The short answer is "emissions". As I understand it, the overlap that results from porting produces a very dirty exhaust.

A second answer is, I think, the market for which the Cosmo was developed. At one time, there was an industry-wide limit of 280 hp in Japan, so going for 500 hp was pointless.

I've been told that there is a difference in the casting around the exhaust ports between the 20B and 13B-rew housings. As a result, you're ahead to just go to the 13B-rew style.

Since I don't do my own engine work, don't take my word for it. Talk to the folks at Pineapple.

 

i definatly will give them a call. about having a 280 HP cap in japan... if they could just tune a rotary better why wouldnt they just use a 13b and juice it up? pettits cars w/ 550HP pass emitions dont they..... im not meaning to argue, i just dont understand maz-duh's approach

 

I'm hoping that someone with more detailed knowledge will jump in. What I have read in various groups is that the Japanese manufacturers had a "gentlemen's agreement" to cap their advertised horsepower at 280. This was an effort to head off government and/or insurance industry sanctions, as well as a horsepower "arms race".

As a result, there was a period where all of the hot cars, for example, the Nissan Skyline, were advertised at 280 hp. When tested by car magazines, many of them were found to have more, sometimes much more, but the gentlemen's agreement on *advertised* horsepower was kept.

Somewhere in the last few years, that seems to have fallen by the wayside. Everyone knew that the "280" was bogus, and, IMHO, the need to compete with German and American high-performance cars pushed the Japanese into advertising real numbers.

As for Pettit's car passing emissions, I wouldn't bet on it. (I went to www.pettitracing.com. The Banzai link brought up a page which extols the car, but does not mention emissions.) I'm not saying that it couldn't. High-flow cats and careful tweaking of the EMC could produce a map that would pass emissions.

That's how Peter Farrell got his first 20B through Maryland emissions. (It helped that the technician at one, specific testing site was a Mazda enthusiast. ) The cat burned out on the way back to the shop from the testing site. Then, the real maps--the ones that would be rich enough to prevent pre-detonation--were restored.

So, to summarize, Mazda's approach was dictated by marketing, cultural and legal pressures as much as by engineering concerns.

A recent example: Based on what I have read, it seems that the RX8s were detuned to generate slightly MORE emissions in order to keep the cats hot during cruising. This decision allowed Mazda to meet the 7-year requirement for emissions equipment longevity. As a result, the mileage and horsepower of the new car have been compromised negatively and generated a fair amount of bad publicity. Those drawbacks were accepted based on management's need to get the car to market AND meet regulatory requirements.

If that sounds a bit bizarre, read "Alice in Wonderland", and it will all begin to make sense.

 

when an oem tunes a production car they have a bunch of other things on the list before power.
1. emissions
2. fuel economy
3. it cant blow up if you put the wrong fuel into it
4. its gotta be perfectly drivable by anyone
5. durability

so the oem tuning is a compromise they have a lot of other things to worry about before power, if you forget emissions, and tune it to only run on high octane fuel, and dont care how long it lasts you can get more power than mazda. mazda does know how to get power btw, they had a 450hp na 3 rotor in the 80's

i got a chance to ride in an stock ecu 20b truck last night, and its butter smooth. since both engines are stock we're gonig to dyno battle the only real difference is that mine has an aftermarket ecu in it

mike

 

oops

 

Good point. I forgot to mention that Farrell's 600 hp was with race gas.

 

Mazda used 13Bs in most of the Cosmo's, only about 25% of the JC Cosmos had the 20B.
What they were looking for was an engine with plenty of torque to handle pushing a 1600kg car through an auto trans with some shred of performance. A highly tuned 13B wouldn't cut it for torque or reliability.

 

beautiful!!!! im completely caught up... thanks everyone for all the detailed info... its kinda starting to make sense now.

BTW mike, let us all know the results of the dyno battle (im assuming hte truck is running a 5speed?). butter smooth is exactly what i thought the first time i drove an FD! i was used to glug glug glug, and shaking from my mustang gt that got stolen..... best thing that ever happend to me . the first time i ever drove a rotary, those were the exact words that went through my head... ahhhhh rotary..... long live the rotary

PS i rented X2 the x-men movie lastnight.... there getaway car was an rx-8.... i smiled

 

the truck is a 5 speed, we're gonna dyno it with the afr chart and i'll match it with mine, and see whats up

 

Wrong...........

Mazda sold about 4916 (13B) + 3937 (20B) = 8853. Meaning 45% were the 20B option

The Cosmo was designed from the MX-03 concept car in 1985 which featured the 1st 3-rotor engine they did. This was to show the world that Mazda was a world class player & give the triple rotor technology a car to be showcased in.

 

Cam's 1 rotor blue FB ended up with a small turbo(don't know the specs) but ended up in the low 200 hp (wheel) range. 204-208 range is what I wrote in my notes of the trip. He was dyno'ing it when I went to visit their new location 2 years ago(January 2001) FWIW, it sounded like ***, made me cringe when he hit full power cause it sounded like my motor when I blew the rear rotor seals(uh, thus running on one rotor)

 

^ sweet, i totally want one!!!

 

I have a dumb question...
I am looking at a factory exhaust manifold from a 20B. Which turbo spools up first?
Common sense says the smaller turbo does but common sense also says the (bigger) turbo with no flapper across the turbine entry does. Help!

Also, from what I can gather the second turbo (whichever one it is) comes in at around 3500rpm, Correct?

 

I think it does the front one - the one that has it's own rotor exhaust passage.


-Ted

 

it works off the front turbo until 3200-3500rpms (ive only been in 1 sequential 20b car and you cant really tell it comes on) and then it opens up the rear turbo to the rear rotor

 

an idea to simplify the twins.
could a guy not remove all the junk that makes the twins
sequential and put a reed valve between the outlets
of the two turbos so that the first turbo doesn't loose
boost through the 2nd turbo, spinning it backwards?
this way the first turbo would start to make boost and
once exhaust flow gets the 2nd turbo up to speed its
flow would just be added to the 1st turbo through
the one way reed valve?
I maybe should have started a new thread for this
but this way only those following this thread will be privy
to this great idea lol
matt

 

isnt that basically non-seq?

 

well i dont think i have ever heard of anyone putting in
a reed valve to keep boost from going from the 1st
back through the 2nd one.
thats part of the problem with going non-seq the 2nd
turbo can be spun backwards from boost blowing back
through it before it has a chance to get up to speed, and
this is from what i understand very very hard on the
2nd turbo, causing shafts to snap etc.

matt

 

The larger front turbo is the primary one. The secondary turbo at the rear comes online at 3500rpm (4000rpm=FD RX-7)

REgards

 

really??? the setups are basically the same with the FD turbos right? i cant remember anyone mentioning this before.

PS how is progress coming on your car/engine??? did you ever work out the bugs w/ the ecu & turbos? i talked to pettit and they are making like 14psi on the stock turbos. they confirmed that they didnt do anything drastic to them... i think they are running non-seq.

anyway, im buying a subframe in a week so my fun will begin soon there after....... im getting scared!!! heath

 

rotormotor> if it was me that you were asking about.
I have been busy lately no time to work on any of the
car projects.
I have been running back and forth to the hospital for
a couple weeks now, nothing is wrong, unless you
consider having kids a problem a prospect i am still a
little unsure about.

matt

 

Thanks for that. The engine is being fitted to an aircraft so small details are kind of important

 

ah it took me a while to figure out what you're saying, interesting. i think theres an easier way to do it, you can put the valve back in the "y" pipe and hook it up so it opens when the second turbo hits boost.

congrats on the kid, matt

 

kids

 

Congratulations! best of luck to you in that department! so am i hearing twins???