F40 questions- real life users (Page 1/3)
cam-a-lot APR 02, 07:16 AM
Hello

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).]

cam-a-lot APR 02, 08:32 AM
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?
J Gunsett APR 02, 08:33 AM
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).]

fieroguru APR 02, 01:48 PM
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).
liv4God APR 04, 02:54 PM
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!
fieroguru APR 04, 07:41 PM
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...


cam-a-lot APR 05, 06:16 AM
Great info thanks.

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).]

fieroguru APR 05, 10:10 AM
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.
cam-a-lot APR 05, 10:48 AM
Thanks Guru

Will try to get some pics- thanks for the input
cam-a-lot APR 07, 08:29 AM
Shifter pics.

Comments?



[This message has been edited by cam-a-lot (edited 04-07-2020).]