I have been following a few of the N/a to 6 port turbo projects on the forum and
have always wondered why the auxiliary ports are always wired open and
the actuator (and all other complimentary pieces) removed.

Is it just easier, or are the power gains negligible if it was functional ?

 

Have you looked at how much that 6port lower intake manifold sticks out relevant to the exhaust manifold? Now add the 6port actuators, airpump and ACV to that. It really gives you very little room to clear all that if you install a turbo manifold + turbo. Not that it's impossible, but just requires more careful measuring. The way I see it is the higher compression 6port will still be have more low end torque than its TII component when you wire the ports open. But it does have it's advantages.

The gains in the end all are the same with wired ports, top end is the same. You do lose some torque on the low end but the turbo should make up for that....

 

Its uncommon to even use the stock intake manifolds on a 6 port turbo setup because the space occupied by the aux port actuators doesn't allow room for the turbo and the setup requires building a spacer or a new manifold. The people that have used the stock manifolds have removed the aux ports actuators to make room for the turbo. I have not seen a 6 port turbo with a custom manifold retaining the stock aux port actuators but it can probably be done.

 

My next turbo-NA will have working actuators. Actually, the doner car was just pushed/dragged into my shop this morning...GSL-SE 6 port going into my '76 Cosmo w/GT30R.

 

i have a cartech manifold that will fit with all the actuators and stuff, turbo is way far back, and tucked in close to the block.

its like an S5 t2 manifold, but skinnier and the turbo is further back, and down

 

Aaron - do you have any data on the effects of 5/6 ports on turbocharged engines? I would be very surprised if they made any significant difference.

From my thinking, you would not want them for same reason that the TII engines don't have 5/6 port actuators. In an NA engine, the extra bottom end torque comes from keeping the intake air velocity up. But the engine is pulling air against a vacuum. With a turbo the point becomes moot. Once you have any significant boost you want to remove restrictions going in, since the air velocities will already be high enough.

It would seem that any significant gains would only be seen at very low rpms before the restriction of having the port closed would come into play (and before you could build boost).

Just a thought. I could easily be missing something here.

-b


They

 

And the little bit of boost response you'd gain would likely cancel out with the extra bends associated with having the TB on the wrong side of the engine, or with the work and money required to build a custom UIM. And then you'd still have a thermally inefficient setup since the turbo would probably have to be super close to the intake (compared to an aftermarket mani.)

Even if a slight gain in boost response is achieved (despite the gain already acheived from the higher compression rotors) it would be damn near useless unless you are autocrossing the car and you have already done the other hundred mods to increase boost response.

Cool stuff...you should post pics.

 

Most of the time a person is driving out of boost. It stands to reason that a stronger out of boost response would bring boost on more quickly. There are also fuel economy and idle quality benefits of keeping the extra timing the aux ports provide under control. Remember that they end up a little bit into the compression stroke so you do decrease engine efficiency quite a bit when you have them wide open at low RPM. The better an engine performs out of boost, the better turbo response will end up. The Cosmo is a heavy luxury car so the idea with this engine is not all out horsepower but to make as much torque as possible in the low to midrange. I'd like to see 300+ Ft-LBs.

Consequently, the intake runners will be quite long and the porting very conservative. The exhaust ports are only going to be widened a little, the primary ports left alone (smoothed), the secondary ports moved up a little bit and the aux ports closed later.

 

Right, and most people are satisfied with the acceleration of a 4/6 port turbo car even at 0 manifold pressure for accelerating from stoplights. I can understand the benefit of keeping them for a heavier more streetable application such as a Cosmo but for an RX-7, unless you have to daily drive your car (in which case I feel sorry for you) and get super excited when you're able pass minivans quickly to make your turn or your exit, keeping the 6PI is not worth the effort.

 

The difference between open and functional aux ports is more noticeable at low and light throttles. Having them functional just makes a more pleasant car, in my opinion. Also a lot easier to tune since vacuum doesn't act like an on/off switch on the highway. Considering how much port area and timing a wide open 6 port engine has compared to a 4 port, the comparison cannot be made. The reduction of low end torque comes not just from the lower velocity but mainly from the intrusion of the aux ports into the compression stroke. Keeping them closed at low RPM is always going to result in a more responsive engine.

Now, the difference in opinion may be a fundamental difference in how people use their cars. For one thing, from spring to winter, I do nearly daily drive my RX-7. Last week I drove it 4 out of 5 days so I expect it to be drivable in all traffic situations. That means being able to tool around town at 2K RPM and then being able to floor it and pass from 2K without having to go down a gear.

A turbo NA with working aux ports has the potential to produce a torque curve probably only matched by the 20B with it's sequential twin turbos. Choose the turbo wisely (ie. the 3076R w/ 1.06 turbine housing) and the thing should make boost from 1500 RPM until 7000 RPM.

 

Thanks everyone for the great answers.

I just moved to a new city for school so its taken me a while to look at all this.

Aaron are you going to be posting on more on your Cosmo build ?

I would like to see how well the functioning 6 port turbo works in application.

 

I was thinking of having the 5th/6th ports functional on mine. I had Firgelli Automations make a 12v linear actuator for me that could be run off my MSD RPM activated switch. That way you can have the ports open for top end but still have the low end benefits of a functioning system without the space hogging factory actuators.

 

Great info-I have been speculating along the same lines. Greater area under the curve approach,

Aaron-What about the VDI on an S5-Should it be disabled or removed? If is is not, is there any advantage to keeping it functional? Disadvantage?

Thanks for your thoughts.

 

anyone ever driven a turbo Honda with Vtec? it's kind of nice actually when you feel VTEC kick in, especially when you can adjust the transition point by manifold pressure. I imagine having a turbo rotary with functioning 6 port system will be kind of like that. There are plenty of turbo Rx-8's that are 6 port. I'm not entirely sure whether they wire open the VDI or variable intake pipe or not, but I know the aux ports do switch on.

 

The Cosmo will primarily be a restoration with only light modding. I'm going to smooth the body lines and such but don't want to do a lot of cutting to the car on account of its rarity. From my research, only 56 RX-5 Cosmos made it to North America. As I happened to have a rusted GSL-SE I figured I would swap engines and turbocharge it for a little more drivability as compared to the carbureted 13B 4 port it came with (all of 120HP).

I will be starting on the Cosmo this fall/winter.

Here's what I'm starting with: http://www.youtube.com/watch?v=xWmHLbUyY0k


I'm going to use the stock actuators but power them with compressed air from the intake. The Megasquirt will switch a solenoid at the appropriate RPM to actually open them.

The nice thing about the stock actuators is that they are very reliable in quite a hostile environment.

At high load and high RPM, the engine will be in boost anyway so I don't see much point in the VDI.

 

My S5 6 port turbo will be having functional 5th/6th ports. I have a Haltech Platnium Sport 1000 to control it. So excited!

 

Its nice in theory, but how do you plan to control them? I thought about doing it with a euro manifold(which i have), but cant really be assed to bother since my 4 port motor works well.

 

If they're S5 actuators they're opened with pressure so just have the boost open them, what's the problem?

 

All of the FC aux port actuators are pressure based. S4 uses exhaust backpressure, S5 uses pressure from the air pump.

Nice thing about a turbo 6 port is that you have a handy source of pressure already on the engine...

 

I'm trying to setup my 5th/6th ports on my Haltech Sport 1000. In the Digital Pulse Outputs there is a dual intake valve and vtec option. Are these the same functions as the 5th/6th ports on the rx7?
Or would it be better connecting the hose to a boost line to open the actuators?

 

i think either will work, you just need something that turns the solenoid on once it hits a certain rpm.

 

I will doing a plug in pin install. On the Haltech Sport 1000 there's some digital pulse inputs that I can wire to. When I select the Dual Intake Valve tab I get the option of adjusting the on/off rpm values, however the inputs all have different voltages ranging from 5v, 8v, to 12v. Is it critical that I wire it to the right voltage or it doesn't matter?

 

Aaron if that's the case I'm thinking about wiring my VDI open and just keeping the 5th/6th ports operational. Question is how do I keep my VDI open?

 

the 6pi solenoid is 12v.

Foxed.ca - Mazda RX-7 Manuals you should read the training manual, it explains how this stuff works