Safe cruising RPM

[Anonymous]

I want to do a rear gear change to a 3:45 . With the tire size I am running the engine RPM at 65mph is 3000. Is this too much on my 200? Thanks. Also is this ratio going to kill my gas mileage ? Thanks.

 

[MustangSix]

An engine in good shape can handle 3000 rpm sustained with no problem. But, yes, your mileage will suffer.

 

[Anonymous]

Be sure cooling system is up to that also.

Just my $.02

Russ

 

[Anonymous]

I think I might compromise with a 3:27 . I have a 2:79 now. Would a 3.08 be a noticeable difference ?

 

[Anlushac11]

8)

Yes but the 3.27 would be my choice. I have a 3.45:1 I am putting in my '80 Stang. In my case I want performance over mileage.

 

[Anonymous]

Let's say, like me, you have the stock 185/80R13 tire:

D= 185 X .80 X 2 / 25.4
D= 11.65
Then, add your wheel size.
11.65 + 13 = 24.65

Lets say you want to cruse at 75 MPH, based on the stock 13 inch tires and peak HP @ 2800 RPM. I went to the Bowling & Grippo web site, http://www.bgsoflex.com/auto.html and selected Best Differential Gear at the left, and this was the result:

Best Final Gear Ratio Calculator by Bowling and Grippo
Input Parameters Are the Following:
Top Speed MPH = 75
Tire Diameter (Inches) = 24.65
Peak Horsepower RPM = 2800
Computation Results:
Computed Best Differential Ratio is 2.74 to 1
Computed Maximum Differential Ratio is 3.07 to 1
That’s why I’m looking for a 2.8 or a 3.0, 8â€￾ rear end for my project.

 

[XFlow_Fairlane]

I think that is why my 170 is getting low oil pressure....3.50 gear in back and all my driving is at highway speeds (60-75mph) looking for a 3.27 and a fresh 200 with a 3.03 bell and a t5 plate for it this spring.


nick

 

[Anonymous]

I failed to mention I can get an 87 Mustang 8.8 with 3.08 for 75.00. It bolts right in to my LTD. Best price I have seen for the same rear with 3.27 is 250.00 . will the 3.27 be that much better?

 

[XFlow_Fairlane]

I would skip the 8.8 rear. there are people in the 12's on 7.5 rears. also the 7.5 is lighter so better milage/acceleration.

nick

 

[Anonymous]

3000 rpm's is nothing to worry about. Even up to 3500 if you engine isn't about to go. I have put on many of miles with mine running 3000-3500 rpm's with no problems at all. I do use Mobil 1 motor oil. I have done this on two different vehicle's. That for me was around 63-65 cruising range @ 3000 rpms.