Highway Revs

[72Thunder]

Hey all quick question,

I will be getting a very well built 350 that will produce quite a bit of power (estimating 300-350 hp and 350-380 ft lbs torque). I have 4.10 rear gears and a turbo 350 transmission. Also on my set up is that my tires are 30" in diameter. I feel like i will be doing very high revs on the highway, (calculated 2700-3500 on various sites) so i want to get away from the 3 speed and go for something that will theoretically give me a little bit better revs on the highway. What is the most recommended transmission that I buy? I am thinking a 700R4 but I've heard otherwise. Basically, I dont want to wreck my engine by sitting at higher revs for extended periods of time.

Thanks in advance!

[leftybass209]

I'm assuming you're looking at automatics. Really the transmission needs are dependent on what you want from your truck. This has been covered several times on this board. If you do a search you should find several threads. I can tell you the 2004r is an easier swap than a 700r4. Benefits of either transmission are minimal depending on your needs; it's an apples to oranges comparison. The 4l60e and 4l80e are options if you'd rather have it electronically controlled. If you like your TH350 but want overdrive, you can always pick up a gear vendors OD unit.

[67 chevelle]

2004r is what I just put in my 67 , with a 500 horse 6.0 ls engine ,373 gears and 31 inch tires , should be up and running in a month or so

[piecesparts]

To each his own, I have a 700R4 on my 84 GMC with a 383 stroker in front of it. I am running 3.73 gears and about the same diameter of tires. Your setup with the 350 tranny and the 4.10 gears puts you at 3200 RPMs at 70 MPH and 2750 RPMs at 60 MPH. if you run the overdrive tranny, you be basically at 2300 RPM @ 70 MPH and 1930 RPM @ 60 MPH. That should keep you effectively in your power band and not outside the optimum performance level of your engine. Remember that you will have to find a way to control the lockup converter. I am using the B&M lockup controller that reads the speedometer signal and is adjustable for the lock and unlock features.

There are many that prefer the 200R4 to the 700 R4 tranny and they both can be built to handle what you are pushing for power. However, prepare to spend some money to get it done right.

[72Thunder]

Awesome, thanks all. The information explains quite a bit! I was told that the motor maxes at 5500rpm and that ill be doing 4 grande on the highway with that set up, unless there was mixed messaging between the machinist and I about transmissions and my current setup. He also stated that if I choose a different transmission, he will upgrade my cam, so im not sure how much this will affect my highway driving revs.

[outdoorsman310]

If you are just concerned with the engine, it should be ok with your current setup.
My 70 has a 4.57 rear and 31.6" tires (265/75/16) and had the same engine and transmission it was at 28-3500 on the highway. After I got used to it I usually drove at about 3500 keeping up with traffic. It did run hot in the summer, but also had a bad fan clutch.

[HSRACER]

A nicely built 700r is super simple to make work. Bit of a pain on the pressure cable adjustment but worth every penny. I just swapped out a turbo 350 with a 700 and love it. I also have two gear vendor overdrives behind my blower vehicles and they work great but are very expensive at over 3 grand all in. I have them for the 650 and 700 horse power motors. I wouldn't spend that much for your power output when a 700 can be made to work fine for less than half the price

[piecesparts]

Originally Posted by 72Thunder

Awesome, thanks all. The information explains quite a bit! I was told that the motor maxes at 5500rpm and that ill be doing 4 grande on the highway with that set up, unless there was mixed messaging between the machinist and I about transmissions and my current setup. He also stated that if I choose a different transmission, he will upgrade my cam, so im not sure how much this will affect my highway driving revs.

When you upgrade the cam, that may mean that you need to think about your torque converter stall numbers. I put a fairly nice roller cam in mine and had to go to a 2300 stall to keep the truck where it would drive properly on the street. Get the combo built right the first time or spend a lot of time pulling things apart to get the parts changed to where it all works.

[franken]

Originally Posted by 72Thunder

Hey all quick question,

I will be getting a very well built 350 that will produce quite a bit of power (estimating 300-350 hp and 350-380 ft lbs torque). I have 4.10 rear gears and a turbo 350 transmission. Also on my set up is that my tires are 30" in diameter. I feel like i will be doing very high revs on the highway, (calculated 2700-3500 on various sites) so i want to get away from the 3 speed and go for something that will theoretically give me a little bit better revs on the highway. What is the most recommended transmission that I buy? I am thinking a 700R4 but I've heard otherwise. Basically, I dont want to wreck my engine by sitting at higher revs for extended periods of time.

Thanks in advance!

That's about the most coherent, concise and sensible early post I've seen.
I think the 700 is a close fit, but I like a manual trans.