Manual trans for early SBC swap? (Page 2/2)
Monstertone FEB 19, 02:48 PM
Regarding the 87/88 Fiero 5 speed transaxle, aka Muncie/Getrag 282 MG2. The common shortcomings that always come up when mating this transmission to a larger engine is, it was never designed to take the amount of torque the larger engine is capable of producing. (repeated off the line dumping the clutch) The alternatives usually recommended are either the Fiero Getrag 4 speed, the F-23, or the F-40. While the latter two are excellent trannie's, they involve a lot more money than the application of a little common sense and keeping the 282 5 speed.

I found these figures on gears ratios for Muncie/Getrag Fiero 5 speed transaxles.
Manual Transmission Gear Ratios
Year ____Style __Code Axle 1st 2nd 3rd 4th 5th rev.
1988 4cyl 5 speed MT2 3.35 3.73 2.04 1.45 1.03 0.74 3.50
1988 V6 5 speed MG2 3.61 3.50 2.05 1.38 0.94 0.72 3.41

OK, this may either sound like a dumb question or, a too good to be true question. The question is, are the final drive gear sets interchangeable? Upping the final drive ratio from 3.61 to 3.35 in the MG2 Tranny would result in approx 9% taller final drive ratio. If this is possible, why has no one done it? Like said, sounds too good to be true. For any of the common engine swaps having more than enough low end torque, it would not only offer lower rpms at highway speeds, but lessen the stresses fed back thru the drive train in the lower gears.
And, if this IS possible, since I am facing a rebuild of my 282 anyway, should anyone have that 3.35 final drive gear set laying around gathering dust, I sure would be interested in taking it off your hands. Please PM me with any offers.

[This message has been edited by Monstertone (edited 02-19-2020).]

Will FEB 20, 08:48 AM

quote
Originally posted by fieroguru:

You can also push 5th gear out of the end of the Isuzu case at 135 mph... I ran an isuzu with a 282 whp 317 wtq SBC for a year and it didn't give up the ghost. Its OK for a cruiser and mashing the throttle in gear, but I wouldn't use it for the 1/4 mile or with sticky tires.



Reminds me... I had a customer pushing about 500 ftlbs out of a 3800SC through a 282 and taking it to track days. The 5th input gear is a heat-shrink press-fit on the input shaft. He was running high speed in 5th, unseated the press fit and then pushed 5th gear off its seat on the input shaft. I tore the transmission down and discovered this. I had the input shaft plated up and ground 0.0005 bigger stock, replaced the gear and reassembled. Haven't heard about any more problems with it...
olejoedad FEB 20, 09:31 AM
Getrags push the intermediate shaft into the bellhousing in high torque applications.
Destroys the tranny and the clutch.
Dennis LaGrua FEB 21, 05:56 PM

quote
Originally posted by olejoedad:

Getrags push the intermediate shaft into the bellhousing in high torque applications.
Destroys the tranny and the clutch.



Yes it all comes down to a transmissions design limits. Exceed those limits and eventually BOOM! It can be said that moderate use of a V8 /Getrag combo will hold up but then why do you need V8 horsepower and torque if that is your driving style?

------------------
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Will FEB 24, 08:24 AM

quote
Originally posted by olejoedad:

Getrags push the intermediate shaft into the bellhousing in high torque applications.
Destroys the tranny and the clutch.



What I've seen reported more often here is popping the right diff bearing boss out of the side of the transmission.
Will FEB 24, 02:18 PM

quote
Originally posted by Dennis LaGrua:

Yes it all comes down to a transmissions design limits. Exceed those limits and eventually BOOM! It can be said that moderate use of a V8 /Getrag combo will hold up but then why do you need V8 horsepower and torque if that is your driving style?




All the failures I've seen here on the forum have been from clutch drops, hard launches and generally being an idiot in first gear. Don't drop the clutch on 285's and it'll be fine...
Monstertone FEB 24, 03:43 PM

quote
Originally posted by Will:
All the failures I've seen here on the forum have been from clutch drops, hard launches and generally being an idiot in first gear. Don't drop the clutch on 285's and it'll be fine...



Will said it all right there. However, not all of us who crave a bit more power than the rather anemic 2.8 feel it necessary to do burn outs until we destroy our trannies.
fwiw: Helical gears produce a thrust factor which must be taken into account in the design of the a gear box. In most cases, the engineers include a safety factor of 1.5 or possibly as high as 2.0 in their calculations. This is to accommodate for discrepancies in materials & QC, not some idiot that stuffs a big engine in a Fiero & trashes the drive train by continuous abuse.
Will FEB 24, 03:56 PM

quote
Originally posted by Monstertone:


Will said it all right there. However, not all of us who crave a bit more power than the rather anemic 2.8 feel it necessary to do burn outs until we destroy our trannies.
fwiw: Helical gears produce a thrust factor which must be taken into account in the design of the a gear box. In most cases, the engineers include a safety factor of 1.5 or possibly as high as 2.0 in their calculations. This is to accommodate for discrepancies in materials & QC, not some idiot that stuffs a big engine in a Fiero & trashes the drive train by continuous abuse.



Also, the analytical parameters--more than just safety factors--have gone up over time. Look at the bracing around the right diff bearing on the case of an F23 vs the case of a 282. The F23 case is obviously FAR stronger, even though the transmissions are designed for essentially the same range of engine power and vehicle weight. They even use the same (toothpick sized) FWD diff splines, so it's not like increased loading is the driving factor.