Rpm's on highway with 3 speed.

[toofastforyou]

So by reading the replies here, I can assume that a TH-400 is very "liveable" on the street...I remember back in the '70's, a lot of muscle cars came out of the factory with huge engines coupled to a three speed automatic transmission and 3.50, 3.73 and even 4.10 rear axle ratios, so I suppose driving the car with 3.42 gears shouldn't be too bad!... It's true that fuel was not as expensive back then as it is today, but that wasn't my point...My point was that driving the car with a three speed and 3.42's shoulds still be do-able today...
If an overdrive is absolutely needed, then there's always the 4L80E alternative. At one point, I was very tempted to go that route but I was told that they were more touchy to get them to work properly in "performance" applications and also they got to have a separate computer to make them work. It's like if there's not enough demand for 4L80E's at the moment in high performance vehicles, but maybe in a few years from now, we'll see... ...So I've decided to go with a TH400 and be done with it! :wink:

Claude.

 

[RED LS1]

who wants to do that much work swapping units anyway?

I have both transmssions, both Torque converters and both bolt on crossmembers. The driveshaft is the same and the shifter takes 10 seconeds to change out. My brother also has a lift in his 26x26 garage right down the street from me. It's probably an hour or two on a weeknight to get the swap done. Not a big deal to have a part time race trans to be confident at the track and not need a trailer to get home.




Heres a different question.... I have access to a 2.75 upgraded first gear ratio for the T-350. In theory, couldn't you run the numericly higher 1st gear and lower the rear gear to 3.23 or so and get the same results as a 2.52 and 3.50 rear set up but get way better cruising manors on the highway?

 

[Dusty Bradford]

I have both transmssions, both Torque converters and both bolt on crossmembers. The driveshaft is the same and the shifter takes 10 seconeds to change out. My brother also has a lift in his 26x26 garage right down the street from me. It's probably an hour or two on a weeknight to get the swap done. Not a big deal to have a part time race trans to be confident at the track and not need a trailer to get home.




Heres a different question.... I have access to a 2.75 upgraded first gear ratio for the T-350. In theory, couldn't you run the numericly higher 1st gear and lower the rear gear to 3.23 or so and get the same results as a 2.52 and 3.50 rear set up but get way better cruising manors on the highway?

I wouldn't even bother with the lower ratio in the 1st gearset. I'd put the 3.23's in it with the 3 speed and forget about the OD.

 

[RED LS1]

I'll be honest. I just finished freshening up the 9 inch and put the 3.50 gears into for the LC2 swap. I was thinking they were the best gears for the motor.

 

[Dusty Bradford]

I'll be honest. I just finished freshening up the 9 inch and put the 3.50 gears into for the LC2 swap. I was thinking they were the best gears for the motor.

Try it and see how you like them with the 3 speed. Lots of T-350 swaps here locally with the 3.42 gear. I don't mind 55-65 mph cruises like that. If I want to run 70 on the interstate I have a truck for that.

 

[RED LS1]

Lots of T-350 swaps here locally with the 3.42 gear. I don't mind 55-65 mph cruises like that.

Pretty much the answer I was looking for. thanks.
55-65 cruises not being a real chore like a 383 W/ 3.73's is what I want to here.

 

[turbo6man]

I have a hybrid with a TH350 and originally started with the 3.50 gears and it was tolerable on the freeway with a 28" tall tire. After posting and getting advice from more knowledgeable members on this board, I changed to a 3.25 rear gear ratio and the car went faster in the quarter mile and is VERY nice to drive around on the street and freeway. I know read you do not want to change ratio but it is food for thought, and I am sure others could chime in and say if your combo would be a good choice for this.
Here is a link to my build and times along the way: http://www.turbobuick.com/forums/hybrids/270436-1963-chevy-ii.html

 

[TURBOPOWERED68]

SO what kind of RPMs are you guys getting @ 70 MPH with a 27 inch tire and 3.42 gears?

 

[stovebolt 34]

If I ask the wrong question or make a dumb comment allow it to my age ( old fart ) . About a year ago I swapped the TH 350 in my 34 chevy to a 200-4r . Had a few teething problems ( built it myself ) .Seems to be working well now . Unless it blows up I'll never go back to the 350 . I love the overdrive . With the 3.08 Nova rear and in 4th lockup it's loafing at 70 mph . Out of lockup in 3rd gear it is turning more rpm's than than the th 350 . Maybe it's the D-5 converter ? Just for the heck of it I ran a switched parallel ground to the TCC solenoid to lock it up in 3rd . Feels so good I almost whiz on myself .

 

[kidglok]

fwiw at 70mph im at 2800 rpm with a th400 and dusty's 9.5" n/l

 

[TURBOPOWERED68]

fwiw at 70mph im at 2800 rpm with a th400 and dusty's 9.5" n/l

what size tire?

 

[kidglok]

what size tire?

Sorry, 27.7" 295/50-16, stock rear gears