I am thinking of swapping in a GSL-SE (FB) tranny into my car, primarily because of the higher gear ratios and also for a possible weight savings. i can get the tranny for fairly cheap, so that isn't an issue, however i'm just wondering if it is worth the trouble? i know what is involved as far as installation is concerened, but if the gains aren't much and if there are any downsides to this (other than a higher cruise RPM), then i would like to know.

looking at the design it is quite similar to the FC non-turbo transmission so power handling should be fine, assuming the tranny is in good shape. this will be going on a stockport S5 non-turbo, and most track use will be autocross, with some being road course use...

 

Other than a few of the gear ratio's there is no difference between the M type tranny in the GSL-SE and the M type tranny found on non turbo FC coupes.

There is no weight savings. There is no lower or higher power handling. There is no reason.

 

ok...well 1-3 gears and 5th are higher ratios, although i haven't calculated how significant it is, in terms of torque multiplication percentage, but 3-4-5 will be a closer ratio...

gear ratios can be found here: http://www.mazdatrix.com/g1.htm

 

I wouldn't bother with it unless I was in desperate need of a tranny and that was the only one I could get my hands on.

Here is a site that has a lot of info on which trannys swap from what vehicles to others, and how to do it (some 1st gen trannys require the tailshaft housing from the 2nd gen tranny for it to fit in a 2nd gen car).

http://mrmazda.no-ip.com/interchange.html#TRANUSAGE

 

I would leave it alone...

 

alright, looks like it is not worth it as a direct swap. well i might still buy it for a spare, and rip it apart for curiousity. i'm interested in seeing how hard it is to rebuild a transmission. ultimately a custom ratio set with a rebuilt tranny would be ideal...

another idea i have, which is probably a better bet, is to take an FC diff, put a 4.3 ring and pinion in it, and put a torsen from either a Miata or aftermarket unit.

 

I just recently bought a hybrid FB/FC tranny where the previous owner put a 12a FB transmission together with S4 FC tail and bellhousings. I haven't installed it yet because I'm away at university and my car's at home. I wasn't even really going to do this, but it was super cheap, so I figured I didn't have alot to loose, besides, I needed to take my tranny out anyway to change a leaking seal.

I made up a spreadsheet to compare the S5 NA tranny with the 12A tranny including post redline shift RPM's, approximate speed in gear at redline, % reduction in gear ratio, the RPM drop for each shift, and the approximate RPM at cruise speed in each gear. The GSL-SE has a taller 5th though (that's the only ratio difference IIRC), and that's the one I would have chosen if it was me doing it from scratch.

I can email the spreadsheet to you if you wish so you can have a look at it, but you'd need to confirm that the stock gearing on your car (1989) is the same as on mine (1991), and you'd need to change the 5th to the GSL-SE ratio on the FB tranny part of the sheet.

Apparently it's "better" to use the FC bellhousing (don't ask me about the details), and using the FC tailhousing puts the shifter in the correct location.

I'll post some feedback once I've installed it and driven around a bit with it (just over a month from now or so probably).

As for it being worth the trouble, well that's a judgement call depending on the cost and condition of the FB gearbox, labour costs (you vs shop), parts costs (seals etc), and the use of the car. If you autocross this mod will put you into SM2, a very fast class, so just keep that in mind too.

 

thanks, that's the kind of info i was looking for (or rather was too lazy to produce myself, haha).

it would be me doing the work, so really it's not the cost, just the time and effort involved with this sort of thing.

about autocross, i just got into it, and i don't really do it competitively (i don't participate for a full season), or at least no at the moment. besides, where i race the classing structure is really simple and a modification such as this may not really make much of a difference.

i sent you a PM about my e-mail. thanks.