Anyone with a 289 and a Toploader...Gears and rpm.

renaissance man · #1 (**permalink**) 01-02-2002, 08:32 AM

Anyone with a 289 and 4-Speed Toploader?

What rear end gears are you running and at what rpm on the highway?

I have 4.10 gears in my 289. I'm running at 3500 rpm at 60 mph, 3700 prm at 65 mph and 4000 rpm at 70 mph. I may go to 3.73 or 3.55 gears...

Any thoughts?

Paul Rose · #2 (**permalink**) 01-02-2002, 12:32 PM

Don't have a 289 or a Top-loader, but if the RPMs & speeds that you listed are correct for your current setup, then:

With 3.73 gears:

3.73 / 4.10 = 0.91

3500 * .91 = 3184 @ 60
3700 * .91 = 3366 @ 65
4000 * .91 = 3639 @ 70

With 3.55 gears:

3.55 / 4.10 = 0.866

3500 * 0.866 = 3030 @ 60
3700 * 0.866 = 3204 @ 65
4000 * 0.866 = 3463 @ 70

Bob Putnam · #3 (**permalink**) 01-02-2002, 12:37 PM

You must have some mighty small tires.

If your numbers are correct, your rear tires are only approximately 23.7" OD.

If that's the case, a 3.5:1 might be better - if your engine is "street" tune and comfortable at 2500 rpm.

renaissance man · #4 (**permalink**) 01-02-2002, 12:42 PM

My tires are 245/45-17 F. and 285/40-17 rear. I think I calculated it at 26.97" diameter. Could be my speedo is a few mph off but I had my wife drive next to me before hooking up the speedo to verify rpm and speed. That's how I got the numbers. The rear end I did verify is a 4.10 Running a 650 DP on the car ideling at about 1000rpm if that tells you anything?

How did you come up with the tire size Bob?
Dave

Paul Rose · #5 (**permalink**) 01-02-2002, 01:32 PM

Not Bob, but:

60 MPH
3500 RPM
4th gear = 1 : 1
Final Ratio = 4.1 : 1
12 inches / foot
5280 feet / mile
60 minutes / hour

( 4.1 * 12 * 5280 * 60 ) / (3500 * 60 ) = 74.2" circumference

74.2 / PI = 23.6" diameter

renaissance man · #6 (**permalink**) 01-02-2002, 01:39 PM

Thanks Paul. Learn something new here everyday. So, either my wifes Town Car has an incorrect speedo or my Tach is off somehow?

More math...knowing that my tire size is ~27". and speed is 60mph..., rear end is 4.10...what should the Tach be reading?

2. How do I correct this?

Paul Rose · #7 (**permalink**) 01-02-2002, 01:48 PM

285/40R17

285 * 0.40 = 114

114 / 25.4 (mm per inch) = 4.49" sidewall height

4.49 * 2 = 8.98" (top and bottom sidewall)

8.98 + 17" rim = 25.98"

So, I think your tire height is 25.98 instead of 26.97.

25.98 * PI = 81.61" circumference

( 4.1 * 12 * 5280 * 60 ) / ( 81.61" * 60 ) = 3183 RPM

So assuming the real speed was 60 (and that your 4th gear is indeed 1:1, which I think is right), then your were turning 3183 RPMs.

Sorry I don't know how to fix it, maybe somebody else can help.

Len Hurlburt · #8 (**permalink**) 01-02-2002, 04:14 PM

Ren,

I have a SB in front of a Toploader and I am indicating about 3000rpm at 70 mph. My rear ratio is 3:31 and I'm using a 295/50-15 rear tire. How long have you had your SMC? A few years ago I had a Cobra Auto Works (CAW) car, which I believe became SMC after going out of business.
Len

Bob Putnam · #9 (**permalink**) 01-02-2002, 04:15 PM

Ren Man,

My recommendation for a gear set would depend on a few things:

Is your Toploader wide or close-ratio?

What is the output of your engine, and how does it run at low rpm.

What is the nature of the majority of your driving?

How tolerant are you of an engine turning high rpms?

Maury Novak · #10 (**permalink**) 01-02-2002, 06:32 PM

Ren Man,
Attached is a chart that shows what RPM to expect at 60 mph in fourth gear (1:1) based on rear-end and tire size. This assumes your tach is correct.

If you don't come close to these reading you need to adjust your speedo. If you have an electric speedo, then adjust per the speedo instructions.

If you have a mechanical speedo, cable from transmission to speedometer, then you will need to change the speedometer gear in your tranny.

If you speedometer reads high, then go with more teeth to slow it down.

If your speedometer reads low, then go with less teeth to speed it up.

Hope this helps.

Maury

Maury Novak · #11 (**permalink**) 01-02-2002, 06:54 PM

Ren Man,

Here is the chart. Sorry.

Rear Tire Diameter
End
Ratio 24" 26" 28" 30"
3.08 2587 2388 2218 2070
3.23 2713 2504 2326 2170
3.50 2940 2892 2686 2507
3.90 3276 3024 2808 2621
4.10 3444 3179 2952 2755

Maury

jwoodard · #12 (**permalink**) 01-02-2002, 07:19 PM

Renman,

Here's a link to a tire size calculator.

http://www.rangerpowersports.com/tech/tiresizes.shtml

Here's a rear end ratio calculator,

http://www.smokemup.com/utilities/calc/rear_end.cfm

And finally, a Speed vs RPM for Tire and Gear Ratio calculator,

http://www.smokemup.com/utilities/calc/mph_range2.cfm

Jim

xlr8or · #13 (**permalink**) 01-02-2002, 10:01 PM

For a fix on the speedo, why not go electric so it will be programmable just by flipping some switches.
But then again I don't know if anyone offers a reverse 180 mph electric.... but it's a thought.

renaissance man · #14 (**permalink**) 01-03-2002, 08:22 AM

Bob,

Based on your questions, here is what I can tell you:

"My recommendation for a gear set would depend on a few things: "

Is your Toploader wide or close-ratio? WIDE

What is the output of your engine, and how does it run at low rpm. Output= ~303hp/306lb' torque.

What is the nature of the majority of your driving? Weekends, Fun around town ~70mph.

How tolerant are you of an engine turning high rpms? Doesn't bother me was curious if this were detrimental to the engine.

Now that my speedo is hooked up, I'll have the wife drive next to me to see how far off the speedometer actually is.