I'm considering the removal of my air pump and all emissions accessories (They ARE accessories, in NC we have no emissions for 95 and earlier now ^_^). However, I'm considering the implications of removing the 5th and 6th port tubes on my 89 gtu.

I know they're there to provide air velocity to maintain higher torque at lower rpms; the question is, does this have a real impact? I'd figure the air would flow easier, and more of it. Also, additional turbulence should be created in the combustion chamber, allowing for a more thorough burn. Does anyone have any dyno proof of this effecting performance either beneficially or adversely?


Thx for any info.

 

It does if your exhaust isnt completely wide open. Any gains given to low-end torque by the aux ports is pretty much negated with 2.5" pipes and straight-through mufflers.

 

Of course it does. Do you think Mazda having been using 6PI on every production NA rotary engine for the last 24 years just for the fun of it?

You need to remember that at low rpm the ports cause far less restriction than at high rpm, for obvious reasons. At low rpm the advantages of higher port velocity far outweigh the disadvantages. At high rpm the opposite is true, which is the reason for opening an additional port.

No, lower velocity (from open auxiliary ports at low rpm) means less turbulence and less effective mixing of fuel and air. The whole point of the system is to increase the port velocity at low rpm for that very reason.

 

Hahah, I didn't say anything about why they DO work. From what i've seen most people are sick of hearing about that. Thanks NZ!
It makes a difference with my setup, especially in the nasty city driving i do all the time (rx7 daily driver)

 

i'd really be more worried about my vdi working than my 5/6 ports...

 

Why would you think one would be more important than the other?

 

If the vdi is working and the 5/6 ports arent, theres a decrease in low end torque. If the 5/6 ports work but the vdi doesn't the car is going have decreased high end power and you're not even going to see any gains from the ports opening. It would almost be equivilent to not having the 5/6 ports to begin with. It's really a trade off, but i've driven around without 5/6 port sleeves in and frozen and with them removed. I'd rather have the top end. I didn't get this car for it's low end torque, that's waht a diesel is for.

 

And if the 6PI is working and the VDI isn't, there will also be a decrease in low-rpm performance.

And if the VDI is working but the 6PI isn't, there will also be a decrease in high-rpm performance.

Do you see how I turned those two statements around to be the exact opposite of what you said and yet still be correct? I don't think you fully understand how these systems work. The 6PI and VDI systems do two totally different things and aren't related to each other at all. You still get the same benefits from one system if the other isn't working.

Nonsense. Mazda rotaries had 6PI for seven years before VDI was introduced. If it worked fine without VDI before why wouldn't it work without it now?

It would only be a trade-off if there were gains in one area to match the losses in another. I've yet to see anyone offer any hard evidence that there's a significant gain from removing the auxiliary port sleeves compared to leaving them in and have then opening when they should.

 

You are assuming that both systems will provide the same gains and losses. With a non-functioning vdi system, it will default to the long runner length. This will increase the low end. If the happens the 5/6 ports will do their thing and increase low rpm velocity and high rpm volume (and thus less restriction). With a functioning vdi system and no 5/6 port sleeves, the high rpm power would be the same as if both systems were functioning. If the 5/6 sleeves were left in and the system is not functioning, but the vdi is, the engine won't be getting the required air and as a result the top end will suffer. So like i said, If i were to choolse between the two, I'd take the vdi system over the 5/6 ports and then take out the sleeves to retain all of the possible high rpm power.

I never said it didn't.

If you read what I said, you'd realize that I was comparing non-functioning 5/6 port sleeves frozen in an open vs. closed position. This would cause a trade off of low end vs high end. With properly functioning ports there would be no loss or gain on each end.


None of this really matters though, because if he takes off his airpump, neither of the systems are going to work anyway.

 

Why are you assuming they won't?

No, it'll only result in high-rpm losses. Low-rpm performance will be unchanged because it's supposed to be closed then. If you fix the VDI valve open you'll get the opposite.

But why would you ever want to choose one or the other? Your whole argument makes no sense because if you have the hardware to run one then you have the hardware to run the other. If one system isn't working properly then you should just fix it.

Yes you did. You stated that: If a non-functional VDI is just like not having 6PI, then how did the earlier 6PI systems work without VDI? Obviously they did.

That is not what you said. You said: Maybe you need to be a bit clearer but that's not open vs. closed.

Exactly, so it should be left in so the engine performs best over the whole rpm range instead of just part of it.