What gear would you use?

[justsomeguy]

This contraption I'm putting together has me a bit puzzled about what gear to run in the rear. Strictly street car, but hard usage. REAL hard. Here's the specs:

SBC or Gen IV - 383-408 CI
450-550 FWHP
6500 RPM Max Shift Point
Tremec TKO600 Trans: 1 - 2.87, 2 - 1.89, 3 - 1.28, 4 - 1.00, 5 - 0.64
12 Bolt Rear
33" Rear Tire
Probably around 1800-2000 pounds all said and done.

The OD in this trans coupled with this size of the rear tire is looking like I need a REALLY steep gear. I mean, 4.56's would put me at 3500rpm at 120mph!!! The dang motor won't even be into it's powerband by then. Should I just use the extremely light weight of the truck as a bonus and run a lower (numerically) gear?

What would you guys do?

 

[Toad]

I mean, 4.56's would put me at 3500rpm at 120mph!!!

Are you sure about this?

Toad

 

[skull]

gears

try here, on where it asks for transfer case ratio, put in 1.1

http://www.florida4x4.com/tech/gearcalc.php


this will help with RPM.


Later

 

[justsomeguy]

Same answers as before. Still 50mph before the first gear shift with a 4.56 gear! Not used to these tall tires...

I've been using this:

http://www.richmondgear.com/101032.html

 

[chevellelovermichael]

if you use the 383, and the vehicle only weighs 2000, then you'll have plenty torque to get moving. just use a 2500 stall converter, full tube headers, and 3.73 gears. you won't be sorry! your first gear ratio will give you plenty of bottom end get up, and the o.d. will be great for m.p.g.

 

[Dr Crankenstein]

The numbers don't lie. You're killing yourself with a 33'' tire. Basically, you have a funny car tire with a sports car trans.

Do you plan to redline the thing for every shift? If you've got 500hp, you don't need to wring it out to 6500. Try shifting at 3500 or 4000.

Think about reasonable numbers. 4.56 gears at 80MPH is 2377RPM, decent highway RPM. Forget about the OD, and you spin 3714RPM at the same speed.

At 120 MPH, powerband should be the last thing on your mind, unless you wanna run Bonneville.

I'd stuff 5.38's in it, and go to the strip.

 

[justsomeguy]

if you use the 383, and the vehicle only weighs 2000, then you'll have plenty torque to get moving. just use a 2500 stall converter, full tube headers, and 3.73 gears. you won't be sorry! your first gear ratio will give you plenty of bottom end get up, and the o.d. will be great for m.p.g.

Manual trans. My Left foot IS the stall. [cl

The numbers don't lie. You're killing yourself with a 33'' tire. Basically, you have a funny car tire with a sports car trans.

Do you plan to redline the thing for every shift? If you've got 500hp, you don't need to wring it out to 6500. Try shifting at 3500 or 4000.

Think about reasonable numbers. 4.56 gears at 80MPH is 2377RPM, decent highway RPM. Forget about the OD, and you spin 3714RPM at the same speed.

At 120 MPH, powerband should be the last thing on your mind, unless you wanna run Bonneville.

I'd stuff 5.38's in it, and go to the strip.

I hear you on the realistic MPH. I mean, it should be a great cruiser geared out like this. Honestly, I'm half tempted to chuck a big-block at it and just forget about the redline. Then again, I don't think I'll need much torque to get this light little thing rolling anyway...

Maybe I should drop a quick change in it.

 

[Old Iron]

My only concern is the rearend
You said a 12 bolt have you addressed the issue of c-clips and installing the c-clip eliminators ?
Bad news when one or both fall off end of the axle I know from experience on this one
I've got 4.56's with 32" tall tires on my 65 Goat. Hwy rpm at 70 is 3500 and you have to consider my stall is 4400 in a powerglide so I don't have the luxury of the OD
Crank's pretty much on but, I think I'd consider 4.88's
Or with the .64 od 5.13'S at 70 would be 2350 to 2574 rpm's this should be about the middle of your torque range

Jim

 

[justsomeguy]

I haven't gotten into the rear yet, but C-Clip eliminators and a new limited slip unit are in the plans.

I'm seriously debating just grabbing up a used Winters quick change rear so I can adjust the ratio easily. I think the race car shop has a used unit laying around for under a grand with disc brakes and wide-five hubs on it already. What kind of HP are these things good for? I know the sprint car guys throw crazy HP at them, but that's also on dirt and not a lot of miles. Would I have reliability issues on the street?

Decisions to make...

 

[Old Iron]

I love quick changes for the reason you said and then the other factor they're just plain kool
You won't have any reliability issues
The HP capability is determined by which rear you get. The
Winters light weight sprint can handle lots of HP where you get into failure is when you launch a well hooked vehicle on asphalt.
Most any of the rears can handle 5 to 600 HP though.
The rears come with 2 different ring and pinions a 4.11 and a 4.56 my favorite is the 4.56.
Gears are cheap for quick changes the big expense is the initial setup and a little noisy on the road (I love the sound of them)
You have my vote for the quick change [cl

Jim
p.s. look into a locker for the rear a spool is annoying on the street