TKO-II .83 OD - Mistake?

[Treachery]

I have a Tremec TKO-II with a .83 5th gear and a 3.73 rear end. I like the strong feel of this transmission and the hardened material that its made of is assuring when banging through the gears.

While the extra revs in 5th gear feels awesome, i feel that it rev's a bit too high.

Without tearing into the tranny, what can i do to bring down the RPMs a little?

[Jack21]

Replace the diff gears with 3.27, or 3.55.

[D-CEL]

Treachery,

I am having the opposite issue. I have a TKO (.68 5TH) with 3.27'S.
I think my rear gearing is to tall. I just bought a set of 3.73's but havent put them in yet. What is your RPM @70 in 5th?
Mine is about 2k with a 275-60-15.
How much rpm are you looking to drop?

D-cel

[McCobra]

This website will let you enter all the variables to come up with the best combination for you. Results are at bottom of page

http://www.5speedtransmissions.com/gear_calculator.html

[dlampe]

treachery,
I have a 3.27 gear set for an 8.8 rear end. If that is what you have, I will make you a great deal! It has less than 500 miles on it.

[Tim Brewer]

Treachery,
Like the other guy's are saying, the only way to change rpm's is by changing the rear gears, I would think twice about getting rid of your 3.73's. You'll turn your fun, quick hot rod into a lazy cruiser. Your rpm's couldn't be that high. If at say 70 mph, what are your rpm's? What size engine do you have? Unless you travel in your car,( I'm assuming this is a Cobra) I wouldn't worry about it unless at 70 it's over maybe 3300 or so.
Tim

[Frank Messina]

For reference purposes, I have 3.27 rears in mine and the same OD as you. I need to be at 60MPH or above in order for my engine to stay happy, which puts me at about 2050 RPM's. Anything less than that and it's back to 4th gear. FWIW.
Frank

[DonC]

3.07 rear end, TKO600R w/ 0.82 fifth, 315/35/17 tires (17" rim, Calculated tire dia. 25.68) 2300 rpm/70 mph.
DonC

[Goober]

D-Cel
I have a SPF with 3.73 and the same trans you have
70mph runs around 2100/2200 rpm. (If you can believe the Smiths speedo)!

Mark

[D-CEL]

Mark,

How much TQ do you make? Are you happy with the ratio? The RPM doesn't bother me at all. Im looking for accceleration!!
How much wheel spin do you get in 1st, 2nd & 3rd
I wonder if I should go 4.10's instead? I run them in my Mustang Cobra w/ a 10 lbs Vortech and I love them. But it spins 7200 (vs 6200)and make 200ftlbs less TQ(390 vs 600)

I too have been questioning the speedo accuracy.

Jason

[Goober]

Jason,
My engine dynoed 448 HP / 465 ft/lbs torque. I personally like the ratio. The engine doesn't come on the cam until 2500 rpm, so cruising around the 2200 mark delivers great gas mileage.
Wheel spin is bad in first with any rearend ratio in the SPF. Because the TKO 1st gear is so low, the best way to launch it (Drag Strip) is use 2nd gear. 1st gear winds up so fast you hit the rev limiter before you snatch 2nd. If I want to, I can spin all the way to 3rd before it really grips.
If you are just using the car for street, go for the 3.73. If you want to drag, go to 4.10s or lower. Your profile says you have a 460, so you have the extra torque that I don't have
Don't worry about the speedo. There is no positive cure, just live with it.

Hope this helps
Mark

[cobrasnake]

I have a 351 stroked to 427, TKO II, 3.73 rear end. At 70 mph, I tach at about 3K - FWIW

[Anthony]

Change your rears to 3.23's or something like that.

[Goober]

Cobrasnake, a buddy of mine has the same setup up as you (TKOII) and runs about the same. He really likes 5th for the track as it doesn't fall back down in the revs like the TKO does.
Mine is pretty tall, but it works great for interstate cruising.
3000 rpm isn't really that bad, look at some of the guys using toploaders with big blocks. Most of them run 3:31 which gives them a little break.
Just my 2 cents
Mark

[cobrasnake]

Treachery wants to bring the revs down. My question is "why". If it's fuel economy or noise - go ahead and change things out and drop your revs. I doubt he is going to hurt his engine reving at 3000 rpm. I rather enjoy having a bit of power on the highway in fifth gear - I was not concerned with fuel economy when I put the package together (at $2+ per gallon maybe I should have - I would hate to give up all those smiles) - I wanted the greater strength of a TKO II. Ear plugs helps with the noise.

Sorry to state the obvious. Again, what is he searching for?

[Treachery]

Thanks for the replies..

First, i must confess that i don't have a Cobra. I have blown '93 Mustang GT with all the goodies one can almost imagine. I found that the conversations and advise in this forum more knowledgeable (intelligent?) than the other Mustang boards.

After a few more weeks driving with the TKO-II, I've learned to love it. The extra power in 5th gear is unbeatable and it makes my car sound more "angry" on the freeway.

My Mustang is already probably one of the most gas guzzling vehicles on the road getting only about 156 miles per full tank of gas. With the stock T-5 tranny, i was getting 175 miles per full tank. Gas is not much of a concern.

At 70 mph, i'm reving at around 3200 rpm but i think my speedo is off somewhat. My RPM gauge and speedometer travel almost in unison. So when driving at 120 mph, the engine is reving a little over 5000 rpm whereas a 0.64 5th gear will be just shy of 4000 rpm. A 0.64 5th gear at 5000 rpm would be about 150 mph. Approx 30 mph difference between the 2 gears! Too much high end is being cut. Not good when your up against a C6 Corvette.

Incidently, i beat a C6 Vette in open highway 1 week before my stock T-5 broke after 11-years! It served me well. After having the TKO-II installed, i noticed the change in 5th gear hence my concern for high-end speed.

I thought of changing the rear end to 3.55 but after figuring that i will lose low-end zip & acceleration. I'll pass on that.

The thought of "balance" plays a profound role in this case. 0.83 5th gear = more response and power but at the cost of high-end. 0.64 5th gear = more high end but at the cost of mid-range response thus the need to go to 4th gear when acceleration is needed.

Here's a thought: granted that my RIMs are the original 16' inch pony rims but with 245/50 R16 tires, would upgrading to a 17 inch help? How about going to a 17 inch rim (wider tire) and a 3.55 rear end?

[crillyiv]

Treachery,
There are a lot of calculators out there to figure out the answers to all your questions. Here is one of them. You can input whatever rim/tire/rear gear combo and most of the trans you are likely to use and see the rpms, mph, splits, etc. Thank Mike Stenhouse of SecondStrike for putting it up for us.

http://www.secondstrike.com/Technical/GearCalc.asp

[Turk]

How did you manage to beat the C6 with your car? What were the speeds when you blew by him?

TURK

[G.R.]

Turk the C6 was just leaving a stoplight when the guy blew past him at 60



















Treachery just kiddin ya go with the flow