Hi, 20B noob here.

I've been looking at the 20B engine lately and it really is amazing. I understand rotaries to a point as I have an RX-8, so I'm not completely clueless.

I keep running across different porting setups for the 20B and I wanted to better understand them any why they work. We RX-8 owners don't usually meddle in that territory because our engines don't gain much from porting.

To the point:

Can someone define for me

"Mild port"
"Street port" and
"Race port"

In terms of port location, size, and shape? Also, explain to me how/why each dimension affects performance?

Can someone tell me how each will affect power and more importantly powerband?

Next, can someone explain to me why the cosmo redlines so low when I often hear of 20B race engines running at 9,000 easily? What's so different about them besides apex seals and...well...porting?

Thanks,
-Falken

 

Street Port is an enlargement of the stock port. The degree of the port is what people will refer to as a "mild" enlargment or a "aggressive/large/race" enlargement.

After there is Semi-Bridge Ports, Full Bridge Ports and most extreme Peripheral Ports or P-Ports.

 

Thank you! But honestly, I don't understand

"Semi-bridge port" or
"Full bridge port."

I understand peripheral port but I was under the impression the 20B already used peripherals. I thought the big draw of the REN was side ports as opposed to peripherals.

Why does anyone bother with enlarging the ports just a bit? What's the downside to big ports?

 

Half bridge is when only the secondaries are "bridged". And a full bridge is when both secondaries and primaries are "bridged". NOW DO A SEARCH.... why do you people have so much trouble with the S E A R C H function

-J

 

I've been sifting through the search results for a while now. Nothing really except people listing their mods, usually including a porting style.

I think I might understand bridge though. When ports are joined offering more port area/better flow?

Also, is there a standard "street port" or "bridge port" dimension/shape or do people just customize the ports and than categorize them by performance?

 

We are mainly limited to our port sizing and shape due to the internal tracks the seals travel in the engine...... READ every single tech article in this first link and don't ask another question till you do .

http://www.yawpower.com/techindx.html

READ this as well.....

http://www.rotaryengineillustrated.c...orks/index.php


-J

 

Because the search function has become a useless POS now on this forum. You search anything and you find 1,5M useless threads.

 

I have reached the section concerning pressure waves, and need some clarification.

I MIGHT understand half of the "pressure wave sign changes when it expands" concept. My understanding is that a high pressure wave carries momentum with it, and when it exits into atmosphere it leaves low pressure behind. But I don't understand is how when a low pressure wave reaches an area of greater area how it converts to a high pressure wave. If the pressure is already low - an it enters an area of greater space - where is it gathering pressure to reflect??

I don't understand.

 

That's because 95% of this forum is ignorant and and retarted and most of the threads on here are pointless. But if you search with the right "words" etc. you CAN find what you're looking for.

-J

 

Google rocks
http://www.mazdarotary.net/porting.htm
http://www.rotaryengineillustrated.com/porting/15.html
http://www.turborx7.com/porting.htm

 

the 3 rotor race engine, also known as the 13G doesnt share many parts with the cosmo production engines. it uses a dry sump oiling system, which is key. it also has different rotors, rotor bearings, apex seals, irons etc etc

the cosmo engines are also setup to pull a big heavy car with an automatic transmission around, so they are designed to make power lower down.

the power difference between the two, is due to the race engine using peripheral intake AND exhaust ports, its rated at 450ps@9000.

 

Is there any way to build a cosmo 20B that revs to 9k?

 

Yes

 

Do you have any further details on the ramifications?

 

the ramification is an empty wallet....

basically theres a 2 prong attack on the cosmo 20b to get it to 9k

prong 1. power: it doesnt make any power over 6200rpms. the stock turbos probably become really restrictive around there, as boost drops off really fast. in non turbo form to make peak power at 9000rpms, you'd need a bridgeport or a peripheral port, traditionally

prong2. reliability: you need more oil pressure, and more oil flow. you're adding loop lines and feed lines for each bearing. a race car would ideally be dry sump. balancing the rotating assembly is a good idea. cooling is also a big issue, over 350hp, in a roadracing scenario, its hard to get enough radiator into an rx7 chassis.

its much much cheaper to just use the big motor as intended, and enjoy the powerband from 3000-6200....

 

Tell me more about balancing the assembly. What would be involved with that? Here is my guess, correct me if I'm wrong: What I have heard is that the motor comes with rotors arranged in a 0-180-0 configuration - which is what is responsible for its choppier sound. Correct? So that would mean that they would have to be somehow arranged in a 120-240-0 configuration. And that would involve a custom E-shaft, which must be a couple of G's itself.

How would one configure an engine to make 3-400HP N/A, with a powerband similar to 13B-REN (i.e. flat increase to 9k)?

 

no! the stock 3 rotor engine is 120 degrees apart, fires 1-2-3. balancing is like balancing a wheel and tire, kinda. you weigh each part, and then spin them, you balance the rotors to themselves, then the e-shaft, counterweights etc etc

to make power up to 9000takes a bridge or peripheral port.

 

What is the procedure for when you find a part out of balance?

 

its kind of a moot point, cause you dont have the tools to do it, but you either add weight, or machine some off

 

Is that the type of thing I can get done for me by the shop that I theoretically would buy an engine from? Or is that a specialty process that I have to do myself?

 

it gets done by a shop.

 

Price?

So where I am at now: A 400hp, N/A, 9kRPM 20B must be firstly rebuilt, than ported, than clearanced, than balanced, than better lubricated, than better cooled, and than better managed.

Correct the above.

 

yeah pretty much, it gets pulled apart, ported, clearanced, balanced, better lubricated, put back together, with a new computer, and bigger radiators.

back in the 90's mazda had a "sports kit" 3 rotor, its essentially what speedsource runs in the rx8 gt cars now, 450hp@9000 rpms. we checked a couple months ago, and mazdausa still stocks a lot of the peices.

peripheral/bridge ports arent really considered streetable either, so the question should be asked, a stock 20b can make 400hp all day long with a turbo, in its stock rev range (3000-6500), that means a stock 800rpm idle, mufflers, you could even make it pass an emissions test, is that a better fit?

 

That IS a better fit. But there is an issue with it.

The problem is where I live. Chicago. They check everything about your car in this city. Your not allowed to modify so much as an exhaust. They don't just have a certain "cutoff point" for failing emissions. They have average data on every car in production, and if your car doesn't fall within that average they check under your hood, and your screwed if ANYTHING isn't OEM.

Which brings me to my second problem. This is an RX-8. An RX-8 is younger than any 20B engine. Thus any 20B in any RX-8 is an engine older than the date the chassis was manufactured, which in my state at least, is specifically illegal.

The only way you can really get around that is to register your car as a race car, which means you can only drive it during, to, and from professional or amateur racing/car events. Granted that is a big *** loophole, as I could get away with car club events, going to the auto show, etc...

But really, no 20B RX-8 can ever be street legal anyways in my state. When I think about it, I don't really need the transportation. I live in a city for christs sakes, there is public transport everywhere, plus we have 2 other cars (other people in my family have priority but its not like we'd be carless)

So I figure, if its not going to be street legal anyways, why not go all out? Thats why I would consider a bridge or PP. It doesn't have to be "streetable" per se, just streetable for a few miles every weekend, or streetable out to the suburbs for a meet, i.e. not confined to a trailer unless on a track, doesnt take 20 people to start it, etc.

I'm just in the very, very preliminary stages of this. As you can plainly see by my questions I have at least a year of research to do. This is where I start.

Next, were talking about an RX-8 here not an RX-7. Boy, if anyone so much as whispers 20B on the 8 forums everyone kills them. I'm hoping to god that RG doesn't tell anyone

I heard bridge ports break. Tell me about that.

 

When I started reading this post...I was like WTF?!? I live in Chicago too and I'm about to drop in a 20B in to my FD so I wasn't sure what the hell you were talking about in terms of not modifying your vehicle . I continued to read on though and realized this was a discussion regarding a 20B in an RX8. That happens to explain a lot. That sucks man that you can't modify your 8. I'm pretty sure you can get away with the basic mods though. Up until a year ago, I was passing with every modification other than a bigger turbo and upgraded fuel system.


I think the cops are what you should be more concerned about. Thirsty, dirty cops who have nothing better to do than to harass you about "exhaust" and "front plate" and if you try explaining yourself threaten you with jail time. That's what I'm worried about PLUS we FD owners no longer have to pass emissions so cops are really my only concern.