[Jeff Walker]

Yes I know it's not a Pontiac, but it's not my vehicle and I know there is a lot of knowledge on this forum.

I am working on a 65 GMC 4X4 and need to come up with a good gear ratio for it. So I need to know from some of you seasoned veterans what is a good cruising rpm for a 283 Chevy. It is a pretty stock combo, with a stock 350 Chevy cam, headers and a 650 Edelbrock.

So what do you guys think?

[engineer]

same as any other stock engine. 1800-2500

[Billy177]

It will run al day at 3000 but milage will suffer

[uneasyrider]

283 is a little rev'er that's for sure and they don't put out a ton of torque so I would say in a 4x4 I'd spin it on the high side at 2,500-3,000 but that's me.

[GRX]

Originally Posted by uneasyrider

283 is a little rev'er that's for sure and they don't put out a ton of torque so I would say in a 4x4 I'd spin it on the high side at 2,500-3,000 but that's me.

Agreed.

Have a 4-cyl (Pontiac 151cid) in my '80 Jeep CJ-7. And I can tell you that high RPMs are needed to compensate for the lack of low end torque. With the vast amount of mods I did to the engine, it pulls nicely past the 7,000 RPM mark now.

[RAIV55]

For 4x4 trucks, especially if used off road or for any towing I'd look at 3.73 gears. Although the cruise rpm might be high it's nothing that will kill the engine. With a 29" tire it will work out to about 3200 @ 75mph.

[b-man]

The first passenger car to use the 283 was the '57 Chevy, the Powerglide cars came with 3.36 gears, standard 3-speed trans cars used 3.55s. Tire size was 7.50-14, this might help you to reference the RPM the truck might cruise at.

Of course the truck with more frontal area and greater load carrying capacity will need more effective gearing than a car would. With a taller truck tire probably something like a 4.11 gear will be necessary.

Any 283 will be happy all day at 3000 RPM. In order to push that truck on the highway at 65 MPH it needs to turn at least that much to stay cool and happy with the short 3" stroke.

[Jeff Walker]

The truck is going to be prmarily a 'pretty' truck. He doesn't plan on using it for towing or off road activities. He is putting on 33" tires on it. I am thinking that shooting for a cruising rpm of around 2600-2800 RPM might work out best. Trying to shoot for the best mileage, but not have it bog down when going up hills.

I am think that a 4.10 or 4.27 ratio might work out good.

[b-man]

Originally Posted by Jeff Walker

The truck is going to be prmarily a 'pretty' truck. He doesn't plan on using it for towing or off road activities. He is putting on 33" tires on it. I am thinking that shooting for a cruising rpm of around 2600-2800 RPM might work out best. Trying to shoot for the best mileage, but not have it bog down when going up hills.

I am think that a 4.10 or 4.27 ratio might work out good.

Maybe even 4.56 gears, that's a tall tire and a small engine.

[RAIV55]

Originally Posted by Jeff Walker

He is putting on 33" tires on it. I am thinking that shooting for a cruising rpm of around 2600-2800 RPM might work out best.
I am think that a 4.10 or 4.27 ratio might work out good.

33" tires @ 75mph, 4.56 = 3500, 4.10 = 3100, 3.73 = 2850

[Jeff Walker]

Originally Posted by RAIV55

33" tires @ 75mph, 4.56 = 3500, 4.10 = 3100, 3.73 = 2850

Looks like you have been playing with the calculators over on Wallace Racing's website too. I am kinda leaning toward the 4.10 gears.

The guy that owns the truck is saying it probably won't see over 65mph too often. His thinking is that the ride will get pretty rough as speeds much faster than that. He may be right since I don't thinkthey weren't too concerned about ride quality in a 4X4 back in 1965. A 4.10 gear will put the engine at about 2700rpm at 65mph. But I do have some time to ponder this. As you can see in the pic, I got a ways to go before it hits the road.

[RAIV55]

Originally Posted by Jeff Walker

Looks like you have been playing with the calculators over on Wallace Racing's website too. I am kinda leaning toward the 4.10 gears.

Auctually I was too lazy for that, we have a Mark William's ratio calculator in the desk drawer.

[b-man]

I have a '70 Chevy C20 with a factory 402 big-block/TH400 combo, has a 4.10 gear and 30" tall 9.50-16.5 tires. I never run it much past 65.

That 'poor little' 283 needs at least as much (more, really) effective gearing as my 402, I'd put at least a 4.56 gear in it especially with 33" tires. Hmm, maybe even a 4.88.

[Cliff R]

Pushing that much weight the little 283 will enjoy things if the cruising rpm's are up near 2800-3000rpm's. I had a stout 283 in a 64 Nova SS some time ago, it LOVED to cruise around 3000rpm's. We frequently shifted it at 6500rpm's at the track, and went thru the traps at 7000rpm's. It wasn't really cammed all that much, but it's a small powerplant and needs to rev to move a lot of air.....Cliff

[Jeff Walker]

Hmmm, maybe b-man's on the right track with 4.56's. My Dad has a 64 Chevy 3/4 ton 4X4 that he has had for a wrecker for many years. That came with 4.56 gears, a 283 and 7.50-16 tires that are 31" tall.

With 4.56 gears and a 33" tires, at 3000 RPM it should be running just a bit under 65 mph. That might be the way to go....

[Cliff R]

Jeff, with a truck, tire diameter plays a MAJOR role in rpm's at any vehicle speed. My Dodge tow vehicle has 4.10's, and tires just over 33" tall. It's only turning 2600 at 60mph before we shift into OD.

MPH X GEAR RATIO X 336 divided by TIRE DIAMETER equals RPM's.

[Jeff Walker]

Originally Posted by Cliff R

Jeff, with a truck, tire diameter plays a MAJOR role in rpm's at any vehicle speed. My Dodge tow vehicle has 4.10's, and tires just over 33" tall. It's only turning 2600 at 60mph before we shift into OD.

MPH X GEAR RATIO X 336 divided by TIRE DIAMETER equals RPM's.

Using your formula puts me a just under 2800 RPM @ 60MPH with 4.56 gears. This also matches what some of the calculators on the Wallace Racing site.

Looks like 4.56 might be the magic number.