This is an old topic but I am a newbie so I need to ask some Q's on this one.

I have NA S4 13b in a 1959 AH sprite (goes like stink!) and I am working on going from a carb (RB setup) back to injection. As part of that I am also going to put the stock LIM back on so I can actuate the sleeves and get some more low end grunt (I don't need any more high end as anything over about 120 mph in an 1200 lb car with an 80 inch wheelbase gets real scary!!!!).

I was considering the RR mod to allow control of the port actuation on an RPM signal which I can trigger off one of the aux outputs form my ECU (MT-4 fuel only). BUT, I think this might be a mistake?

RR based the need for the mod on the fact that the factory system could open the sleeves at different RPMs due to varying load. Isn't this exactly what you would want???? I think the argument that having them acutate at the same RPM is a good thing may be flawed. After all, the whole point of the sleeves is to increase flow velocity under lower load conditions by closing off two intake ports. The intent is to do this whenever flow conditions are low, regardless of RPM. What am I missing here????

The exhaust acutated system does what the Mazda engineers wanted. It opens the ports under high flow cxonditions and closes them under low flow conditions regardless of any other factor. Assuming one has an intact exhaust system and the pitot tube is sensing flow why on earth would you want it to work any other way??? Engines are air pumps and the Mazda guys wanted to pump the right amount of air based on engine load, not RPM???

 

There's not much superior to the stock system. However, if you want to free up your exhaust, you get that trade-off.

 

When Mazda went to the S5 and started using the air pump to actuate the sleeves what trigger signal did they use? Did they use RPM?

 

RPM, load and throttle position

 

I prefer the S5 air pump method of port actuation. It works consistently, and isn't affected by exhaust mods (reduced backpressure) or clogged cats.

EDIT: If you can change your trigger points in the ECU, you could customize port actuation via a vacuum solenoid such as what is used on the S5.

 

The trigger point can be vaired but only to a single setpoint.

Given that Mazda used RPM, load and throttle position I think I am back to my original argument which is that you DONT want it just on RPM (ala the RR mod). The issue is velocity of the AF mixture and keeping it high. Triggering actuation on soley RPM doesn't accomplish that under all conditions. The change on the S5 gives a more reliable source of pressure but still used a three parameter formula to trigger the open / close status. This combination of parameters is automatically mimicked by exhaust flow so that is why they origianlly used the pitot tube as the pressure source.

Where this becomes problematic is when the exhaust is modified or leaks or the tube gets clogged or breaks. In my case (no cat and open ehaust with a header) the pressure in the exhaust for a given velocity is less than what the factory assumed when sizing the sensing tube so it changes the acutation point (fixed pressure required to actuate but different pressure for a given flow than originally assumed). What this means for me is I have no baseline to use to figure out what size tube I would put in the exhaust steam to get the same opening / closing as the factory intended versus AF flow. The factory setup uses the exhaust pressure plus velocity pressure to open the actuators. Therefore a lower exhaust pressure will require a higher flow to create the same combined pressure and actuate the sleeves. This means the factory setup with an "open" exhaust must see higher flows before the sleeves open (higher combination of load, RPM and throttle opening).

Not sure WTF to do!!!!

Most liklely I will go to an independent pressure source triggered by RPM and simply live with the compromise. I can pick an acutation RPM that opens them mid range while accelerating through gears but keeps them closed while crusing in 5th. For my car assuming I don't need to cruise at greater than 100 mph I will need to set it at about 4300 rpm. Any one have input / care?