The spring rates here are interesting, but then again I've never set up a car with this type of suspension.

On my NA Miata with 130HP and 2450lbs for PTE/TTE I run 1000lbs/in front springs and 400lbs/in rear but this is also to make up for the stock sway bars because of classing constraints...

 

Not the Gas Adjust but I have a pair of KYB AGX shocks on the back of my 85 Mustang. They work fine. I like the ability to adjust rebound

The best non-adjustable shocks I ever used were PRO WB735 racing shocks. They are gas - twin tube shocks that can be had in a number of valve settings. Mine have a compression valve = 3 (soft) and a rebound valve = 5 (stiff). They have welded spherical bearings at end so adapters have to be made and the OE lower shock mount has to be drilled to 1/2" and you will need spacers at that end too. They sell for something like $50-60 each from places like Pitstop USA.

 

Apples and Oranges. You can only compare wheel rates when dealing with different cars/spring locations.

For example an old Solo II C Prepared Mustang I used to campaign had 1600lb front springs and 870lb rear springs located in the stock locations. That car also had the biggest OE front sway bar and a rear sway bar - also in the stock locations.

 

Those sound cool, maybe next time, I am on a budget and just bought the front coilover pieces and tires too

 

Not trying to jack the thread, just thought I'd up date what I found on springs.
I ended up with 450 Front and 275 rear springs. I may come down on the front 25 to 50 lbs. As I like the ride a little better. Lap times seem to stay the same between 400 to 450. But I'm not sure yet how the koni's struts look on the dyno. I may need a rebuild (it's about time).
But with the changes in spring rates. I took off a hair shy of 2 seconds.

Looks like I will be going with Penske all around. Fronts are custom and will not be ready for awhile.

 

Glad this working out for you. Two seconds is allot of time.

I like my SA Koni shocks/struts but they do seem to slow my car's response in transition. Which makes it pretty sucky in an autox. On a race track the car is in its element and can be pushed hard comfortably. Would like to switch to DAs on the front at least in the future.

 

Some updates...

Drove the car in a track day recently at RPM (Raceway Park of the Midlands - used to be called MAM) and was pleasantly surprised. Picked up 15mph on the main straight and 10-12mph on the shorter straight between turns 4 and 5. This compared to when the car was a IT car.
Overall the cars drove great but man am I rusty at this driving thing! Since then I have just been doing maintenance to the car and making plans for the future.

Job one is working on the installation of the Jerico 4spd I bought earlier this year. To that end I installed a Mazda specific conversion input shaft, reassembled the Hightower top-mount shifter assembly and buttoned up the case. Next I will start working on modifications to the RX4 bell housing I have and the design of an adapter.

This transmission has a pretty close ratio stack:

1.78:1 first
1.43:1 second
1.18:1 third
1:1 fourth

Eye candy.....

 

So much transmission.

I'd like for the exact gear ratios of a S4 turbo II to be in a "slick shifting" 600tq capable unit from some magical company, and also only being $1500...

Darn it. WPC the S4 I suppose.

 

I did allot of research on transmissions over the winter. The closest I found to what you are looking for is an OS Giken gear set for an FC/FD transmission. Per the OS Giken rep I spoke with getting one built required a 6-12 month wait. So get your order in today!

 

One of my good buddies rebuilds all the transmissions for SCCA Spec Miata here in California. He has my spare S4 Turbo II box now and we intend to tear it down and see what's available. Yea, I've seen their gear sets, thank you for the suggestion! I'd almost be inclined to machine/harden my own at that price.

 

Oh, so that's what Hightower does. Pretty self explanatory once you see it.

I'm actually starting up a 13B Miata build for STU (well, really, mostly Midwestern Council until it's sorted) - using an RX-8 box with a Miata tailshaft housing to start with, but really undecided what to do for a "real" transmission. Just worried about only having a 1.8:1 to 1:1 spread with a 4-speed, you know? But then, the 4-speeds are the only really "affordable" choice.

 

All the tracks I run on this area have one turn that a 1.8:1 ratio would be perfect for. Much lower than that is too low. For example the stock box's 2nd gear is too low to use. I mean if you are going slow enough to use a stock 2nd or a racetrack you have probably just crashed or spun of track.

The only hassle I have seen with a first gear like this is that is hard to move around in the paddock. Also, an autox is out of the question.

The trick is to get the car in 4th gear as soon as possible and keep it there as long as you can. This Jerico is fully rollerized so when it is in 4th the counter shaft gears are not creating any drag.

The side mount Hightower uses the same shifter. The rails run through the tailshaft housing where it mates to the main case. That setup would actually be a little better for me but this gear box has no time on it....better deal.

 

I was just doing the math on a spreadsheet - EP at Road America (at least for a few I watched) goes from something like 48mph at the slowest corner to 133mph at the top end which... I guess should work actually. I had been looking at an Elite (or whoever) sequential 6 speed with around a 2.2:1 1st gear, but there's about zero chance of finding a used one of those over here, questions of how to get service parts in a hurry... plus the 100 pound weight penalty. Hm.

 

Nice gearbox. I eventually want to get something similar for my car but I know its spendy

 

So what did you find in your searches as viable transmissions? I am running the Miata gearset now and it works pretty well, much better than the stock RX7 ratios but I believe we are pretty marginal for endurance racing. The engine I have now is putting down right at 200hp at the wheels on a pretty conservative dyno, and I expect next year’s S5 bridgeported engine to make close to 240 so I would like to find something more robust. The rules say I can swap in any transmission that came in a production car but I don't think I could slide the Jerico through a team already got busted for something similar. A Turbo2 transmission is an obvious choice but then I am back to wide ratios.

Looks like you can build a pretty close ratio T5 if you use the .8 5th gears. Don't know if that would be a good choice or how hard it would be to make it fit.

This was from the last race, although you really can't blame this one on the transmission, the rear u-joint was locking up and vibrating the tailshaft housing until it broke right behind where it was supported by the mount.

 

Hey 650, you broke that one real well!


I looked at V8 muscle car transmissions, alternate gear sets for Mazda transmissions and race transmissions like the Jerico.


Quick Time makes bell housings that adapt a number of V8 transmissions to a 12A/13B that is using a turbo flywheel.


There are some decent ratio combinations available for the Super T-10 but I read that these kinds of transmissions don't like to shift at high RPMs. A T-5 could be an option but the good G-Force ratios don't come with a dog-ring option. Also the 5th gear in a T-5 is hung on the back of the main case in a single shear bearing. Not real strong.


Alternate ratio gear sets for the FC/FD transmission are unicorns. I exchanged emails with an OS Giken US sales rep and found out it is a 6 month wait just to get a production run scheduled. None of the gear sets I found on eBay are actually in stock. Given all of this even if you could get a gear set, how would you service it later when it fails?


Alternate ratios for the NA RX7 transmission are available from Quaife.. Per Jesse Prather - www.jesseprathermotorsports.com - delivery times for sets and replacement parts are inconsistent but you can get them. He does installations and had a few complete gear boxes for for sale last year. Give him a call - very good person to work with. This option would give you a stock looking gear box


What about a later RX8 transmission?




For me, the Jerico is the best option because it is a no compromise racing transmission. I am currently working on an adapter that will allow me an RX4 bell housing so I can use my NA flywheel.

 

350/370Z transmission is another interesting looking option. I've seen a couple people working or offering adapters to bolt them to 13Bs. For less work, RX-8 transmission is probably your best bet - maybe plumb in a cooler and electric pump too. It helps that the RX-8 boxes are showing up on car-part.com for pretty cheap nowadays.

 

I am going to PRI this year so I will check out the G Force and Quaife booths. I have some contacts in the UK who are big Quaife customers so maybe I can get a deal through them…

 

I think the 370z trans is pretty stout, collins adapters may make a 13b adapter

 

Just realized I can just ask as you have one... about how big is the main case part of the Hightower box? Width and height especially. Kinda working on figuring out if it'll fit in a Miata trans tunnel. No hurry.

 

Looks like your car has come out outstanding! I have been unable to work on my car till the end of 2016. I got my engine back together the last day of 2016. I did the bridgeport on it and I milled off the rotors to 4050 grams. I going to a 48 MM Weber and running carbon apex seals. I rewoeked the oiling system and modiyied the E shaft by taking 0.001 off the ends and opening to oiling holes. fixed the relief valves (front and rear) to up the pressure. I am running a Firzana(not sure of spelling) aluminum flywheel. I have to fab some spacers 3/4 OD by 0.315 thick to take up the gap on the chutch to pressuer plate. The spacers will be placed under the steel friction plate on the flywheel to lift it up 0.315. I also am running the Miata gear box. I will be buying a new set of Toyo slicks

 

Hightower uses a Jerico case so the dimensions are the same with a few exceptions. A Hightower modified case is narrower because they machine off the shift finger bosses on the left side and seal the holes. A top shift Hightower like mine is around an inch taller than a normal if you use a fined top cover. A flat top cover could be used to get some tunnel clearance back.

When I get back to the shop I will get some measurements using the input shaft/out put shaft center line.

 

Yeah, I'm not sure if I like the idea of the top shift or side shift better for my application - after notching the trans tunnel to fit my fat ... er ... seat, I'm worried about finding space in a Miata tunnel for the trans and sufficient exhaust plumbing for a rotary. For that matter, hacking up the top of the tunnel doesn't bother me either given the amount of surgery happening on this shell anyway. I literally have no idea of Jerico / Hightower dimensions though (and I've come around to see that something like it is the only really reasonable solution) so I appreciate it.

 

So made some more measurements today.

The fined cover on my trans is 7.125" above the input shaft centerline at it highest point. With a standard or Hightower side shift you can subtract and inch off of that measurement.

The top of the shifter ball on my Hightower transmission is 18.75" above the output shaft center line. Compare this to a Mazda NA transmission where the top of a factory shifter is 13.25" above the center line of the output shaft. So, there will be a little bit of a Rat-Fink effect with a top shift Hightower. At least the pivot point of the Hightower shifter is allot higher than the OE trans and the throws are shorter in all directions. Shift effort is also pretty light.

To install the Hightower I have in an FB the top of the tunnel will have to be opened up from factory shifter hole to a point that is 10-12" farther forward. Room has to be made for the shift rods that will come through the tunnel. Also room has to be provided to facilitate the installation of the shifter once the transmission is in the car. So, an aluminum cover will need to be made that can be easily removed for service access.

In contrast, installing a standard side shift transmission means cutting out the side of the tunnel from the shifter hole to just about the gas pedal. This is needed to provide clearance for the forward shift fork and shift rod. Once this is all covered up the side of the tunnel is right next to the driver's right leg/foot.

The best solution would be a Hightower direct connect side shift. The shifter hole might need to be opened up but shift rods don't need any extra room. I had a chance to buy one but it had time on the dog rings and the one I bought has never been used.

Hope this helps.

 

Thank you, that does help. I actually found some more dimensions on the Roush Yates parts site too, so between what you added and those, I think I have enough info to make a high tech composite fitment mockup (by which I mean plywood).

Personally, I think that since I'm going to be notching the trans tunnel side for seat fitment, cutting holes in the top of the tunnel might be preferable for me - I'm a little worried about fitment issues between a side mount shifter (even one of the Hightower ones) and my leg/seat. Or the exhaust.

I know, I know, I could just build an FB instead and have a bit more room, but having wishbones instead of struts and a live axle is appealing as heck.