How hard on engine and driveline is this?

[Mark1972]

My current setup has me rolling down the highway at 2900rpm. That's 60 miles/hour, or 100kms/hour here in the land of metric. This may be a dumb question, but how much harder would it be on the engine/driveline going 2900rpm for long distances, like 2-3 hours at a time, as opposed to lower rpm driving in city, or having higher ratio gears and a little taller tire? I run 3.55's, with a 255/60-15 tire. I would have loved 3.23's, but I couldn't pass up the deal on the rear end. It's an 8 1/4" with a Yukon Dura Grip. Now my wife and I seem to be doing more cruising at highway speeds, and I'm wondering if there's anything I should be keeping a closer eye on because of the rpm? For the record, this is my '70 Satellite two door with a 440/727. About 475hp at the crank. I also find it cool that I'm still getting 14mpg on the highway. I think that's pretty good.(based on a US gallon. 16.5mpg Imperial). Thanks all.

 

[Fran Blacker]

That's not bad, yes more wear but not bad. Ran my Satellite with 3.54's 26.5" tire 350miles from CT to Niagara Ealls 2900 to 3100 for 6 hours. Had stock 64 Olds Starfire vert came with 3.55's factory standard equipment.

 

[Mark1972]

I always thought if I got an 8 3/4, I'd build two members for it. A 3.91 for fun, and a 3.23 for cruising. A little taller tire with a 3.23 would be about 2400-2450 rpm. Until that day, I'll just keep an eye on everything. I run 10-40 conventional Driven Hot Rod oil, and the rest of the driveline is full synthetic. I just hit about 5,000 miles. Maybe next spring I'll pull the diff cover and change out the oil.

 

[66 Sat]

I wouldn't worry about that rpm at all.

If you were at 3,500 or 4000 rpm a different story, but where you're at is probably in a sweet spot anyway. Depending on your set-up (camshaft etc) if your too low the engine is not operating efficiently.

If you can lower it by a couple of hundred rpm then good, but I wouldn't be concerned at where you're at if it's a good compromise with acceleration.

 

[GTX JOHN]

I think you are fine!
If you had a 8 3/4 you could even go 2:94 or 2:76 and cruise
@ 80 plus all day.

In my experience the rings will wear a bit more but the bearings will
show no difference at all. The engine will run 50,000 miles either way baring
a disaster.

 

[33 IMP]

3.55 is a decent compromise gear, and imo,under 3000 is nothing to worry about. Stock gear in a 55 chevy.
I commuted for seven years with a 4.10 geared rr, at 3500-3700 fwy rpm with a 440. It wore out a bit quicker than a 3.23 or 3.54 would have, but the 4.10s were stock, and the only ratio less than that for a dana at the time was 3.54, and the difference in rpm was not worth the expense of the swap.
Simple and easy solution for your car? The tallest tire that will fit in the wheelwell.
Put a 235/75x15 on it, and you'll HAVE 3.23 rpm!

 

[dvw]

Hell I run a 4.30. Driven Detroit to Columbus . Noisy and may use a touch of oil. But it won't hurt it.
Doug

 

[WileERobby]

It'll hurt your wallet, in the cost of petrol. That's about it.

 

[64BEL]

I just drove 90 miles each way to a show on Friday. With my 3.54 Dana, and 15" tires, I'm turning around 3500 at 70-75mph on the interstate and 3000 at 60mph on the 2 lane highways. It just cruises right along, no issues.

 

[WileERobby]

I just drove 90 miles each way to a show on Friday. With my 3.54 Dana, and 15" tires, I'm turning around 3500 at 70-75mph on the interstate and 3000 at 60mph on the 2 lane highways. It just cruises right along, no issues.

Are those 15" tires on 14" wheels ? 1/2" sidewall, eh ?

 

[64BEL]

Yup - the rubber band look! To clarify, 15" wheels with 245/60 tires on the back.

 

[dadsbee]

Just keep pushing the pedal. My 340 Dart Swinger gets 10 miles per US gallon. The hemi Satellite about 8!

 

[WileERobby]

Just keep pushing the pedal. My 340 Dart Swinger gets 10 miles per US gallon. The hemi Satellite about 8!

I stopped worrying about gas mileage on these cars about.... about... ok........ I never worried about gas mileage on these cars.

 

[Mark1972]

Ok. Well that makes me feel better. Eventually I will go with a little taller tire. The longest trip I'd like to do is about 160 miles one way, and I'm not for seeing any issues. I always have my spare tire, jack, a small toolbox with tools, spare belts, etc. I love cruising in this thing at about 45-50mph. Sits about 2400-2500rpm, and just seems to love it. Thanks again all.

 

[WileERobby]

Ok. Well that makes me feel better. Eventually I will go with a little taller tire. The longest trip I'd like to do is about 160 miles one way, and I'm not for seeing any issues. I always have my spare tire, jack, a small toolbox with tools, spare belts, etc. I love cruising in this thing at about 45-50mph. Sits about 2400-2500rpm, and just seems to love it. Thanks again all.

View attachment 1512716

 

[451Mopar]

Going from the 27" 60 series tire to a 29" 70 series tire would be pretty close to the change you would get with 3.23:1 gears.
What stall speed converter? Doing the theoretical math, a 3.55:1 gear with 255x60x15 tires (diameter of 27.05") would be 2646 RPM @ 60 MPH with zero converter slippage.
To get 2900 RPM the tires might be smaller or the converter has almost 10% slippage at that speed.
I like the 3.55:1 ratio with the 518 OD transmission.

 

[AR67GTX]

I used to think a 3.73 gear was the best compromise but now I’ve come around to the 3.54/3.55 is the best compromise. I have an old Corvette with a 4.11 and Muncie and its pretty tiresome at anything over 60mph, especially with side exhaust.

 

[Mark1972]

Going from the 27" 60 series tire to a 29" 70 series tire would be pretty close to the change you would get with 3.23:1 gears.
What stall speed converter? Doing the theoretical math, a 3.55:1 gear with 255x60x15 tires (diameter of 27.05") would be 2646 RPM @ 60 MPH with zero converter slippage.
To get 2900 RPM the tires might be smaller or the converter has almost 10% slippage at that speed.
I like the 3.55:1 ratio with the 518 OD transmission.

2400 stall. My calculations showed the same as yours, and it's still 2900 at 60mph.

 

[cosgig]

I wouldn’t think another thing about it. You said it’s a happily running car, it’s telling you everything is alright, I would listen to it. Nothing you have is out of line with any daily driven car of the era. Drive like the wind, Bullseye!

 

[70bigblockdodge]

Two words, over drive. You will have you newer car up for sale. Nothing like lumbering down the highway at 80+ and 2300 rpm.