What Transmission For High Output? (Page 1/1)
rehoward SEP 26, 08:00 PM
I recently bought a decent 1985 Fiero that I plan to modify. My palns as of now are to drop a 3800 V6 in it with
a factory blower with the intent to eventually ditch the blower and turbocharge it.

Since the engine will produce far in excess of a stock V6 I am wondering about the best choice for a
manual transmission? The car came with a standard manual transmission but I am wondering if it will hold up to
300+ hp? Is there a better choice to use? I am sure this is a topic that has been discussed a lot so I
am seeking posts regarding this or other sources of information on the topic. Thanks for the help.

Randy
82-T/A [At Work] SEP 26, 09:05 PM

quote
Originally posted by rehoward:

I recently bought a decent 1985 Fiero that I plan to modify. My palns as of now are to drop a 3800 V6 in it with
a factory blower with the intent to eventually ditch the blower and turbocharge it.

Since the engine will produce far in excess of a stock V6 I am wondering about the best choice for a
manual transmission? The car came with a standard manual transmission but I am wondering if it will hold up to
300+ hp? Is there a better choice to use? I am sure this is a topic that has been discussed a lot so I
am seeking posts regarding this or other sources of information on the topic. Thanks for the help.

Randy




Hi Randy, is your transmission a 5-Speed (coupled to a 4 cyl originally) or a 4-Speed (coupled to a V6)?

The 4-Speed in the Fiero is more than capable of handling 300hp. The 5-Speed transmission that was coupled to the 4 cyl engines is NOT capable of handling 300hp. It's an Isuzu transmission and generally cannot handle the output of even the stock V6.
buddycraigg SEP 26, 10:40 PM
agreed.
You want the 4 speed, or the 5 speed getrag.
but why not use the auto that comes with the 3800?
rehoward SEP 27, 04:00 AM
The trans in my car is the 4 speed manual with V6 so it sounds like it might survive if I don't drag race with the car, which I have no intention of doing.
I would like to improve its performance both in power and in handling ability and make it a real road machine of a sports car. Hence, I am not
going to use an automatic trans. Is the Getrag 5 speed more stout than the V6 4 speed that I already have in the car? Or, will a 3800 manual
trans fit in the Fiero? I am not sure if the 3800 in FWD form even offered a manual trans?
82-T/A [At Work] SEP 27, 07:30 AM

quote
Originally posted by rehoward:

The trans in my car is the 4 speed manual with V6 so it sounds like it might survive if I don't drag race with the car, which I have no intention of doing.
I would like to improve its performance both in power and in handling ability and make it a real road machine of a sports car. Hence, I am not
going to use an automatic trans. Is the Getrag 5 speed more stout than the V6 4 speed that I already have in the car? Or, will a 3800 manual
trans fit in the Fiero? I am not sure if the 3800 in FWD form even offered a manual trans?




The 4-Speed has absolutely no problems handling the 3800. Supercharged, or turbocharged. People put it behind big V8 swaps without modification.

The 5-Speed Getrag is much harder to find, there is a very limited number of them out there, and it definitely cannot handle the same amount of power as the 4-Speed manual can. The only reason why they went with the 5-Speed Getrag on the V6 was to provide better gearing. It's built to be able to handle decent power, and can definitely handle the power of the 2.8 V6. But it does not compare to the amount power the 4-Speed can handle.

Someone on here years ago posted torque ratings that the transmissions could handle. The 4-cyl 5-Speed (Isuzu) was... SAD... to put it lightly. The 5-Speed Getrag was decent (can handle a built Quad-4, etc.), and the 4-Speed Muncie could support something like 100+ more foot-pounds of torque. I'm hoping someone can post that chart...
olejoedad SEP 27, 02:08 PM
As mentioned by 82TA, you need to be more concerned about how much torque the V-8 will be making.

Torque is what breaks transmissions.

The 4-speed is good, but remember too that Archie had the internals of the 4-speeds he used in his V-8 swaps cryogenically treated to improve their strength.

There is no guarantee that a 38 year old tranny will hold up.

[This message has been edited by olejoedad (edited 09-27-2023).]

Dennis LaGrua SEP 27, 08:16 PM

quote
Originally posted by buddycraigg:

agreed.
You want the 4 speed, or the 5 speed getrag.
but why not use the auto that comes with the 3800?



I have seen and read of too many 3800 swap Muncie and Getrag failures and would not feel comfortable using those light duty boxes with a high output engine. You could cryo treat the trans for a bit more strength but the failures that I have seen didn't come from the steel gears but from a blown apart case. If you must have a stick certain versions of the F40 can be made to fit but the swap process is far from easy.
I would just use the 4T65eHD that came with the engine and be done with it. A few years ago forum member Darkhorizon (Scott) ran 9.87@142 mph with a 3800 turbo and this transmission

------------------
" 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 "