Decreasing RPM at High Speeds

[ty.forestcom]

1988 Ranger 2.9L, 2wd Standard Cab Long Bed.

Good Afternoon everyone.

So my Ranger I believe has 3.73 gears. I’ve got a FM132 and 2.9. The truck has a good bit of torque under 45 mph. I cruise on the highway at about 2500-2700 rpms, ~ 60-65 mph. I don’t care about low end torque at all. I’d like to be able to cruise at least 75 but wouldn’t mind 80-90 mph. (All suspension is new, it’s very low and handles great). Tires are 225/55-15. 8 inch wide, Billet Welds. I need to be under 2500 for long drives. I am planning to drive cross country this summer and need a solution.

I am thinking of swapping my gears to 3.27 or even 3.08 if possible. Has anyone had experience with this? I have a 7.5 rear axle. Can’t find much online on someone else doing this, is it as simple as I’m hoping or going to be a job?

Thank you,
Tyler

 

[Curious Hound]

Easiest way is to find another 7.5" or Ranger-width 8.8" axle with the gear ratio you want. A 7.5" will be the closest to a "bolt-in" solution. Try reading this article.

Ford Ranger Rear Axles (1983-2011) - The Ranger Station

Explore the 7.5-inch and 8.8-inch Ford Ranger Rear Axles (1983-2011), how to identify them, gear ratios, and detailed specs for each model.

www.therangerstation.com

 

[Roert42]

According to this chart going from a 3.73 to a 3.08 rear would drop you about 500 rpm.

I’d imagine a 3.08 would be pretty miserable around town, but worse case you could always swap it after your trip if you decided it was too tall.


Gear swapping in an axel can be complicated if you go by the book. Plenty of people have not gone by the book and it’s turned out ok. You need a few hundred dollars in specialty tools and a lot of patience.

Gear Ratio & RPM Guide For Larger Tires - The Ranger Station

This Gear Ratio & RPM Guide will enable you to see how many RPM's your engine will turn based on gear ratio and tire size.

www.therangerstation.com

 

[Curious Hound]

According to this chart going from a 3.73 to a 3.08 rear would drop you about 500 rpm.

I’d imagine a 3.08 would be pretty miserable around town, but worse case you could always swap it after your trip if you decided it was too tall.


Gear swapping in an axel can be complicated if you go by the book. Plenty of people have not gone by the book and it’s turned out ok. You need a few hundred dollars in specialty tools and a lot of patience.

Gear Ratio & RPM Guide For Larger Tires - The Ranger Station

This Gear Ratio & RPM Guide will enable you to see how many RPM's your engine will turn based on gear ratio and tire size.

www.therangerstation.com

Not sure if you looked. But the tire size he mentiined is only 24.7" diameter. I think he'd be ok with a gear change on those Hot-Wheels tires.

 

[bobbywalter]

the ranger setup 2.9 is a truck engine in its oem form...more tq that hp.

its pathetically low power by todays standards but top dog back in 86.



what you propose...its good on paper. the 2.9 makes peak tq around 25-2700.... based on that ....possibly a 308 gear would be perfect...in theory. but thats not how shit works dynamically.

hp otoh is sorry at 2500. very low. in that regard its what makes it a peaky engine by some peoples standards. in a merkur it is a riot. so in your truck this should be fun too...with 205 60 15 tires it needs 360 gears to do that fun and hold 130 mph top speed ....

there is a balance....at 1 to 1 you can do pretty good. in overdrive your gonna fall on your face at those wind loads in hills. 170 ftlb and 60 hp is a big ask.

the rpms it will run at 100 mph with 3.73 gears wont hurt that engine at all.


i would wager your economy will be much lower with 308 gears at 90 mph than with 373.

 

[bobbywalter]

Not sure if you looked. But the tire size he mentiined is only 24.7" diameter. I think he'd be ok with a gear change on those Hot-Wheels tires.

I dunno bout that .... These hot wheels look pretty beefy...

 

[Roert42]

Not sure if you looked. But the tire size he mentiined is only 24.7" diameter. I think he'd be ok with a gear change on those Hot-Wheels tires.

I think I buggered up my conversion

 

[ty.forestcom]

I think I buggered up my conversion

24.7 sounds about right, they don’t look like the wheels he sent.

 

[Curious Hound]

24.7 sounds about right, they don’t look like the wheels he sent. View attachment 141218

It's easy. There are probably hundreds of tire size calculators online. You type in the metric size, hit "calculate" and it spits out the dimensions that are more meaningful to us.

 

[Roert42]

It's not that hard to convert metric tire size to a height in Inches.

25.4mm = 1"

225/25.4=8.86 (convert your metric tire width to inches)

(8.86*.55) * 2 = 9.74 (tire width X side wall ratio = side wall height. x 2 for top and bottom)

9.74+15 = 24.74" (add the height of the sidewall and the height of the wheel)



or if you're weird you can convert the wheel size to metric and do everything in mm.

 

[Shran]

I have a Ranger 8.8 axle with 3.27 gears that I would just about give ya if South Dakota is anywhere near your travel route. I'd even help you install it - 98% bolt in swap for your truck. Came out of my low mileage 94 when I swapped for 3.73's.