20b In A Glc
09-28-2003, 02:41 PM
#402
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Thread Starter
Join Date: Nov 2001
Posts: 2,284
I need you guys to put your thinking caps on.
If you've seen my pics in this thread, you'll have noticed that I got a 20B exhaust flange and a few U bends to build myself a header. I also have a couple cast iron manifolds from a 12A and a 13B. I was going to slice the end off the 12A one and mate it to the front of the 13B one originally. Then I thought of the weight and the poor flow and decided to just get the flanged and stuff. The price was right, so it seemed like a no-brainer.
Well, the reason why I'm bringing this up is because there was barely enough room for the RB 12A header to fit in the GLC. It was ovaled to fit a 13B, and one of the pipes was dented in to clear the idler arm.
I won't know if three header pipes will fit untill I get the engine in there. I'm also not sure if the iron manifold will fit either.
What are your thoughts on the flowability of a 'log' style manifold and three exahust pulses per revolution? It's an option which may need to be used.
If you've seen my pics in this thread, you'll have noticed that I got a 20B exhaust flange and a few U bends to build myself a header. I also have a couple cast iron manifolds from a 12A and a 13B. I was going to slice the end off the 12A one and mate it to the front of the 13B one originally. Then I thought of the weight and the poor flow and decided to just get the flanged and stuff. The price was right, so it seemed like a no-brainer.
Well, the reason why I'm bringing this up is because there was barely enough room for the RB 12A header to fit in the GLC. It was ovaled to fit a 13B, and one of the pipes was dented in to clear the idler arm.
I won't know if three header pipes will fit untill I get the engine in there. I'm also not sure if the iron manifold will fit either.
What are your thoughts on the flowability of a 'log' style manifold and three exahust pulses per revolution? It's an option which may need to be used.
09-28-2003, 06:14 PM
#403
Senior Member
Join Date: Sep 2002
Location: Vanderhoof,BC(Canada)
Posts: 5,542
Originally Posted by Jeff20B' date='Sep 28 2003, 11:41 AM
I need you guys to put your thinking caps on.
If you've seen my pics in this thread, you'll have noticed that I got a 20B exhaust flange and a few U bends to build myself a header. I also have a couple cast iron manifolds from a 12A and a 13B. I was going to slice the end off the 12A one and mate it to the front of the 13B one originally. Then I thought of the weight and the poor flow and decided to just get the flanged and stuff. The price was right, so it seemed like a no-brainer.
Well, the reason why I'm bringing this up is because there was barely enough room for the RB 12A header to fit in the GLC. It was ovaled to fit a 13B, and one of the pipes was dented in to clear the idler arm.
I won't know if three header pipes will fit untill I get the engine in there. I'm also not sure if the iron manifold will fit either.
What are your thoughts on the flowability of a 'log' style manifold and three exahust pulses per revolution? It's an option which may need to be used.
If you've seen my pics in this thread, you'll have noticed that I got a 20B exhaust flange and a few U bends to build myself a header. I also have a couple cast iron manifolds from a 12A and a 13B. I was going to slice the end off the 12A one and mate it to the front of the 13B one originally. Then I thought of the weight and the poor flow and decided to just get the flanged and stuff. The price was right, so it seemed like a no-brainer.
Well, the reason why I'm bringing this up is because there was barely enough room for the RB 12A header to fit in the GLC. It was ovaled to fit a 13B, and one of the pipes was dented in to clear the idler arm.
I won't know if three header pipes will fit untill I get the engine in there. I'm also not sure if the iron manifold will fit either.
What are your thoughts on the flowability of a 'log' style manifold and three exahust pulses per revolution? It's an option which may need to be used.
09-28-2003, 07:08 PM
#404
Senior Member
Thread Starter
Join Date: Nov 2001
Posts: 2,284
The iron manifold may also stick out too far. 
But I think I may have found a solution. I might use part of the old 12A header and cob it together with some U bends to clear the idler arm. Remember I mentioned the 12A flange was ovaled? I could cut the pipes off it and weld them into the 20B flange.
09-29-2003, 02:03 AM
#406
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Thread Starter
Join Date: Nov 2001
Posts: 2,284
Thanks for the encouragement.
The next prob I've got to iron out is the AF mixture, and how to get it distributed evenly from the bottom of the carb into the LIM runners. Heh, I guess all these not-quite-fully-figured-out ideas from my many brainstorming sessions are now needing a stamp of approval before they go on the engine. The different exhaust possibilities are a perfect example, as described above. Now it's time to discuss and finalize the intake architecture.
If you've been following my progress thus far, and I hope you have... my good little children, I decided to put my faith in peejay's idea to use a V8 valve cover as a sort of box-plenum with a cheap V8 carb sitting on top for the look of confusion on peoples' faces as they stare at the engine bay wondering why a carb is on the valve cover. The idea is to have a sealed chamber where the AF mixture can get pulled into whichever runner wants it. Well, if you know about flow dynamics, you'll know that that is not a very good idea, mainly due to the engine's length. Basically, your front rotor will pop because fuel has mass and will tend to fly toward the rear rotor during acceleration. The middle rotor is ok since it's directly below the carb.
What's my solution? Well, I'm working on that right now. So far, I think I figured out a super cheap way to route the AF into each runner. I'm going to get some aluminum stretch/flex hose for heat risers etc. I think 1.5 to 2 inch will work. I'll fab a little mini-plenum to fit below the carb and it'll have at least three outputs, each with a hose on it, going down to the three secondary runners (they have nice factory "streetports" and no injector bungs to cause flow irregularities or whatever). Or maybe I'll do all six? Maybe if there's enough room (doubtful).
I'll test a length of flex hose in some gas to see if it'll hold up. Sometimes they are half aluminum foil and half paper, or plastic. The ridged surface inside the hoses should be beneficial, if I understand Sterling's ideas correctly. They'll all be kept safe inside the valve cover.
Note: all four barrels of the carb will mix together in the mini-plenum before entering the hoses.
My question for you guys is about the three secondary runners vs all six (pri and sec) idea. Remember, the 20B and 13BRE have the largest secondary runners of any production Mazda rotary. Do you think I'd lose tons of power if I just used the secondary ports only? My exhaust ports are still stock with their restrictive sleaves and everything, so I'm guessing I wouldn't lose hardly any. I could be grossly wrong though.
The next prob I've got to iron out is the AF mixture, and how to get it distributed evenly from the bottom of the carb into the LIM runners. Heh, I guess all these not-quite-fully-figured-out ideas from my many brainstorming sessions are now needing a stamp of approval before they go on the engine. The different exhaust possibilities are a perfect example, as described above. Now it's time to discuss and finalize the intake architecture.
If you've been following my progress thus far, and I hope you have... my good little children, I decided to put my faith in peejay's idea to use a V8 valve cover as a sort of box-plenum with a cheap V8 carb sitting on top for the look of confusion on peoples' faces as they stare at the engine bay wondering why a carb is on the valve cover. The idea is to have a sealed chamber where the AF mixture can get pulled into whichever runner wants it. Well, if you know about flow dynamics, you'll know that that is not a very good idea, mainly due to the engine's length. Basically, your front rotor will pop because fuel has mass and will tend to fly toward the rear rotor during acceleration. The middle rotor is ok since it's directly below the carb.
What's my solution? Well, I'm working on that right now. So far, I think I figured out a super cheap way to route the AF into each runner. I'm going to get some aluminum stretch/flex hose for heat risers etc. I think 1.5 to 2 inch will work. I'll fab a little mini-plenum to fit below the carb and it'll have at least three outputs, each with a hose on it, going down to the three secondary runners (they have nice factory "streetports" and no injector bungs to cause flow irregularities or whatever). Or maybe I'll do all six? Maybe if there's enough room (doubtful).
I'll test a length of flex hose in some gas to see if it'll hold up. Sometimes they are half aluminum foil and half paper, or plastic. The ridged surface inside the hoses should be beneficial, if I understand Sterling's ideas correctly. They'll all be kept safe inside the valve cover.
Note: all four barrels of the carb will mix together in the mini-plenum before entering the hoses.
My question for you guys is about the three secondary runners vs all six (pri and sec) idea. Remember, the 20B and 13BRE have the largest secondary runners of any production Mazda rotary. Do you think I'd lose tons of power if I just used the secondary ports only? My exhaust ports are still stock with their restrictive sleaves and everything, so I'm guessing I wouldn't lose hardly any. I could be grossly wrong though.
09-30-2003, 03:39 AM
#409
Senior Member
Thread Starter
Join Date: Nov 2001
Posts: 2,284
Hmm, maybe I'll just scrap that idea.
I spoke with a fairly smart rotary guy and he said the front rotor will die on a 20B if I do what I was going to do. The reason why is the 20B is such a long engine. Fuel has weight and all that. I feel like I'm repeating myself... So what is stopping me from mounting the carb a little further forward on the valve cover? Or what if I took inspiration from a chevy 250 straight six? It had a single barrel carb on a cast iron manifold. The front and rear runners are really long.
I spoke with a fairly smart rotary guy and he said the front rotor will die on a 20B if I do what I was going to do. The reason why is the 20B is such a long engine. Fuel has weight and all that. I feel like I'm repeating myself... So what is stopping me from mounting the carb a little further forward on the valve cover? Or what if I took inspiration from a chevy 250 straight six? It had a single barrel carb on a cast iron manifold. The front and rear runners are really long.
