Technical Your RPMs at 70mph

Looking for input from you guys that actually put some highway miles on your hot rods and customs. I am curious what RPMs you are comfortable living with at 70mph. I want to hear from guys running original trans and rears. I know a modern OD trans can achieve low RPMs at highway speed, I want to hear from guys still running a 3spd.

What is your set-up and what RPM are you turning at 70 mph?

Are you ok with driving 500+ miles at 2700+ RPM?

What problems have you had associated with running constant higher RPMs?

I am asking the question because I am at a cross road on a current build. All of my other cars are 3spds, although my 49 ford is still using the original 3sp w/OD.

 

59 bel air, 235, three speed od, 2400 at 70, 215 75r 14 tires. when they were new people drove cross country at that rpm, why not in 2017?

 

30 A pickup, w/ 283 /Powerglide/3:23 10 bolt.

RPMS at 70 are about 2800.

 

52 Ford, w/52 Merc flathead(basically stock). Originally a Fordomatic car, switched to 3spd/OD, original 3:90 rearend. I usually don't run over 65 because I like to be nice to it. Just under 2500@70. Want to swap out to 3:55 gears in stock rearend.

 

32 Ford with a banjo rear using 3:78 gears and 16x7.00 tires. Speedo isn't calibrated but I keep up with the slower set of interstate traffic at about 2600 so I assume that is 70 MPHish. I have a 3:54 gear set but haven't machined it for the 32 rearend yet. I don't know if I'll ever get a round tuit.

 

i am running a stroked 327 with a 55 chevy 3 speed and rear axle that has 370. 3k at 70 all day long.
i was running 456 gears but swopped to the 370 for a trip to maryland we took.

 

http://www.crawlpedia.com/rpm_gear_calculator.htm

 

My truck isn't traditional, but here's my info anyway;
1949my Ford F1 truck with 1971 Caddy 500ci and TH400 trans. I originally had 4.11 gears in my 9". While fun to drive around town highway driving was out. I did some wheelin' and dealin' and came up with a Traction-Lok 3rd member with 2.75 gears. My speedo isn't to accurate but at about 70MPH I'm turning about 2100 RPM.

 

The first time I built my truck, it had a 261 Inline 6 , stock 3 speed and stock 3.90 rear gears. I was only comfortable doing about 55 mph and it would be at 3000 RPM. Reliable as hell and never missed a beat. This time around though I wanted more power so I am going with a 327 / 700r4 and 3.23 10 bolt combo. RPMs should be about 1900 RPM at 70.

 

Thanks for the input so far.
In my 29 A, I'm running a stock flathead, 3spd and banjo rear with 3.54 gears. 65mph is about 2500 rpm. It's comfortable there. 70 mph is nearly 2700 and it seams to be really wound up and starts to run a little hotter. Funny how 200rpm starts to make a difference.

 

My RPU runs a 350 TH trans with 2.91 gears in the quick change. 70mph = 2300 rpms with a 29" tire. .

 

When I first got my car(handed down from my dad), the OD wasn't hooked up. The car would run hot on the highway at 60mph or more. The OD took care of that. A hell of a lot quieter inside too.

 

3.36 gear, 31" tires- 2550rpm at 70, works for me.

 

My T RPU is running a Chev 301 and Powerglide with a 3.78 Banjo rear and 29'' tires. At 70 its turning 2900 rpm.
With your motor running hotter at 70, check your water pump is not turning too fast. Your crank and water pump should be about 1-1 ratio. JW

 

29.5 tall tire, 4.11 gears, .69 OD manual transmission, 2250 rpm's at 70 MPH. 427 Ford on a Dart Windsor block, get's 17 MPG on the long drives on the highway. 14-15 if you pass a lot of slower cars on backroads.

 

3400 lb Fat Fender Ford-350sbc/700R4/3:42 ratio/29 inch tire=1940 rpm@70MPH-converter locked

 

http://www.4wheelparts.com/off-road/gear-ratio-tire-diameter.aspx?gclid=CIOX4qmyw9ICFdG2wAodfAgHRA

 

Not seventy on mine and poor gas mileage back then. I had 4:57 rear 33" tall tires about 65 mph I was at 3200rpm it was runnen good no problems but I was scared to blow my motor wich I did. But now .64 o.d. 3:54 rear 31 3/4" tall tires 1700rpm mpg haven't had time to check yet

Sent from my Z981 using The H.A.M.B. mobile app

 

My 35 tub with 700R (0.7) , 3.54:1 diff with 235/75/15 (29") churns over at 2,010rpm at 70mph and 28mpg.
My old 390 powered 66 Fairlane with 3.89:1, C6 and 205.75.15 was running at around 3,400rpm with a great sound from the pipes and 14mpg

 

I re read your question. On my 370 Pontiac motor in a 26 Roadster it has 3.73 gears, 4 speed,28.5 tall tires, @ 70 it's turning about 3100. I think it would go 500 miles easy and I drive it 70 on the highway a lot. All the old cars I remember as a kid ran that high of rpms on the road and everybody drove them everywhere.

 

Came back from Korea in 75 and picked my 69 Camaro 427 4speed 4.88 gear and drove it to Detroit. Stayed off the interstate for most of the trip ran 55-60 turning 3200 rpms. Got 7-9 mpg ,had to change valve springs when I got to Michigan. That 580 lift solid cam took a toll . Great trip though. Stopped and raced an army buddies friend in Mo. and blew the driveshaft . Went to a junkyard and found a good one. Headed on down the road.

 

Inline 292, T-5 , 30" tall tires, 3:55 gears. 1950rpm@70mph. 22mpg.

 

Hello,
We had a 58 Impala with stock 4:11 gears and stock tires. We ran about 2500-3000 rpm all over town and on road trips. But, when we installed the 4:56 gears for the drags and short cruises around our local area, we ran around 3500rpm. For the local cruises and races, that was fine. The round trips were about a normal 10 miles, which was done weekly. When the car was a 3 speed in the beginning, it was fine.

But, once we put in the C&O Stick Hydro, that seemed to push the rpms up higher. (For each 4:11/4:56 install.) One time, after a week of drag racing at Lions, (4:56 gears) we were going to Pomona to watch the Winternationals. It was about an 80+ mile round trip. We thought if we kept it at 55-60 mph, it was fine for us. But, on the way home, there were many people in hot rods and cruisers that kept looking at us and hearing the motor rev so high on the freeways. They kept moving their hands from the up position to the down position like shifting to 3rd.

At first, we thought they were waving at us and admiring a cool 58 black Impala running on the freeway. Then we realized that they were telling us to shift. When we had the C&O installed, the stock 3 speed column shift lever was still in place and used. The white ball on the end of the lever was very obvious when it was in the final drive position in the C&O. The location of the shift lever was almost in the 3 speed, 2nd gear position. They were telling us to shift down to 3rd. When we figured that out, we all chuckled and shook our heads, no. That, made those hot rodders look at us like we were crazy.

Jnaki

For the local weekly 10 mile round trip cruises, it was fine and the motor did not strain as much as on an extended 60+ mile run. On those longer drives during Easter Vacation (Spring Break) to Newport Beach and San Diego, it was a little hectic when the 4:56 gears were in place. But, you can never be too prepared for any race challenges in new locations.

 

I'm running a 355 SBC worth about 400 HP, mated to a M20 4-speed and a 3.70 rear. 3000 RPMs at 70, which was annoying with glass packs, just changed to turbo mufflers and the ride is a lot nicer. I'm going to a 4.10 rear soon, the cam I have likes higher revs around town and a few extra on the road aren't bad. But really not bad to drive at that RPM range, very responsive in 4th gear.

 

'51 Pontiac with a non-HAMB friendly 4.8 Vortee/4L60, 2200. '48 Diamond T with 6.0 LQ4/4L60 and 4.10's, 2300. Happy all day long.

 

My 63 Belair 2 door post car with a 350/ Tremec 5 speed and 336 rear runs 75 MPH at 1900 RPM.

Gary

 

Blown 354 Hemi, Tremec 5 speed. 2000rpm 75mph

 

Have over 70000 mi on my avatar. Mild 8BA, S10 5 speed, 3:73 rear and 235/75x15 rear tires. 60 mph is about 2050 rpm. Sweet spot on a relatively smooth highway is a honest 60 to 65 mph. We ran up to 75 mph on our trip to Bonneville, but was not like driving our 09 Mustang at that speed. The point I am trying to make is 60/65 is probably a more realistic all day cruising speed. I would use a 5 speed even though it is not "traditional" It will be hidden and you can adapt an old Ford stick. In Short, I would figure on 2300 rpm max for all day cruising. Just my $.02 worth. You are going to have one sweet ride!!

 

Just remember with a 70mph speed limit, outside of metro areas that means the traffic flows at 80mph or more. Are you having thoughts of a T-5 for your new coupe?..... I would give it some serious thought! Just modify the frame and trans. mount so that it looks like Henry did it.

 

I suppose that HWY RPM is dependent on the engine and how it is built. if your car is all stock in good shape and 2700 is what it spins @ 70 you are probably OK. In '49 the speed limit in most states was between 60 and 70 unless you were in Oregon, one of the Dakotas or Nevada where there was open speed law.

As far as highway driving I put a lot of miles on my motor on the hwy, like 150K plus and my sweet spot is between 3K and 3200.granted I built the motor ( from a crank shaft) and it is built to run.

here is something to remember, these old cars are noisy compared to a late model car. They rattle shake and roar. Just because it sounds like it is going to com apart does not mean that it is going to come apart.