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oil injector question-- converting a 12a to EFI

Old 12-13-17, 10:36 PM
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ON oil injector question-- converting a 12a to EFI

Hello fellow Wankelers!

I have a fresh 12a street-port (maybe the last one ever built by Dave and Mazdees?) huffing through a RB holley.
For a few reasons, I've decided to put EFI on it. It raises a question of how to best handle the MOP oil delivery. I'm considering using the oil injectors from a 13b, installed in the primary intake runners, close the the intake ports of the side housing. The 13b uses four injectors, of course, and the 12a has only two outputs on the MOP.

I've noticed while googling pics of the injectors, the rotor housing injectors appear to have a different diameter 'spray hole' than the manifold injectors do. They are also different lengths. I'm not concerned about length, but I'm curious if one type of injector has a different flow rate than the other type. I don't have any injectors on hand (planning on buying new) and I don't have a 13b car shop manual on hand.
Does anyone have a set of oil injectors handy who can measure or eyeball the spray hole diameters and let me know which (if any) is bigger than the other?
Secondly, does anyone have a 13b manual handy who can tell me if they list the flow rates of both types of injectors? (perhaps in the MOP test procedure)

This info should help me decide which type of injector to buy, or if I should have 4 injectors being fed by the 12a MOP with T-fittings. I can get a sense of flow rate from the 12a shop manual's test for the MOP, and compare. I suspect the oil volume given to a 12a is probably similar or more than a 13b, as I've just recently read somewhere that metered oil volume had decreased over the years with newer engines being fed less than older engines. (unverified, just read)

A third question, does anyone know if a 13b 4-outlet MOP will bolt onto a 12a engine with no issues or significant modification? If yes, that makes using 4 injectors 13b-style a no brainer, although I'd still need a mechanical connection to the throttle valve to vary the oil volume dependant on load.

Thank y'all kindly! This site, you peeps and RX-7s all rock!


(passed the mustang, felt like I was parked when the Porsche went by)
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Old 12-14-17, 01:08 AM
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I believe you would need a GSL-SE front cover to go with the 4 outlet injector.
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Old 12-14-17, 02:27 PM
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Why not premix it and not worry?
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Old 12-14-17, 07:01 PM
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Originally Posted by lduley View Post
Why not premix it and not worry?
i use a bit of idumitsu premix as a safety cushion. i do a lot of driving and find myself filling up sometimes 3 times a day. it's tough to gauge exactly how much is left in the tank and figure out how much oil to add. A wonky fuel gauge aggravates this issue. i don't want to carry a jerrycan around to mix the right ratio on the spot, and there's a small risk of finding myself without adequate oil in a time of need. For me, surviving on premix is a pain in the butt. For street driving, I'm happy to rely on the MOP and add a little extra idumitsu on track days.

I've just been told from another source that an FC front cover is the way to go to gain 4 MOP outlets, EXCEPT the front cross member won't bolt up. so it sounds like sticking with the original 2 output MOP is the plan.

This leaves open the questions about the injectors.
Thanks again for the help, ladies and gents!
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Old 12-15-17, 07:45 AM
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It is not much of a jet. It just oozes oil out onto the hottest part of the apex seal.
Be sure to use the small sleeves to reduce cavity volume loss during decal (and subsequent starvation during acceleration).
See attachment for volume needed with estimates to 9000 rpm.
Also attached ... apex seal temps. Or why the MOP is so important...... Notice the center of the seal temperature with a peripheral exhaust port .
Attached Thumbnails oil injector question--  converting a 12a to EFI-mop-vs-prremix.jpg   oil injector question--  converting a 12a to EFI-apex-temp.jpg  
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