I'm considering a TCI/ TH400 with a 2.75 low gear set instead of a typical TH400 with a 2.48 to coupled to my 3.08 rear gear to harness a bit more power at take off. This will be matched up to my SBC 400CI/460HP/470TQ with Holley EFI.
I've considered a TH200R4 but the 3.08 would not do the swap justice, a better choice would be a 3.55 regarding that.

So the question is regarding the 2.75, is it a good upgrade choice ?

Any thoughts ?
Thanks

 

The third choice would be a 700R4 or a 4L60E. The lower first and second gears works great with the tall 3.08 diffs. I ran the 406 and 700R4 in my signature in my 80 Vette with 3.08 gears. It was a good combo except with my engine not liking low rpm, my cruising speed in 4th OD gear and the converter locked, it was 80 mph and above for my engine to happy. Your's engines not as high strung as mine so 70/75 mph should be really nice.

You can get 700R4's and 4L60E's that will handle 500/500 torque/hp no problem from a multitude of builders. Just check their reputation first.

Mike

 

I went through the same issues when I was planning my build and was determined to keep the automatic trans.
I ended up ditching the auto and going with a TKO-600- RR 5 speed with the 2.87 first gear and .82 fifth gear.
After pricing out a new TH400 or 2004R, built to take the HP/TQ of my new motor, swapping all the parts, and purchasing a quality torque converter the price was about the same, but I still couldn't find the gearing I wanted.
So I went to the manual.
Check out all the options available.

 

Thank you ! Your timing was perfect.

 

I have never understood the logic behind worrying about things that you use the least. How much time are you ever in first gear compared to top gear. So when you do all your calculations just worry about top gear. figure out tire diameter, final effective final ratio, and rpm. The best setups for street are OD trannies with 3.73 - 4.56 gear ratios.

I used to own a 67 Camaro RS/SS 350 4 speed. When I bought it, it had a 2.73 rear end because the owner did highway commutes. It just sucked slipping the clutch to get going, but then it was off to the races. I sold it before I could go with a 4.56 and a TKO 600 with .64 OD. I didn't like the handling of a 67 camaro at high speeds, so I just wanted something to get to about 130 mph as fast as possible.

 

OP call Ron at TRC trans in Chatsworth, he can build you a bulletproof 400..or 700r nobody has broken one yet
Stands behind his work, is fair and a racer to boot he gets this stuff. Builds his own converters, works on a lot of hot rods.
Hes on Topanga below Devonshire. Been using him since the late 80s..good manual trans guy too (nice job on my T56)

 

[QUOTE=gkull;1599172568]I have never understood the logic behind worrying about things that you use the least. How much time are you ever in first gear compared to top gear. So when you do all your calculations just worry about top gear. figure out tire diameter, final effective final ratio, and rpm. The best setups for street are OD trannies with 3.73 - 4.56 gear ratios.

I totally agree, however those of us who do drive on the highway, who do have 3.08 or 3.36 rear end gearing and want to keep it, the first gear ratio can be a factor and something to look at for all around street-able driving so we are not on the clutch to much starting from a stop.
I also agree that a set of 3.55 or 3.73 rear gears and a .64 fifth gear is a great all around street set up, however I personally don't like the .64 fifth gear with the 900 rpm difference between forth and fifth gears at highway speeds when downshifting on an incline or decline.
With my 3.36 rear end gears, and .82 fifth gear TKO-600, I can cruise at 2379 rpm's @ 70 mph and downshifting to forth only brings the rpm's up to 2900 which is where I'm currently at with my TH400 all the time @70 mph.
This gearing will work great with the tons of torque of my 496, and cam selection.
A small block 350/383 build may be different.
As always, do your research and pick the setup that's right for you and your driving plans.

 

Talked to Ron at TRC transmission in Chatsworth today and decided to rebuild my TH400. He was very confident it would handle my engine and coupled a new torque converter along with the 3.08 rear end will do just fine. Noting "drive it" then I'll know. I'm good with that.
And I must add I've had a few conversations with Art Carr of CPTransmission.com very helpful, knowledgeable, about his 200R4 setup, sure worth consideration.
Funny, one can sure go down the rabbit hole rebuilding a car.
Thanks for all the advice.

 

yup, nice quiet low rpm cruising vs doing donuts in a parking lot.... which would you rather have?

 

I'll just add this for the conversation value.

Why would I need or want to use a lower gearerd Turbo 400.

The "low-gear" (2.75) planetary gear set offers a 11% increase in 1st gear over the stock ratio. As an example, with a 3.73 rear the car would launch as if it had 4.10 gears. It generally improves the launch capability of all cars with a higher rear axle ratio. This has a real advantage for vehicles weighing more than 3500lbs. This option can also be used to reduce the rear axle ratio by 10% or more to lower engine rpm at highway speeds and improve gas mileage.

 

I wish I would have known this prior to swapping over to manual.
I could have kept my TH-400 and been in a reasonable cruising rpm range on the highway.
Thanks

 

He ought to be able to leavea harder and hwy cruising is still at a liveable rpm nothing wrong with that . Lets face it 3.08 are not great from a standstill

 

You are creating the same condition the 700r4 has, big rpm drops between 1-2 shifts. Now your car will be sluggish in 2nd gear after feeling like its going to rip apart everything in first gear... get a 4 speed or swap the rear gears and get an overdrive.