MTC_75vette

I am currently running a 75 vette with a trex cam full bolt on carb'd ls1 with a th400 trans and 3.70 gears. The car is street/strip and when driving around town or doing quick highway runs its great. But I am having issues with long highway travel as my rpms are at 4000 going 65 mph. I would really like to be able to cruise at highway speeds while maintaining decent MPG and RPMs. I was wondering what anyone with a modded ls in c3 vette has done and what their opinions were. I was told a 700R4 cant handle the power and that if I convert to a t-56 it doesnt fit properly and I will run risk of breaking with more violent launches. My budget is limited so I cant convert to manual and then replace the entire rear. I was told I could maybe get a built 4L60 with a electronic controller for a decent price and easy install any thoughts? Also I looked into a gear vendor overdrive but heard they dont fit in my car.

Gordonm

How much power are you making?
I have run a T56 in mine for 2 years now behind a Gen 1 SB. I am in the middle of converting to LS3 power with about 520 HP. The T56 can handle or be built to handle a good amount of power. Yes launching it on slicks will shorten its life. It was not a bolt in either, it is big but does fit without cutting up the car.
There are OD automatics out there that can be built to take quite a bit of HP. Start searching around. I'm not much on automatics so I can't help to much.

MTC_75vette

Thanks for replying...good to hear you got a t56 in there I am def considering that route if it can be done without to much modification. My car now is making about 420 to the wheels but I am doing heads next that should bring it up to 450-460. How does the interior of your car look with the t56? I read that the shifter needs to be moved further back than the stock location.

Gordonm

Yes the shifter is definitly further back. With the Gen1 SB it was quite far back. With the LS motor it moved it up 1 1/2 from the Gen1 location. I have seen some guys make a shift handle that comes up in the stock spot. I chose to just make a hole where it comes out and make a custom shift plate. I will have to do it over again now that the shifter comes up a little further. Not a problem because I also put in Vintage AC and changed the heater and AC control.
I suspect mine is going to be in the 450ish WHP and shoould have no problem with the T56. Im not drag racing but I do drive it pretty hard. It will see the strip when it is all done. I did also put a 12 bolt conversion rear in it.

Rikoshay

Pic's please!

I'm dying to yank the tire old 350 out of my 1980 Vette and replace it with the 5.3 that's sitting on the stand. Was planning on taking a week of vacation in November but my boss called and said business is picking up, so put it off until December.

I'm using a 4l60e, not nearly as much HP as you are planning to use.

MTC_75vette

Rikoshay did you do any research on the 4l60e on how easy its install is on the c3?

Rikoshay

Yes, I already have the 4 position shifter kit installed inside the car.

The 4L60e is like 2-7/8" longer, but the LS engine is shorter. I need to crawl under my car with a tape measure and determine the distance from the back of the motor mount to the tailhousing of the trans. Trying to reuse my stock driveshaft by adjusting the position of the motor mounts.

I will be running the modified 700R4 tailhousing with a reluctor/speedo ring on the tailshaft. I got it used, and didn't come with the adapter plate (6bolt to 4bolt), so I had to make my own.

The whole set-up from Shift Works is around $500.

mika_

Hi!

You may find some answers from this thread:
http://forums.corvetteforum.com/c3-t...l60e-swap.html

Afterwards Brent sold the car and two weeks ago the same car ended up in my carage So far I've been really happy with the combination of C3, LS1 and 4L60E

BR,
Mika

User-c3

I have an LS1 with a T-56 in my 78 vette. Freeway driving is incredible, 6th gear on the freeway is amazing. RPM's are so low I almost cant even stand it because of my exhaust drone. I did modify the crossmember, and cut a whole in the tunnel and reweld a small amount around the shifter to close it up, but not really a big deal. I plan on running close to 500hp in the next year, and dont see any problems coming into play. The trickiest part to figure out is fabricating a bracket for the clutch mastercylinder for the correct angle.