Ford Mustang Forum banner

1 - 20 of 24 Posts

·
Registered
Joined
·
2,467 Posts
Discussion Starter #1
How would i know what my car has doing 65 mph in 5th gear im doing almost 2000 rpms....stock tire size from the factory....
 

·
Registered
Joined
·
1,456 Posts
your ratio is 2.73 or 3.08, with the tire size i can tell which one
 

·
Registered
Joined
·
2,467 Posts
Discussion Starter #3 (Edited)
your ratio is 2.73 or 3.08, with the tire size i can tell which one
The tire size is stock...what came on the car i dont know the size off hand tho....I checked my door tag too it says "Z" i think that means 3.08 no?
 

·
Registered
Joined
·
941 Posts
thats odd cuz im at 75mph at 2k
 

·
Registered
Joined
·
1,364 Posts
If I remember right, I'm at about 2000 RPM's at 60 or 65 with my 3.55's. It's been awhile since I've driven my car. There used to be a gear ratio calculator on this site, but I can't find it now.
 

·
Registered
Joined
·
2,467 Posts
Discussion Starter #7 (Edited)
I just tried it too....didnt work...I am going like 1950rpm @ 65 mph in 5th gear so i think i should be 3.08's ????
 

·
Registered
Joined
·
1,364 Posts
Keep in mind I suck at math, but I did some quick calculations. If I remember correctly, the diameter of the stock tires is approx. 25.6".

25.6 x 3.14 = 80.42 circumfrence of tire
80.42/12 = 6.70 circumfrence in feet
5280/6.70 = 787.82 revs/mile
787.82 x 3.55 = 2796.75 engine revs w/ 3.55:1 axle ratio in 4th gear (1:1 ratio)
2796.75 x .68 = 1901.79 engine revs in 5th gear @ 60 MPH (.68:1 ratio)

I've got the actual formula to figure this in a book somewhere.
 

·
Registered
Joined
·
1,456 Posts
ok, if the door code for the axel is 'Z' then your axel is an 8.8" traction-loc with a 3.08:1 ratio
 

·
Registered
Joined
·
941 Posts
so i guess i got 308's
 

·
Registered
Joined
·
2,467 Posts
Discussion Starter #13
ok, if the door code for the axel is 'Z' then your axel is an 8.8" traction-loc with a 3.08:1 ratio
Ok so thats not to bad is this the better rear 8.8 im guessing yes?
 

·
Registered
Joined
·
1,364 Posts
All '85 Mustang models had a 7.5" axle. Ford didn't start putting the 8.8" in the Mustangs until '86 and only in the 5.0L models. Unless someone has swapped out your axle, your '85 has a 7.5". Also, if you use the calculator posted above, plug in the info (stock tire size of 225/60-15, 2000 RPM, 65 MPH, and the '85-89 T5 5th gear), it gives you a ratio of 3.45:1, which is an available ratio for a 7.5" axle.
 

·
Registered
Joined
·
2,467 Posts
Discussion Starter #16
All '85 Mustang models had a 7.5" axle. Ford didn't start putting the 8.8" in the Mustangs until '86 and only in the 5.0L models. Unless someone has swapped out your axle, your '85 has a 7.5". Also, if you use the calculator posted above, plug in the info (stock tire size of 225/60-15, 2000 RPM, 65 MPH, and the '85-89 T5 5th gear), it gives you a ratio of 3.45:1, which is an available ratio for a 7.5" axle.
How can i tell if the rear is an 8.8?? Also the car does seems to have a decent gear in it ....I seem to be like 2500 rpm or so in 4th at like 60 but this rear isnt that strong tho right?
 

·
Registered
Joined
·
8 Posts
i ran a 4 banger 7.5 in mine right after i swapped the my engine. i ran that for like 4 months and i beat on it. it was still working fine when i pulled it out. idk ive heard mixed opinions.
 

·
Registered
Joined
·
1,364 Posts
How can i tell if the rear is an 8.8?? Also the car does seems to have a decent gear in it ....I seem to be like 2500 rpm or so in 4th at like 60 but this rear isnt that strong tho right?
You can tell by the shape of the inspection cover. A 7.5" will have flat sides on the top and bottom with round ends. A 8.8" will have four flat sides. The summit catalogs have the gasket shapes printed in their gear section if you have one and want to look at that.
 

·
Registered
Joined
·
2,467 Posts
Discussion Starter #19
Ok thanks ill take a look after work...:bigthumbsup
 

·
Registered
Joined
·
2,796 Posts
....a ratio of 3.45:1, which is an available ratio for a 7.5" axle.
The 3.45:1 rear axle ratio was not available with V8s, in any year.
 
1 - 20 of 24 Posts
Top