20B in the Series I JC Cosmo (90-92) had a silver manifold
20B in the Series II JC Cosmo (93-95) had a black manifold

20B engines were produced in batches of 1000 at a time, and divided into "runs"
- First run (problem engines) 001 to 999
- First run (A series) A001 to A999
- Second run (B series) B001 to B999
- Second run (C series) C001 to C999
- Third run (D series) D001 to D999

The last series you may see are the E's. These engine's were complete Mazda crate engines that were only available from the Mazda spare parts division. None of them came out in a car from the factory.

If there is no letter infront of the number you have a first run engine.

Differences between the run numbers are strength.

The first 2000 motors (first run) are the ones that Mazda had the problems with, and had changed lots out on warranty to the newer motors. Main problems were with the intermediate housings, not the eshaft as many people believe.

Most of these engines were the first to turn up in AUS and NZ as they were all removed from Cosmos in Japan, returned to Mazda & then sold off to various wrecking yards in Japan. Supposedly the dealerships weren't allowed to dismantle these engines. They were to be returned to Mazda complete & in return Mazda would send a brand new upgraded one back to the dealer.

Stock first run motors have a short life and its not a matter if they will fail, rather when, especially under higher boost levels (anything over 12psi).

The strengthened housings of the 2nd run (B to C) make the motor much more reliable and hold higher boost. These are the desirable engines.

As for the strength of the eshaft I have only heard of a couple people having problems in that area. I have never seen even a picture of a 20b eshaft failure.
Any problems mentioned with the eshaft however are on fist run engines.
If the center rotor fails it is more to do with the weak intermediate housings than eshaft flex.

I have heard and seen a pic of a 13b eshaft which had failed just in front of the flywheel, and since the 20b shaft is no thicker in that area I would imagine that would be where to expect it to fail as well.
There is a extra bearing in the 20b to support the eshaft so it's no worse than a 13b for bearing area.
Reving a rotary to high rpms stresses the eshaft more than high hp at low rpms.

The 20b eshaft is lots strong enough if the rpm is kept below 7000rpm which seems to be where the power drops off anyhow.

The eshaft has been wrongfully blamed for causing engine failure, when in reality it was the fault of the weak intermediate housings.

Early motors 001 all the way to the late C motors have the dowel pins that have the step, and in the later ones the stopped using the step dowels and went back to using all the same pins. Cant imagine what the idea was to use a pin with a step on it - there doesn't seem to be a benefit at all.

I have also seen a few engines arrive here in Australia with the numbers ground off. This seems to have happened in North America as well. If they were ground off in Japan, they will still have the number stamped on the front plate under the alternator(cant get the grinder in there to get that one!).
Most of these engine's have been rebuilt for test purposes by the factory by using bits & pieces from various engines, hence the grinding off of the conflicting numbers.

 

that about sums it up.

matt

 

the only thing i will argue you over is my engine is #246 and i got the coil brackets complete, the starter, fan, ecu, harness etc etc. mine is an early motor and the car was not put back together, it also had about 50k miles on it. the engines had never been apart also
i will argue that we have no idea that they recalled any cosmos. they may have made the dealers send in fauly motors complete on an exhauge basis, like they do here in the us, but i doubt they had a recall. my point is we have no info one way or the other.

mike

 

Yes, most of this info is just hear say. All of what I posted is a collection of various info from the forum and the net... so there is sure to be mistakes in it. Thanks for pointing that info out.

Anyone else see any changes that need made?

 

mazda only changed out motors which failed.
my #454 is the same story as j9fd3s
it has never been apart and
came in the front clip to my house, runs strong
but will be changed out of the b motor I have built
soon, and I cant wait to open up that early motor
to see the differences for myself

matt

 

thats the way they do it here, the dealers get a rebuilt exchange motor. in japan though they might have gotten new, and then the old ones are usually sold off. they are supposed to be thrown away, but we knew when we sent 6 speed miata trannies back that they would end up in someones car

mike

 

Series-I = 1990-1993 (JCESE)
Series-2 = 1994-1995 (JCES)

1st batch 000 - 999 from cars JCESE-100031 - JCESE-100830

Suplus engines must have been "spares"

2nd batch A000 - A999 from cars JCESE-100831 - JCESE-101???

Never imported a Cosmo with a black manifold & we have done every year version from 1990 - 1995.

A-series motors (2nd batch) are ok, the shaft problem was no more for them.

Many of the first batch powered Cosmo's had engine failures under warranty. Even if the engine was suspect, it was changed. The dealership were under orders to crate the 20B back to the factory where a new engine would be sent back complete.

The dead ??? engines would be sent to the wreckers where back hand deals ment they found there way to the exporters & many early series motors came down under in the mid 90's. At one stage you could get a 20B for AUS$1800

High boost wasn't the problem with the early engines. It was the "snap torque". The engines would load up to 95% peak torque inside 1 second at a low 2000rpm. Thats what made them pop. Early engines with single turbo's running 15psi would be fine as they would have to rev to get that power. less lateral loading at 4000rpm+ you see.

Its almost always the centre rotor (as stated) that goes, been there, done that. Centre part of the shaft is the point of most flex.

I have seen the later C-series engines with the extra meat on the side plates. yet they seem to be as reliable as any other A-series plus engine.

Engines with the numbers ground off are factory re-built engines that have been used as warranty replacments to keep costs down. This was done later in the Cosmo run & not earlier.

 

I heard the latter series engines had extra dowel pins. If this is true; and if the 20b housings were replaced with 13b housings(larger exhaust sleeve), would the 13b housings have to be modified for the extra pins?

 

no extra pins
matt

 

So where are model #'s located on the motors

 

on the tops of the housings next to where it says 20b

 

Do later 20B engines really come with black intake manifolds? I have never - ever seen one that was black, except in a couple of (easily obtainable) mazda paintings. The only black ones I've seen were Hammerite coated by Pettit. Unless someone can come out and say, definitively, that they have seen Cosmos with black intake manifolds under their hoods, I think maybe its better to just check the stamped numbers and strike the color from the "how to tell them apart" list.

 

Question for all you 20B guys:

What kind of hp would a N/A 20B make if ported the right way, and ran by a stand alone ecu?
I realise it would have to be rebuilt with higher compression internals, etc. Just curious! I like what that Jesus Pedilla has accomplished with his N/A 3 rotor FB...

 

possssssssssssibly 300rwhp in streetable form. large streetport etc.
i think this would be part of the ultimate fc

 

Thanks Node, 300RWHP huh? hmmmmm..

I've thought about doing something like this for a while now, but after seeing what Jesus P did in his FB made me realise what a great reliable rotary that would be.... Actually Dave Lemon @ M-Trix has an N/A 3 rotor too with NOS....
I have a T60-1 turbo'd, Wolf Driv'n 91 TII now with a street port, but i don't like some of the lag issues for auto-x'n...Its not terrible, but I had better.

.... I wish I could drive an N/A 3 rotor...good luck I know

I may have to look for some parts here...

Brad

 

Some 20B's did come with black intake manifolds. (actually charcoal color) if you want I can post a few pics of some. I can't confirm what years or models had these, but I know there are a couple forum members who have them. I think it's either "Turbo 3" or "usfdr" that has one...

 

Thanks man. That's interesting though. I wonder what the black signifies. I can't imagine it being a random thing. Maybe the last year of production only?

 

Can't be the last year of production. I have had about 80 Cosmo's through the shop since 2000. Mazda only sold 363 in 1995. I have seen 3 1995 models. None of them & any of the other 80 have ever had a black manifold.

What you may find is they are rebuilt engines & the rotary shop such as RE-Amemiya paints them to signify one of there own re-builds

 

Ok, that sounds a bit more likely to me. Like what Pettit does.

 

I believe that some actually did come stock in that black color. But have never seen any. Odd.
http://www.se-rx7.com/20b/ that picture definately gives me beliefs that some came with the black intake manifolds stock

 

That's a painting.

 

Its a mazda officail painting from what I belive is from the eunos cosmo brochere ( I can't spell )

 

Right, I know it's a Mazda Official painting, but those are not always exact representations. There are also a couple of photos that are "official" Mazda releases where the intake manifold looks black, but could just as easily be shiny silver, just caught in the wrong light. I'm not trying to argue for argument's sake. I just have this feeling that the black manifold might not be as significant as we're all making it out to be. We still have no idea why only some (seemingly random) intake manifolds are black. Until we know that, I don't think that having a black intake manifold automatically indicates that the engine is more desirable than one with a silver intake manifold.

 

Nevermind, I did some research and usfdr's intake manifolds were powdercoated black.
I'm starting to speculate that black ones are just painted/coated ones, generally rebuilt engines...

 

Looking up several posts.........Now where did I read that before...........