Highway cruising

[N PRGRES]

When I am tooling down the interstate at 70 mph my engine is running about 3000 rpm give or take.  Tires 245/60/15 and 3.10 rear gears.  I want to take a trip with the car thats 2 hours each way and that high of RPM unnerves me a bit.  What do your engines run at highway speeds?

[rkellerjr]

Before I switch to the 200r4 I had a TH350 and my rear end is a 3.23. At highway speeds I was running about 3000 and 3500. I've taken many trips with that setup and the motor was fine. And I'm talking 7 hour one way trips and back. Car never skipped a bit.

[kentucky yeti]

3000 won't hurt anything.   That's pretty common rev's.

[roadking77]

I have 2.70 (I think, 2 something anyway) gears. My cars sweet spot is about 60 mph. Low rpms, quiet and purrs down the road. All of the sudden it hit me one day 'Hey, when this car was made the speed limit was 55! duh, I guess they knew what they were doing'!! My first long drive was about 2 1/2 hrs away. I was planning on back roads as I was leary of getting on the highway. There was one stretch that I had no choice. The ironic part was the car ran better at 65 mph on the highway than it did putting along on back roads. I dont plan on any long distance road trips soon but the highway doesnt scare me at all now. These beasts were made to get out and run I think you will be fine.

[N PRGRES]

Thanks, I have run it down the highway for about 30 minutes at those speeds and was actually very happy with how well it did, other than the steering gear being worn.  but yeah, in 81, I can't drive 55 was the motto lol. 

[b_hill_86]

I’ll just reiterate, I drove mine about 2 hours one way last year with 27” tall tires (just a little taller than yours) and a 3.08. I’m around 2700ish at 70. No issue.

[FormTA]

Ya, my car was fine but I had 273 gears and th350 but now with ls and 4L60E I'm like 1500. For me it's the rest of the car seems no quite up to it. I'm talking about 70+. I think my problem is more precise wheel alignment and maybe driveline angle. (I have a slight vibration over 60). I know these may not apply to you but the wheel alignment may. Just how stable/comfortable is the car at the speeds you'll be diving? Like others said, 3k is really normal rpm hwy driving. But if it wanders, pulls or darts now that will get old trying to maintain a lane. Also lose steering can be exaggerated at higher speeds. Just a few other things to consider.

[N PRGRES]

Honestly it’s actually a very good driving car, only to be better with the new gear box I just got. The whole suspension is new

[stros]

Ya, my car was fine but I had 273 gears and th350 but now with ls and 4L60E I'm like 1500. For me it's the rest of the car seems no quite up to it. I'm talking about 70+. I think my problem is more precise wheel alignment and maybe driveline angle. (I have a slight vibration over 60). I know these may not apply to you but the wheel alignment may. Just how stable/comfortable is the car at the speeds you'll be diving? Like others said, 3k is really normal rpm hwy driving. But if it wanders, pulls or darts now that will get old trying to maintain a lane. Also lose steering can be exaggerated at higher speeds. Just a few other things to consider.

My LS3 and 4L70E is around the same rpms with 3.08 gears.  It actually seems to drive pretty well up to 75mph with the PTFB suspension bits.  I am just paranoid that some crazy person is going to hit me staring at it on the freeway, plus zero safety features doesn’t add to the confidence level.  I’ve been taking it out for a few 3-4 mile highway runs of late just to stretch the engine a bit.  The traffic here sucks anyways so it’s just more fun to drive the back roads into work once in a while.

I was also at about 3000 rpms with the original Pontiac 400, at least up until it overheated and then died😀.

[nUcLeArEnVoY]

Ya, my car was fine but I had 273 gears and th350 but now with ls and 4L60E I'm like 1500. For me it's the rest of the car seems no quite up to it. I'm talking about 70+. I think my problem is more precise wheel alignment and maybe driveline angle. (I have a slight vibration over 60). I know these may not apply to you but the wheel alignment may. Just how stable/comfortable is the car at the speeds you'll be diving? Like others said, 3k is really normal rpm hwy driving. But if it wanders, pulls or darts now that will get old trying to maintain a lane. Also lose steering can be exaggerated at higher speeds. Just a few other things to consider.

My LS3 and 4L70E is around the same rpms with 3.08 gears.  It actually seems to drive pretty well up to 75mph with the PTFB suspension bits.  I am just paranoid that some crazy person is going to hit me staring at it on the freeway, plus zero safety features doesn’t add to the confidence level.  I’ve been taking it out for a few 3-4 mile highway runs of late just to stretch the engine a bit.  The traffic here sucks anyways so it’s just more fun to drive the back roads into work once in a while.

I was also at about 3000 rpms with the original Pontiac 400, at least up until it overheated and then died😀.

Why do you suspect it overheated? The cooling system in my '79 400/4-Speed is completely overhauled and it barely reaches operating temp around town if I'm not using AC. Getting onto the freeway at 55+ MPH is the only time the temp will creep up to the first tick on the temp gauge or past it. I've never been on the highway long enough to see how high it'll go mostly because of a vibration I get at 60+, at least during the daytime but I'm wondering if my car is at risk of doing the same thing as your's.

I'm running around 2300 RPMs at 55 MPH with the original BW ST-10 4-Speed and stock 3.23's, so figure 70 would be like 2900 or so. 

[FormTA]

I haven't started looking into it yet but that us the same rpm that may car starts to hum/vibrate. It's not horrible but I wonder what it is. Everything is new on my car including a balanced drive shaft. I'll start by checking the driveline angles. It's just interesting to me that someone else has it at 60mph too.

[stros]

Why do you suspect it overheated? The cooling system in my '79 400/4-Speed is completely overhauled and it barely reaches operating temp around town if I'm not using AC. Getting onto the freeway at 55+ MPH is the only time the temp will creep up to the first tick on the temp gauge or past it. I've never been on the highway long enough to see how high it'll go mostly because of a vibration I get at 60+, at least during the daytime but I'm wondering if my car is at risk of doing the same thing as your's.

My 400 engine was on its last legs - it had all sorts of issues hence I had to replace it.  Your engine may be in better shape.

[5th T/A]

It's funny on how our perception of a normal cruising RPM has changed through the years. When I was about 20, I worked with a guy who had a 1969 Nova SS396. The car was set up for drag racing, but was also his daily driver, he was running a 4.88 rear gear. A friend owned a 66 GTO convertible, also his daily driver. He was running 4.10s and never thought twice about taking it on the expressway, this was before the 55MPH national speed limit. At that time 3.23 or 3.42 were thought as cruising gears.  Another friend owned a 70 Judge, it came from the factory with 4.33 gears. He never hesitated to take his car on the expressway. It did have a very aggressive 60 punch in fourth gear without down shifting.

On my 80 TA, I am running the stock 2.41 gears with stock size 225/70/15 tires. With a Turbo 350 transmission at 55MPH, I am turning about 1900-2000 RPM. I mostly avoid local expressways with 65MPH limits where in reality most are driving 70-75 MPH and some way faster. I am not against cruising at 70MPH but with so many distracted drivers and road debris I prefer rural back roads. Truth be known, foot to the floor shifting 1st to 2nd at a 5700 RPM I am hitting second at almost 70MPH. For that reason, I have thought about changing rear gears to maybe a 3.08 or 3.23.

[nUcLeArEnVoY]

I haven't started looking into it yet but that us the same rpm that may car starts to hum/vibrate. It's not horrible but I wonder what it is. Everything is new on my car including a balanced drive shaft. I'll start by checking the driveline angles. It's just interesting to me that someone else has it at 60mph too.

Sometimes I wonder if my driveline angle is to blame. I have these performance shock/strut/coil spring shocks in the rears in addition to leafs that raise the rear end of my T/A like an inch or so, but I don't see how that should dramatically influence the driveline angle enough to cause an issue. Have you looked into tire balance?

[N PRGRES]

It's funny on how our perception of a normal cruising RPM has changed through the years. When I was about 20, I worked with a guy who had a 1969 Nova SS396. The car was set up for drag racing, but was also his daily driver, he was running a 4.88 rear gear. A friend owned a 66 GTO convertible, also his daily driver. He was running 4.10s and never thought twice about taking it on the expressway, this was before the 55MPH national speed limit. At that time 3.23 or 3.42 were thought as cruising gears.  Another friend owned a 70 Judge, it came from the factory with 4.33 gears. He never hesitated to take his car on the expressway. It did have a very aggressive 60 punch in fourth gear without down shifting.

On my 80 TA, I am running the stock 2.41 gears with stock size 225/70/15 tires. With a Turbo 350 transmission at 55MPH, I am turning about 1900-2000 RPM. I mostly avoid local expressways with 65MPH limits where in reality most are driving 70-75 MPH and some way faster. I am not against cruising at 70MPH but with so many distracted drivers and road debris I prefer rural back roads. Truth be known, foot to the floor shifting 1st to 2nd at a 5700 RPM I am hitting second at almost 70MPH. For that reason, I have thought about changing rear gears to maybe a 3.08 or 3.23.

You know, statistically, rural roads are much most dangerous than highways 😳

[5th T/A]

“You know, statistically, rural roads are much most dangerous than highways 😳”



You have a very valid point that I try not to think about. Still, I prefer the relaxed pace of a winding country back road with hardly any traffic 😊. I suppose if I am not  constantly on guard, that makes it even more dangerous. I guess I shouldn’t mention that I frequently ride my motorcycles on the same roads and riding a motorcycle is statistically many times riskier.

[N PRGRES]

I also prefer back roads but there are situations where those aren’t feasible as they make the trip much longer. In those cases, the TA will need to traverse the highway. I have no issues just cruising along in the far right lane and letting the morons blow by in the left ones.