Glenn M

I'm curious what you Boosted guys think (400 - 450 RWHP), 87 2.20 Auto trans & diff or 89 2.54 auto trans & diff? Assume they are both LSD. I see where some 90 and above guys want the 2.20 diff but is that with the 5 speed.

The gear spacing and diff 2.54 rear is a better match for NA cars but what about boosted?

Thanks,
Glenn

hacker-pschorr

Is the final ratio the only difference? I thought the gear spacing was a bit different between these boxes.

Glenn M

Supercharger- twin screw, would it be different for a Vortech?

Thanks,
Glenn

Glenn M

Ratios are also different between the boxes. Guys with the 89 autos have told me the spacing is much better than the 2.20's trans cars.

Thanks,
Glenn

Bill Ball

If you want to go over 200 MPH, you'll need the 2.2.

jorj7

I found that the 1:2.54 FDR is better until you get over 500 rwhp, but that's only
because I'm more concerned with top speed then RPM at freeway speed. That's
with a Vortech SC where the horsepower increase dramatically with RPM. I currently
have a 1:2.20 ring/pinion in my 90 S4 tranny with PSD and over 500 rwhp. YMMV.

hacker-pschorr

I would go with the 2.54 for that reason, reguardless of how the power is made.

In other news, I have an 89 - 2.54 auto in storage that needs a home


Does anyone have the WSM charts for these transmission? I cannot find mine right now - I'm buried in 944S manuals.....



Someone page Kibort.....

dr bob

I think I'd be looking at the 2.20 axle for this, since it gives more gears to choose from after the wheel spin stops. With all that power, you can gain some cruising comfort without sacrificing normal driving-range performance. Plus add some to the top-end capability.

Glenn M

My 87 has 2.20 no LSD, I have an 89 2.54 with LSD I was going to put into the car.

I would like an 8 disc LSD.

Thanks,
Glenn

soupcan

I have an 87 2.20 with LSD that I would trade for an 2.54 with LSD but, I think I would need some LSD to get the energy to swap them out.

dprantl

Let's just say you can't go wrong with a twin-screw setup and the 2.2. You will get better gas mileage cruising on the highway in top gear, and you want a longer 1st gear so you don't burn tires so much. There's so much torque at low RPM anyway that there really is no reason to have shorter gears.

Dan
'91 928GT S/C 475hp/460lb.ft

Vlocity

I'm running the 2.74 LSD with a 5 speed on my Twinscrew with 10 Psi.

It is awesome crawling off of the corners and I still am only into 5th gear on back straight at MidOhio, the rest of the track I run, I never get out of 4th.

Ken

Glenn M

Ken,
That must be a hoot!

Seems split between the 2.20 and 2.54. Great points on both sides.

What king of RPM difference at 65-70 cruising?

I've only driven a Murph 87 Auto non-LSD SC'd car (Don T.) and it was great!

Maybe better to leave the 2.20 non LSD and get used to the car, less drama.

I appreciate all the comments/guidance.

Thanks,
Glenn

mark kibort

for most tracks, road racing that is, if you are not making over 400rwhp, the 2.2 has ideal gearing for most tracks, including those back east. remember the gear spacing is about the same , with exclusion of 5th. It really depends on what operational speeds you will be frequenting, and what RPMs you want to be in those respective gears /speeds.

mk

IcemanG17

It all depends on your goals.....with 4-450whp the top speed of the 2.54 will probably be slightly higher...since you really need 500whp to push the tall 2.20 gears.....

Since I own a 2.20 stock automatic....and have driven or been in many 2.54 automatics, including some boosted ones Heres my impression:

In 1st and 2nd gear both feel pretty similar....not much difference really since both are within a few MPH of each other.... the single biggest difference is 3rd gear.....since in the 2.20 its a 140mph gear vs about 120mph in the 2.54...so when you shift out of 2nd in a 2.20 at say 85mph...the rpms really drop...vs the 2.54 at say 80mph the gearing is much closer.....

Honestly with the type of HP you plan on running...it really doesn't matter in just about anything but top speed......since my impressions of 260whp-ish stock autos will be FAR different than 450whp-ish autos......extra power really overcomes differences in gearing...