I recently bought a 1986 Fiero with the 2.9 V6 engine. I would like to swap a GM 3800 SC motor into it
but am concerned about the maual transmission being able to handle the power of the supercharged motor.
The Fiero came with a 4 speed manual trans. Will that transmission hold up to 350-400 hp? Is there a
better one to use?

On a related note. What combination of clutch and flywheel will fit this 3800 swap? Given the light weight
of the car, do I really need to buy a high performance clutch for it? I will use it for spirited driving but not
for drag racing so no brutal launches or anything like that. Just road racing types of useage.

Thanks!

Good info in this thread

https://www.fiero.nl/forum/Forum2/HTML/134227.html

shem

The four speed from the 86 2.8 V-6 cars will live behind the 3800 SC.....unless you beat on it.

Get a spare transmission.

A stock clutch will not hold the torque.

[This message has been edited by olejoedad (edited 07-29-2023).]

Not a big fan of the Getrag or Muncie behind a powerful new engine. Joe is probably right that if you don't go full throttle very often the box will last but I would consider that those transmissions are very old and most have not undergone a rebuild. As the temptation to use the power is always there; I know a few guys that blew them up driving aggressively. My solution was to use the 4T65eHD transmission that GM designed for use with the 3800SC.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

I agree with Dennis - GM put it he 4T65E-HD!behind the 3800SC for a reason.

If you want the manual, fine.

But it can and will be broken....

The obvious thing to do with an un-rebuilt transmission is to rebuild it before pushing more torque through it.

Otherwise, consider the Getrag F23 or F40 transmissions.

Clutch requirement is determined by engine torque, not engine horsepower, nor vehicle weight.

Road racing is tough. thedrue has killed Muncie 4-speeds with not much more power than stock, after several hours of road racing duty.

If transmission durability becomes an issue, you can always install a larger supercharger pulley to reduce the torque.

V-8 Archie used the 85-86 four speed behind his SBC swaps.
He had them professionally rebuilt with cryo-hardened internals.
They could still be broken.

I once talked to one of the designers of the GM manual transmissions several years back. He did evaluation and test work on both the Getrag and Muncie. He stated that putting more than 200 ft lbs into these transmissions is considerably beyond their design limits. One of the many weak points is the case that can and will crack.
When I was doing 3800SC swaps several years ago one was for a young guy with an 86 that could not resist stomping on it. We installed a Spec 3 clutch and told him to drive conservatively. He didn't listen. After a few "high performance" runs he parked in his driveway. As he backed out the next day he heard a thumping sound. He got out looked and saw a large oil slick on the ground. He had cracked the case. After that he found a well used 4 speed, installed it and sold the car.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

As the owner of a 3800 SC Fiero with a manual trans.. I would have to agree with Dennis.

I have had 3-4 Fieros with 3800 SC motors, and by far the least headaches were the ones with the automatic HD trans. Yes, standard is more fun once in a while, but is it worth the extra headaches with clutch, flywheel, axles, etc? Probably not.

If I could go back, I would stick with an automatic 3800 SC and enjoy driving the car more instead of tranny issues

Yes, it can last if you don't stomp on it- but if you won't stomp on it, you may as well keep the stock engine. What is the point of installing a 3800 SC or V8 if you are going to baby the car? Just to impress some old guys at a car show sitting in their lawn chairs?