ideal rpm at highway speed

Just wondering what rpm a 302 with a c4 trans with a 28" tall tire would run best at on the highway at 70mph. I think I have 3.80's in my 8" rear right know but it runs 2500 rpm at 55mph right now and I want it to run at 70mph most of the time. I was thinking of 3.00's but don't want to spin it at a rpm that is ok for the engine. Thanks

 

my 331 (302 stroked) with a 3.90 gear and a T5 runs nicely at 1700-1900 at highway speeds.

 

this depends a lot on the cam/heads/intake.

However, a stockish engine seems to like 1700-2100. Any lower and you're lugging, any higher and you're wasting fuel spinning it that high.

 

http://project33.com/tiresize.cfm

 

268H cam, edelbrock e street 2.02 aluminum heads and an offenhauser tunnel ram with 2 450 edelbrocks. The carbs are set up so the secondaries do not open at all. It is more for looks than performance.

 

my 48 dodge truck with a 1969 327, 2OO R4 and a camaro 3:36 geared rear-end turns 19OO RPM's at 60 MPH and 22OO at 7O MPH.

seems to run good at this RPM level.

Later

 

Non-overdrive, keep it under 3000 @ 70, 2400 if you want any fuel economy at all. With OD and/or taller tires, 2000-2200 is good, under 2000 is where you get with really tall gears.

 

If you had the tq curve or peak, you might want to be just were it starts its fastest climb.

 

tour cruising RPMs should be halfway between peak torque and peak horsepower for the best efficiency.

 

Tunnel rams suck for low end torque. It may not pull hills well if your rpms are where normal is for a more modern street car. My newer trucks and my street rods run about 2200rpm at 75mph. I run the 700r4.

 

I think mine turns 1800 rpm @ 70 mph..
Tremec 5-speed and 3.55's out back..

 

Here's everything you need to calculate RPMs. gearing, tire size or whatever you need to know....

http://www.currieenterprises.com/cestore/calculators.aspx

 

With that combination you have something in the 3:00 to 3:25 range would be about right, IMO. I ran almost the same setup as you in my 27, 302, stick trans, 3:70 gears, and a 29.5 rear tire. It was not bad at highway speeds, I think turning about 2200 at 65-70 mph. But when I built the 331 stroker I thought the cam I was running would like more gear, so I went to 4:30's. I love it around town, and it pulls like a frieght train, but at 60 mph I am turning 3000, which after a 5 hour trip gets real old, real fast.

My 23 had a TH350 with 3:00 gears and a 30 inch slick in back. That setup was ideal IMO. I still had enough power (probably the light weight helped) and it pulled fantastic gas milage. Once coming from Billetproof I actually got 30 mpg on one leg of the trip, but usually it got 24-26 with no problem.

Don

 

Exactly. If you want your best fuel mileage you want your engine to be running where it is the most efficient, that would be right at the bottom of its torque curve. It is called a sweet spot by most if the really old guys.

If you don't have a dyno you can tell pretty close by the seat of your pants, put it in gear and drive it. You can feel where it is starting to pull well. That is your sweet spot.

 

I have 302 c4 ranger with 3.08 I can roll at 70-75 all day it's perfect imo! Just got back from 1800 mile trip it was perfect! 6.70 tire