Ims rpm
 

Does anybody know the ratio of IMS rpm to crank RPM?

Might be a long shot, but without having a ruler to my crank cog at this moment, does anybody also know the ratio of RPM for the idler pulleys/alternator/PS pump?

Thanks

The intermediate shaft is driven by the crankshaft via a duplex roller chain with a transmission ratio of 0.67:1 (24 teeth on the crankshaft and 36 teeth on the intermediate shaft).


Porsche Workshop Manuals > Boxster (986) F6-2.5L (1998) > Engine, Cooling and Exhaust > Engine > Cylinder Block Assembly > Auxiliary Shaft > Component Information > Description and Operation

Thanks, that answered almost all my questions.

Do you happen to know the ratio of alternator to crank? The workshop manual and the bently book dont cover it.

I have found these references saying that the stock crank pulley circumference is 454mm and the alternator pulley circumference is ~166mm (taking the 53.9mm diameter and converting to circumference). This would give a ratio of ~2.7:1.

This was the best that I could find.

Mantis versus BBI pulley size

Amazon.com: NEW ALTERNATOR PULLEY PORSCHE 911 SERIES BOXSTER 0-124-515-073 996-603-012-02: Automotive

Awesome, thanks!

Now for the kicker...do you know how many balls are inside the main bearing inside the alt?

Hah! You got me. I have no idea. :)

Can't argue with your math, but it doesn't make sense. The IMS is run off the crank and drives the cams via a chain drive. Since the cams operate at 1/2 or 2x (can't remember which) the crank rotations to ensure proper timing, .67/1 ratio would mean the cams would be wildly out of sync with the crank. What am I missing?

Good point. I'll take another look...

The cams are reduced again to get cam->crank ratio of 0.5:1. Its shown in the cam section