Rear end

[Britishstev56]

I do a fair amount of highway driving and my rpm is up around 3000 at 80 mph, my buddy has same car 347 t5 and he,s only pulling 1800 at 80 .I have not got under car yet to if there is a tag just wounding what gear to go to to get rpm down some

[jhv48]

You probably have a .82 fifth gear ratio in your trans while he has the much taller .64/.62. Yours is designated a road-race ratio, his is called an overdrive ratio. Both have advantages and disadvantages.
You can change out the fifth gear in your trans but it won't be cheap. A lot depends on your engine as well. If you have a revver rather than a torquer, you could be out of your power band if you try to swap to a lower fifth gear ratio.
I swapped from a .64 fifth to a .82 fifth because I got tired of having a 1000 rpm drop between fourth and fifth gears and was tired of rowing back and forth between fourth and fifth when traffic slowed or I wanted power to pass. I now have a useful fifth gear, but then I mainly cruise at 70-75 mph at 2800 rpm.
If you regularly cruise at 80mph, then you might benefit from the taller gear.

[Clois Harlan]

If you have a .82 fifth gear you would probably have a TKO 600 trans and not a T5. Also, your buddy may have 3.08 rear gears and you more than likely lave 3.50 or even 3.73 gears. Easy to check but look it up on google.

[Britishstev56]

Thank guys when I get a min will climb under car

[jhv48]

Easy way to tell if you have the overdrive fifth gear.

Do your rpms drop about 1,000 rpms when you shift from fourth to fifth? If so, you have the .64 overdrive. If the 4-5 shift is like going from 3-4, then you have the .82 fifth gear.

[Dwight]

Here is a link to gear calculator.

If you have a Mustang T-5, I think you can use the 3550 in the drop down on the transmission chart.

What size tires are you running?

Have you GPS the speed to check you speedometer?

4.10 gears with 295/50/15 tires will be close to 3000 at 80 mph.


Dwight


Second Strike Gearing Calculator

[Britishstev56]

Hi thank u for the link worked great could not find tag on rear, spun wheel counted drive shaft kinda worked out I have 3.25 rear may go down to 3,08 .I know I will loose out on up and go but I can cruise at 80mph at lower rpm