so i got my 455 with my turbo 400, but im tryin to figure what kinda gears i need to use with it. now im maxin at like 65 mph. i think im in the 4. somethings. im thinkin like 3.42 or something close anyone with this combo let me know what you got and how well its workin

 

That's a bit unusual... 4.10's would get you to top out at 100 to 120 mph, not much more...and it would sound something like a leer jet passing 30 feet overhead crossed with a dying moose in your ears. There should be markings on your rear differential case that will indicate what gearings it has.

I wouldn't think 3.42 would make you top out at 65...that just doesn't sound right at all.

 

What kind of car? What is the id number stamped on the passenger side axle tube?

 

Did you mean you typically don't drive faster than 65...and your running 4000+RPM?
Either way, if your looking to select new gears, you have a simple math problem. The TH400 has a 1:1 final drive ratio, so to find out how many rev's your engine does at some MPH you only need:
Tire circumference, rear gear ratio, and some unit conversions. I set up an excel spreadsheet with my ideal highway cruise speed and let it calculate engine RPM with various gear ratios before I made my choice. Then I selected gears based on my tolerance level to noise and gas mileage.

 

I have 3.42's with a 400th and a 68 350.

Runs great, but since I switched to HEI the car's revving 500 RPM's too high.

With the points I was doing 2600 to 2700 at 65, now I'm at 3000 at 55

 

Changing to an HEI will not change the RPM/miles per hour formula. That is purely a function of gear/tire combo (and transmission or clutch slippage, as applicable). Perhaps your tach needs calibrating?

C.J.

 

So are you saying that your car won't physically go faster than 65 miles per hour or that you are redlining your tach at 65 miles per hour?

What is your tire size and what is your rpm at 65?

C.J.

 

3:23's or 3:31's aren't bad for highway..

 

yea its "sounds" like its redlining. i don't have a tach in it just yet. but it f-ing screams at around 65. i just tore the rear apart today and it has 3.73's in it. something seems really off with this to me. a lot of people are racing there cutlass' with 4.11's and mine just seems like its ...... sucking. lol but when im doing like 30-35 the speedo is almost buried just pass 80 or 90 (can't remember what is the final number on it) someone mentioned a torque converter issue.... dunno seems like im missin something but the car goes like a bolt of lighting till 65 or so. like i said rough estimate being my speedo dosen't work and no tach.

 

oh and tires are like 245 65 15

 

There is a great gear calculator on the Richmond gears website. You can play with it to figure exatly where to want to be for your combo.

 

I have a 461BB/400TH and 3:90 gear and 65mph is the most I would run on the freeway, if I stab it I could jump to over 100 then bump neutral and coast a bit. I dont use the car on the street anymore and I dont remember the tire size.

 

Know what this sounds like? The gear selector is stuck and it's in the wrong gear... check your linkage! TYPICAL GM vibrations have the better of you sometimes and the simplest thing can be the biggest problems!