F40 6spd conversion research

[TGP37]

If it was built by the hands of mankind, it is doomed to fail periodically. Just hope it isn't the wrong thing at the wrong time causing tragic loss.

[NateD4]

I'm not seeing the nylon caps. Have any better pictures (perhaps I'm not looking enough).

I'm putting the F40 into my Fiero with a 3900 as well. I'll have to check into the oil issue.

Any idea when you will get your transmission out and apart? I'm curious to hear what went wrong.

If its something as simple as a nylon cap on the shift mechanisms I'd like to know so I can remedy it prior to installing into my car.


BTW the new F40 is that a zero mile unit from e-bay?

[Joseph Upson]

I'm not seeing the nylon caps. Have any better pictures (perhaps I'm not looking enough).

I'm putting the F40 into my Fiero with a 3900 as well. I'll have to check into the oil issue.

Any idea when you will get your transmission out and apart? I'm curious to hear what went wrong.

If its something as simple as a nylon cap on the shift mechanisms I'd like to know so I can remedy it prior to installing into my car.


BTW the new F40 is that a zero mile unit from e-bay?

You really aren't seeing those plastic looking covers on the ends of the shift forks next to the gears in that link?

I purchased the new unit from a Fiero Forum member with 0 miles for a great price shipped. It was a real blessing because I found it right when I needed it.

Not sure I'll have time to disassemble the current tranny as I also plan to rebuild the Forged motor and install the two together in Feb.

The proper gear oil is GM P/N#21018899, or GL-4; 75W80 it's full synthetic.

[mfuller]

Joseph - Which gearset do you have in your F40? The MT2 or MU9?
It seems that the MT2-geared trans is easier to come by, although I kinda prefer the sightly shorter gearset in the MU0.
Quaife offers a limited slip diff for the MU9 F40; do you think it would work on a MT2 F40?

[Joseph Upson]

Joseph - Which gearset do you have in your F40? The MT2 or MU9?
It seems that the MT2-geared trans is easier to come by, although I kinda prefer the sightly shorter gearset in the MU0.
Quaife offers a limited slip diff for the MU9 F40; do you think it would work on a MT2 F40?

I have the MT2 or first year GM application and the reason it is easy to come by is very likely because the first year tranny had problems and bad press that were immediately addressed by the following year with an upgraded detent system, synchronizers and gear ratios for a little quicker acceleration and easier shifting. These trannies are basically the same except for the upgrades and therefore everything should be interchangeable.

Since my tranny is in a Fiero and I have 245/40R18s on the rear, I don't need a limited slip unit, even with the stroked, high compression, boosted 3900 I couldn't spin the tires, it's all squat and go. More importantly, I managed 33 mpg hwy with a limping (one low compression cylinder) motor on the way home to swap out the damaged motor with the MT2 and want to see what a fresh motor with proper tune and use of lean engine mode will do with it. If the motor had not been damaged I believe it could have pulled off 38 MPG as I purposely under estimated on the fuel receipts for a solid 33 MPG avg over about 160 mile stretch, tank fill to tank fill.

[NateD4]

I eventually saw the white-ish plastic caps when I wasn't using my phone to view the page. Amazing how a bigger screen can help....

I guess I'll see how my gears hold up. Our builds seem almost identical except I'm using the LZG block with DOD and the 'ordinary' intake manifold instead of the G6 variable tuned one.

I can't help but wonder what heat treat GM put on the gears.

Also any idea how much power you are putting through it? I suspect this tranny should handle 500 HP with a fair amount of abuse.

Also what is going in your forged bottom end (how is that different from the current build).

As I stated I'm getting ready to do a similar build. Forged crank, Carrillo rods, custom pistons, custom cams... the works essentially... The only difference is that I'm opting for 10.25:1. I'm curious though how well your engine handled low octane fuel (87 or 89).

[Joseph Upson]

I eventually saw the white-ish plastic caps when I wasn't using my phone to view the page. Amazing how a bigger screen can help....

I guess I'll see how my gears hold up. Our builds seem almost identical except I'm using the LZG block with DOD and the 'ordinary' intake manifold instead of the G6 variable tuned one.
(87 or 89).

I was just thinking about that block yesterday to address city MPG and the potential to push past 40 MPG HWY. The talk about turbos improving fuel economy must be referencing hwy driving because it certainly doesn't seem to do anything for city driving probably because of the effect stop and go traffic has on the turbo likely pushing it to near boost when taking off from a stop repeatedly.


I can't help but wonder what heat treat GM put on the gears.(87 or 89).[/QUOTE]

Also any idea how much power you are putting through it? I suspect this tranny should handle 500 HP with a fair amount of abuse.

Also what is going in your forged bottom end (how is that different from the current build).

As I stated I'm getting ready to do a similar build. Forged crank, Carrillo rods, custom pistons, custom cams... the works essentially... The only difference is that I'm opting for 10.25:1. I'm curious though how well your engine handled low octane fuel (87 or 89).[/QUOTE]

[Joseph Upson]

I eventually saw the white-ish plastic caps when I wasn't using my phone to view the page. Amazing how a bigger screen can help....

I guess I'll see how my gears hold up. Our builds seem almost identical except I'm using the LZG block with DOD and the 'ordinary' intake manifold instead of the G6 variable tuned one.(87 or 89).

I was just thinking about that block yesterday and the potential for improving city mpg as well as possibly pushing past 40 mpg hwy. A turbo may help hwy mpg but it doesn't appear to make a difference in city driving unless you drive it aggressively and go through a full tank in about half the usual time it takes driving moderately.

I can't help but wonder what heat treat GM put on the gears.(87 or 89).

Shot peened gears.

Also any idea how much power you are putting through it? I suspect this tranny should handle 500 HP with a fair amount of abuse.(87 or 89).

Using my GTech module I managed 263 lb/ft at the wheels on the stock 3900 with minimal tuning and the manual says that it under estimates based on other inefficiencies not to mention the general error involved regarding inaccurate data; weight, pitch value on launch and being stuck to the windshield. The modded engine made the car feel like it had lift bars on it and acceleration from a stop was amazing. I'd estimate near 400 lb/ft considering it also had meth injection and less intake heat. There was no comparison between the two on launch. Torque and clutch dumping is what destroys your tranny.

Also what is going in your forged bottom end (how is that different from the current build).(87 or 89).

The bottom end is stock except for the forged rotating assembly. The engine will be restored to pretty much the previous state by replacing the damaged parts.

As I stated I'm getting ready to do a similar build. Forged crank, Carrillo rods, custom pistons, custom cams... the works essentially... The only difference is that I'm opting for 10.25:1. I'm curious though how well your engine handled low octane fuel (87 or 89).

Make sure you use greater than 5.7" connecting rods if you are using the internal crank trigger, well even if you aren't. MAKE SURE you check all internal clearances, I have to investigate to find what broke the long arm of my oil squirters off, the rod or the piston. Then again this is if you are planning to stroke the motor. I still have the steel 3.43" crank with radiused journals to get rid of.

As for fuel, the first 7 psi stock motor install did fine on 89 octane with a poor tune and no intercooling. I had several lean spots in the datalog under boost that did not detonate. The high compression motor did okay on 89 with mild boost. The problem with establishing a definative assessment of it is that the knock sensor was bad causing me to pull far more timing than it needed resulting in poor performance areas from being excessively retarded. That fact alone might have cost 1 mpg due to less than optimum ignition timing.

I didn't get to the bottom of it until the replacement motor was showing the exact same knock problem in areas I knew it never had a problem with on 89 octane, except it was using 93 at the time so it had to be false knock.

Given my results you shouldn't have a lick of trouble with the compression ratio you plan to use and even less so if you install an intercooling device and run a cam with at least 216/213 duration or greater on mid grade to premium fuel at 7 psi. I hit in excess of 15 psi on premium with the stock 9.8:1 compression motor several times, with a little less cam than the specs I just listed and no intercooling, not even meth injection. That should give you a good idea of what kind of cushion you have. I also didn't use a spark table severly reduced from the stock TGP table.