JGriff

I recently acquired a 1990 S2, and the PO put in a 1989 Turbo S tranny (with LSD and oil cooler) after the OEM unit was damaged at a track event.

I've put up a page detailing the swap, including the differences in RPM/MPH for each of the gearboxes. This may help shed some light on the subject (i.e. whether 5th is OD or not).

On that note, what do you folks think of this swap? If you get a chance, please read the page, look at the charts (there is one page showing all RPMs and MPHs), and give me your thoughts.

Also, would this swap affect my odometer and speedometer at all, and if so, by how much? Would it be insignificant?

Here's the gearbox swap link:

944 S2/Turbo S Gearbox Swap

Thanks.

Jim

Tom Pultz

Did he happen to say what broke? Ring & Pinion perhaps?
You can't determine whether 5th is "overdrive" from the charts. You have to look at the actual ratios. 5th gear in both the turbo S and the S2 is "overdrive" by definition because the ratio is less than unity (1.0). The Turbo S 5th gear ratio is "shorter" than the one in the S2, which puts 4th and 5th closer together since both gear boxes share the exact same ratios for 1st-4th.
I'd have to drive two identical cars back to back to see which one I preferred. My gut feeling is for the street I'd take the stock gearbox, but for the track I might want the Turbo S.

I think if you put the gear box parameters into one of those acceleration programs you will find the stock S2 gearbox will give faster overall acceleration because of the numerically lower drive ratios.

The only thing that might be faster is a true 0-60 since you can do 60 in 2nd gear without having to shift. Other than that I'd say it would be slower on the street.

Like the PO found out, things could change on the track given the circumstances of the speed through the various corners and the track you drive.
Not to be a smart a$$, but what do you think? Look at the charts. 3000 rpm in 5th gear is 73 mph with the S2 and 79 with the Turbo S. That's 6 mph by my old math

JGriff

Yep, the Ring and Pinion broke. I don’t know if when it broke, if anything else was affected. As my page stated, he was more of a “track” guy, so that is why he decided to put in the Turbo S tranny.

True. That’s why I enjoy 3rd and 4th so much.
That’s good to know. I didn’t look closely enough to realize that 4th and 5th are closer together now.

Ditto. This is the only S2 that I’ve driven, so I really can’t offer a valid seat-of-the-pants comparison. Maybe someday we can drive each other’s car… to get a feel for the difference.

The PO was more of a “track” guy, so that is why he felt that it was a worthy swap. He was the type of guy that had a trailer etc., to take the car to the track. I don’t think he cared that much about the impact that the swap had on daily street driving. I haven’t owned the car long enough to make a decision as to whether I hate it or love it yet (the swap that is… not the car. I love the car.)

I don’t see this car as a drag racer, and I don’t usually succumb to “Stoplight Grand Prix” races, so it may not bother me all that much. Depending on how much I choose to auto-x and track the car, I may end up feeling that it was a worthwhile swap. Only time will tell.

True. I am going to graph these two charts at some point, in order to get a better picture of the difference, and to understand what rpm is best (to upshift) for each gear. By studying the graphs and charts, and experimenting a bit, I hope to find the best rpm shift points to maximize power/speed in each gear. I was looking at the charts last night, and I’m thinking that 5000 rpm might be a good point to shift at in each gear. I’ll have to try it and see.

True. There may also be an advantage at an auto-x, for not having to shift out of second all that much (or at all, depending on the course).

True. That is what he experienced, and that is why he said he did it.

True, that is the obvious. But I was thinking a bit further, on a % basis, and looking back at the charts, and calculating the % at different rpms (2k, 3k, 4k, 5k, 6k) in 3rd, 4th, and 5th gears, the % difference varies. In third gear and fourth gear, the % difference is 14%, while in 5th gear, the % difference is 8%. I guess I should remember that when I see a speed trap ahead.

So, this would mean that my odometer would be different by either 14% or 8% also, depending on which gear I am travelling in, right? The overall effect on my odometer would be some kind of average of these, I suppose. I guess I should take that into consideration when figuring maintenance schedules, since the odometer will show less than actual, right? I’ll probably use 14% when figuring it, since I spend most of my time in 3rd and 4th gears.

Thanks for all your help. I greatly appreciate it.

Jim

Tom Pultz

After I posted my response regarding the speedometer differences I thought to myself...hmmm, the Turbo S trans may give you the same readings as the stock transmission. Why? Because the speedometer/odometer gets its signal from the transmission, and the Turbo S may have the appropriate gear drive/sensor/whatever so that it provides the correct information to the speedometer. Otherwise, you'd need different speedometers for the various combinations of transmissions. I'll look at the PET CD and see what I can find.

I guess the easy way to find out is to just drive the car and see what the indicated speeds are at a fixed rpm in each gear... then compare to the charts.

There are times when I drive my son's Turbo S that I wish my gearbox had longer gearing. The problem is, he's got 300 HP and 350 ft-lb of torque in his mildly modified car, and that torque makes a HUGE difference in how the car behaves in each gear. Basically, the Turbo S doesn't care what gear it's in, it just goes

JGriff

Thanks. That would be great if you could. I'd like to try to get as much info as possible, to help put my mind at rest (at least as far as knowing what is really going on with my car).

I was planning on doing that... as soon as all this d*mn snow melts, and my driveway is free of ice!! Once I get the car out of the garage for a nice drive, I'll bring along the charts and compare it at different rpms/speeds.

That's for sure!! It surely must be a blast!!

Thanks for all your help.

Jim

944Ecology

The Turbo S tranny will read exactly the same speed as the S2 tranny, primarily because the speedometer sender is driven off the output flange. The output flange is mechanically coupled to the halfshaft, which is mechanically coupled to the rear wheel, so the speedo will read exactly what it would, whether a turbo, an S2 or a NA transaxle...

JGriff

[quote]Originally posted by 944Ecology:
<strong>The Turbo S tranny will read exactly the same speed as the S2 tranny, primarily because the speedometer sender is driven off the output flange. The output flange is mechanically coupled to the halfshaft, which is mechanically coupled to the rear wheel, so the speedo will read exactly what it would, whether a turbo, an S2 or a NA transaxle...</strong><hr></blockquote>

Thanks!!

That is more or less what I found, when I compared my speeds/rpms in different gears to the charts.

It was "off" a little bit, but not by much. I'm thinking that the difference may be due to different tire sizes on the rear i.e. 245s vs the 225s that were standard on the S2.

Thanks again.

Jim

TaboII

Ok I finlaly can speek here with some experience.
I have an 87 944 na and swaped out the gearbox with and 87 turbo with the oil cooler version. I can say that if the conversion was done correctly your tac and speedo should read correct as long as the pickups where swaped from your old gear box to the new. IMHO I have longer gears that is to say a higher top end because of the swap and installed a MSD igniton system to compensate for the low rpm trouble that is so promenent in these cars. No problems at all!!! <img src="graemlins/bigok.gif" border="0" alt="[thumbsup]" />

JGriff

[quote]Originally posted by TaboII:
<strong>Ok I finlaly can speek here with some experience.
I have an 87 944 na and swaped out the gearbox with and 87 turbo with the oil cooler version. I can say that if the conversion was done correctly your tac and speedo should read correct as long as the pickups where swaped from your old gear box to the new. IMHO I have longer gears that is to say a higher top end because of the swap and installed a MSD igniton system to compensate for the low rpm trouble that is so promenent in these cars. No problems at all!!! <img src="graemlins/bigok.gif" border="0" alt="[thumbsup]" /> </strong><hr></blockquote>

Thanks for the feedback. I'm glad to hear that you are enjoying the swap.

I don't know if the pickups were swapped on my car. Before I bought the car, I asked the PO if the swap had any impact on the odo/speedo, and he said that it didn't. I don't know if he knew for sure, or if it was based on his subjective evaluation from driving it.

Regardless, it seems okay to me so far.

You mention low rpm trouble in these cars. Is that in all 944 models, including the S2 models? What kind of trouble are you talking about? What does the MSD do to help the problem, and is it an easy install?

Thanks.

Jim

Riff

Jim-

I am in Providence and you are in Boston??? Perhaps we can do that back to back drive someday to see the real world differences of the gearbox swap. I'll be at the NER AX's during the year, hopefully we'll run into each other.

There was another 951 gearbox for sale with an Guard Transmission TB LSD that I was seriously considering, but couldn't quite figure out if I would be happy with the swap. Trying to interpolate feel from numbers is tough, much rather have hands on experience.

Cheers,

JGriff

[quote]Originally posted by Riff:
<strong>Jim-

I am in Providence and you are in Boston??? Perhaps we can do that back to back drive someday to see the real world differences of the gearbox swap. I'll be at the NER AX's during the year, hopefully we'll run into each other.</strong><hr></blockquote>

Actually, I am in Auburn, which is right next to Worcester. I am only about 45 minutes away from Providence (via Rte 146).

It would be great to do a comparison test drive between the two cars. I'm not sure if I'll make it to any of the NER AXs this year. I'd like to, but we are expecting our second child in May (another boy!!), and I'm sure we'll have our hands full. (Our other son is 19 months old... and he keeps us hopping, all by himself!! Yikes... wait until his baby brother arrives!!)

If we don't meet up at an AX, maybe someday we can work out a time to meet somewhere... your place, my place, or a place in between.

[quote]<strong>There was another 951 gearbox for sale with an Guard Transmission TB LSD that I was seriously considering, but couldn't quite figure out if I would be happy with the swap. Trying to interpolate feel from numbers is tough, much rather have hands on experience.

</strong><hr></blockquote>

I don't blame you for not jumping right into it, without first driving one to see if you like it. I would have done the exact same thing. (Although, you could say that I did take the plunge, by buying my S2 with the swap, without test driving another with an OEM gearbox, for comparison...)

I'm guessing that if we do get together to drive each other's cars, one of us will be disappointed... either me with the swapped gearbox... or you wishing you had bought the one mentioned above...

We'll have to see.

Keep in touch.

Jim