Rpm is too high on 67

[Bulldog88]

I have a 67 with a 283 and a 400 trans, when Im on the hwy it sounds like the engine might blow if i give it too much gas, I dont know where there at because I dont have a tach what can I do to bring the rpm's down?

[1low]

taller gearz or taller tires

[wwotr]

Originally Posted by Bulldog88

I have a 67 with a 283 and a 400 trans, when Im on the hwy it sounds like the engine might blow if i give it too much gas, I dont know where there at because I dont have a tach what can I do to bring the rpm's down?

Yep. A common problem.
I have a 72 GMC, V-8, 3:73 Gears and a Turbo 350.
I usually run about 2200-2500 RPM's at 55-60 Mph, but I love the sound!

[Bulldog88]

Im running rallys with 275 60 15 on all fours, what gears should it have, and what gears should I install? There is a plug on the side of the 400 trans that has two prongs on it, but there is nothing pluged up on it will that affect anything?

[70STOVEBOLT]

Originally Posted by Bulldog88

Im running rallys with 275 60 15 on all fours, what gears should it have, and what gears should I install? There is a plug on the side of the 400 trans that has two prongs on it, but there is nothing pluged up on it will that affect anything?

Depends on what you are doing with the truck. If it's just a driver, no pulling or hauling, I would put a 3.42 in it. It probably has 3.73's now.

[ChevLoRay]

That plug on the side should be for the electrical kickdown. Should be a switch near the carburetor that is actuated by the right accelerator movement. However, if the original carb/intake has been changed, there's a real good possibility that it was tossed....as mine was.

I had my valve body modified and then went with the smallest vacuum modulator (black) and I can effectively kick it down when needed, even though it isn't possible when passing someone.....as I would like. I have a LOKAR Hi-Tech switch to install whenever we get around to putting the drivetrain back into the chassis...maybe this summer.

But, what you have is what GM built...back in the day. A 700R4 would give you an overdrive, for some $$$.

[Captainfab]

Even with 3.42's his engine will still be turning about 3200 @ 70 mph with those tires. That 283 shouldn't mide some rpm's though. If mileage is a concern, I would step up to 3.07's, an overdrive trans, or taller tires.

Originally Posted by 70STOVEBOLT

Depends on what you are doing with the truck. If it's just a driver, no pulling or hauling, I would put a 3.42 in it. It probably has 3.73's now.

[special-K]

Originally Posted by Bulldog88

I have a 67 with a 283 and a 400 trans, when Im on the hwy it sounds like the engine might blow if i give it too much gas

Just use the backroads,or does it sound like that there,too? J/K!

It's ok,you are just used to overdrive. Back when these trucks were new people drove the 70 mph speed limit hiways all day long and never gave it a thought. I love the sound. New stuff just drones down the road