FB sequential gearbox: the good the bad the ugly...any suggestions
 

I would like to use a sequential gearbox in my build (85 GSL-SE wide body (RE IMSA GTU kit) - RX7Club.com - Mazda RX7 Forum). Anybody have any input on (as the title says) the good, bad, or just plain ugly stay away far far away options?

Check out this YouTube channel. He built this RX-7 with a sequential trans. He is also a member here on the forum.

https://www.youtube.com/@dzmazzei

Street car or race car?

Most true sequential trans have straight cut gears and dog rings, not ideal for the street but doable if you dont mind regular service.

You can get a sequential shifter for a T56, that might be a bit nicer on the street and is easily adaptable.

Conversely, the BMW DCT trans is the hot new choice. I'd like to go that route when I find a bag of cash.

-Alex

Check out HGT https://www.hgtprecision.com/. The have 4, 5, and 6 speed sequential gearboxes and associated parts such as bell house, shifter, etc. I don't believe they have a kit for FB's as they do for FD's though. A custom drive shaft and likely a clutch setup has to be sourced by purchaser. While streetable, in general it removes the civilized aspect of the passenger area except when cruising in the 1:1 gear ratio, which has no gear whine as it is straight through. With the proper control system/parts, no clutch no lift up shifts and no clutch down shifts are possible. Oil change frequency/cost are higher. Torque and HP ratings are much higher than many options available for RX-7s. Some of the Tremec options are likely to be a more practical, much less costly solution.

For the track, a sequential or even just a dog-ring transmission with a normal shift pattern can be awesome. For the street...not so much. If you want to know what that might be like, watch a NASCAR race and in particular in-car footage during a caution. The current Cup Cars have a sequential 5spd transaxle. So that it what you would be dealing with on the street.

The benefit of a racing transmission is the ability to get a close gear ratio stack with allot of gears that can be used on track. With a street gear box you are lucky if you can get 3 forward gears that can be used in racing. And no, I do not factor OD gears in that count. So I get the advantage of a sequential or any other dog ring racing transmission.

I have a Jerico in my race car and it has been fine for the most part but I wouldn't say it was easy to do. Another H-Pattern option would be the EMCO transmission that Mazda Motorsports sells. It is more of a bolt in than my Jerico was but I have heard that it is was $10K installed in 2021 for one of those things. Likely not that cheap now. JPM has had experience with the EMCO and had input on their development.

Thanks all. Basically this will be a track car, that will still be licensed for the street for the occasional play time on some of our fabulous mountain roads.

dk_davis: What do you mean by "in general it removes the civilized aspect of the passenger area" ?

Regarding: "it removes the civilized aspect of the passenger area". When you have straight cut gears, you get gear whine and it is very noticeable. So in street driving situations, non-go fast stuff when you may wish to talk to a passenger, or listen to the radio, i.e. civilized stuff you have to deal with the gear whine or be in the 1:1 ratio where it is quiet. Since rotaries are not torque monsters any speeds less than about 30-35 mph require being in a ratio that whines. Trying to get the minimal gas mileage available by using the overdrive results in gear whine. Sometimes hot rod stuff doesn't impact a large breadth of a cars usage abilities thus some driving situations can remain civilized. But I feel a straight cut geared transmission significantly cuts down on the number of those situations. Possibly somewhat similar to people that like noticeable brap brap and louder exhausts as those lose some civilized aspects of use also.

A trans with straight cut gears will be louder than the exhaust. Even with a rotary.

A dog box is not really tolerant of street driving. They wear more the lighter you shift, you have to bang them into the next gear with authority.

Sequentials are nice when you have a dog box because it is almost impossible to miss a gear, just reef the lever, no worry about getting lost in a gate. Downside is that you can't skip gears. And because it is a dogbox, you still have to shift with authority. The thing to do with a sequential is to have a paddle that controls an air solenoid, and a nitrogen tank that feeds an actuator. Can't shift so slowly that you damage the transmission if you have a few thousand PSI pushing on the shift mechanism :) But then that needs to be refilled on a regular basis so not at all suitable for street use.


Any dog box is a PITA on the street because of all of the lash in the drivetrain, unless you have a non ported engine and a 50lb flywheel.


IMO, if you want a sequential, get an automatic. They work a lot better and are a lot more streetable...