So some interesting observations are becoming apparent with my new toy. It appears that the motor is not original, and could be a bit of a franken-rotor. I was hoping that someone could confirm what I already suspect.

https://www.rx7club.com/picture.php?...ictureid=21558

The car is a 1990, but the lower intake is an S4 what my research indicates. It does have the S5 front cover and VDI intake.

The 5/6 port actuators were removed along with the air pump and ACV. The 5/6 ports were wired open. I would like to re-install the port actuators and have the VDI working again. Will it work if I use the pressure outlets from the spider on the S5 and plumb them into the lower intake manifold? I figure that the pressure from the spider should work just like it should as if from the split air pipe on the S4, maybe even better.

https://www.rx7club.com/picture.php?...ictureid=21562

I have an air pump, ACV, S4 actuators, and all the solenoids and electrical seem to be in place. I plan to do it this way, but want to utilize the RX-7 comunity for any thoughts or concerns.

Thanks

 

From an air line standpoint it is fully compatible. They work the same way. Air pressure. The S5's work off of the air pump which I personally like better. The biggest difference in regards to the actuators themselves is that the S4 actuators pull the sleeves open whereas the S5 actuators push them open. They aren't interchangeable between manifolds though.

 

I have both actuators S4 and S5. I noticed the difference on movement (pull-in vs. push-out). The S5 actuators will not fit on an s4 manifold, so no opportunity for them to operate backwards. I will try things out and post my results.

 

the S4 NA LIM does not bolt up to the S5 middle intake manifold.

 

Only the rear bolt hole is different. It can easily be redrilled to fit. Everything else lines up. The EGR passages however do not. They are in the center under the primary ports on the S4 and under the outer ports on the S5.

 

Well, the motor currently runs okay. The power doesn't seem to keep increasing above 5000 rpm, but I believe that makes sense because the VDI does not have any pressure source. I don't know what improvements to the low end would be with 5 and 6 ports no longer wired open. Basically, I am just looking to have the engine running smooth through all entire range. The pictures show it definitely has an S5 upper intake and an S4 lower intake. How it was stitched together I don't know without disassembly.

 

It's likely an S4 block that was adapted to work in an S5 car. Swapping over all the S5 manifolds, front cover & electronics is one of the easier ways to mix and match between series.

Here's a writeup on adapting the S5 UIM: http://homepage.mac.com/carldavis/intake.html, but this one used an S5 LIM. As mentioned, the S4 LIM can be used by redrilling the rear bolt hole. That's how I did it for my S4 NA engine.

 

One thing to know about the S4 vs S5 actuators is that they don't open with the same amount of pressure. The S4 actuators start to open at just under 1.5 psi whereas the S5 actuators start to open at around half a psi and are fully open around 1.5 psi. If they are being opened by the air pump through the stock solenoid this isn't going to be an issue but if you were running the reverse of your setup, say and S5 manifold on an S4, and actuating it though exhaust pressure, they'd open much earlier.

 

I didn't see it noted but the S4 LIM has a flange where the charge air for the actuators flows through. The S5 actuators just use rubber and metal hoses to connect it to the solenoids.

 

Correct. The S4 actuators get their air through the lower manifold. The vacuum nipple feeding them goes to the manifold.

 

I am hoping to play with this arrangement over the weekend. As stated by YaNi, the S4 actuators are operated through the lower manifold. I intend to use the S5 spider with the tubes near the actuators, and install a fitting into the manifold. Pressure should come from the spider as intended for an S5 and just go through the manifold instead of directly to the actuator.

I don't know if the solenoids will overcome operating pressure differences between the S4 and S5 actuators. What rotarygod says about this working okay with S5 electronics makes sense. The true test for me will be to actually try it.

Thanks for chiming in guys, report and pictures to come.

 

That's the real question. Will you get enough presssure from the air pump to open them? The air pump is designed to move air. Not to pressurize it. Fortunately there is a screw on the bottom of the S4 actuators that you can adjust to vary the needed pressure.

 

you mean port air passages. and actually this is ok, as they both do all their business in the lower intake.

you might have a couple of vacuum lines that go in strange places, but s4 lower/s5 upper could be made totally smog legal, and functional.

and also that would be another way to tell if its an S4 engine, the EGR valve is on TOP of the center housing.

 

Well, I ran into a snag. The rear port is sticky and will not operate smoothly enough to close after opening. Looks like if I want to get this to work, I will have to take off the manifolds after all. That being said, I will do the S5 lower intake adaption demonstrated by Carl Davis. Otherwise I will just live without the extra few horses for now.

 

I use my car as my daily driver. I have a sticking aux port actuator which I'll get around to fixing in a couple of weeks. I was driving around with the ports wired open but decided to close them. As a daily driver this was a great idea as I didn't realize how much power in the usable powerband is lost from leaving them open full time.