RPMs

[macdodd]

I'm running about 3k at 72mph,,,is that ok or will it hurt the engine. Running a 350/305 heads. What would the red line be or close to it? Its a '69 Chevy short bed C-10.

[jessemthompson]

That depends on a lot of factors. I would say 4500-5000 to be safe

[Swar]

I have a 350, 4 speed manual. Mine runs 3k at 60mph. Been driving it a long time, never had any issues.
Small blocks can rev out no problem, but it's better for the engine to change rpm rather than stay at one for a long time.

[macdodd]

I'm running P235 60r 15s on it,,,,was thinking about changing the rearend gears,,,but if the speed vs rpms sound ok,,,I'll leave it alone,,,,might put equal lock rear in it,,, it has a 3 speed auto in it. I just want to be able to drive it on the interstate roads sometime, like to the mountains from Florida,,,without burning something up.

[Swar]

Yea if you're looking to travel with it, the lower you can get the rpm in top gear, the better. An auto with OD would be ideal.

[Boog]

3g at 72 mph is more than i like for sustained periods of time. 22 to 2500 rpm is more to my liking. And wont use near as much fuel either.
235/ 60 tires are rather short at around 26". You could switch to a taller tire like a 255/70 at around 29" that will make a good reduction in highway rpm, change rear gear ratio(more expensive) or install od tranny( still more expensive). Or just drive slower and no body wants to do that 😉

[macdodd]

LOL,,,,well,,,I wouldn't be on the interstate all the time,,,,,the truck is lowered all the way around,,,so can't go to much higher on the tires. Gonna have nito shocks put on it to control the bottoming out.

[TBONE1964]

Here is the simple fact. Engines wear and the faster they spin, the faster they wear. Excessive RPM's will accelerate the time of death on any engine.

2K at 70 MPH will live much longer than 3K at 70.

Nice truck by the way.

Take care,
Tom

[leftybass209]

Originally Posted by TBONE1964

Here is the simple fact. Engines wear and the faster they spin, the faster they wear. Excessive RPM's will accelerate the time of death on any engine.

2K at 70 MPH will live much longer than 3K at 70.

Nice truck by the way.

Take care,
Tom

This is pretty much the no frills way of putting it. Reduce your RPM's and increase your engine longevity. So when you ask, are you going to hurt something? YES, you are hurting the longevity of the engine. If you don't have roller components, you are also drastically increasing wear on your valvetrain.

[burnin oil]

Low RPMs wont always decrease wear. If it is lugging a lot the cylinder pressures are higher than a motor that is at low throttle and high RPMs. Pretty much every sb I have seen has passed 100k miles without major issues no matter if it came in a truck with 4.56s or a car with 2.73s. It also takes enough RPMs to properly drive accessories like the water pump and power steering pump. A lot of guys used to get themselves in trouble running 3.07s and adding an OD trans. Best mileage and longevity happen at a happy medium. 3k RPMs is high but shouldn't have a problem lasting a long time. I run my truck down the interstate at 75 MPH for hours on end with 4.10 gears and no OD. If the truck has a 4v carb try to adjust it so it is only on the primaries at 3k RPM. I have been around a lot of Qjets that were on the secondaries when on the interstate.

[GASoline71]

You guys do remember that these trucks ran at those RPM's for many years when they first came on the scene. It was normal to cruise with a 350 cubic inch engine at highway speeds close to 3,000 RPM's when these trucks were built. Nowadays we are all conditioned to low RPM cruising speeds with newfangled fuel injected engines and super duper overdrive transmissions that put our cruising RPM's almost below 2,000 RPM's.

Having a rig run at 3 grand for short periods of time at highway speeds isn't going to hurt that 350 in the least (maybe robbed of power with the 305 heads ). It will hit you in the wallet though. Like burnin oil said... the secondaries will probably be cracked and suck up some fuel.

Gary

[GRX]

Well said Gary!

Oil pressure at 3k rpm is what I would be most concerned with. You might be amazed at the distinctly different wear patterns on internals between an engine which cruises at highway speeds consistently, and one which idles at the job site all day.

[ole dollor]

how big is your gas budget , and how far are the gas stops apart....lol

[Boog]

Real good looking truck Macdodd. Using the Richmond gear calculator it puts your rear gear at around a 3.42 for a 27" tall tire. If so it is a good all around ratio. It may just be the angle of the pic but those rear tires sure look larger than 235/60/15.

[BruthaMan]

I drove a four hundred mile trip almost every week last year, working on a remote project.

Two hundred miles up, two hundred back at the end of the week. First few trips, I tried to drive at 70 mph, but was around 3400 rpm.

I eventually backed it down to 60 mph which was right around 3000 rpm. I have 4:10 rear gears. Fun from stop light to stop light, but a screamer on the highway.

Truck did fine, but I did have to replace the water pump. Changed the oil meticulously every four weeks. Mobile One and added ZDDP plus. Some say isn't necessary with synthetic, but I wanted all the insurance I could get.

Would also run a little Marvels Mystery oil in the gas once a month too.

[jhwkns]

Mine runs 73 mph a 3,000 rpm. That's a .373 gear and 275/60/15 tires. I road trip with it frequently. It's never been a problem.

[Kimjongthrill]

@boog i was thinking the same thing about the rear tires, maybe 275/50 is what they are?

[macdodd]

Well,,,,I'm gonna run for awhile without changing rear end gears and see what happens. Like afew have said in here,,,just not used to the high rpms of the older engine and the noise,,,LOL. Very true,,,we've got used to the modern engines and no noise,,,LOL. Any suggestions on oil? Gonna change it soon, I used a oil additive and it really helped quiet the enging down,,,seemed to up the oil pressure too. Thanks for all the input,,,,been years since I've had a vehicle like this,,,,LOL,,,,I love it,,,,,be safe out there,,,,,Bill