XR4Ti Archived Tech Articles

    T-5 and Differential Gear Choices - this covers the topic of the 4.03 and 3.97 first-geared T-5 as it mates up to both the 3.36 (auto) and 3.64 (manual) differential gearing, with a supplemental section on the SVO T-5 ratios.

Date:         Sun, 8 Nov 1998
Subject:      Re: Need correct choice of T5 ratios for XR project.

List Members,

I am going to add on to my original post dated 11/3/98...  Chris Anglin wrote:

> The 4.03 first gear from the 85-86 TurboCoupe
> box worked out perfect in my XR4Ti.  Why?
> I swapped an automatic out (3.36 rearend gear)
> and put the T-5 box in.  If I had the manual
> transmission rearend gear (3.64), this might
> not be so pleasant.

Last night I got the opportunity to drive list member, Marshall Baugh's, XR4.
Just like mine, his was orignally an automatic XR equipped with the 3.36
differential gear.  He put a T-5 in that is very similar to mine, a '90 2.3
'Stang T-5 with the 3.97 first gear.

This is all fine and dandy, right?  So why should it be any different than my
XR (4.03 first, 3.36 rear).  Well, he broke the 3.36 rear end (or at least
something in the driveline).  He chose to replace the whole rear suspension
and differential.  The rear gear that went in is now the 3.64.  This is where
things get exciting.

I suggested that the 2.3 T-5 first gear gearing (uh... yeah), which has never
been lower than 3.97 (according to my info) might not be too pleasant with the
3.64 rear gear ratio.  I was wrong and right....

I only got about ten minutes to drive the car.  There is a noticeable
difference, sure.  But it wasn't as bad I was expecting.  I thought it would
be a brutally short first gear.  It wasn't bad.

According to CarTest and the numbers I entered, the torque peak in first gear
came about 2 mph lower with the 3.64 than it does with the 3.36.  That isn't
all that bad.

Naturally, the car felt quicker.  Not a whole bunch, but it was more neck-
snapping.  Which makes sense, as everything happens quicker.

Ah well, enough is enough.  I think I have gotten my point across.  I might
take some getting used to the 3.64 on top of the 3.97 first.  It might annoy
you.  If you are an autocrosser, you might be able to launch in second and get
into the first turn quicker without having to upshift.  Who knows.  It has


I haven't posted this information (as of this moment), but I'd like to 
interject some other points.

I believe Jeff Jackson posted to this same subject line shortly after I 
posted.  He stated that he liked the gearing of his SVO T-5 the best.  I 
have driven the car and can say that the 2-3 shift is more properly 
spaced than any other T-5 I have shifted.  When I got my autocrosser back 
on the street recently, one of the things I noticed was the odd spacing 
between 2nd and 3rd.  It seems like the rpm drops a little too much.

If I have the need to rebuild my tranny in the near future, I am going to 
look seriously into the SVO gearing.

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Published by Chris Anglin.