BOOSTD 7

Ha ha ... beatcha to it Evil

DELTA_Rotary

This should clear alot of questions up. Thanks guys.

So are you going to move all the 20B threads in here now?

repuguru

Everyone says building a mongrel 20b is a nightmare. I am interested to know what is unique to the motor other than the E-shaft,thru bolts,and 20b centerhousing?

87GTR

iTrader: (61)

if I didnt have a 20B already I would do a Bridge Port on 89 - 91 motor.
well more like a drill port.

instead of milling out all the area in for the port you drill 3 or 4 hole
just to provide a little extra flow.


my next project after I finish the 20B would be ummm a 4rotor 13b from the NZ guy I think PP would do just fine

Tony

Evil Aviator

Hehehe, yeah, and if you bought a 20B engine tomorrow, you would probably have it running before mine, too.

I don't think that's a good idea, but it's up to the other moderators. I think that we should just start from scratch. It will only be a short time before the basic questions are asked, anyway.

Well, it depends on whether you are building a 20B, or just a custom 3-rotor engine. Anyway, you would also need a 3-rotor intake manifold, throttle body, fuel rails, and oil pan. If you want to make it a twin-turbo like the original 20B, then you will also need 2 turbos, a turbo manifold log, and wastegate. Since I have known people to get working 20B-REW engines for $2,000-4,000 USD, I don't see any reason to fabricate one of your own. Back in the day when the $20,000 USD 13G was the only 3-rotor in town, then maybe making your own was worth the trouble. Why not make your own RX-7 from scratch, too?

repuguru

What if you don't want to run a turbo and use low compression rotors. What if dont plan on running an elaborate injection system.
All the 20b's I read about require major mods to allow them to work in the U.S cars. Thousand and thousands of dollars just to make that $3000 block run. I just would like to figure out a way to create a strong torque motor with out spending $25,000 for a firebreather
Why would I assemble an RX7 from scratch when I can go down the street and pic up an Auto Trader and buy one?
I haven't seen any J-Spec Cosmo 20b's in there for sale lately.

Evil Aviator

Good luck. Please keep us posted on your progress.

My point exactly.

www.corksport.com/
www.mazdatrix.com/usedpts.htm
www.fc3s.org
www.rotaryengine.com
http://www.nippon-motors.com/performance_engines.htm

Also check these for occasional deals on a 20B:
https://www.rx7club.com/forum/forumd...?s=&forumid=13
http://pages.ebay.com/ebaymotors/ind...sPageName=ML01

repuguru

Thank you Evil for all of your links. Unfortunately they are all links for low-compression 20b's w/turbos. I have looked at some of those before. Not the engine I am really interested in, too many things would need to be discarded to build the unit I described. Thank you for the wish of good luck on finding info about building the mongrel. I was hoping I could find some ideas here.
Maybe one of my fellow Rotorheads will respond that can help me find out a little more about the non-fictional 20b w 13b parts as opposed to trying to show me how little I actually know.

Node

iTrader: (1)

whats a 20b?

Evil Aviator

It is a low-compression 3-rotor engine with twin turbos.

j9fd3s

iTrader: (3)

im about a week away from starting mine, with a stock 20b engine, wiring harness, ecu, injectors etc

all of the 20b's ever made were twin turbo low compression, if you want a non turbo high compression i know of one thats apart for sale cheap, you would still have to buy rotors though.

mike

repuguru

Is the high comp rotor from a NA 13b the same exact shape and outer dimensions as the 20b low comp rotor? Of course am not going to assume anything here.
Whats the compression ratio on a 20b rotor?
Whats missing besides the rotors on the 20b that you know of being apart? Whats broken, if any thing. Why was it dismantled?

Node

iTrader: (1)

why is it called a 20b if it has 3 rotors, why not call it a 32b or 3tt. Mazdas Stupid. I hate mazda!

DELTA_Rotary

I dont know if this is correct of not but 13B = 1.3 liter, 20B = 2.0liter, 26B = 2.6 liter. I really have no basis for my posts its just something I noticed. I know there are other rotaries engines that have other numbers like 12A and so for but its just something I noticed.

j9fd3s

iTrader: (3)

as far as i know the compression is 9:1 like the comtemporary 13b's, and it is the same "shape" thats the most expensive part for them to modify at this point. the only things that are 20b specific are the e shaft, front and middle steel, and mazdacomp used to sell the rotors as light wight rotors, but ive never had one in my hand so i dont know.
i didn't bother to find out why it was taken apart mine was in the mail already. pm me if you are interested im sure its still available

mike

Evil Aviator

Yes, the 12A is 1.2L, more or less (OK, less, but close enough). The only production rotary engine in somewhat recent times that doesn't make any sense to me was the "13G" 3-rotor.

All of the modern "B" engines have interchangeable rotor sets. The 20B-REW came with 9.0:1 compresson rotors, which are really more of a mid-compression rotor when you consider the 8.5:1 and 9.7:1 rotors of the other B engines.

Node

iTrader: (1)

ha ha, im suprised some of you took me so seriously, and yes, a 20a is a dream engine.
Wanna race?

Evil Aviator

Don't worry, I don't take you seriously; I just couldn't resist the opportunity to rag on both you and repuguru at the same time. Hey, I gotta be Evil.

Race? What, your bicycle? Hmm, I may take you up on that once I get my starter mounted. I think I may be able to take you if I get a big enough battery.

repuguru

Better watch it Evil A. I heard there is an Anti-REPUguru running around here somewhere. Not the same ray of sunshine I am.
The rotors I have in my supply of parts are from the 74-78 13b. They have a 9:2:1 comp ratio.
Who would someone trust to balance a 3 rotor rotating group. Will the standard 13b flywheel and counter weight work. I understand that all the 3 rotor engines are set up for Automatics from the factory, which may not be a bad thing. I want to use it in my truck, so an auto set up wouldn't be a bad thing to have. And since I don't really want to set it up with a turbo I really don't think this thing will see over 350hp, so maybe that will open up choices to tranny options that will live with the beast.

Jeff20B

iTrader: (13)

Or you could get the RB light steel flywheel which I'm 99.8% sure will bolt to the 20B rear counter weight. But then again, with a 20B pushing you, an automatic would be just fine.

j9fd3s

iTrader: (3)

its just a regular looking counter wieght and yes a racing beat flywheel will bolt right on

mike

repuguru

Is that auto tranny hard to find here in the states?

It seems that most of the swaps don't involve using the auto from the Cosmo JC. I know I have seen the whole 20b unit shipped to a friend with the auto attached. He sold the motor before he ever did anything with it though.

I wonder if somewhere out there is an adapter to mate a GM auto to a Wankle? One of their trannies could handle the torque if a Mazda unit was not available.

I guess Roger Mandeville's shop or Jim Downings shop could balance the rotating group.

peejay

There is a kit available to mount a '74-up rotary to a Ford T5, provided that you already have a '74-78 bellhousing. (I'm told a T2 bellhousing would also work) I don't know if that's a good idea. 5.0 wisdom dictates that if you buy a Mustang with a working T5, SELL IT before it breaks, because it WILL break and it's worth a lot more in working order (rare) than broken (very plentiful). However due to the nature of the beast they make lots of cool race trannies for the cars I keep thinking about a Liberty trans swap into a rotary...

The reason manual transmissions are so rare at GM is because they usually don't have one that can handle the torque, however they have plenty of automatics that can. (T5s for instance ae only rated to 300lb-ft - when 305 and 350 engines were available in Camaros, a 350 meant auto-only, while you could get a T5 behind the 305) That said I'm sure you can have a GM automatic mated to a rotary. There's a pic in the RB catalog of one of their drag engines mated to what is obviously a Chevy bellhousing

repuguru

I'll go look at the pic. A good old American tranny with a shift kit. I'd love to get a higher stall speed torque converter. I don't think you'd have to go to high with the converter for the 3 rotor to achive the desired launch though.

Jeff20B

iTrader: (13)

Or you could keep using the Mazda Jatco tranny with a shift kit and valve body adjustment like I'm going to (stock CD Cosmo tranny). It can handle at least 450HP (not sure about torque rating). It would probably break at 600HP though.