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| Diff change in '88 GT 5-spd (Page 2/2) |
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Z3SpdDmn
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FEB 27, 12:29 PM
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I don't think it would be that drastic of a change. Its 8.5% difference. So, if top speed in 1st gear was 35 mph, its now 32 mph. If you were going to shift at 20 mph, you're now going to shift at 18.3 mph. If you were going to shift at 15 mph, its now 13.7 mph.
Conversely, cruising rpm would work in the inverse. If 2500 rpm was your cruising engine speed, that will move to 2732 rpm for the same velocity. 3000 rpm would become 3279 rpm. That would be totally acceptable to me. Appreciated, even.
I went from a 3.23 to a 3.64 in my BMW 128i, which is an 11.3% difference and it really woke up the car. The stock gearing feels a lot taller in the Fiero than the stock gearing did in the 128i. I think it would be a really nice improvement. Its just a bummer that its such a big job to pull off!
NOTE: 3.61 to 4.10 would be 12% change. That could also be conceivable, but I think the 3.94 would be a nice spot.
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Anthony
'88 Fiero GT 5-spd "barn find"
www.DriveFasterNow.com[This message has been edited by Z3SpdDmn (edited 02-27-2020).]
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pmbrunelle
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FEB 27, 12:58 PM
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| quote | Originally posted by Z3SpdDmn:
NOTE: 3.61 to 4.10 would be 12% change. That could also be conceivable, but I think the 3.94 would be a nice spot.
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You shouldn't be comparing final drives like that between different transmission families.
Instead, multiply the final drive by the speed gear ratio, to compute the overall reduction in each gear. That's how you can compare apples with apples. The overall reduction is what you can perceive from the driver's perspective.
Taking the M17 Muncie for example:
1st: 3.31 x 3.65 = 12.08
2nd: 1.95 x 3.65 = 7.12
3rd: 1.24 x 3.65 = 4.53
4th: 0.81 x 3.65 = 2.96
The stock Fiero ratios can be found here:
https://en.wikipedia.org/wi...smission_gear_ratios[This message has been edited by pmbrunelle (edited 02-27-2020).]
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Z3SpdDmn
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FEB 27, 02:33 PM
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| quote | Originally posted by pmbrunelle:
You shouldn't be comparing final drives like that between different transmission families.
Instead, multiply the final drive by the speed gear ratio, to compute the overall reduction in each gear. That's how you can compare apples with apples. The overall reduction is what you can perceive from the driver's perspective.
Taking the M17 Muncie for example:
1st: 3.31 x 3.65 = 12.08
2nd: 1.95 x 3.65 = 7.12
3rd: 1.24 x 3.65 = 4.53
4th: 0.81 x 3.65 = 2.96
The stock Fiero ratios can be found here:
https://en.wikipedia.org/wi...smission_gear_ratios
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Oh. You mean because the 4.10 isn't even compatible with the 5-speed Getrag? So be it, then.
Thanks.
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Anthony
'88 Fiero GT 5-spd "barn find"
www.DriveFasterNow.com
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pmbrunelle
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FEB 27, 07:15 PM
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Fieros were factory-equipped with transmissions from three major families:
Muncie 4-speed family
Fiero, MY8 transmission code
Fiero, M19 transmission code
Fiero, M17 transmission code
Isuzu family
Fiero, MT2 transmission code
Getrag 282 family
Fiero, MG2 transmission code
Within a single transmission family, the parts will interchange to some degree, allowing for customization...
These transmission families were not exclusive to the Fiero, so compatible gearboxes having other ratios can be found in other cars.
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pmbrunelle
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FEB 27, 07:41 PM
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Even if we stay within the Getrag 282 family, I recommend multiplying out the resulting overall reduction ratios.
Lets say you replaced the Fiero gearing for the Quad 4 gearing:
Fiero Getrag
1st: 3.50 x 3.61 = 12.64
2nd: 2.05 x 3.61 = 7.40
3rd: 1.38 x 3.61 = 4.98
4th: 0.94 x 3.61 = 3.39
5th: 0.72 x 3.61 = 2.60
Quad 4 Getrag
1st: 3.50 x 3.94 = 13.79
2nd: 2.05 x 3.94 = 8.08
3rd: 1.38 x 3.94 = 5.44
4th: 1.03 x 3.94 = 4.06
5th: 0.80 x 3.94 = 3.15
So, you say that you go from a 3.61 final drive to 3.94, so that's a 9.1% change. 1st, 2nd, and 3rd are indeed changed by 9.1%.
However, notice that the 4th and 5th speed gears are different.
Comparing the overall reduction ratio change for 4th:
3.39 -> 4.06 gives a 19.7% change
Comparing the overall reduction ratio change for 5th:
2.60 -> 3.15 gives a 21.2% change
So always compare transaxles using the overall reduction ratios, because the final drive alone doesn't represent the full story.
On a traditional front-engine RWD car, you can discuss how just an axle ratio change will affect the car, because the transmission itself (containing the speed gears) remains constant.
Edit: I'm not actually sure about the Quad 4 ratios; I went off wikipedia. The purpose of this post was to explain the importance of computing the overall reduction ratios, using an example to aid in comprehension.[This message has been edited by pmbrunelle (edited 02-27-2020).]
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Will
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FEB 28, 09:49 AM
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The Quad 4 configurations are a mish mash... The early ones had shorter shifted gears and the 3.61 final, while the later ones had the same shifted gears as the V6 Fiero, but also the 3.94 final. The Achieva SCX (RPO: W41) cars had both the short fifth and the 3.94 final.
There are three different 1-2 sets: 3.50/2.05, 3.77/2.19 and 3.50/2.19.
I found a 3.50/2.19 set for the transmission for my Northstar car, threw a 1.03 fourth in the box, but kept the Fiero 0.72 fifth and 3.61 final. I have a 3.94 on the shelf that will be going into the box as I get the car back together.[This message has been edited by Will (edited 03-03-2020).]
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Z3SpdDmn
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MAR 01, 08:49 PM
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| quote | Originally posted by pmbrunelle:
So always compare transaxles using the overall reduction ratios, because the final drive alone doesn't represent the full story.
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Understood. I was initially looking at ONLY a final drive change in the transmission. However, if this Quad-4 Getrag is an option and already has a 3.91 in it, that could be a great combination. It would run about 500 rpm higher on the highway, but that wouldn't be the worst thing. I don't drive it long distances.
What cars was this Quad-4 Getrag with the 3.91 in? If I was to look for one, how would I search for it?------------------
Anthony
'88 Fiero GT 5-spd "barn find"
www.DriveFasterNow.com
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Will
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MAR 02, 11:29 AM
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| quote | Originally posted by Z3SpdDmn:
Understood. I was initially looking at ONLY a final drive change in the transmission. However, if this Quad-4 Getrag is an option and already has a 3.91 in it, that could be a great combination. It would run about 500 rpm higher on the highway, but that wouldn't be the worst thing. I don't drive it long distances.
What cars was this Quad-4 Getrag with the 3.91 in? If I was to look for one, how would I search for it?
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Here's info I used to locate the transmission(s) which had the gears I installed in my Northstar car's transmission
http://www.60degreev6.com/v...6-282-gearing-by-rpo
| quote | Originally posted by Will here:
In the 282 article section, there is this info:
Quad 4 Getrag 89 1st...3.50 2nd...2.19 3rd...1.38 4th...1.03 5th...0.72 FDR...3.61
1990 1st 3.50 2nd 2.19 3rd 1.38 4th 1.03 5th 0.81 Axle 3.61
1991 1st 3.77 2nd 2.19 3rd 1.38 4th 1.03 5th 0.81 Axle 3.61
1992-1994 1st 3.50 2nd 2.05 3rd 1.38 4th 1.03 5th 0.72 Axle 3.94
1991-1993 W41 1st 3.50 2nd 2.05 3rd 1.38 4th 1.03 5th 0.81 Axle 3.94
Isuzu L-Body 1st 3.73 2nd 2.15 3rd 1.33 4th 0.92 5th 0.74 Axle 3.83 V6
Getrag All years J and L body 1st 3.50 2nd 2.05 3rd 1.38 4th 0.94 5th 0.72 Axle 3.61
W Body V6 1st...3.77 2nd...2.19 3rd...1.38 4th...1.03 5th....0.81 FDR...3.61
What are the RPO's for the various transmissions?
MG2 was used in Fieros and with V6's. It had 3.50 first, 2.05 2nd, 1.38 third, 0.94 fourth and 0.72 fifth with 3.61 FD.
The MV5 (I think) was used in W41's and has 3.50/2.05/1.38/1.02/0.81/3.94
The MY5 (I think) was the W-body 5 speed with 3.77/2.19/1.38/1.03/0.81/3.61
I don't know what RPO's the other transmissions had. Does anyone?
I think that a project I have in mind would work best with the '89 Q4 gearset listed above, but I'd have to put the conventional bellhousing onto it. But I don't know what RPO transmission to look for. Any help? |
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pmbrunelle
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MAR 02, 12:44 PM
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Once you know what applications you're looking for, then head on over to:
http://www.car-part.com/
The website allows you to search the inventory of all affiliated junkyards.
When I bought a junkyard transmission, I inserted a (carefully trimmed) small wood stick into the differential side gear. The stick allowed me to count differential turns vs. input shaft turns for each gear, confirming that I was indeed about to purchase what I was looking for.
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