I came across a 3800SC 88 GT with an F40 trans. Looks to be a properly done swap. I already have a nicely done 88GT 3800SC with a getrag, and am contemplating switching transmissions.
My question is this. Other than the "cool" factor of having a 6 speed, can anyone tell me any day to day benefits? Also, in terms of durability, I don't really drive my car hard since I am worried about blowing up the Getrag. Would an F40 allow me to be able to hammer the car more without the same worries? The F40 is out of a G6, and has custom axles, and appears to be shifting and working great. The same engine mounts are used (purple reign) as my car, so I am assuming the engine location is the same and it "should" be able to get swapped over.
Any advice would be appreciated
I should add, I have very limited mechanical skills with cars, so I would be leaning on a friend or two with Fiero swap experience locally. My concern is that if the engines are in slightly different positions, the custom axles may not work...
[This message has been edited by cam-a-lot (edited 04-02-2020).]
Also, please chime in on gear ratios. I had an F23 in the past with the stock gear ratio from the cavalier, and it was really not well suited for the 3800 motor. Is the F40 a better gear ratio, where first and second gear are actually usable?
I can tell you yes on the durability. I have 400HP (LS3) at the rear wheels and have drive it hard for over 5 years. It is nice to have the 6th gear for gas milage and interstate driving. The only problem I have with it is first gear is to low so I mainly drive using 2 thru 6th. Just my input.
Jack
[This message has been edited by J Gunsett (edited 04-02-2020).]
Having the F40 mated to my 382 whp LS4 for the last 6.5 years (55K miles), I have zero concerns about its durability. It has withstood a lot of 7200 rpm WOT upshifts, burns outs with 285 width tires on the street as well as at the track, and general abusive driving... never given me any issues.
Early on, I only used 1st gear as a bump gear to get the car moving from a stop. If I was rolling through a corner, I would keep it in 2nd. Many of my 1/4 mile runs were launching in 2nd. Once you were in 2nd, it was go time and a lot of fun!
I spent about 2 months switching between my LS4/F40 car and a SBC/F23 car daily (drive my car to work, drive the other after work to validate and tune the swap. The F23 always felt like it was missing a gear and spinning to many RPMs. Sections of the road where I would be in 3rd with the F40, I was in 4th with the F23. If I was in 5th with the F40, I would be looking for 6th gear in the F23 and frustrated is wasn't there. 6th with the F40 also quieted down the cruise volume from the engine as it got out of the drone range. The only redeeming quality of the F23 is that it shifted like a hot knife through butter. Slipper smooth vs. the notchy/cluncky feel from the F40 (the F40 is a gated shifter inside the transmission with stiffer detent springs).
A few years back I swapped in a 3.09 final drive in my F40, which made 1st much more useful, gave every gear longer legs, and allowed an even lower cruise rpm. Now I can reach 45 mph in 1st, 84 mph in 2nd, 130 mph in 3rd and cruise at 80 mph @ 2080 rpm. The 3.09 really made the F40 even more awesome, but is costly to do (requires buying and importing transmission from Europe, disassembling 2 transmissions and gear sets, swap the 2 main shafts and 3.09 ring gear, then reassemble).
Fieroguru, what kind of fuel economy are you getting with the ls4/F40 combo? Before and after the gear swap. Also do you still have DOD enabled? Thanks!
29 mpg has been my best before and after the 3.09 swap. The difference was before I would get 29 at 70 mph, now I get 29 at 80 mph (but only about 26-27 @ 70)
The old camshaft (DoD compatible, but I never got DoD to work with the manual trans) has too much overlap to get optimal fuel economy below 1800 rpm, so it is being replaced with one with less duration, higher lift, and negative overlap. That should get me over 30. My old SCB/getrag swap with 100 less hp never got above 22-23 mpg...
The F40 in the car I am looking at has an aluminum flywheel. My Getrag has a balanced flywheel that won't be compatible with the F40
If I get someone to help me swap the transmissions between the 2 cars, is it possible to swap flywheels and somehow have them balanced without removing the engines?
My current flywheel is fully balanced to the rotating assembly. I would assume cables and shifter mechanism would also be a direct swap..
[This message has been edited by cam-a-lot (edited 04-05-2020).]
Unless your 3800SC has a lot of custom parts in the rotating assembly, you should be able to swap flywheels between the two 3800SCs w/o issue.
GM typically doesn't balance rotating assemblies to flywheels, they have weight specs for each component and keep all the component specs within range and end up with an overall assembly that is balanced within spec (but not perfect). When you start installing lighter or heavier aftermarket pistons, wrist pins, rods and crankshafts, then those parts were not built to GM specs and you will need to re-balance the combo. However, even when this happens it is a good idea when possible to balance the assembly at the crankshaft and keep the flywheel to factory specs because it is a wear item and will likely be replaced at some point.
For piece of mind, you could take both flywheels to a machine shop and have them measure the counter balance of each. Then ask them to match the aluminum one to the steel one.
Can you post a picture of the shifter assembly with the center console removed? I am pretty sure it is a modified 4 speed, but If want to see if the cable sleeve mount position was moved (DIY modification to use 2 getrag select cables - which have been prone to buckling and breaking the shift cables). Depending on how the shifter was modified and the cables used, you might want to consider changing it to a more durable setup that uses a stronger shift cable.
I drove the car today. Shifted pretty well... took a little getting used to.
However there was a loud noise unless I depress the clutch. I think it was a throwout bearing. Supposedly it is brand new, but it could be defective? I took a video with audio, will try to post
Mine is a little worse then most due to the choppy camshaft. After a while, you simply learn to either turn the car off or keep your foot in the clutch when stopped idling.
You can make is a little better by mixing a couple of redline transmission fluids, but it won't eliminate it.
About the only way to eliminate it would be to run the factory dual mass flywheel (wrong crank pattern and imbalance for the 3800).
[This message has been edited by fieroguru (edited 04-08-2020).]
Thanks for the info.... makes me want to re-think all the time and effort to get this car and swap transmissions. I think it would drive me nuts listening to that noise... Makes the car sound really shitty at a red light . Food for thought....
The big thing to keep in mind, is that you have total control on it making the noise or not.
It only happens if all 3 things happen at the same time, choose to idle the car, shifter in neutral, and the clutch released (foot off pedal).
I have logged 55K miles with mine and almost never hear it, because I make a conscious choice not to do those 3 things together. The easiest way to not hear it is to keep the clutch pressed when you come to a stop (do not put it in neutral and release the clutch while waiting for the light to change). This is a very minor change in driving style for a much stronger, better driving transmission.
It is your car and only you know what you can live with and what you can't...
So based on what you are hearing in that video, this is the standard rattle that is common with these swaps and it is not harmful other than being annoying to listen to ?
Clutch pedal effort seems minimal , so I suppose I could get used to just depressing the pedal..
There is no other solution ? Custom made flywheel ? I have access to machine tools and gear shops and could likely get one made if it would help
[This message has been edited by cam-a-lot (edited 04-10-2020).]
My clutch rattle is mild compared to what I hear in the videos (more like Paul's F40). How often do you have the engine at idle and the clutch pedal released? I am either driving down the road or at a stop with the clutch depressed. I have had the F40 installed in my Fiero for over 13 years and this has never been a problem for me.
Originally posted by cam-a-lot: There is no other solution ? Custom made flywheel ? I have access to machine tools and gear shops and could likely get one made if it would help
The 3 things that would make it happen less: Run the stock dual mass flywheel Run a heavy (25+ lbs) traditional flywheel Run a stock camshaft
All of these would smooth out the idle oscillations and make the input shaft gears less prone to rock back and forth.
For my LS4/F40 swap, I violated all 3. 12 lb single mass flywheel with an aggressive camshaft and choppy idle. Even with the rattle issue, I would do the exact same thing if I had to do it over again.
I listened to Paul's video, and it doesn't sound nearly as bad as the one I posted.
I suppose I could change my driving style and just depress the clutch when I am at a red light- Could get used to it I suppose
Just wanted to make sure that nothing ELSE seems wrong with the sound it is making, since it sounds really loud to me- like something else could be causing it than the standard F40 rattle that Paul has
Without being able to see it and hear it in person from various areas of the car, it is hard to know exactly what it is, but the starting/stopping with the activation of the clutch is just like the normal input shaft rattle.
Is there oil in the transmission? (lack of oil would make the normal noise louder).
Great info thanks. 
