Not sure if this is the correct forum so move if needed

im looking at swapping to the 350/70z trans. Looking at gear ratios the z trans has a 6th gear at .79. The looks to be .71

clearly not much different. I’m wounded if there are companies out there building taller 6th gear for the z transmission.

my other concern is short shifter. I currently have the Mazda speed replica short shifter and love the throw on it much shorter than the RE short shifter. Would like to find a short shifter close the the one I have for the z tans

 

a surface level google search shows there are no off the shelf solutions for a CD 6th gear. the solution is to change diff gearing if you want taller gearing. i cant imagine what kind of driving would require such a mod though. you don't want to be cruising at such low rpms with a single turbo rotary anyway. if you have to accelerate at all then it would REQUIRE a downshift. even with a 3.9 at 80mph, the cruise RPM is good. how low are you trying to go?

my car has a 4.7 and cruising on the highway is annoying. my temps will hit 91c and stay there cruising at 4k rpm where at normal speeds it will stay ~87c.

shifter feel and preference can be conditioned. just because it doesn't feel the same or similar "RIGHT NOW", over time it will feel just fine. also bear in mind the CD shifter is outside of the transmission and has an external linkage whereas none of the rx7s do. due to the design, the shifters are going to have different feels.

 

I haven’t driven my car in at least 18 years. From what I recall when cruising I’d be around 4,500 or so rpm.

Seeing that 5th in the FD is close to the 6th I would imagine I’d see the same cruising rpm. I’m looking to cruise at a slightly lower rpm when driving 80 mph or so and keep temp down. If I need to down shift to escalate at that speed I’m ok with it.

as far as short shifter I did see that linkage for the z trans is external. With my Mazda speed replica short shifter it is smooth and has very close shift points which I like. I want to try and have something similar if I go with the z trans.

as far as looking for a 6th gear option and a quick google search I’m not seeing anything. I did find a company that makes stronger gear set so reached out to them about a 6th gear option

 

1st gear in the CD is a big reduction, you run the auto diff gears with them. Should be fine.

I can't fathom how you were doing 4500rpm cruise unless you had 5.xx diff gears with a factory box or were actually in 4th. I have an OS-G close ratio set unless cruise is closer to 100mph for you?

At ~120km/h I think my FD with 4.77 diff gears was around 3600rpm with a shorter than standard 5th?

 

yea, cruising at 4500rpm with a 4.7 is ~90mph i think. in a 3.9 or 4.1 car, thats of course much faster. my speedo is in kmh and not calibrated for the 4.7 so i have no real idea how fast I'm ever going lol. i think you should drive your car again and reacclimate to the ecosystem before making decisions if possible. or drive one in general to reestablish a base line.

 

I could be off with numbers but I recall stock car cruising on freeway seemed to be higher in rpm. Now my comparison at the time was driving Gallardos daily and recalling 6th gear being much lower. Yes different car not turbo but it was much lower. I’m not looking for something drastic but would like to go slightly lower if possible

 

I could be off on numbers but recall it being higher in rpm . Car was stock.

 

car is being built as we speak can’t recalibrate with it.

with a different trans car will have different feel.

 

There are a couple of really good cluster guides here on the forum, switching km/h mph, also using the variable resistor to correct the stepper output for the needle. I trued mine with a gps. Drilling a hole in the side of the cluster made it significantly easier.

 

Its not a situation of not knowing how to do it, it's a situation of finding the motivation to WANT to do it. My speedo has been useless since 2017 😎 why break the streak?