capt. bill1

Has anybody or does anybody know someone who has used a two rotor Cosmo motor in a third gen?

If so, where did you/they get the rear housing to mate up to a manual transmission?

Did you/they cut down the Cosmo intake manifold so it would fit under the stock hood?

Is the two rotor Cosmo just a three rotor Cosmo with one less rotor?

j9fd3s

iTrader: (3)

the 13b cosmo is like a 3 rotor cosmo, witch makes it the "missing link" between the t2 and the fd. so basically, it has the 4x 550 injectors and air flow meter of the turbo 2 and the sequential turbos, and side feed primaries like the fd. it also has a couple of thing unique to the cosmo's, dual thermostats and weird exhaust sleeves, and larger intake runners.
the easiest way to bolt it in an fd would be to use the fd rear housing

mike

capt. bill1

My understanding is that the fd rear housing will not work.

j9fd3s

iTrader: (3)

why not? the fd and 13 cosmo share intake gasket bolt patterns, they have the same turbo drain in the rear housing, the only difference is the runner for the intake

mike

cach22

the fd rear housing won't work as the port is quite a bit different to that of the cosmo. As for mating the manual fd box to the cosmo engine, i havne't tried though i have mated a s4/5 gearbox up with no prob, so unless the bolt pattern of the fd box is different then it should bolt up, i am not sure if the engine mounts are the same, as i have my cosmo motor bolted into a 1st gen therefore don't use the side mounts

cheers

Lance

capt. bill1

Thanks Lance. That is the way I understand it too.

crispeed

You can port the FD housings to match the RE ones!
I've done it many times before!

crispeed
87 Rx-7 TII
9.204@150.47mph
2600lbs
un-tubbed

fdracer

capt. bill why would you use a cosmo motor over the fd one? any other advantages other than the larger im runners?

crispeed

The intake manifold on the Cosmo is much better in my opinion. The TB on the REW is better though. A combination of both is the better setup.

crispeed
87 Rx-7 TII
9.204@150.47mph
2600lbs
un-tubbed

j9fd3s

iTrader: (3)

we have noticed that the 13b cosmo and the fd have the same intake bolt pattern why cant you just put a cosmo intake on the fd motor?

mike

peejay

You'd have to port the FD engine's runners so that you don't have the undesirable port mismatch of a large port feeding a small port. Small feeding big is good, big feeding small is bad!

fdracer

porting the engine's runners is easy and is done w/ every streetport, so what would be the point of using the cosmo instead of the fd motor? btw, is the cosmo engine still called a 13b rew or is call something else?

setzep

Funny you say that because on my cosmo engine the intake manifold runners are about 1/4" smaller then the port on the block! I would have thought they would have done a better job matching the two up when they designed the engine. The intake needs to be ported ~ 1/4" downward to match correctly on the sec ports and ~1/8 on the primarys.

j9fd3s

iTrader: (3)

a little tibit, the cosmo engines are both rew's and they were out before the fd engines. rew stands for rotary engine twin turbo

mike

peejay

the cosmo engines are designated 13B-RE, only the FD engine is designated 13B-REW. Despite the fact that it has two turbos, the Cosmo twin turbo engine is *not* an "REW".

setzep: mazda engineers are not stupid. the mismatch that they designed in acts to bias the port flow. air still flows very well in the "forward" direction but does NOT want to flow easily in the "backwards" direction. you could port the intake manifold and see a very small flow gain in the forward direction but you'd also see a LARGE flow gain in the backwards direction.

engines don't make power by moving air backwards in the intake tract, which is why the system is designed with a bias like that. don't port-match it.

setzep

Hmm... interesting. I guess that makes sence. So you think it's mainly designed like that to help fight reversion?

fdracer

i thought rew stands for something like "re-engineered wankel". the fd's motor is different from the 13b in the fc so for some reason instead of calling it the 13c, they just decided to call it the 13b rew. if wouldn't make sense for the re to stand for rotary engine, because all the other rotaries before the 13b rew didn't have the re moniker.

peejay, the stepped interface isn't really necessary for a turbocharged engine, because the intake charge is under pressure, air really doesn't reverse itself and make it's way back up the intake tract. it helps a little under vaccuum if your port velocity is too slow to prevent reversion, but under boost the laminar flow that match porting produces is better than an offset interface. the mismatched ports btwn the im and intake ports actually cause reversion.

peejay

Air is always under pressure. Sea level is 14.7psi. If you're running 10psi boost, then that's 24.7psi manifold pressure. Nothing magical happens when manifold pressure exceeds ambient air pressure. Standard flow principles still apply. The only difference is that with a turbo engine, you can just turn up the boost to make up for shitty ports, but wouldn't you rather have an engine that makes as much power on lower boost?

The FD engine is called the 13B-REW because the W stands for "double". As it's explained to me, W rolls off the Japanese tonque easier than just double. I don't speak Japanese so I will take their word for it.

The 13B in the FC is actually very similar to the 13B in the FD, as opposed to the 13Bs used from 1974-1985. Mazda kept the name 13B for the same reason the 12A retained its name when it was redesigned: they wanted to maintain name recognition.

crispeed

The intake manifold runners on the Fd's are also smaller than the port on the block.
Reversion is a problem with the stock setup. Poor exhaust manifold design along with too restrictive turbos, exhaust system etc. are some of the many reasons. Have you ever wondered why the secondary runners are always full of carbon.
With the proper setup reversion is reduced too minimum.
I have many bridge ported turbo motors running that got fully ported and polished intake manifolds and there are no signs of carbon build up in them even after many miles of street use. I've also seen ported and polished intake manifolds that suffer with the same problems as stock ones due to restrictions. I've never lost any power with a ported intake manifold.
There is a lot of power hidden in the intake manifold!

crispeed
87 Rx-7 TII
9.204@150.47mph
2600lbs
un-tubbed

j9fd3s

iTrader: (3)

the factory book ive seen lists the 20b-rew and the
13b-rew for the cosmo, we know about the fd first cause thats the first one we saw

mike

13BAce

My friend bolted his S4 transmission to his FD motor. So the FD motor should bolt up to the Cosmo motor.

setzep

I'd like to see that

setzep

hmm... You woulden't like to give me some pointers on how to port/polish my intake would you?