[Scott Stoneburg]

On a 1967 GTO. We swapped the rear gear from a 4.11 gear to a 3.23. Because the owner didnt like how many RPMs it would turn to cruise The owner still is looking to make it smoother at highway speed. Now @ 60 mph its turning 2800. He is looking to be able to easily cruise at 75 to 80, and really wants more low end power. I thought going back to the 4.11 gear and a 6 speed. (Tremec Magnum 6 speed) or should he just stay with the 3.23 and go 5 speed? Any thought or recommendation from guys who have made the swap to a 5 or 6 speed?

[65madgoat]

Get the Tremec TKX 5 speed so the floorpan does not need to be cut.

Has multiple OD gearing options.

Done.

[steve25]

I would have kept the 4 series gears and put in a Hone overdrive, as its a great way to go if the car has no H or X pipe in the exh system.
It handles big power, but you also due to its design get 2 in between speeds out of a 4 speed besides the overdrive!

[Gary H]

Go with a 3:73 or 4:11 gear and the 5 speed overdrive. I've done that combination for multiple customer's cars and it works out great for both low end and highway cruising.

[65madgoat]

The 3.23 are ideal with a .72 overdrive. No need to change rear end gears. Or could get the .81 OD version even but 1st gear is not as steep (but not likely needed with Pontiac torque).

TCET18083 TKX GM


3.27

1.98

1.34

1.00

0.72 OD

3.00 reverse

[soupman]

I just put in a TKX 5 speed with 3:27 gears (9 bolt BW). I have the .64 overdrive and 2.87 first gear. Love this combo. At 70mph just a hair over 2000rpm. The TKX is physically smaller than the TKO with same torque rating plus they upgraded the shifting mechanisms for 7500 rpm shifting , not really applicable for Pontiac’s. I did a lot of research on the 6 speeds and decided wasn’t going to use the 2 overdrives as much.

[TB1]

I have TKX with 2.87 first and the .68 OD with 3.23 gears and I love it With the cam in my car which is Speed Pro CS1175R 224/234 @.050" HFT which is similar to the summit 2802 it cruises along at 70 mph right around 2000 rpm with no bucking or grunting power range is said to be 1600-5000 or so rpm perfect for what I'm doing. Bigger cam and these gears maybe not so friendly at this rpm/speed. The TKX is nice as said below very little is needed to install only a couple small cuts to make the shifter fit in the stock location on my 65 LeMans

[TPM]

I also recommend the Tremec TKX 5-speed....very happy!

[Tim john]

Very pleased with my TKO 600 5 speed & 3:73's. The TKX was not announced or available when I did the enhancement.

Tim john---

[Formulajones]

I've had/have both 5 and 6 speeds. While I think they both have their benefits they also both have quirks I don't like but for what the owner of that car is looking to do Scott, the Tremec 5 speed will do everything he is looking for.

On our own personal vehicles I've run different Tremecs with .63 overdrive using 3.27 rear gears as well as 3.73's. The .64 version with 3.55's and several other swaps all with the 2.87/ .64 combo ranging from 3.50 to 4.10 gears.

He'll probably be really happy leaving the 3.23's and going this direction.

Generally with 3.73's and no overdrive, with a 27" tire I'm doing 60 at 2800. So he must have an extremely short tire to be turning that kind of rpm to do 60 with 3.23's.

[67GTONUT]

2800RPMS @ 60MPH with 3.23's ??

Something does not seem right there.....

BTW ...... Love my TKX with 3.27 1st gear....

[lust4speed]

Number one complaint on the 6-speed is its huge size -- you will basically remove the complete tunnel on the 67. My TKO-600 required two dimples with an air hammer for clearance and the new TKX shouldn't need any tunnel alteration. Number two complaint is the car I drove with the 6-speed had a 3.90 rear and the RPM's were something like 1,700 with the .500 overdrive at 65 MPH. Number three is while the engine is loafing along with the 6-speed overdrive the 4.11 pinion (and driveshaft) is hauling a$$ and creating a lot of heat and wear at higher speeds. Might also want to do a critical speed calculation to see where the estimated driveline failure point will be.

[chuckies76ta]

Originally Posted by 67GTONUT

2800RPMS @ 60MPH with 3.23's ??

Something does not seem right there.....

That was my thoughts. Must have orginal 4 speed tranny.


I'd leave the 3.23's and install a 5 speed tranny as mentioned. The .72 would be nice.



I have 3.73's with a TKO600 .82 OD. Cruises nicely for the speed limits here at 65 and 70 mph. Also have to consider where engine is happiest at cruise.

[The Champ]

Originally Posted by 67GTONUT

2800RPMS @ 60MPH with 3.23's ??

Something does not seem right there.....

2800 RPM's at 60 - only if he has 23.25" tires...

If tires were 26.5 - RPM's would be around 2400 - 2500.

[Scarebird]

Currently TKO 600 0.82 OD with 3.08's

Given a second shot I would have kept the 3.42's and run 0.67 OD

Note however that your diff ratio determines prop shaft speed - narrower shafts may get too close the critical speed for comfort with higher numerical ratios. A wider aluminum shaft may make this issue go away.

[track73]

I took out the 3.43 rear gear and installed a cast iron T-10 with a 3.42 first gear and put it through a 2.73 rear gear. I had the Camaro rear end hub to hub and figured that it would be ok with the huge low end torque my engine makes. (look at my signature), I cruise at 70 about 2500 rpm. And I can cruise in town in 3rd read with the final drive around 4 to 1. And, I use 4th like an overdrive. But light throttle driving at 1500 rpm is no problem in 4th. These big engines with Rhodes lifters create so much low end torque the drivability is really good. .

[tom s]

I have been using the 3.42 ST trans for years in a couple early big cars.I have 28 in tires on the 62 GP with 2.68s in the back and have not found it necessary to pull back to 3rd very often.434 CI with a 068 cam.FWIW,Tom

[Formula8]

Unless you get a screaming deal on a 6 speed, there is no practical advantage to the 6 speed and it will represent a lot of hassle that could have been avoided if what you are trying to achieve is simply lowering the RPM on the highway while having a nice shifting close ratio gearset.

I absolutely loved my TKO 600 with .64 OD and 3.73's behind my mild SFT 455. The 433 and OF cam are not all that happy lugging around in 5th gear at speeds below 55. I am now running FI and a 26" diameter tire which has improved things a bit.

If I had it all over to do again, I would definitely go for the TKX and probably do the 2.87/.81 with a 3.42 gear.

[soupman]

The TKX is much smaller than the T-56. I see no reason to have the 6speed. The TKX fits the older cars so much better. Here is my TKX. Plus you can get many different combinations of offset shifters.
I have the 3:27 with 2.87 first gear and .64 OD. Formula8 is right with using 3:42, my car is very light so I get away with the 2.87/3:27 combo, heavier car might like 3:42 or 3:73.

[pokey1]

4:11 and 6 speed here with 29" tire. Have had it in for 3 years now and love it.