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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.
Looking through the papers Mazda talked about the IO 80° BTDC IC 80° ABDC for the PP to be optimum. Was wondering if anyone else had followed that guide line in cutting their PP holes and placement? Using my cad I'm looking at a hole center of 215 mm from the bottom housing leg and then approximately a 50 mm hole to achieve this timing. Anyone else find similar? Will try and confirm with a degree wheel when I get around to getting my 2nd practice housing cut. Just looking for confirmation on whether that appears correct if anyone had followed the same timing.
my friend has a set of JDM P port housings, and the way they did it is pretty nice because its simple.
the P port is straight, 90 degrees to the oil pan surface. they made a sleeve with a flange to support the intake flange. cut 1 into the rotor housing is the ID of the port and goes all the way through. cut #2 is the OD of the sleeve (its near enough 50mm), and the second cut goes into the wall of the Trochoid by about 1mm, this gives the sleeve a flat part to sit on, so it makes it really easy to assemble and seal up.
having the intake flange separate from the actual port sleeve allows some misalignment, and its actually setup so that the MFR intake manifold will bolt right up.
FWIW, a 50mm diameter hole will leave 15mm of surface on either side of a 13B. You wouldn't want to go much narrower than that. I also found that it is crucial that the sleeve extend at least partway into the inner jacket wall and have a close tolerance fit. If you don't, the rotor housing will crush slightly due to being unsupported.
After screwing around making my own, I figure that the $1500 or whatever that new peripheral port rotor housings run is money well spent.
The boring and sleaving was the easy part, machining on the mill with a boring bar and lathe work on the sleave Was more looking for confirmation on the dimension for the port location, 215mm from the oil flange/housing foot to center of 50mm port.
Yeah, everything I have seen suggested the rally cars used the same MFR rotor housings (and rest of engine) as road racing. And since the rally cars were built in 1983, that means "early".
The rally cars were a glorified privateer effort, and they used as many pre existing components as possible.
here is a summary of known info. basically its semi complete. in the USA nobody ran the 13B in an Rx3 (maybe RB did, they went drag racing and to Bonneville), it would have bumped them from GTU to GTO. the later stuff, i have a Mazdaspeed Japan catalog, and it has the 20B in it, no relation to the JC Cosmo engine, it is a 450ps slide throttle EFI dry sump. and then there are pics of the R26B apart, and the rotor housings are different. i think the drawing in the SAE paper is to scale (SAE 920309)
it is perhaps also worth mentioning that when the factory went turbo they switched to the bridgeport as it has less overlap, as seen in the RB Bonneville FC
Been looking for a copy of the SAE paper, but several years ago the SAE cracked down and started threatening people for hosting them free because they want people to buy the paper off the SAE website. Sometimes you can still come across a free download, but haven't found it yet.
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