1970 L47 400 BB Torque and HP chart

[geezer#99]

My buddy built a towing rig for his 5th wheel holiday trailer.
71 gmc with L88 spec 427. 12.5 to 1 compression. ZL1 cam. Idled rough at 1100 rpm. Hooked to a turbo 400 and 4.56 gear. Pulled at 65mph at 3200 rpm all day. Surprised a lot of people when he’d pull out and pass.
Rpm won’t hurt your motor.
I’ve run lots of big blocks from 396’s to LS6’s. They all liked 3000 rpm or more.


Looking at that chart, torque peak at 3000 is right where you want to run.

[Tom]

Originally Posted by geezer#99

Rpm won’t hurt your motor.

They hurt your ears, and your sense of vibrations, and your fuel tank. Revving high is annoying as all hell with a 4 wheeled vehicle.

[geezer#99]

Originally Posted by Tom

They hurt your ears, and your sense of vibrations, and your fuel tank. Revving high is annoying as all hell with a 4 wheeled vehicle.

You Prius drivers are all the same!

[Steeveedee]

Originally Posted by geezer#99

My buddy built a towing rig for his 5th wheel holiday trailer.
71 gmc with L88 spec 427. 12.5 to 1 compression. ZL1 cam. Idled rough at 1100 rpm. Hooked to a turbo 400 and 4.56 gear. Pulled at 65mph at 3200 rpm all day. Surprised a lot of people when he’d pull out and pass.
Rpm won’t hurt your motor.
I’ve run lots of big blocks from 396’s to LS6’s. They all liked 3000 rpm or more.


Looking at that chart, torque peak at 3000 is right where you want to run.

Agreed. My (aftermarket) tach's busted for some reason. I have a new tach to put in it. I'll have to put that in and take the truck out and see if the wife can stand the noise. We're limited to speed because of her ear balance issues; she gets weird/dizzy over 55 MPH already, so even if we were to go to a state that allows speeds higher than 55 MPH, we won't be doing that. Guess I'll have to drive it in second gear for that noise test.

Originally Posted by Tom

They hurt your ears, and your sense of vibrations, and your fuel tank. Revving high is annoying as all hell with a 4 wheeled vehicle.

I already only get 7 MPG when towing. I'm hoping that this doesn't kill it more. My wife only said that we'd better make sure that the saddle tanks are fixed! Given the fact that going up hills sends the vacuum gauge to basically zero, I'm sort of thinking that not having to go so deep into the secondaries in second gear might actually help mileage. As for noise, we'll have to wear noise-cancelling headphones, I guess.

My wife was complaining about how her dad had a trailer before that he towed with no problem. I know from my own experience with it that it ran hotter than a pistol pulling that trailer, and didn't pull hills all that well, and that was a much smaller trailer.

Whatever happens, I'm sure that the expense of a new vehicle will be way over what I'm thinking of doing. She's talking about selling one of the econoboxes and getting a new Suburban, but those new things are crazy expensive and don't get THAT much better mileage, anyway. I'm retired, she wants to retire. A new vehicle payment is way more.