Square on the Interstate

[adamj]

Not speed, but rpm is what the real question is here. Someone posts, "I can do 80 all day no problem!" - Sure that's fine, but you need to look at your own vehicle and see if that's reasonable for you. With an overdrive trans, larger tires, and say 3.73 gears, that should be fine, but if you have 4.10's and a manual transmission then forget about it, you're not going to be going 80 mph.

I guess the question is what's the safe long-term rpm for highway driving for the engines of this era? They're not high-reving engines... For me, just by feel, I don't like to go above 2750 rpm, it just feels too fast for the stock sb350 I've got, (could be different if you have a different cam or a built up engine). It seems happy at around 2500 rpm.
What do ya'll feel comfortable with pushing the engine at for sustained periods?

 

[vkh]

Not speed, but rpm is what the real question is here. Someone posts, "I can do 80 all day no problem!" - Sure that's fine, but you need to look at your own vehicle and see if that's reasonable for you. With an overdrive trans, larger tires, and say 3.73 gears, that should be fine, but if you have 4.10's and a manual transmission then forget about it, you're not going to be going 80 mph.

I guess the question is what's the safe long-term rpm for highway driving for the engines of this era? They're not high-reving engines... For me, just by feel, I don't like to go above 2750 rpm, it just feels too fast for the stock sb350 I've got, (could be different if you have a different cam or a built up engine). It seems happy at around 2500 rpm.
What do ya'll feel comfortable with pushing the engine at for sustained periods?

I cruise at 80 mph on the freeway which is 3000 rpm atm, use to be 3500 with my 3.73s. I know it's abit high for regular abuse but it feels happy to me. My engine is a 454 with a 218/228 cam, large oval heads, headers and edelbrock performer intake. I have alot of fun with it

 

[hirschdalechevy]

These are really nice trucks, buddy.

Thanks man , I love the 70's square's

 

[hirschdalechevy]

Not speed, but rpm is what the real question is here. Someone posts, "I can do 80 all day no problem!" - Sure that's fine, but you need to look at your own vehicle and see if that's reasonable for you. With an overdrive trans, larger tires, and say 3.73 gears, that should be fine, but if you have 4.10's and a manual transmission then forget about it, you're not going to be going 80 mph.

I guess the question is what's the safe long-term rpm for highway driving for the engines of this era? They're not high-reving engines... For me, just by feel, I don't like to go above 2750 rpm, it just feels too fast for the stock sb350 I've got, (could be different if you have a different cam or a built up engine). It seems happy at around 2500 rpm.
What do ya'll feel comfortable with pushing the engine at for sustained periods?

My blazer is around 2600 rpm at 65 , for long trips my rule of thumb is 3000 and below but out in the waste lands sometimes I like to haul ass for a while.

My girls truck is 2400 ish at 65

 

[MikeB]

I guess the question is what's the safe long-term rpm for highway driving for the engines of this era? They're not high-reving engines...

I found a document saying the 87 V1500 350 engine had these torque specs:

250 lb·ft @ 2800 RPM for trucks with less than 8500# GVWR
295 lb·ft @ 2400 RPM for trucks with more than 8500# GVWR

So, if your engine is stock, I think it would probably like to run a little below peak torque RPM at highway cruising speed, and at peak torque RPM when carrying or pulling a load. However, I can't see it being a problem running it a couple hundred RPM higher.

Back in the 1980s, they were probably geared with the 55 mph speed limit in mind, but I doubt running a constant 70 mph, even at 2800-3000, RPM would have hurt anything except your ears!

 

[donnieray]

Interesting thread here. My 86 C10 sees 250 mile trips on I-95 on a regular basis and short trips daily. 3000 rpm at 75 mph and feels right at home. Carbed 355, TH400 and I believe 343 gears. Rear tires are 275/60 15 and 28" dia. 3000 used to seem kind of high but now seems normal, my 84 K with 350 and 4 speed od and 32 12.50 BFG's clocks 2000 rpm at 70. Both seem to be right at home on the interstate.

 

[MikeB]

My 86 C10 sees 250 mile trips on I-95 on a regular basis and short trips daily. 3000 rpm at 75 mph and feels right at home.

I must be a wimp, because my 69 pickup (now my son's) with a mild 350, 3.08 axle, and 29" tires always seemed like it wanted an OD gear at anything above 65 mph. But when I was a kid, I had no issues with 26" tires and a 3.55-3.70 axles at 65-70 mph.

However, the 4.56 gears I had behind a fairly hot 283 and Muncie M21 in a 57 Chevy was a bit much. In fact, I tried to stay off the freeways as much as possible, even short trips. But it was insanely quick off the line through 3rd gear, and would outrun just about anything for a block or two. Can't believe I street-raced back then and never got a ticket. At least we did it on wide non-residential streets.

 

[donnieray]

I must be a wimp, because my 69 pickup (now my son's) with a mild 350, 3.08 axle, and 29" tires always seemed like it wanted an OD gear at anything above 65 mph. But when I was a kid, I had no issues with 26" tires and a 3.55-3.70 axles at 65-70 mph.

Well don't get me wrong, the truck and I both would like another gear but, it is what it is. The C10 became my daily driver when my daughter totaled her car and I gave her my VW JETTA.

 

[MikeB]

Well don't get me wrong, the truck and I both would like another gear but, it is what it is. The C10 became my daily driver when my daughter totaled her car and I gave her my VW JETTA.

I wasn't challenging your statement, I was just saying highway RPMs didn't seem to be a concern back in the day. Maybe it was because smaller engines like the 265, 283, and 327 were more comfortable at RPM than a 350 and larger. ???

A guy I know had a 64 Corvette with the 340hp/327 and 4.11 gears back in the day. He said he drove from Dallas to Houston (approx 250 miles) at least twice a month to see his girlfriend, and doesn't remember the revs being a problem. Now he has a 70s Nova with 3.42 gears, and says the engine revs way to much on the highway. Go figure. Must be youth vs. old age.

Oh, have to add this. When I got my 69 C10 with a 307 and TH350, and 3.08 axle, the thing sounded like it was totally stressed at 60 mph or faster. I then replaced the single exhaust system and stock muffler with dual exhausts and turbo mufflers It was like I had a new free-revving engine under the hood! That was 27 years ago, and is still the most noticeable improvement I've ever made to a car or truck.

 

[MikeB]

Duplicate, but can't delete.