about doing a Rolling road session yet.

[G40supercharged]

Stock supercharger pulley is 75mm so 65mm one makes it spin 75/65 times faster. Normal peak pressure is about 1.7 bar absolute (i.e. 0.7 bar boost above atmospheric pressure) so the smaller pulley gives you about 1.7 x 75 / 65 = 1.96 bar absolute or around 1 bar of boost. Get a boost gauge if you haven't got one and you should see 1 bar as you get close to the red line if everythink is working OK. The 65mm pulley is about the smallest you want to go. A small pulley makes more difference to tuning a G40 than anything else and will increase torque across the whole rev range rather than just peak power. I would guesstimate your engine between 130 - 140bhp.

[JonnieG40]

Cheers for the reply. The guy I bought it off said it was 160bhp which I thought was a bit optimistic! I was guessing around 130. I might be doing a rolling road session soon to find out for sure