Originally Posted by Wolf Hobbies

Thanks to Jonny Socko for the reminder. This has been mentioned a few times but the thread is getting so large it is really hard to backtrack through the whole thing.

There have been a lot of questions about pulleys. Not all of it has been accurate. There are two internal ratios used on the E4s. The E4FS uses the 1.8 internal ratio and all of the others use the 2.0. The E4FS uses 34 tooth pulleys on the diffs and 18 tooth center pulleys. All the rest use 35 tooth pulleys on the diffs and 17 tooth center pulleys. All the cars use 17tooth side pulleys. Side pulleys and center pulleys are not interchangeable.

The manual has an error on the part number for the 17 tooth center pulley. The correct part numbers are as follows:

503155 35 tooth diff pulley
503201 34 tooth diff pulley
503197 17 tooth side pulley
503222 18 tooth center pulley
503236 17 tooth center pulley

There has also been a lot of talk about mixing and matching pulleys to compensate for belt stretch. We have tried this and have not had any good results.