Highway driving....RPMS

[R/T Boy 67]

If you have an open diff, with both tires off the ground, turning in opposite directions, you will be waiting a long time for the drive shaft to make a revolution.

 

[65moneypit440]

GV is going in, 3000-mile road trip coming up. 3.23 gears, 235/70/15.

 

[Dennis H]

GV is going in, 3000-mile road trip coming up. 3.23 gears, 235/70/15.View attachment 748437

Love that Tach,

Rocky

 

[Don Frelier]

GV is going in, 3000-mile road trip coming up. 3.23 gears, 235/70/15

So your tach reads around 3,500 rpm at 65?
With 3.23 gears and 235/70 tires I would expect around 2,750?
That's a fairly large discrepency, sure the tach and ratio are right?
Speedometer is accurate as well?

 

[Fran Blacker]

GV is going in, 3000-mile road trip coming up. 3.23 gears, 235/70/15.View attachment 748437

You sure you have 3.23's in there? Looks like 3.73's, ran 3.54's 3000 at around 65 mph.

 

[Don Frelier]

If the tach and speedo are correct, it's probably higher than 3.73.

 

[BSB67]

GV is going in, 3000-mile road trip coming up. 3.23 gears, 235/70/15.View attachment 748437

And I would hope that your WOT shift point is a bit higher

 

[Dennis H]

And I would hope that your WOT shift point is a bit higher

My 440 stops pulling at 4850 per the chassis dyno. No reason to go upstairs.

 

[BSB67]

My 440 stops pulling at 4850 per the chassis dyno. No reason to go upstairs.

Factory with the cast iron intake go 5200.

What was your peak hp, 4300? Smaller than factory cam?

 

[Dennis H]

Misspoke i guess. Max power at 4850. I’ll dig up the dyno sheet. 30 over slightly warmed up Comp Cam.

 

[BSB67]

Misspoke i guess. Max power at 4850. I’ll dig up the dyno sheet. 30 over slightly warmed up Comp Cam.

That makes more sense. What intake?

 

[Dennis H]

Edelbrock RPM 850 Demon at the time. 415 rwhp.

 

[65moneypit440]

I’ve double-checked the tach, checked the speedo with other cars and using the mile marker/clock method, and saw the “3.23” on the ring gear myself. You’re right, it doesn’t add up. I just want it to come down.

 

[Don Frelier]

is the tach possibly set up for a 6 cylinder?
8/6 = 1.333 which is equal to about how far off I think your tach is.
Just an idea.
Does it have any dips switches or jumpers, see if you can get a manual?
I have 3.23 in both my 66's and I wouldn't say they scream at highway speeds.

 

[33 IMP]

Please don't take this wrong,it's NOT meant as an insult, but did you count the teeth on the ring and pinion, or jack the car up and recheck the ratio?
The numbers on your tach and speedo correspond to a 4.10 gear, and if that's what you have, I can understand you think it's screaming.
I checked with the Wallace calculator, if you have 3.23 and 28" tall tires, 3500 should get you 85 plus mph. 65mph should be around 2700, not 3500.
For what it's worth, I have a 4.10 geared car with 28" tires, and it runs almost exactly 3500/65mph.

 

[65moneypit440]

Ok, here’s the deal (relating to post 42). My 904 is a 1987 “non-locking” unit, so the torque converter is still slipping in high gear. I’m told it can’t be corrected easily in my old car. Neither can the GV be installed without more floor-pounding and pipe-bending than I feel comfortable with. The overdrive is going back to El Cajon, and the tach is coming out. Thanks for your comments Don, Dennis, Fran, and 33 Imp, ‘preciate it!

 

[Cojohnso1]

3.55's wouldn't bother me at all with no overdrive.

Once drove a 78 Trans Am from California to Illinois, 4 speed with 3.73's holding it at 5000rpm through every tank of gas.

That didn't bother me (or the car) either

3.54:1 is solid all around gear ratio for street. I have 28" on rear. And it hums great. About 2800 @ 60 MPH. The 440 is not super fast thru the gears. Doesn't really start pull decent until 70+. Would love that new Passon 5 speed with .70 OD with a set of 4.10 or 4.56 rear gear? Then the BB is in its power range quicker. Bet it would shave a near full second off 1/4 time. High 13 to high 12?

 

[66 Sat]

Well after reading this thread I finally got around to checking my ratio this morning. Jacked the rear up, 3.23 and a sure grip! I thought I had a 2.93 open rear. That explains why it hooks up so well out of T junctions.