I'm building an LT1 to put in my '88 T/A, and I've got a rebuilt 700R4 now. I'm just wondering:
1)What kind of gas mileage an LT1+T56 combo would get?
2)How hard/expensive is it to swap a 700R4 to a T56?
I want a stick, but the 700R4 is growing on me....does the T56 get better gas mileage than the 700R4? Thanks,

 

The T-56 will not only get better mileage....it'll get better mileage with deeper gears. I went from a 700-R4/2.73 stock setup to a T-56/3.70 and gained about 2mpg on the highway. In-town mileage stayed about the same.

The T-56 is almost a direct bolt-in. Since you're using the LT1 you already have a compatible flywheel.....the only thing you'll need that can't be found in a stock LT1 car is a crossmember, which you can get from Spohn for a reasonable price. You'll have to drill the firewall for the clutch hydros, cut a hole in the trans tunnel for the shifter, and get a speedo adapter (or modify the tailhousing,) but other than that it bolts right in.

 

I get 22 mpg on the freeway with a zz430 , t56, holley carb and 4.10's

 

Really?? I get around 25-28 mpg on the highway with my stock LO3, and 2.73's....I'm really considering switching to a T56, mainly for the better gas mileage!
My planned setup will likely be a stout LT1 putting (hopefully) around 400 RWHP, and most likely 3.73 posi gears. Can anyone estimate mileage with this setup?

Honestly...how hard is it to swap from 700-R4 to a T56?..is there a good T56 swap page? DO you T56 swappers have any regrets about going to the 6-speed?

 

Interesting....My LT1/T56 in my 4th gen only gets 20...and thats all highway miles.

 

The T56 is the best manual transmission I've ever had the priviledge of owning. I despise automatics, and my 700R4 couldn't even hold the power of a Goodwrench 350 with a few minor bolt ons.

The swap is fairly easy with the right parts. It isn't cheap though, so don't kid yourself up front. The T56 is an expensive piece of hardware, but everything you need can be had for about $2,500. Get a T56 from a '94-'97 car. The '93 trans has a super deep 1st gear that isn't well suited to tall rear gears. The post '97 LS1 T56s are too complicated to adapt.

You will need:
Pedals (3rd with hydraulic clutch or 4th gen will work)
T56 ('94-'97 F-car)
Crossmember (Spohn or Skulte)
Hydraulics (sealed system from '93-'97 F-car)
Flywheel for LT1 (since that's what you're using)
Clutch for LT1/T56 setup
Torque Arm Mount ('93-'97 F-car)
Speedometer (signal adapter or new Autometer electronic speedo)
Console plate (3rd gen stick car, still available new)
shifter boot ('93-'97 F-car)

Your driveshaft will work fine. Be sure to get all the hardware you can with the T56. A few brackets and bolts from a 3rd gen car will make it look stock. The firewall pad will have punch outs for the clutch actuator. Use it as a template and cut the firewall. Have a friend or a lift and a trans jack because the T56 is a heavy, heavy trans. Everything will just bolt right in. You will need to do a little bit of wiring, but nothing outrageous.

My car turns about 1,950 RPM at 80MPH in 6th gear with a 3.73:1 rear gear. The F-car trans cuts your rear end gear in half in 6th gear (0.50:1 overdrive). The mileage improves, but the smiles per mile improved most dramatically!

PM me if you have any questions.

 

Wow that is kinda low. My 95 M6 gets 29mpg on the highway on one tank and would be higher if I didn't merge so damn hard

 

I get about 300-320 miles per tank. Divide by the 15 gal tank and get 20-21 MPG. My window sticker says 19C and 29H....

 

I'm getting about 17 mpg with my new motor and T-56 (see sig.)

But, I have the little 3.23 geared G92 rear and the six-speed. I will be switching to a Moser 12 bolt with 3.73's next year sometime and I'm sure the milage will suffer a little more.

It's gets WAY less when racing!

Who cares about gas milage anyways, especially if you are going to build a stout 400 + HP LT-1 ! Most Hot-rods dont get that great of gas milage. But the six-speed is the ONLY tranny to have and it's the only thing to hold up so far! I got tired of blowing the guts out of my "built" 700r4's and a manual tranny car is way more fun to drive, IMO.

Just my $.02