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Username Post: Engine revs verses road speed.        (Topic#375809)
greenock 
Poster
Posts: 77

Age: 57
Loc: New Zealand
Reg: 11-10-09
10-07-24 09:00 PM - Post#2874494    

Hello,
Just wondering if someone may have this information.
I'm wanting to know the engine revs verses road speed on my 52 Bel Air, powerglide with standard running gear.
The handbook recommends shifting into top before forty miles per hour, and not changing down over forty miles per hour, it would be interesting to know much the old girl is revving,
Many Thanks,
Ian.

1932 Special Sedan
1952 Bel Air powerglide
1958 Impala Convertible
Greenock- circa 1854 - New Zealand's oldest American house.
Greenock Garden, Karaka, Auckland.


 


ss3964spd 
"6th Year" Gold Supporting Member
Posts: 4729
ss3964spd
Loc: Fairfax, Va
Reg: 12-21-00
10-08-24 04:27 AM - Post#2874502    
    In response to bobt

There are a number of RPM calculators you can use to figure out the RPM at various road speeds.

You need to know the gear ratios of the Powerglide, the rear axle gear ratio, and the diameter (height) of the rear tires.

Example; the rear axle ratio in my '66 Impala is 3.31:1, tire height is 27", and the transmission's final gear (4th gear) is 1.00:1. This works out to 2677 RPM at 65 MPH.

http://www.csgnetwork.com/multirpmcalc.html

Dan

If I recall correctly my memory is excellent. My ability to access it is not.


 
52_Belair 
Senior Member
Posts: 294

Loc: Canby, Oregon
Reg: 03-25-03
10-08-24 08:49 AM - Post#2874510    
    In response to bobt

In '52 the PG was a two speed but it didn't automatically shift between Low and Drive. If you wanted Low range you needed to manually select it.



 
52_Belair 
Senior Member
Posts: 294

Loc: Canby, Oregon
Reg: 03-25-03
10-08-24 09:07 AM - Post#2874511    
    In response to greenock

The gear ratio in Low is 1.82:1

So in L the engine RPM at 40 MPH would be about the same as 72 MPH in Drive. I don't know what the RPM would be at that speed though.



 
greenock 
Poster
Posts: 77

Age: 57
Loc: New Zealand
Reg: 11-10-09
10-08-24 01:28 PM - Post#2874517    
    In response to bobt

I think you misunderstood my question bobt.
I have done many miles in my car know exactly how this great old transmission works.



1932 Special Sedan
1952 Bel Air powerglide
1958 Impala Convertible
Greenock- circa 1854 - New Zealand's oldest American house.
Greenock Garden, Karaka, Auckland.


Edited by greenock on 10-08-24 01:35 PM. Reason for edit: No reason given.

 
greenock 
Poster
Posts: 77

Age: 57
Loc: New Zealand
Reg: 11-10-09
10-08-24 01:34 PM - Post#2874518    
    In response to 52_Belair

Thanks for the information 52-Belair.
I can work that out easily now.
Many Thanks.


1932 Special Sedan
1952 Bel Air powerglide
1958 Impala Convertible
Greenock- circa 1854 - New Zealand's oldest American house.
Greenock Garden, Karaka, Auckland.


 
52_Belair 
Senior Member
Posts: 294

Loc: Canby, Oregon
Reg: 03-25-03
10-08-24 04:54 PM - Post#2874522    
    In response to greenock

When you figure out what the RPMs are let me know. Of course I guess I could use one of those calculators myself.

You probably know the differential ratio is 3.55:1



 
Dand1960 
Newbie
Posts: 1

Age: 64
Loc: London Ontario Canada
Reg: 10-10-24
10-11-24 08:15 AM - Post#2874572    
    In response to greenock

Why not just connect a tachometer to it and run the car down the road. That way (if you are so inclined to) you could document any and all rpm values; during whatever diving scenario you are in.

Dan.



 
52_Belair 
Senior Member
Posts: 294

Loc: Canby, Oregon
Reg: 03-25-03
10-11-24 09:28 AM - Post#2874575    
    In response to Dand1960

Well in my case that would mean buying a tach that will work on 6v and from what I have seen they are kind of expensive for something I would only use once and don't plan to mount in the car.

OTOH it would be nice to have a tach to check my idle speed.



 
Airlifter 
"9th Year" Gold Supporting Member
Posts: 963
Airlifter
Age: 79
Loc: Tazewell county, Virginia
Reg: 06-07-15
10-12-24 05:06 AM - Post#2874594    
    In response to 52_Belair


This is the formula I use. I also multiply by 1.1 for torque converter slip.
(Axle Ratio * Vehicle speed * transmission ratio * 336.13/Tire Diameter)
366.13 is to convert the result to RPM (63360 inches per mile/60 minutes per hour*Pi)


1951 styline deluxe sport coupe w/'60 261 engine & 54 powerglide

1965 Corvair Corsa 140 hp 4 speed convertible


Edited by Airlifter on 10-12-24 05:14 AM. Reason for edit: No reason given.

 
52_Belair 
Senior Member
Posts: 294

Loc: Canby, Oregon
Reg: 03-25-03
10-12-24 08:42 AM - Post#2874600    
    In response to Airlifter

I compared your formula with the online calculator.

The formula matched for a manual transmission but gave a 206 RPM higher number for automatic. I suppose yours would be the more cautious method.



 
radioheaterwsw tires 
Newbie
Posts: 36

Reg: 08-24-14
10-12-24 01:22 PM - Post#2874612    
    In response to 52_Belair

THere's no lock up converters in these old automatics and a manual is direct drive unless the clutch is slipping (lol). What is the slip factor in these old PG's while going say 60MPH? Have never heard anyone say or read anyhwere what the percentage might be.



 
52_Belair 
Senior Member
Posts: 294

Loc: Canby, Oregon
Reg: 03-25-03
10-13-24 12:49 PM - Post#2874648    
    In response to radioheaterwsw tires

The online calculator did show a higher RPM for automatic compared to manual to account for some slippage, but the formula posted by Airlifter had more slippage.

But yes, who knows what the actual slippage is? My guess is that it would be less at higher speed than lower.



Edited by 52_Belair on 10-13-24 12:50 PM. Reason for edit: No reason given.

 


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