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miktu
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Hello, could someone tell me what standard size ring and pinion should be on my stock 1987 avanti. It is somewhat sluggish off the line and I thought about changing the ring and pinion gears to help with this. I do not know where to find out what size I already have to be able to shop for different gears. Has anyone changed out gears before to help with this porblem? Help is needed.

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Hello, could someone tell me what standard size ring and pinion should be on my stock 1987 avanti. It is somewhat sluggish off the line and I thought about changing the ring and pinion gears to help with this. I do not know where to find out what size I already have to be able to shop for different gears. Has anyone changed out gears before to help with this porblem? Help is needed.

I can't answer directly, but I think your car has a GM 10-bolt differential (count the bolts around the outside of the rear of the differential case) and I would guess the standard axle is a 3.08. You can determine your present ratio by lifting the rear wheels off the ground with a floor jack or two, and with the transmission in neutral, put a mark on the driveshaft and on the outside of a tire, then rotate the driveshaft slowly until the tires make one revolution (someone else needs to watch the tire mark), counting the differential revolutions (better yet, rotate the tires ten times while counting driveshaft revolutions, then divide the driveshaft revolution count by 10).

I think higher ratios of 3.42, 3.73, 4.10, and 4.56 are available for your differential. Bear in mind that changing the differential ratio will cause speedometer error, and your highway mileage may suffer.

Any good driveline shop should be able to make the change.

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