I have come to dislike the idea of using exhaust backpressure to operate the auxiliary ports. After a short and unproductive search, I have turned up little in the form of results. Can anyone detail some of the pros and cons of converting a 6-port S4 engine to 4 intake ports. I would assume the selection of intake manifolds would shrink, but would there be changes in performance? Would I lose all bottom-end? Would top-end gains be worth it? This is to performed on a car not destined for street driving, so streetability and legality is not an issue.

 

I don't think you'll want to do this unless you put a turbo on it, and that can be difficult and costly from an NA base. If you don't turbo it I think you'll lose high end power by not having the 5th and 6th ports. There are plenty of guys who'll know further details.

 

ditto ^

 

Actually, I have a 4 port engine (91 TII) and I intend to run it N/A (it is heavily ported anyway.) The 4 port engines are reputed to breathe better. It is true that you will lose some low end, but the 4-port has better high end (especially with big ports.)

N/A is a little more reliable (can feel the flames now) and 200 rwhp is very realistic on a standalone and streetported 4-port engine.

Another thought, you could remove the port actuators or install electric solenoids to actuate them. The latter option would even retain your low end.

You could also install an air solenoid and take air from the fresh air pump to open the ports (like the s5 does.) I think that both these topics are covered in previous posts.

 

The purpose of the extra 2 ports is to close them to provide "smaller" ports for good low-end power (& mpg, emissions), and open them to get "larger" ports for high-end power. If you go with 4 port, you have to choose one or the other. I'd guess that the conversion would be expensive and a bad idea, considering all the trouble Mazda went to to make the 6 port system (and the well-known gains). Just rig up an air pump to activate your 5th and 6th ports. A search should tell you how. And after that you can still port your engine for more power.

 

Yeah, I have read a couple of those posts. I saw the whole air-pump-actuated idea and the electric one too, but for some reason, I have some apprehension towards those 2. I like the electric actuated idea better than the other, but it also seems to be the harder of the two. Hmm, decisions, decisions. Yeah, the 4-port idea works with me because I will eventually turbo this engine, but only after I get tired of NA/get lots more money, whichever comes first.

 

Syonyk has an air compressor to do this, and it's currently just on a manual switch in the cabin. Personally I dislike that method, because of the manual switch and the noise is annoying, however it could be linked to an RPM switch instead, so at least it would come on right when you want it to. I'd personally go electronic though because it should be quiet.

 

Like I said, I do like the electronically-actuated idea over the air pump, but it just seems complicated. I'm just a wuss when it comes to working on electronics because I'm always afraid I'm going to F$@^ something up even though I have installed all my stereo systems in all my cars with no problems, and I am the one all my friends ask to hook up their stereos. I guess it is true, you are your greatest critic.

 

I'm going to try to actuate them via vacuum pump, or maybe even put a small stepper motor on them, if I can get a bracket in there to make everything work. I would suggest something like that. The staged port system makes sense, in my opinion, as it uses completely different resonance tuning in the upper RPMs, and so is really superior to just having an intake manifold tuned for one frequency.

 

An alternative is to go w/ one of the Racing Beat exhaust solutions, which have a feed from either a header, or a presilencer... which provides enough back pressure to actuate the 6pi.

I have an 87, & a presilencer w/ this tube & it works just fine. No RPM switches, no extra pumps. Since the OP mentioned that legality is not an issue, going this route in place of cats... shouldnt be a problem.

 

The s5 uses air pump actuation. It's no big deal, and it's cheap to setup. Electric actuated is a bit more expensive. I'd think even if you screw up the air pump actuation it won't break anything. You'll just lose some horsepower when it actuates at too high/low of an rpm (or not at all, or stuck open). You just adjust the valve until it actuates at the right rpm.

 

Maybe use servo motors from an R/C car to open the ports, you'd still need some kind of rpm switch.

 

I actually considered going with power door lock actuators (which can be made to bolt on in the place of the pneumatic actuators.) I got lazy and figured out how to tweak a spring so that mine still open at 3500 with only .75 psi instead of 1.6 psi. (The spring is connected across the piston of the actuator, cancelling some of the internal spring force.)

 

I had two concerns. First (and foremost): The door lock actuators are not designed for high temperature applications (Which the area above the exhaust manifold most certainly is.) Second: The response would be immediate (rather than gradual opening between 3500 and 4500) and the ports would have to be signaled to close (which isn't such a big deal really.)

I am very thankful that I thought to observe the ports before I upgraded my exhaust.

Sorry about the double post.

 

the first time I road in russ's car I almost crapped myself when he turned it on. I had idea what it was! it is pretty loud...

 

also I would like to add that the four port irons have more room for aggressive ports

 

In what way? The center iron is basically the same casting between 4 and 6 port. The 6 port front and rear irons already have more port area then most ported 4 port housings (put them side by side to compare and you'll be surprised) with loads of space so you can port them to the point where it's stupid. The main problem with porting out the 6 port irons is that if you go to the max, you end up with huge ports that are going to make power above 7K and nowhere else...

 

5W33T DOOD!!!1 My RX-7 is gonna be teh highest revvin 13b ever!! 18k rpms, here I come! I do plan on porting those housings out pretty heavily, but not to the point where it is flat below 7k. Jeez, that wouldn't even be good for racing, at least not for me. I don't have the kind of money to balance that engine for over 9k rpm, rebuild it all the time, and all else that comes with going crazy with a rotary like that. I certainly don't want to have to worry about the clutch and **** disintegrating at high revs and nailing me like a shotgun.

Holy ****, I just noticed you have almost 15000 posts, Aaron. Wow. That's a lot.