drifted

Hello.
Question to rotary heads. What are the pros and cons of earlier 4 speed trans. from cosmo, vs stock first gen or 5 speed turbo II trans. I believe that torque would be greater of 4 speed, but since these trans were build in 70' are internals stronger or weaker. Can it withstand ratio of +400 h/p on motor. Also my buddy had 3 speed in his first gen earlyer in the days. Did it come as an option for rotary wehicles(or maybe Toyota's), of was it custom/retrofit?

Thank you and g.day

Whizbang

the early rx7s 4spd is the same as a 5spd less the 0.825 gear

drifted

thanx. i was hoping for closer gear ratio w/ 4 speed, or at least longer pull on 1st gear. how about miata trans which i read about. how strong the internals are in comparison to T2?

...thank you for reply

Jeff20B

iTrader: (13)

Interesting. I have a close ratio 5 speed out of a '78 RX-4. 1st gives a longer pull, 2nd is close to first, 3rd is close to 2nd, 4th is 1.00 as usual. 5th is very tall.

This trans won't fit an '81-'85 1st gen very well due to shifter position. It might fit a '79-'80 but I've never tried it in one. It did fit well in a GLC but the stock rear diff gearing was too tall at 3.727 making 1st feel kinda like starting off in 2nd all the time, and 5th was too tall to be useful (4th was used on the freeway). I'd say if the rear gears were 4.somethng, this tranny would be better.

For now though, I've got a stock '79 5 speed to try. Its 1st is lower so should work better with the current tall diff gears. 5th will be useable too. Plus it's lighter and plenty strong enough for the car.

drifted

my present set up in 12a which i will mild port and turbo (but i have to see first if the side seals are any good because ive had some problems before tear down of the car. Option #2 is to use one of the 2 13b's that i have. The body is SA 1980 with same transmission, so it is good to hear that it has a longer pull on lower gears. I've had couple fb's but they had different wheel size so could not compare apple to apple.

I am considering 4 speed from 70's cosmo, and I don't care so much about shifter location, since car is down to frame. Reading jeff20b reply i see that this cosmo trans might have a longer lower gears which it might help for city street traffic racing (and occasional sideways)
ps: most likely i will be runing chevy 10 bolt rear end, out of z-body camaro or corvette(?), since i have it in garage, but im not sure gear ratio there....
thanx for follow up and more info

Jeff20B

iTrader: (13)

'77-'78 is the tranny year you're looking for. You don't want a '74-'76 because they have short 1st and 5th, and far ratios making fast shifting unpleasant.

BLACKrotor92

iTrader: (3)

i have a 4speed tranny that came out of my rx2 re but i also want to know and get down to it..is the 4speed better or 5speed?

Siraniko

iTrader: (13)

yup yup yup. I had one in my 74 RX-4 but sold it in 1993.

GORacing

Ok, first part of your questions... pro and cons and durability at 400hp-
74-78 4 and 5 speed ribbed case trans are strong gear boxes and will hold up pretty well, but the syncros are not very forgiving and are easy to bend with hard or improper shifting, (makes it increasingly hard to get into gear without grinding), and you have to change out the plastic shiter bushing with a metal one (easy to do)...
79-80 4 and 5 speeds are pretty much junk for anything with hp...
81-91 5 speeds are kinda ok strength wise, if you dont beat on them too badly...
87+ turbo II and 3rd gen ribbed case trans are the strongest of the rotary gearboxes, but require the use of a larger dia flywheel or hacking up and redrilling of the starter mount to move the starter in for the smaller N/A flywheels...

Second part 3-speeds? I have not seen any 3 speed trans options available for any Mazda rotary powered vehicle from 1970 on up, (let alone in a 1st gen) in the states unless it was an 3 speed automatic... and since most of the major Japanese auto manufactures get their trans from the same source...

As far as ratios go... you need to pick your intended use, then you can use vehicle wieght, and tire size to set your rear gear and trans ratios... of the rotary powered cars there is 11 basic gear set combos ( with 6 1-4th gear sets and 9 5th gear combos, plus gearsets from Miata and RWD 626 which use the same basic trans internals, within trans types), available from 1974 to 95. I have a chart that could dig out if you are interested. Also, if you can find a friendly trans shop, they are a great source of gear set info and can show you what other makes have gear sets that will interchange within the Mazda trans case...

Jeff20B

iTrader: (13)

Early ribcase 4 and 5 speeds had the same 1st through 4th gears. As for which is better, I don't know. I installed an early 4 speed in my MG Midget 13B project but haven't had a chance to do the minor things to get it running yet. It has a tallish rear gear at 3.7 so I'm thinking it won't need a 5 speed, but wouldn't turn one down if I could get one to fit - the car previously had a twin dizzy RX-2 12A and top mounted starter tranny (again same gears, as mentioned above), so the rear mount that was hacked in place was reused with the 13B and '74 tranny. I didn't want to spend any real time to swap in a better (let's say '81-'85) tranny without having driven it much first. I'll know more once it's driveable again.

drifted

hmmmmm. what would i want to have?...
i know!! long first...and short second to third so can smoke them all on both
i dont know gear ratio chevy rear..i have to open it up. wheels are 245x45x16's ssslick..

GORACING: chart will be strongly appreciated if you have it handy

GORacing

10 bolt rear - 2, 3 gen Camero?, most likely high 2's or maybe low 3's, later models had Dana's still not going to be much gear there for a rotary (if stock there will be a metal tag off one of the rear cover bolts that has the ratio on it... Vettes are IRS... better off with a 8" or best a 9" Ford (easy to id externally), even the 79 + mustang rears (8.8" if I remember right), would be a better option, cheaper gears, less labor $ to get them set up than a 10 bolt, plus easier to find disc brake setups, not to mention the later model ford 5 lug pattern is the same as Mazda's...

Trans ratio chart attached

drifted

thanx because this question has been bugging me for while. to complicate the scnario rims which are fitted to widebody offset i have are 5 lug and what it seams to be 4.5" bolt patterd (but it might be in metric rims are euro). S.CHEVY 10 bolt dont fit because it has 4.75" so i had to get new bolt shafts = $300. dillema.

i should just go with jaguar independent!

GORacing

Ugh... something to think about... while I hope you can find enough Jag IRS parts in good condition and at a favorable price, so, just remember what ever you put in you will have to maintain later on down the road and those units are expensive to buy stock parts for let alone performance related (gear sets etc...), not to mention they may not readily be available at your corner auto parts store...
the plus side to the jag rear is that there are a number of aftermarket manufactures that make shinny parts, sub frame assembly kits and individual mounting brackets (thinking outside of the [] - street rod/ custom car application)... there are even subframe kits for 60-70 era Corvette rears...
What about using a 2nd or 3rd gen rear IRS sub frame assembly, I have one I am going to use in a 27 Track T street rod project... real easy to set up mount points for... the tract is wider than that of a 1st gen so rims may be easier to source, plus if you are talented enough you could widen the unit up and only have to find longer half shafts...

Just more food for thought...All in all, if you are going real budget and ease, stay with the straight axle setup...

drifted

thank you for excellent info.i m still 3-4 months before rear end build up will start. yes ..indep. rear is just an speculation, most likely will proceed w ford or chevy w/ custom axles made. at this point i will be for look for ford rear, since i can still get some dollars back for chevy axle assembly that i have. thanx again for following up on questions, i will research further more this issue of the rear end, as the right time comes by.
have a good day

rautox-7

You just found the weakest link of the miata. Don't use a miata tranny as its hp cap is 250hp. At 300 hp, you've just invented the holy hand grenade!