The Stovebolt Site Forums The Shop Area Engine Shop how fast could i go?

Hi, i have a 57 GMC pickup that i got from my uncle that i am working on. It has a Ford 390 engine, a 4 speed toploader transmission, and 4.10 gears in the rear axle. I know that this is a wierd setup for a GM and I plan on keeping all of this the same. My question is how fast will i be able to go with this combonation? it's not going to be a racer when im done, i just dont want to poking along in the slow lane when im driving. i want to be able to drive highway speeds easily.
Thanks

How tall are your rear tires and how high do you want to spin that 390? There are many online calculators for rpms. I have a formula to do the math the old fashioned way, but it's out in the garage.

Devin

Here's one good calculator
http://www.onlineconversion.com/bigger_tires.htm

Just for guessing and illustration purposes:
3000 RPM
30" tire
4.10 axle ratio
1.0 transmission ratio
= 65 MPH

Early top loaders were direct 4th. 77,78 offered a .81 OD. The early 80 top loaders with the aluminum case offered .81 as well as a .70 OD. So a lot of it depends on which top loader you have. Even if you have the direct 4th, the FE motor will go faster than you you can keep your 57 on the road and certainly faster than you can stop if it you have to make a panic stop. But keep in mind that the faster you go, the more gas it will guzzle.

You should easily be able to run 80 or 90 unless you put real short tires on it. The motor will be spinning fast and drinking lots of fuel...

Ok Thanks, I just wanted a ballpark figure so i know what i will have incase i wanted to change anything.
Thanks a lot

All about those gears, I had a '65 3/4ton that would run 80 all day long even with a 5.some-odd rear end on 16.5 wheels with tall rubber on em. It had a 327, started with a 4-speed out of a mid 70's Vette and ended up with TH400.
Stopping power was good coz I always kept my brakes in good shape. That & I'm a firm believer in the term "moving is optional, stopping is mandatory".

Would it be possible to have a shop put in that .81 OD gear for fourth? Could you swap them out? Or would it just be easier or better to change the rear axle ratio?

you couldn't 'put the gear' in your current trans, you'd hafta find a trans that's already got it .... and it depends on just what the trans is you have now, hooked to a Ford, it may be a Ford trans .... easier or better is a personal choice, based on yer bank account and parts availability

Bill

The Ford toploader was a product of Ford engineering. It was produced in well over 100 different models. I have had limited experience with them because I mess with Y-blocks as well as GMCs. However, a transmission shop that specializes in the 60's and 70's muscle car boxes would be much more qualified.