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?
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).
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.
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).
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?
__________________ Current car
2000 Boxster 2.7l red/black
Previous cars
1973 Opel Manta
1969(?) Fiat 850 Convertible
1979 Lancia Beta Coupe
1981 Alfa Romeo GTV 6
1985 Alfa Romeo Graduate
1985 Porsche 944
1989 Porsche 944
1981 Triumph TR7
1989 (?) Alfa Romeo Milano
1993 Saab 9000
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...
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1999 996 C2 - sold - bought back - sold for more
1997 Spec Boxster BSR #254
1979 911 SC
POC Licensed DE/TT Instructor