Originally Posted by afterburn27

5. NA FC's have the OMP 'vacuum' lines plumbed in before the throttle body... no vacuum there. And they use the same exact oil injectors as FD's. Oops, I guess Mazda messed up! This should be proof enough.

Originally Posted by Moejoe

If you have them off, why put stock bacl on SS is not that expensive and you know you will not have any issue with them . 14 years of heat and aging can make them brittle.

Originally Posted by Mahjik

Actually, this is what I would question. If Mazda changed them from the location of the FC's, there must be a reason. There is no denying that the FD location is a source of constant vacuum. While it might not but much all the time, it still is vacuum period. Maybe there is some use for the vacuum from that location as Mazda could have found a most easier way to get filtered air.

Originally Posted by Mahjik

It doesn't really matter as none of us are privileged to the actual Mazda technical documents about the car. So we are all just arm-chair mechanics guessing at its intended purpose.

Originally Posted by DamonB

The vacuum lines to the OMP injectors are plumbed to a filtered air source that does not see boost pressure. This means they plumb between the air filter and the compressor inlet as this is the only area that is filtered and sees vacuum 100% of the time.

Why do these vacuum lines exist? The OMP pumps oil into the motor via the injectors which really are just simple nozzles. When the manifold pressure is negative (vacuum) the engine is literally sucking on everything connected to the intake tract, this includes the oil injectors. The vacuum line provides a leak path to the oil injector so that when the engine is under vacuum and "sucks" on the injector it doesn't suck all the oil from the metering tubes. Instead the engine "sucks" filtered air through the leak path created by the vac lines and the OMP oil lines are not placed under excessive vacuum which would quickly empty them. If this happened the OMP would not be in complete control of the amount of oil ingested as whatever oil the OMP admitted into the tubes would be immediately sucked out rather than metered in small "doses". Without the leak path at the injectors the engine would merely suck as much oil through the tubes as it could get anytime the engine was under vacuum.

When positive manifold pressure is present the one way valves in front of the vacuum lines inside the oil injectors close. If there were no one way valves present inside the injectors manifold pressure would leak into the OMP system and pressurize the sump. Not only would you have a boost leak, you'd be pressurizing the sump. Both bad. When positive manifold pressure is present the OMP has to overcome the boost pressure inside the engine in order to deliver oil inside the motor but that's not very difficult since the diameter of the injector nozzles is so small.

An analogy of this would be you sucking soda through a straw. Imagine built into your straw was a pump that was supposed to control the amount of soda passing to your mouth as well as deciding how often to deliver a sip of soda to your mouth (this is what the OMP does. It decides when you get a sip and how big that sip is). If the pump were merely built inside the straw there are only two openings present; one in your mouth and the other in the drink. If you were to suck hard enough you could suck as much soda through the straw as you wished because you could suck it right through the pump, even if the pump were attempting to deliver a smaller amount of soda. If we inserted a tee into the straw between your mouth and the pump whenever you suck on the straw you'd merely suck air through the tee, allowing the pump to be in complete control of how much soda is delivered to your mouth no matter what you do at your end of the straw. We'd also install a one way valve in that tee so that when the pump is delivering soda to your mouth none of the soda goes out the tee, it all goes into your mouth.

As many have done you could eliminate the vacuum lines all together and leave the vac nipples on the oil injectors bare but that's not a good idea. This allows the engine to ingest unfiltered air anytime the engine is under vacuum. Everyone claims the OMP system works fine without the vac lines attached and they're right. The OMP system will work fine but your engine is ingesting dirty air everytime it's under vacuum. Poor choice.

My posts in this thread have further description on how the OMP works:

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/omp-how-works-modification-amecu-discussion-regarding-premix-60867/

Originally Posted by afterburn27

I'd be interested to see where the TII oil injectors draw air from. I would assume that Mazda moved it to a location that does not see boost. I'm tired of reading about oil injectors , maybe I'll look into it this weekend.

Originally Posted by Mahjik

Uh, there are boosted TII's from the factory.

Originally Posted by Mahjik

However for ever post that you come up with that says it needs filtered air, there's a post just like it that says it needs a vacuum source. Other thread on the debate:

https://www.rx7club.com/showthread.p...ght=vacuum+oil

There are knowledgeable people on both side. However, none of them worked for Mazda and were also part of the team which designed the car, so you can pick and choose who you believe and who you don't.