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Naturally Aspirated Performance ForumDiscussion of naturally-aspirated rotary performance. No Power Adders, only pure rotary power!
From the "12A" to the "RENESIS" and beyond.
My first post here goes.
im from the uk so we don’t have as much look with parts and engines. I’ve picked up an 84 12a engine, never been split, so I’m going to be rebuilding it And either bridge or street porting it. And then am going to fab my own twin 40 wrap over manifold, using dhla or dcoe’s due to an abundance of them over here. Going to have to run a side alternator for space for the twins. Exhaust wise it will pretty much just be 2 pipes straight out will put 1 box in if needed as it’s going in the rear of a vw beetle.
So so has anyone ever had a go at there own manifold? I’ll update this thread as I go.
I can't imagine that the time and effort would be more economical that buying a proper manifold. A streetport with a large single DCOE would be fine enough, and there are manifolds already produced.
I can't imagine that the time and effort would be more economical that buying a proper manifold. A streetport with a large single DCOE would be fine enough, and there are manifolds already produced.
i did think this mate but I fancy doing something different and possibly not done before. Also any manifold for me has to be imported and is around 300 to get it here. I can fab one for 100 so I’ll probably have a go if it doesn’t work then I’ll look at importing one. But thanks for the input whiz bang.
A pair of 40mm DCOEs should work; two 30-32mm chokes per rotor is right in the realm of the same venturi area as one 42-44mm choke which is about right. It's not done as much anymore, but there used to be some shorty carbs-coming-straight-out-the-side-of-the-engine style manifolds to take a pair of DCOEs for these engines. Only thing is wraparound manifolds might end up with more runner length than you'd want for a healthy bridge port.
A pair of 40mm DCOEs should work; two 30-32mm chokes per rotor is right in the realm of the same venturi area as one 42-44mm choke which is about right. It's not done as much anymore, but there used to be some shorty carbs-coming-straight-out-the-side-of-the-engine style manifolds to take a pair of DCOEs for these engines. Only thing is wraparound manifolds might end up with more runner length than you'd want for a healthy bridge port.
That’s what I wanted to hear. I’ll be keeping the manifold as short as poss but thought it would be the easiest way with the most space. Can always cut the manifold down and make a short side one if needed. May end up jus going streetport to be fair I’ll have to see and have a look into a few builds.
Mazda used to size the carb so that the venturi diameter = runner diameter.
twin DCOE on a short manifold would probably work really well, it seems like eliminating the bends in the intake helps a lot.
Ah did they. I’ll have to look into the space with a short side manifold once the body’s back on the pan but if it’ll fit I’ll do that saves moving the alternator also. Just wanted to build something a bit different and always loved the look of duals.
Only downside with an off-the-wall carb setup like you're contemplating is you're pretty much going to be on your own for figuring out jetting. In the end though, it's just an engine, lots of ways of giving it fuel and air work.
Only downside with an off-the-wall carb setup like you're contemplating is you're pretty much going to be on your own for figuring out jetting. In the end though, it's just an engine, lots of ways of giving it fuel and air work.
luckily I’ve been working on old aircooleds with various twin set ups for a while so hopefully just a case of try what I think will be best and then tweak it from there. Once I get going I’ll get this thread started with some photos etc I case anyone else is even thinking of going this way.
So I managed to strip the engine the other night. All looked ok apart from the front housing that’s wrecked. 😩😩😩😩
Foooookeddd.
Proper wrecked. So obviously I’m gonna have to search for another or is there any way I can use this as it’s gonna be like finding a needle in a haystack over here???
Other housings not as bad slight wear and a bit of scorching around exhaust. N code centre iron ready for porting.
