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| Diff change in '88 GT 5-spd (Page 1/2) |
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Z3SpdDmn
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FEB 25, 12:26 PM
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Hi folks,
I have a low-mileage '88 GT 5-speed and I've been refreshing the suspension over the last month or so, with a few upgrades thrown in. I fear that it might actually become a good car to drive. Which leads me to the next area of driving pleasure... engine and acceleration.
Now, before anyone says anything, I am not interested in doing an engine change in this car. Period.
However, I'm considering a diff ratio change. The gearing is so tall as it is, it could really liven up the acceleration with a lower (higher number) final drive ratio. I don't drive on the highway much, so I'd be perfectly willing to accept higher revs at cruising speed.
While I'm in there, I'd consider installing an LSD, but the power level doesn't really warrant it. I'm not autocrossing or tracking the car.
I did try searching, but couldn't come up with the info that I was looking for. Specifically, what final drive and/or diff ratio was my car built with and what are my options for swaps? Next, what is involved to perform the swap? I've changed a diff in a RWD car, but not in a FWD/transaxle.
Thank you!------------------
Anthony
'88 Fiero GT 5-spd "barn find"
www.DriveFasterNow.com
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Gall757
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FEB 25, 12:40 PM
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lou_dias
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FEB 25, 01:03 PM
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To go along with what I was saying... I had a magazine from ~1988 that mentioned the getrag on the Cavalier "GT" in a review having 3.42 final drive.
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lou_dias
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FEB 25, 04:09 PM
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Will
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FEB 25, 04:17 PM
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| quote | Originally posted by Z3SpdDmn:
I did try searching, but couldn't come up with the info that I was looking for. Specifically, what final drive and/or diff ratio was my car built with and what are my options for swaps? Next, what is involved to perform the swap? I've changed a diff in a RWD car, but not in a FWD/transaxle.
Thank you!
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The car was built with a 3.61:1 final. The only other gearset for that transmission is 3.94:1, used in some years of Quad 4 powered cars.
Not sure what that has to do with anything.[This message has been edited by Will (edited 02-25-2020).]
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Z3SpdDmn
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FEB 25, 10:21 PM
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| quote | The car was built with a 3.61:1 final. The only other gearset for that transmission is 3.94:1, used in some years of Quad 4 powered cars.
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Thank you! A 3.94 would work nicely. Do you know if this ring gear swap is possible? Or, would it require the entire trans to be swapped over?
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Anthony
'88 Fiero GT 5-spd "barn find"
www.DriveFasterNow.com
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Will
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FEB 26, 10:57 AM
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You'd have to either swap the V6 bellhousing onto the Quad 4 transmission--including resetting differential bearing pre-load using special tooling--or swap the Quad 4 output shaft & ring gear into the V6 transmission, which is more work.
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Z3SpdDmn
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FEB 26, 11:58 AM
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| quote | Originally posted by Will:
You'd have to either swap the V6 bellhousing onto the Quad 4 transmission--including resetting differential bearing pre-load using special tooling--or swap the Quad 4 output shaft & ring gear into the V6 transmission, which is more work. |
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Thanks for scaring me out of it 
Maybe I'll build up a separate transmission at some point to then just swap in. Look for me to revive this thread in about 10 months 
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Anthony
'88 Fiero GT 5-spd "barn find"
www.DriveFasterNow.com[This message has been edited by Z3SpdDmn (edited 02-26-2020).]
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olejoedad
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FEB 26, 03:07 PM
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I would look closely at the 85-86 four speed.
The gearing is perfect for the 2.8 in 1st, 2nd and 3rd. 4th is an overdrive, it turns about 3k at 70 mph.
Top of 2nd is 60 mph at 6000 rpm.
3rd gear pulls hard.
Ratios are properly spaced, unlike the getrag.
A 3.94 diff in a getrag would make 1st gear useless with a 2.8....you wouldn't get across an intersection without needing to shift.
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fierofool
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FEB 26, 04:27 PM
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If you really want to get up and go, you'll need 2 transmissions. A case from the 85 or 86 4-speed and change out the guts from an 84 4-speed. You will have a 4:10 final drive. But like Joe said, 2 gears to get through an intersection. The reason for the case change is for the stronger 85-86 case. RPM is about 3500 at 60.
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