Boost and VVIS

[clayne]

You will of course see vacuum with a compressor further up the chain.

Read my paragraph above on how we control the oil injection meter valves on the 13B engine. It's the exact same routing.

They use vacuum (and progressively more when on-boost) to control the oil injectors.

 

[sjs]

You will of course see vacuum with a compressor further up the chain.

Read my paragraph above on how we control the oil injection meter valves on the 13B engine. It's the exact same routing.

They use vacuum (and progressively more when on-boost) to control the oil injectors.

Well I'll take your word that you have something working that way, but it seems like a backwards approach to me. There's a good reason why MAP sensors are used for precise control. Monitoring vacuum/pressure at the manifold is an accurate measure of load. I'm no expert on Wankles and not clear on the theoretical reason for driving something off the suction in front of the throttle, but I suppose there must be a good one. I guess precise control is not all that critical for oil injection, but I wouldn’t recommend this approach for most things. Do you know how much vacuum you see there?

 

[clayne]

Some older cars that are carb'd with vacuum controlled distributor advance are configured this way, some with advance routed to manifold - depending on how they wanted to change the advance on/off throttle.

It's really not just a Wankel specific thing, it's just a matter of "need a vacuum source, boost or not."

Since the oil injection valves Mazda is using on the 13B are simple vacuum controlled valves they needed a source of vacuum, boost or just standard load. Without tapping pre-compressor it would be the same conundrum with the VVIS. They'd have to have a funky valve that permitted vacuum *and* varying levels of positive pressure.

I'll tee my boost gauge to there in a couple of days and let you know what I see on and off boost, idle and cruising.

Also, the CVCS actuator doesn't really need precise control either. It just needs a source of vacuum, regardless of boost. I guess you could always get one of those mini vacuum pumps and mount it inside the cockpit next to the shifter. Just pump-pump-pump when you want some low-end. Talk about a hack and a half...

 

[sjs]

Some older cars that are carb'd with vacuum controlled distributor advance are configured this way, some with advance routed to manifold - depending on how they wanted to change the advance on/off throttle.

It's really not just a Wankel specific thing, it's just a matter of "need a vacuum source, boost or not."

I owned & worked on many of those older cars over the years, and the common term for what you describe is "vacuum advance". However, that was something of a misnomer because the vacuum actually reduced advance at low load and added advance at high loads (low vacuum) so it would more acurately be call vacuum retard. The line for it was always tapped in after the throttle plate so it saw ~20in at idle and none at WOT, just like a MAP sensor.

I guess you could always get one of those mini vacuum pumps and mount it inside the cockpit next to the shifter. Just pump-pump-pump when you want some low-end. Talk about a hack and a half...

Now that's funny!

 

[the nsxnut]

Good content.

Clayne, thanks for your analysis of this. I learned a few things from your input, and am contemplating a 'custom' (read: hack job ) mod to see if I can adapt my system to get best of both worlds...

 

[DDozier]

I hope this makes since but the answer to this problem seems simple to me. The problem is vacuum, or rather lack off. Why does this need to be operated by vacuum at all, Why not make it a electromachanical control instead of vacuum. The ECU gives us a voltage output at the RPM range it wants the VVIS to change, that voltage output activates a solonoid, to open a vacuum source, to a contol a vacuum actuated solonoid.

Why not just remove the vacuum controlled solonoid and in its place install a electromagnetic solonoid. They are cheap and easy to get, have the required force and pull range to actuate the mechanical plates in the intake. For those of you running an aftermarket engine management systems can use one of the programmable outputs to control the operation of the solonoid and have a ton of variables to control the solonoid.

The only draw back that I see and is surely the reason that the factory chose vacuum as the source of movement in the solonoid is duty cycles, most of the electromagnetic solonoids I have seen have a rating of 100,000 cycles min. but these items are aprox. $30.00 and can be replaced in less than 15 min. So even if you had to replace it every two years wouldnt that be better than it not working at all or being stuck in the wrong mode for max power.

If someone is interested I have a parts list and sources for the parts needed and pin munbers for connection to the factory wire harness. As i do not have a FI setup I cannot test this myself but I am sure the solonoids will function the same.

Just my .02

 

[sjs]

Dave, that's essentially what I had in mind when I suggested BZ could come up with an electronic solution controlled by the AEM. I'm glad you came through in his absence. My tired old TT is a great test bed for such things so send me what you have. I think I'd still prefer to find a simple way to let it work as designed (assuming one desires to maintain the butterflies at all, which seems possible with a BBSC), but barring that your approach would be a great addition to the kit. So before I butcher my manifold I could see how the idea works.

 

[warren1205]

This is great information! thanks