What is the biggest cubic inch engine anybody has used in front of one of
these 6-speeds ?
Pro-Touring or Drag Week kind of application.

Thinking of using some form of this tranny with 4.56 rear gears and a 572 or bigger.

I know you can break anything, but how are these 6-speeds holding up
and what kind of abuse are they living through ?

If your going with big power, then take the trans down to the case and replace it with premium parts. There are a few racers on here that use it, but not in stock form. Throwing down earth moving torque in a stock trans will be short lived. I only use auto's, so I don't know whom to recommend for upgrade parts, sorry.

That 572 must be really down on power to need 4.56's?

450 hp Vipers come with 3.07's and 6 speeds, and seem to move fairly quick.

Might want to look into a supercharger to up the power on that 572 a bit and then you won't have to run them dump truck gears.

On the gears, I just figured the 4.56 would work well with the .50 sixth gear OD.
Plus, the more rearend gear you have, I would think the more torque you can get away with pushing through the tranny.

What is the weight and tire diameter of your car?

Earlymopar, car is still being built little by little, but the tire will be a street type radial,
like the Hoosier 29 x 18.50. I don't want to go any bigger than 29.
I would guess the weight will end up probably no less than 3000, hopefully no more than 3200~~3400.

I messed with this calculator and ended up going from a 3.91 gear set to a 4.56. But, I have a 30.7" tire diameter. I was most concerned about hitting my target engine RPMs at specific speeds and gears as well as how I intended to use the car.

https://www.tremec.com/calculadora.php

I put a viper t56 in my Duster like 10 years ago. Not big power buts it’s behind a 400bb with a small cam, Headers, usual stuff. The plan was to swap in a 431 but I haven’t touched it since. It’s set up as a pro touring/ cruiser. I have 3.73s with 26” tires. Sometimes id like to try 4.10. I’d also like to change the cam but I think that will also require a little more gear. The way it is now I pretty much can’t use 6th until I’m over 70 mph. I’ve beat on it but not like weekly trips to the track.
When I planned it out I tried to get close to viper final drive ratio but the engines are apples to oranges kind of comparison.

James, is your tranny still stock internals ? I would imagine it shifts pretty nice.

Liberty Gears can set you up with a Tremec in a few different flavors depending on usage and budget . Check out their site for options and gear ratio charts. Most of these 5 or six speeds have a really deep low gear and if you go with a 4.56 first gear will be useless . I have a 3,27 low gear in my Richmond 5-speed and 5th gear is 1.1 so 3.23 or 3.54 are both good gears for a street/strip application.
Gus

Hi Fourgear,
I'm lucky enough to have several Richmonds also for different projects. They do have typically more first gear
than the Tremec-type 6-speeds. The Richmonds are very good, but Richmond is terrible about making replacement parts.
In favor of theTremec, they supposely have better synchros than the Richmond, so they can be shifted at a higher RPM.
I still think the Richmonds have bigger and stronger gears than the Tremec.

I have a T56 maganum behind the 468" early hemi in my 31 Plymouth hot rod coupe. With 4.57 rear gears and 30" tires, and a 280 degrees at .050 cam, I can't even use 6th under 70 mph. But it really rolls nice down the freeway and gets really good fuel mileage.

You might as well figure on starting out in second.

The choices are wide ratio at 2.97 2.10 1.46 1.00 .74 .50 or close ratio at 2.66 1.78 1.30 1.00 .80 .63

It seems to me that 1st and 6th are pretty useless on the wide ratio. So I went with the close ratio. Still 6th is too high speed unless driving on the Autobahn. I would recommend you use the close ratio, and use the 4.56 gears, or maybe ever 4.88.

Don't get it from American Powertrain, worst customer service ever.

The ratios are 2.66 1.78 1.30 1.00 .74 .50

So yes 2.66 x 4.56 = 12.13 WOW lots of first gear.

Sixth gear final is 2.28, so with a 29" tire that's 1850 RPM at 70 MPH.

4.11 rear brings the 70 MPH down to 1667 RPM, and it's still a lot of first gear at 11:1 total ratio.

Looks like 4.11 would be better with a great big motor.

You'd need an RV cam to lug a .50 6th with 4.11's.

Well how would it be with a big motor and a cam with a real wide lobe center / not much overlap ?

With a big torque monster motor, it's hard to make use of 6 gears unless your trying to go 175 mph or pull a 20,000# trailer.
But still 1600 rpm at 70 mph, is probably not efficient.

Joel, I found the specs for the viper V-10 cam and it is quite small.

https://www.viperclub.org/vca/threa...specifications-708-stock-gen-one.648094/

For sure I would have a bigger cam than that.