I don't like going down the freeway at a shrieking 3500 RPM. How much extra gearing would getting 3.70 diffs get me and how much on average does it cost?

What are you driving? I'd guess it was an EA82 Manual.

With my GL-10-Turbo, it loves 3500rpm. anything much lower lugs it.

OH yeah, if it was a manual you'd have to open the tranny up and put a 3.7 diff in, unless the tranny is from a turbo. Automatics are 3.7 too, I believe. You probably know all this since you are asking about gear ratios.

it gains you a good bit. the 3.7 drops the rpm's alot...like 750 RPM off the top of my head. makes a huge difference in gas mileage as well. my automatics get BETTER mileage than my manuals because they are geared much better for highway driving (i have all XT6's). they are basically the same but for all highway driving the auto gets 28 and the manuals get me 27 mpg. the difference in mileage would be much larger if it was comparing manual transmissions but the XT6 never had a 3.7 manual trans option. that's one reason i like the automatics, they are much quieter on the highways. get a 3.7 in your manual trans i would expect a decent gain in gas mileage and definitley quieter rides.

I'm not sure of the costs, but here is a parts list for a manual tranny. You'll need a tranny, rear diff and axles out of a turbo car. I'm not too sure about an auto conversion, but I know you'll need the tranny and rear diff, you may not need to change the axles.

Probably not worth the cost. Yes, it does lower the cruising RPM, and yes it should decrease the amount of fuel that you use at cruise. BUT... it would take you many months if not years to amortize your investment in parts and labor.

 

And the EA81/EA82s have such a short stroke that running at 3500 (or even 4000) rpm is not such a big deal. Read all the posts about still seeing original crosshatching on engines with 200k miles on them.

All automatics do not have 3.7 final drive ratios. The owner's manual says they do, but this is a MISPRINT. If you check the tag on the rear diff of any nonturbo automatic 4 cylinder, it'll be 3.9.

 

All turbo cars are 3.7. All nonturbo cars are 3.9.

 

Changing to 3.7 by swapping transmissions will probably not change much- I've noticed that the 5 speed turbo cars I've driven still rev at around 3500 rpm at 70mph. The internal gearing is different. To get a serious advantage you'll probably have to open your transmission and replace the actual differential gears.

TROGDOR, it wasn't the ratio that I was talking about, it was the axle, I heard somewhere that autos had a 25 spline axle like the turbos, going to a 3.70 turbo tranny with 25 spline axles, you might not need to change the axles with an auto tranny.

TROGDOR, it wasn't the ratio that I was talking about, it was the axle, I heard somewhere that autos had a 25 spline axle like the turbos, going to a 3.70 turbo tranny with 25 spline axles, you might not need to change the axles with an auto tranny.

Turbo ATs (at least 3AT) have a different spline count (23???) than the turbo manuals.

Turbo ATs (at least 3AT) have a different spline count (23???) than the turbo manuals.

Thanks, like I said, I had heard something different, but never checked it out.

Thanks, like I said, I had heard something different, but never checked it out.

My response should have had a melancholy emoticon... I found out about the differences when I had hoped to (ab)use my turbo 3AT's "Lifetime Replacement" axle receipt by getting replacements for a turbo manual.

 

It kept me honest...

Oops, my mistake.

 

Yes, the turbo 3sp autos have 23 spline axles, and the turbo MT's have 25 splines. Also, the 4 speed autos have 25 spline axles... correct me (again) if I'm wrong, but those trannys were only used in turbo sedans/wagons? Some nonturbo 4WD XT's got 4EAT's, and as for the spline count on them... anybody want to yank one and count? My bet would be 25 spline.

I guess "not worth it" is the answer I'm looking for. Something spinning around 50 times per second just seems so fast to me.

My engine spins approximately 210,000 reveloutions. in my 45 min commute down the highway, thats over 11 miles the pisons travel. And that dosen't bother me, just kind of suprised.

 

 

 

Matt

WOw, you must have a lot of time in your 45 min commute to figure out all that there "mathematics with yer 'piston travel' "