Are these RPMs Correct?


Calypso Ranger

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1992 Ranger with 2.9l 4wd with 5speed manual. It’s got an 8.8 with 3.55 gear in it. It’s on 31 inch tires. On the highway at about 65/70mph I run about 3000 RPM in 5th gear. Is this right? Seems high to me.
 


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pjtoledo

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my 2005 with a manual 5speed 3.73 rear gear, 28" tires does about 2500 at 70. are you sure about that 3.55 gear??
 

RonD

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You have an FM146 trans in 1992 2.9l Ranger 4x4, with these ratios: (1st)3.769 / 2.210 / 1.516 / 1.00 / 0.812(5th)

You can look here: https://www.crawlpedia.com/rpm_gear_calculator.htm

3.55 with 31" tire in 5th gear at 65mph should be at 2,000RPM

With 4.55 axle 2,500RPM

So yes, something is not right, like the Tach
 

Calypso Ranger

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You have an FM146 trans in 1992 2.9l Ranger 4x4, with these ratios: (1st)3.769 / 2.210 / 1.516 / 1.00 / 0.812(5th)

You can look here: https://www.crawlpedia.com/rpm_gear_calculator.htm

3.55 with 31" tire in 5th gear at 65mph should be at 2,000RPM

With 4.55 axle 2,500RPM

So yes, something is not right, like the Tach
My door card says axle:95 so it has to be 3.55 open 8.8 unless it’s been changes but at idle it’s definitely correct so i’m not sure what’s wrong with it. The only thing that makes me think it’s been changed is that sometimes I can get both tires to spin which makes me thing it has a limited slip. Thanks for the reply btw
 

Calypso Ranger

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My axle code is 95 which means 8.8 open with 3.55. But sometimes i’m pretty sure both tires will spin so maybe it’s been changed.
 

rusty ol ranger

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My axle code is 95 which means 8.8 open with 3.55. But sometimes i’m pretty sure both tires will spin so maybe it’s been changed.
Has your speedo been recalibrated for larger tires?

If not you actually pry running closer to 80.
 

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Assuming 27.5" tires on a 1992 Ranger, smallest stock tire on '92 Ranger 4x4
And 31" now
At 65MPH actual speed would be 75MPH

That would be a 300RPM difference, in 5th gear

I would jack up the rear axle, block front wheels
Put trans in Neutral
Spin one tire
If the opposite tire spins in the same direction you have Limited slip, if it spins in opposite direction then OPEN differential

Put a mark on the drive shaft and pinion housing
Put a mark on the inside of the tire
turn the tire one full revolution and count the times the drive shaft goes past the mark on the housing
3 and a 1/2 times would be a 3.55 ratio
3 and 3/4 a 3.73
4 times a 4.10
ECT......

You can change the speedometer gear, 5 minute job, to correct speedometer for 31" tires
 
Last edited:

Calypso Ranger

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Assuming 27.5" tires on a 1992 Ranger, smallest stock tire on '92 Ranger 4x4
And 31" now
At 65MPH actual speed would be 75MPH

That would be a 300RPM difference, in 5th gear

I would jack up the rear axle, block front wheels
Put trans in Neutral
Spin one tire
If the opposite tire spins in the same direction you have Limited slip, if it spins in opposite direction then OPEN differential

Put a mark on the drive shaft and pinion housing
Put a mark on the inside of the tire
turn the tire one full revolution and count the times the drive shaft goes past the mark on the housing
3 and a 1/2 times would be a 3.55 ratio
3 and 3/4 a 3.73
4 times a 4.10
ECT......

You can change the speedometer gear, 5 minute job, to correct speedometer for 31" tires
Sounds good man, i’ll give it a go. thanks a ton
 

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My door card says axle:95 so it has to be 3.55 open 8.8 unless it’s been changes but at idle it’s definitely correct so i’m not sure what’s wrong with it. The only thing that makes me think it’s been changed is that sometimes I can get both tires to spin which makes me thing it has a limited slip. Thanks for the reply btw
WTF you doing at idle that lets you figure out rear end ratios? Black magic?
 

Calypso Ranger

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WTF you doing at idle that lets you figure out rear end ratios? Black magic?
i mean the tach is right at idle and i looked up my axle code
 

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