transmission gear selection questions

[Whizbang]

since i am going to have to drop the fuel tank here soon and see why the pump is getting no fuel, lets talk about a future upgrade i am planning!

The transmission replacement!

The stock rx7 transmission has some piss poor gear selection. The stock 12a gearbox is shown below.

3.674 (1st) 2.217 (2nd) 1.432 (3rd) 1.00 (4th) 0.825 (5th)

The spread does not take advantage of what the engine can really do. For the sake of my build, the Mazda Comp Manual PDF (see the FAQ) has some good information on the Mazda Competition Transmission. If you want one...well that sucks because your looking for a surviving used one.

BUT the information i did get from the PDF is the gear selection of the comp. transmission.

2.350 (1st) 1.608 (2nd) 1.240 (3rd) 1.00 (4th) 0.881 or 0.839 (5th)

This information is priceless for the sack of want to do. As a bonus, that setup was used with the 4.88 final drive and a 12 PP. Ill be running a 4.78 with a 13b Bridgeport. So i am close to that the "perfect" setup would be.

So why does it matter that i know the ratios of a transmission i cant buy anymore? Well thanks to people with more time and money than i have, there are bell housings and other adapters to run other transmissions on the Mazda Rotary.

The transmission i want to use, if i can find an adapter for the GM 1-1/8" 26 spline, is the Richmond Gear Super T10 with the 2.43 (1st) 1.61 (2nd) 1.23 (3rd) 1.00 (4th) non overdrive and is only about 1500 dollars.

The ratios are very very close to the Mazda Comp.

But i dont know of a GM adapter, ill have to look, but if i cant find one, the option for the Ford T5 adapter exists.

The ratios for the Richmond Gear Super Street 5spd are:
2.89 (1st) 1.85 (2nd) 1.31 (3rd) 1.00 (4th) 0.77 (5th)

OR there is also the Richmond Gear 4+1 5pd with

3.27, 4.06, or 4.41 (1st) 2.13 (2nd) 1.57 (3rd) 1.23 (4th) 1.1 (5th)

I do not like that setup for one reason, first gear is useless with a 4.78.

I think i need to call Summit and see what other options not listed in the catalog are....

[Whizbang]

as for the miata transmission here is what i found

Ratios:
1st 3.136
2nd 1.888
3rd 1.330
4th 1.000
5th 0.814
Final Drive 4.300

That is basically a split between the stock rx7 and the mazda comp transmission. I think i need to go talk to some people who have been racing with these ratios and get some advice.

[Whizbang]

someone referred me to here:

http://www.awrracing.com/store/produ...roducts_id=395

New 5-Speed Quaife Synchromesh Gearkits for Mazda Miata and RX7. Heavy Duty, semi-helical, close ratio gearsets are available in two configurations for both performance street and race applications. Available for 1.6 and 1.8 Miata and RX7. Quaife 5 speed Gearset for 1990-2005 Miata and 1981-1992 RX-7. Also fits 2006-2007 MX-5 5 speed box with slight modification. Available in two different ratio sets. Installation is available by AWR for $595.00.
RATIO SET 2 2.350 1.550 1.240 1.000 0.886

to the tune of 2800 dollars...

[Rogue_Wulff]

Originally Posted by Low Impedance

as for the miata transmission here is what i found

Ratios:
1st 3.136
2nd 1.888
3rd 1.330
4th 1.000
5th 0.814
Final Drive 4.300

That is basically a split between the stock rx7 and the mazda comp transmission. I think i need to go talk to some people who have been racing with these ratios and get some advice.

Mostly true, however most 5spd Miata's were equiped with a 4.10 rear gear.
The 4.30 or 4.10 Miata ring and pinion is a direct fit for the FB rearend, as the FB and auto trans Miata shared the same 3.90 R&P.
The Miata trans internals can be swapped into a N/A RX7 trans case by simply milling ~3/8" off the front of the splines on the input shaft.

Using a 4.78 or 4.88 R&P really requires the hardened driveshaft front yoke/ roller bearing tailshaft mod. The driveshaft will reach RPM's too high for the stock yoke and tailshaft bushing to be properly lubed, and failure will only be a matter of time.

There really isn't any set "Perfect" trans/rear gear ratio setup, it all depends on how/where the car will be used. What works great at one track, may suck badly at another track.

[Whizbang]

the other reason for getting rid of the stock smooth case stuff, was that i wanted a transmission that can take a beating. Rotaryshack said they could make a version of their adapter plate for the GM trans, so if that turns out to be true, ill probably be going that route.

[BLKTOPTRVL]

It isn't impossible to make your own adapter.

I put an '80 Mustang Five Speed into my '71 Pinto.

To do so, I had to make an adapter plate. I used a half inch aluminum plate and traced it to match the 5 speed on one side and the engine on the other. (After tracing the shape I wanted, I took the plate to a machine shop to have it cut out.) I bolted the adapter onto the tranny by sinking the heads of the bolt below the surface of the plate, and then bolted the assembly to the engine.

For the Pilot, I replaced the bearing with an oilite bronze bushing.

It ran fine for years until I sold the car. Never had any problems with it.

[Whizbang]

the miata box and the rx7 box STILL have the same 1st to 2nd shift lump with about a 3800 rpm drop. but the 2 - 3 - 4 is much better....

i think the best overall though is the Richmond Gear Super Street

The drops are never below 6100 rpms and the 5th gear would still leave a 3800 rpm engine speed while cruising at 70 mph...

if i want to not worry about the freeway ever, then i think i would opt for the Richmond Gear 4+1 but the 5th gear 1.1 ratio and a 70 mph engine speed of almost 5500 rpms is a turn off to that.

The T10 box might be slighly better, but there is no overdrive gear and the difference isnt that big between the Super Street and itself.... Ill have to check its other ratio combinations to see if anything can be gained

[TheDriver216]

Originally Posted by Low Impedance

someone referred me to here:

http://www.awrracing.com/store/produ...roducts_id=395



to the tune of 2800 dollars...

Now since its "Heavy Duty" would it be a possibility of it holding up as well as a T2 transmission on a turbo 12a?

[Whizbang]

hard to say really. im sure if you make ENOUGH power, you can shred anything.

[Whizbang]

Here is the data i processed:

I used an assumed shift point of about 9600 rpms. The true shift point may be lower (about 9000) once i finish my engine build, but generally, this gets the point across.

Mazda 12a Gearbox w/ 4.78 Final Drive on 205/50 R15 Tires
9600 rpm shift point (assuming bridge ported engine)

70mph = 4136 rpm

*Top gear yields 16.9 MPH / 1000 rpms and top speed of 162.5 mph ( @ 9600 rpms)
*Top speed in 1st gear = 36.48 mph
-Changes into 2nd gear at 5793 rpm dropping 3807 rpm
*Top speed in 2nd gear = 60.45 mph
-Changes into 3rd gear at 6201 rpm dropping 3399 rpm
*Top speed in 3rd gear = 93.60 mph
-Changes into 4th gear at 6704 rpm dropping 2896 rpm
*Top speed in 4th gear = 134.035 mph
-Changes into 5th gear at 7920 rpm dropping 1680 rpm
*Top speed in 5th gear = 162.467 mph



Mazda Miata Gearbox w/ 4.78 Final Drive on 205/50 R15 Tires
9600 rpm shift point (assuming bridge ported engine)\

70 mph = 4081 rpm

*Top gear yields 17.152 MPH / 1000 rpms and top speed of 164.662 mph ( @ 9600 rpms)
*Top speed in 1st gear = 42.74 mph
-Changes into 2nd gear at 5780 rpm dropping 3820 rpm
*Top speed in 2nd gear = 70.993 mph
-Changes into 3rd gear at 6763 rpm dropping 2837 rpm
*Top speed in 3rd gear = 100.778 mph
-Changes into 4th gear at 7218 rpm dropping 2382 rpm
*Top speed in 4th gear = 134.035 mph
-Changes into 5th gear at 7814 rpm dropping 1786 rpm
*Top speed in 5th gear = 164.662 mph

[Whizbang]

Richmond Gear Super Street w/ 4.78 Final Drive on 205/50 R15 Tires
9600 rpm shift point (assuming bridge ported engine)

70 mph = 3860 rpms

*Top gear yields 18.12 MPH / 1000 rpms and top speed of 174.071 mph ( @ 9600 rpms)
*Top speed in 1st gear = 46.379 mph
-Changes into 2nd gear at 6145 rpm dropping 3455 rpm
*Top speed in 2nd gear = 72.451 mph
-Changes into 3rd gear at 6798 rpm dropping 2802 rpm
*Top speed in 3rd gear = 102.317 mph
-Changes into 4th gear at 7328 rpm dropping 2272 rpm
*Top speed in 4th gear = 134.035 mph
-Changes into 5th gear at 7392 rpm dropping 2208 rpm
*Top speed in 5th gear = 174.071 mph



Richmond Gear 4+1 5spd w/ 4.78 Final Drive on 205/50 R15 Tires
9600 rpm shift point (assuming bridge ported engine)

70 mph = 5515 rpms

*Top gear yields 12.693 MPH / 1000 rpms and top speed of 121.85 mph ( @ 9600 rpms)
*Top speed in 1st gear = 40.989 mph
-Changes into 2nd gear at 6253 rpm dropping 3347 rpm
*Top speed in 2nd gear = 62.927 mph
-Changes into 3rd gear at 7076 rpm dropping 2524 rpm
*Top speed in 3rd gear = 85.373 mph
-Changes into 4th gear at 7521 rpm dropping 2079 rpm
*Top speed in 4th gear = 108.972 mph
-Changes into 5th gear at 8585 rpm dropping 1015 rpm
*Top speed in 5th gear = 121.85 mph

[Whizbang]

well i found an adapter for the chevy, so i may be going that route since the T10 is a cheap option and has basically any ratio i want. That or the T56 richmond...

[Whizbang]

well this ordeal is coming back into possibility again. I am currently trying to compare some options. The biggest is if i can find a clutch from OS Giken to fit one of the T5 input shafts splines. If im that lucky, then i will for sure be running a T5 behind the engine. If not, then ill probably just opt for a Turbo II transmission for a while.

[RETed]

Be careful...
A lot of these "V8" transmissions cannot handle revs that high.
There's a good thread in the evil forum on this...I think in the 20B section?
It's very tempting to go through the Summit Racing catalog with those prices, but it's not really an option.
I think the only serious option is to get one of those T56(?)'s from a Viper...
That can't be cheap.


-Ted

[Whizbang]

i know the factory produced models are sub par, but i have a couple deals on Tremecs and TKOs which should stand up to punishment just fine.