My old N/A five speed in my 87 GXL has seen better days. I have needed a clutch since I bought the car 30,000+ miles and twenty plus years ago. I am also having some syncro issues, too. Synthetic oil in about 400+ miles of driving seems to have helped some. I am not really ready to pass judgement quite yet.

I am looking to get an S1 RX8 gear box. I know that a S1 is weaker and geared differently than and S2. I will need mounts, t2 clutch, an extension for the shifter, driveshaft, etc. However, for a cheap price of $250, I can get one.

Should I just wait for an S2/buy new or just live with the old box and get an new clutch? Certainly, it would be cheaper, easier to just do the clutch. Let's just set aside cost for the moment and decide that way. Is a scrap yard S1 too risky to buy? It could break quickly or already have issues.

Also, I have a 3.9 rear to pair with the new gearbox. I would like to track the car at some point.

 

As someone who has spent plenty of time dealing with FC chassis configurations, my strong advice is to pass on the S1 RX-8 transmission. Even at $250, it is a false economy that will ultimately cost you more time, frustration, and money than doing a proper upgrade.

 

I actually run a S1 rx8 trans in my rx3 and I LOVE it! I think it is a great upgrade. I know there are a few FC's that run them at DGRR. I would say..... go for it! You will like it.

 

u might get a good conduion S1 box so go for it
no mater what this S1 box is aleast 20 year newer then ur current box

 

I can't really comment on the RX-8 box. I would like a six speed in my FC but since I plan to go turbo the S1 is probably a no go for me, but they are cheaper and much easier to find than the S2 so sometimes I think of just getting one anyway. What I did want to comment on is the rear gearing. I think 3.9 is the wrong way to go. The manual trans S1 Rx-8 had 4.44 rear gearing and the automatic had 4.3. IMO going shorter like the 4.3 from a GTUs (if you can find a set) would be better. Mine came with the 4.3 and I always liked it. I think it would pair nicely with the Rx-8 box. I drove a friend's vert with the 4.1 years ago and mine definitely felt better gearing wise. His had more mods than mine at the time.

 

I run a 4.44 in the rx3 but I also have a much smaller rolling radius than the rx8 since i run 15in wheels. I turn a little over 4k rpm's at 80mph in 6th which is just fine with me.

 

I actually have a 4.44 in th car now since that is the ratio that came in the Rx-8 rear end I swapped in a few years ago. I like it. I don't recal what my revs are at 80mph. Just a little lower than your's I think since I'm still running the stock GTUs gearbox with a .756 5th gear Running 17's but the tire size I run is roughly the same diameter as the stock 16's were.

 

There is a lot here to consider. One of my big issues is that I would struggle with on a S1 transmission would be the lack of a hole at the shifter housing. And add to that, since I have the 3.9 already, it will likely work better with the the S2. I will probably wait for and S2 even it is 3 times more expensive. And I do plan on a higher HP build eventually, too.

From what little I know, the RX8 boxes are based on the competition gears. They just add the extra gear for first gear. The S2 is a bit wider at and 1st and 2nd, I think. 3rd is not spaced super well and 4th just totally sucks, it is just so wide. With a 4.3 rear, 3rd and 4th gear is much better but 1st gear is way ,way less usable. However, if you have a lower HP engine, it works well and is faster.

What I fear with that 4.3 setup and a higher HP engine, grabbing second coming out of a corner, if you are throttle happy, you would probably spin tire fairly easily.

Ultimately, the trans/rear gear that I really need will be what keeps my engine in the power band easier and works well on the roads/tracks that I would go around. In my testing on GT7 (I know, a video game, go ahead and chuckle), this combination at 230hp, is no faster or slower, for the most part on a one mile track than every other combination of the S1, 2 and rear gear combos listed here, that I tried. You will have faster or slower 0-60 times and lower fuel consumption but mostly, only lap times matter, for me. Second is fuel consumption.

The worst times was the 4.30 rear at 230 HP, not by much. Naturally, the results will vary some by track, though.

The best at 150hp was the 4.3. I am average at video driving so, there is that too. The best mod between all of the different gear box/ rear gear changes listed here, was better tires, by far.

Just as a side note, when testing a 5.12 rear end and the competition gears vs. the 3.9 and the S1 box, the 5.12 won on short track by just a little, a track that was 1:40 lap time, the 5.12 lost by 10 seconds. On a long track like you lucky people in France that ride at Spa, the 5.12 looses badly on the long first straight away. Dirt tracks are likely very different though.

Thanks to @peejay for pointing out the 3.9/S2 combo to me after inquiring about the 5.12 setup. Even if you can keep the rear gear from overheating, the drive shaft spins so fast that is causes premature wear. Also, he pointed out that his rally car was most fuel efficient around 4,000 rpm or so, if I remember correctly.

Also, this not very helpful for those of you that don't go for lap times. Gas mileage or racing your friend light to light at low speed might be all that you really care about so, choose wisely.

 

I see I'm not the only one who uses Gran Turismo as a test bed. I did something similar a few years ago to compare the ratios of the n/a and TII gearboxes. Also tested the Rx-8 though I don't know which series as this would have been in GT6. What I found was the difference between the two Rx-7 boxes was negligible, the competition gears were an improvement, and the Rx-8 has the best ratios of them all. Test was done with 4.3 gears as that's what I had in my car at the time. As of late I've found the stock 370z ratios to be good and it has a little taller 6th .794 vs the Rx-8 .843 which I think would work better on the highway. Works better in game when I need more top speed. I actually use the370z ratios in my 6-speed rotary powered 600pp to 700pp cars alot. I also have a 5-speed set I created for the FD and FC that uses a tall 1st gear with the 3rd through 6th ratios of the 370z in place of 2nd through 5th. I only mention the 370z box because there are a couple of adapter kits out there to put it in the Rx-7. This is the way I would like to go but it's just so cost prohibitive at this time.6 speed, good ratios, supposedly shifts good at high rpms, available adapters to make shifter relocation a simple bolt on affair and claims it can handle 750hp. Win/ win if one can afford it.

 

So I did some testing in GT7 this morning and discovered that posted some wrong information maybe. When I went to change the gears in the cars I was using as a test car( Efini RX-7 they just added because it's fully adjustable gearboxes are a 6-speed) I discovered I had been using the S1 Rx-8 6th of .843. In game the S2 6th is.787. I have confirmed this from a PDF I found of the 2011 specs from Mazda.

My results were the opposite. I contribute it to a possible difference in driving styles. I've always used a 4.3 in the Rx-7 in the games until GT7 and have switched to using a 4.44 most of the time. All my braking and what gear I need to be in for corners is all based around those ratios. 3.9 is a big change and for example some corners I could stay in 3rd and carry speed with the 4.3 I need to be in 2nd with the 3.9 and was coming in too hot at first. Anyway, in the end I was about 1.5 seconds faster around Brands Hatch with a 4.3 with either the S1 or S2 box vs a 3.9. Like you mentioned the 4.3 seems to cover up the bad 3rd and 4th gear. 4th is horrible with the 3.9 to me. What I really learned is I don't want a S1 or S2 Rx-8 gearbox because of 4th gear (S1 is marginally better). The 370z 3rd and 4th ratios are better and fix that. So I want to do the 370z gearbox swap even more now. How what I like to call my fantasy land of GT7 transfers to the real world I don't know, but I think some of it is valid

P.S. Car used was 91 Efini Rx-7 with engine balance tuning giving an 8200rpm redline set to 276hp with full suspension on Sports Soft tires with front and rear aero adding downforce.

 

Thanks for the reminder about the 350z one. I will have to do more "testing". funny thing is that when I typed the adapter kit into my search, I had it bookmarked already.

I remember seeing a build thread with this transmission. I thought that there was some... adjustments...... that needed made to the trans tunnel. Maybe, I am just remembering wrong.

It's likely a mod that will be to expensive, for now, unfortunately.

 

IIRC the trans tunnel needs a "big hammer" adjustment. I did some quick searching and both the 350z and 370z use the same ratios. Not sure what the actual differences are but one of the companies that make adapters to put a T56 bellhousing on the CD009 had three different ones for the different year ranges.
The transmission itself isn't the expensive part. Looking on Car-part.com the older 350z ones are cheaper and easier to find than the S2 Rx-8 ones. Average $800 to $1500. The 370z's are more than the Rx-8 box but much easier to find. Multiple ones within 500 miles of me. Problem is the Fisch kit is like $3000 or more plus cost of transmission. ROTARY to CD009/CD00A Adapter System – FischRacingTech There is hope of a cheaper option though, there is a guy in this thread JK40C/CD009 Transmission from 370Z on 13B - Page 14 - RX7Club.com - Mazda RX7 Forum that made his own adapter a couple of years ago and used a TII bellhousing. I commented on the thread but no response. I need to PM him and hope he's still around.

 

Replacing the RX8 4th gear with the 6 speed Miata 4th gear works well. According to an AI search, in the real world, it can be done. Also, I asked if the complete gear set can be swapped, that was also a yes. Certainly, the Miata set isn't as robust, even though the weight of the box and ratios are very similar.

Comparing cost though, not sure.

 

I didn't mention the Miata 6-speed since I'd done no research of if the Miata 6-speed gears could be swapped in, in the real world similar to how people put the 5-speed gears in the n/a Rx-7 gearboxes. In my previous test I had used the Miata 6-speed as well and it was actually the best of the Mazda gearbox ratios. Which series of Rx-8 gearbox will the Miata 6-speed gearset swap into? This sounds interesting. For someone with no plans of going turbo this could maybe be a more economical option to get good ratios than the 350z/370z gearbox swap given the cost of the adapter kits. That said I haven't looked up the cost of a donor Miata gearbox yet.

 

It would likely be expensive and S1 only, think. I typed this into the search and got slightly different answers. And I also clicked the link, refreshed and got two different answers.

https://www.google.com/search?q=six+...t=gws-wiz-serp

Swapping 4th seems strange because the gear mating type is different, I think and might be possible

https://www.google.com/search?q=swap...t=gws-wiz-serp

Fear not race fans... someone has a drop in option.

https://speedtekautoracing.com/produ...gearset-dogbox


All of these mods are for the S1 box. Will the drop in set be strong as a dog configuration? Let's hope so.

And after all of that, the Nissan box might still be the better option.

Edit: I did find other options for the drop in dog style with a search,too.

 

That Speedtek dog engagement gearset is intriguing. I've kicked around dog boxes as there is a company that does face plated dog engagement gears for the TII gearbox, but I really want a 6-speed. Speedtek says they handle 600BHP which converts to 591.78hp which is more than I plan to make. Since they are in Australia I wonder if that price is in Aus. dollars. If so, it's less than $3000 in US dollars plus shipping. I've found S1 boxes for under $500 in my area, so total cost may be less than the 350/370z conversion IF I could do the gearset install myself. I wonder how hard it is to do transmission work. I think I'll test the Speedtek ratios tomorrow.

 

I am not sure that you could easily street those type of gears, unfortunately. I am kinda curious is that or other companies could build ones with more street-able version.

I think there is a way to make the S1 series tougher, reliable and add the 4th gear. I need to do more research.

 

Well, I tested the Speedtek ratios and I like them, but back to the real world. I'll have to see what direction I take this car before I commit to dog engagement. I'd like to start doing track days and head in a more track focused direction while at the same time keeping it street able as it will be mostly driven on the street, but not as a daily driver. I've watched videos and you can drive them on the street, but you have to "learn" how to as you have to drive them different than one with synchro's. Maybe there is gearset for the S1 that fixes it's issues. This guy put straight cut gears in his but it was $9000 I'm assuming Australian which is still $6351.57 US dollars. It may be they are out there but the 350/370z option makes more financial sense depending on the application.

 

Yeah, it is the Gold standard according to AI. You would have to be one motivated person to do it another way, from what research I have done so far, as long as you are talking 6 speeds anyway. The synchro's are different from the Miata to RX8. If the Miata gears do fit on the RX8 shafts it is a lot of work to remove every gear, synchro, fork and replace/upgrade. The nice thing is that if I was to try a S1 and run it on the track, Mazda makes upgraded Miata parts that address the weaknesses in the earlier made 6 speed boxes, I think. You just need to be verified for their race group with one event a year to buy the parts. It might be an affordable option then. I am going to put a pin in this for now and research when I have time.

If anyone has any input, please let me know. thanks!