I recently switched my final gear from the 4.44 to the 4.77 to better suit my track needs and get the sensation that my turbo spools a little faster even though its not bad
everything worked out, I love the 4.77 but i am suffering a little bit from the JDM 5th shorter gear ratio (.806:1).
car runs around 3800rpm at cruising speeds (~75mph)
to switch to a US 5th gear ratio (.719:1) cruising speed of 75mph will be around 3400rpm
it is definitely an improvement but if i can get something with the taller gear ratio that would be preferred

i am seeing online that NA S5 FC with no LSD supposedly had a 5th gear ratio of .697:1 and that will drop me to into the 3300rpm ,which is slightly better but the chances of finding that are slim to none

1. Has anyone retrofitted a ratio of around .60:1from a different make or model? that will drop the cruise rpm to ~2800rpm.
2. the counter gear gets larger as the ratio drops numerically . Is there enough room in the trans case to drop to an .60:1?
3. the main gear will have to be smaller. the fifth gear will not be pushed (famous last words) but i do understand that making the main gear smaller there wont be enough "meat" to be a strong gear

Any input is welcome,
Thank you

 

Mazda makes its own transmission, in the FD's case, the R type. you are limited to the gearing that Mazda has made for it.

the NA FC uses the M type, and is completely different

 

i did not know that but thats good information. i might be "stuck" with the .719 from the US model

i am wondering if you know what the differences are between them?
would the shaft diameters be different?

I will reach out to Liberty and see if he offers any options even though i suspect that his options will be straighcut synchroless gears

 

basically everything, shafts are different

https://www.rx7club.com/general-rota.../#post12484060

https://www.rx7club.com/general-rota...guide-1153243/

 

great! back to the drawing board lol
Thanks dude

 

A few companies can make custom gear sets, main shafts, etc. Liberty and OS Giken, I think there are others

 

liberty doesnt do helical gears. i already have 2 transmission from them. Os giken doesnt do custom
OS giken 5th gear from their gearset is actually shorter than the oem 5th gear (.820:1 vs .806:1)

 

I'd be interested in a cruiser 5th gear ratio too if you find anyone. I called a few places in 2021 but didn't get anywhere.

 

i spoke to paul from liberty’s gear. I gave him the objective he said he will something for me on Monday. I ll keep you posted.

do i assume that you are using the US 5th gear? Or are you using a jdm transmission?

 

One of my friends picked up a rear drive R32 Skyline and discovered that whoever owned it in Japan installed a set of 5.14 gears in its R200 diff
Makes the 4.87 in my RX-7 seem tall! And I don't have a pair of turbos shoving air into an RB26 either...

 

4.77 is not too short. The jdm 5th makes it a little less than optimal because you cant really get it to quiet down on 5th while cruising(~75mph).
the concept of my car is to be wild when i need it and also civilized when i am done.

never the less there are final gears for the fd in australia that are 5.1 5.3 and 5.8.

all i want is to gain around 800 rpm while cruising thats all lol

 

Let me know what liberty says. I will likely need a main shaft, and the OS gearset is too close ratio for the street, 1st is just too tall. I have a JDM trans.

Of course I keep wondering if a T56 Magnum is just a better solution..

 

the mainshaft upgrade has served me extremely well for 8 years now.

i have tried the os giken both on track and on the street. The ratios were good on track but the 1st gear is just too tall for the street for my liking.
Overall it didnt feel like a good compromise for a street/track setup.

the t56 may overall be a better option given that it is a 6speed tranny. I never really looked into them to know what ratios and options are available.

I feel that the oem ratios are great for the track and street use using a shorter final gear

 

you might consider a Nissan CD009 6-spd swap, but not sure the shorter ratio gaps will make up for a 4.77 and 5-spd. It’d need a 4.21 rear gear to equate to that steep FC OD ratio. So a 4.11 would be a little steeper and a 4.30 a little shorter.
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CD009 are almost identical gaps to FD 1-3 and top gear is about the same as Euro FD, from what I see.

 

the thing is your 1st gear with the 4.77 is mostly useless. I might even recommend the 3.91 combo to give an intermediate highway gear in 5th that’s still useable on the track with an interstate OD in 6th with the track gearing not so far off given the shorter rpm drop differences. The 1st gear compound ratio becomes almost equal to a factory USDM 1st gear/4.10 then.

The 4.10 would give you what you’re asking for though and gives you some better range to 140+ mph. You’re dead meat above 125 mph with what you have now.

These were based off a 24.8” OD tire.



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and I did manage to find an 8” 3.73 R&P from a B2600 2wd truck


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with any swap you need to consider if it’s compatible with the manual REW rear iron plate or requires the Auto iron. If I was looking for a CD009 kit then I might consider the Fisch Racing kit. They all have some unique considerations though.

 

What do you dislike about cruising at 4,000rpm?

Im being genuine.
You probably have exhaust/mechanical resonance/2nd order harmonics you can cancel with a little work and you wouldnt know if you are at 3,000rpm or 4,000rpm.

My example would be my FC.
i had 3.5" turbo back exhaust on it (JIC Spec 90). Insanely loud cruising on freeway. Just one cannon muffler in the whole system

I put Racing Beat 3" twin muffler rear section on it and it was better, but would still wear me out on the 200mile trip to the track.

Then I rebuilt the Spec 90 rear section with just a Vibrant street power 3.5" straight through muffler instead of the cannon and ~8" exhaust length added to the downpipe to meet my new turbo location and the thing was nearly silent at all rpm cruise just because it had no 2ndary harmonics.
I just got lucky, but one could get there with a little work.

Engine mounts, diff mount and exhaust frequency tuning.

I had 4:10 and jdm short 5th, but 4th cruise at 4,000rpm or 3rd cruise at 5,000rpm on the freeway was also just fine.

 

I do have quite a bit of drone and it is more noticeable now with the 4.77.
i am running 2 5x8" mufflers 3.5" inlet/outlet, 14inches in length straight through and a 4" downpipe.
i previously had a 3.5" downpipe and the 4.44 and while i did have a bit of drone it was much better.
You are probably right, something is resonating but even then, i do prefer having a little lower rpm for cruising

I am not saying its unbearable as it is but i want to quiet it down. age is catching up to me i suppose

 

The problem with all that is that we are interested in a cruising gear that lowers the rpm at cruise speeds - not 8k rpm.
The 6th gear of the CD009 at 0.79 results in a higher rpm than the stock FD ratio cruising at 75-80 mph highway speeds. Hence RRR's reference to a 0.6x 5th gear.

 

The CD009 T56, DCT and all these options out there are great but i have already dialed in the car very well in terms of ratios/clutch etc and i already have 2 transmissions. One is a full chromoly straightcut dog box and the other one is an OEM+ (upgraded mainshaft).
So changing it to a different system will be a lot of money and time wasted.
Also, the class i am racing my car in, prohibits these kind of swaps even though I do not technically race it anymore but that's secondary.
the 1st is completely unusable on track and you are right TeamRx8 but my car is not a track only car. i even have a/c for my daily comforts haha
My other transmission has an insanely tall 1st gear that i use on the track (1.96:1) but i absolutely hate using that transmission on the street even though i was using it for several years.
I absolutely love running the OEM+ transmission on the street and track with the 4.77. with the 4.44 it was pretty great too but the 4.77 i shift fewer times.
the only drawback with the setup as is, is the cruise rpm and yet again it is not terrible . i can live with it. the US 5th gear will be an upgrade for sure. the question is to see what else is out there to make it even more ideal


So over the years i have known that mazda uses these style of transmissions on all their cars hence the question for the taller 5th from perhaps a different model. I did not know that the FD uses a completely different transmission and thanks @j9fd3s for pointing out these details

 

ok, good luck on a custom gear pair then.

 

For me just going from short S4 usdm TII 5th to shorter JDM S4 5th made 5th gear acceleration much better with 4.10 rear.

Made 120mph--->170mph much shorter time.

With your 4.78 rear 5th is now going to be used even on short tracks.

Have you thought throug trying to get a taller 5th and the impact on the track?

It is going to hurt acceleration where you really need it (back half of short straights and all of long straights.)

 

yeah... mostly an exercise in futility...

 

How about sticking with the 4.44 and swapping to BNRs or testing Markus's replacement compressors/exhaust wheels? It it's torque you want, maybe Turnip the Boots a bit?

 

you’re actually wrong on this relative to his situation; not sure if you misunderstood or didn’t read it correctly because the CD009 with 4.10 gear will cruise ~100 rpm less than the FC 0.697 gear pair and 4.77 rear gear. I won’t go into it further since he seems to have brought up a trans swap in error per his subsequent post, except to say that the CD009 with 3.91 gear will beat the 5-spd with either 4.30 or 4.44 gear in every regard.

I only mention it because your post suggests not being fully aware of the situation. I get that there are reasons people don’t want to swap the 5-spd out, but he mentioned a T56 swap which is the only reason I went into it. My apology otherwise.
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