Howdy

I've got a '66 car i'm putting a 12 bolt under, to replace the original 10 bolt.

A tremec TKO500 is in place and i'm wondering what ya'll would recommend gear wise to put in the 12 bolt

I'm at around 450 HP for a daily driven car that will play on the strip too
i'll be keeping the original 14" tires

anyone have experience as to what the best rear gear would be?
i'm debating between 3:73, 3:90, 4:10

I've had a few people tell me completely different things
a buddy said he runs 2700 RPM at 75 MPH on the highway with the 4:10, which sounds lilke an exaggeration

it'll definitely see some 2 hour-long highway trips, here and there

thanks!

Check out the link below. I'm quite sure it'll take guessing out of the game :)

http://www.keislerauto.com/tools/gm_analyzer_5sp.html

The TKO500 has a 3.27:1 1st gear so you don't need steep rear gears to launch well. I wouldn't run more than a 3.73 at the most. Might want to go taller than that even.

My 327 vette has a TKO 500 and a 3.90 rear. It is steep, I cruise at 80 indicated with 28 inch tires at about 2800 RPM. Hard to be sure the way the speedo bounces. I like deep gears with my 327 but if I had a bigger motor I'd shorten up .

I have a TKO500 with a 3.42 ring and pinion. I cruise at 72mph at 2,000 rpm. I have a 28" tall rear tire.

I wouldnt want the 5th gear any higher as it would become useless.

My launch ratio is 4.43 with the 3.27 first gear and I wouldn't want it any lower or it would be useless.

Thus 3.42 is absolutely perfect in my book and I beleive you would be making a big mistake going with a ring and pinion as low as the 3 you mention. Go 3.42 and definitately not lower than 3.55 for a 15" tire.

Screw up on the ratios and it will be a shame and you will be kicking yourself in the but. Get it right and the trans is a dream.

Go 3.42 for a 15" tire! And if you insist on keepin the little 14" tires, go 3.36. If you go to a higher numerical ratio, you will be sorry.

i'm trying to stay with the original rims...
car looks stock - all original

until you look and see the aluminum heads, raised hump for the tremec, etc :)

why would your launch ratio be worthless with a 3:73? gonna spin the tires ridiculously?

I run 3.42's with my TKO and 26.1" tall tires. Can't imagine running anything numerically higher than 3.42s out back, 1st gear is very short as it is and I can get the car rolling just by letting out the clutch.

For street driving the shorter 3.27 first gear is nice for dicing around in stop and go traffic but I would prefer the TKO 600 with the 2.87:1 1st get to minimize the RPM spread between 1st and 2nd gear.

If you have a big cam that doesn't "clean up" until a certain RPM make absolutely sure you pick a rear gear such that your RPM's in 5th gear at your normal highway speeds are above the "clean up" point-- otherwise you'll be dropping down to 4th gear or speeding up to get the RPM's up enough for the cam to clean up.

I am running a 3:08 rear with a tko 500 in a BB vette. 1st gear is plenty low to launch for "normal" driving. (seemed fine at the track too) 5th gear is wonderful. I am running around 1600-1800 RPM for normal 55-65 MPH driving.

I am running 3.73's in my 12 bolt and a TKO 600 with the 2.87 first. My tire is 26.5". I am 2100 @ 70mph in 5th. I ran my stock 3.31's for a while and hated it! It felt like it lugged at 65 and 70 on the highway.
I hope this bit of info. helps.

Will

why would a 3.73 read gear make the gearing worthless you ask.. that trans has a 3.27 first gear. Your effective launch ratio would be equivalent to a 4.84 ratio! If you put a 4.10 rear gear in there, like your buddy has, your launch ratio would be equivalent to a 5.32!! You could climb telephone poles with that. 1st gear would be done as soon as you let out the clutch..probably be easier to drive if you started out in second gear. 1st gear will be next to useless.

You mention this is a street car that will see long highway trips. Go 3.36. A 3.36 ring and pinion will still give you a 4.36 launch ratio!! ..more gear than those little 14" tires can handle. Gear it right and enjoy the overdrive on the highway along with the great gas mileage.

The '94 Formula has the 6 spd with a 3.42 ratio as stock with a 26" tire.

thanks for the info tokyo, i hadn't thought about the first gear in this trans, was just thinking it was similar to a muncie

the 2:56 in it right now, won't hardly let me shift into 5th on the highway, so something is gonna be changed, and soon :)

The '94 Formula has the 6 spd with a 3.42 ratio as stock with a 26" tire.

True, but the T-56 only has a 2.66 1st gear. The TKO has a 3.27.

any idea what your normal m20 muncie has as a first gear, for comparison sake?

any idea what your normal m20 muncie has as a first gear, for comparison sake?

M20 (Wide) 63-65 2.56 1.91 1.48 1.00
M20 (Wide) 66-71 2.52 1.88 1.46 1.00
M20 (Wide) 71-74 2.52 1.88 1.46 1.00

Yes 2:56 is way too high and I can see how that would make your 5th gear useless/ too high for normal highway driving.

The "effective launch ratios" I mention above would be similar to the rear gearing if you had had a traditional old 4-speed in the car with about a 2.52 first gear.

I am running 3.73s with my TKO and it is extremely too low. You are out of first in a couple seconds. I want to go with 3.08s but I will probably change to 3.42s.

hi,

i am runing 600 .64 od...with 3.7 285-40-17
very happy

http://www.project01.net/site/videos.htm

1st to 5th and 2nd to 5th gear accelaration if you want to check gearing on

the road :)

regards
sami