wthdidusay82

iTrader: (15)

Im looking into putting the s5 intake manifold and vdi on my streetported s4 na, was wondering if this is a good upgrade or is it only going to slow my car down at lower rpms ?

The vdi opens at 5000-5800 from what i see... 5800 is kind of high considering that my redline starts at 7000. When the vdi is on, this is whats opening the 5/6 ports correct ? Id want my 5/6 ports to open at a good time (not too late, not too early) , just to to have that smooth power curve.. (using rpm switch etc) ... this would mean i wouldnt need to use the exhaust pressure tubes to run my 5/6 ports correct ???

Others have told me that im better off just keeping my s4 intake manifold since its streetported...

Another thing i was lookin at is possibly porting whichever manifold I am going to use, and possibly the throttle body.

next upgrades i will do is short ram cold air intake, full exhaust, and safc.

what would be the advantages and disadvantages (if any) for using the s5 vdi intake manifold instead of my stock s4 ?

Aaron Cake

iTrader: (1)

Most would agree that the S5 intake is very well optimized for the stock ports, but changing those ports breaks all that. I have no personal experience, but years ago I saw some dyno graphs posted that pretty much agreed. So you may actually lose power going to the s5 upper.

wthdidusay82

iTrader: (15)

why are they good for a stock port engine but not good for a streetported engine ?? i dont get it

could i just get the vdi conversion ?? would that help me out

wrankin

The VDI is not directly related to the 5/6-port actuators. They are separate systems and use seperate actuators. Also, is there an issue with the control of the VDI considering that you are using an S4 engine harness. (I don't know)

What the VDI does is change the length of the intake runners for higher RPM operation.

-bill

Jaguarx7

I just run the VDI off the same hose that goes to the 6PI, the VDI actuator opens at a higher pressure then the 6 port actuators, so it all works out. I think VDI would help high end regardless of port (though you may have to change opening time to get the most out of it).

wthdidusay82

iTrader: (15)

i saw someone with the vdi setup on an s4 using an rpm activated switch connected to the vdi through the air pump to control the vdi by using an rpm setting (say 4800rpm) for when it turns on/open the 5/6 ports or whatever

could i adapt this to my s4 intake manifold without using the s5 intake manifold ?

ddub

Because that intake setup and the VDI and stuff is tuned/optimized for STOCK port. Mazda did a lot of research and tuning for it to be on a completely stock engine and stock port. As you change things and especially porting this "tune" is no longer set up correctly for the engine and air flow so you can actually lose power. This is why with the RX-8, for example, lots of people lose power on aftermarket intakes or straight cone filters over stock intake, same concept just a lot more complicated system than the VDI for the s5.

Dom_C

i have a streetported s4 with the s5 upper (vdi) and it works great. i know when i had it stock port and switched over to the s5 stuff it made a big difference. Sense the rebuild and port i have no put the s4 intake mani back on. . maybe a good experiment though. but i don't have the funds to dyno it to really see the difference. The s5 stuff seems to work very well with my street port. Damn can you feel it when the VDI comes on. i ahve it hooked to a toggle so i can open the vdi when ever i feel like it. Just my o2
Dom

rotarygod

iTrader: (1)

The S5 manifold is tuned for stock ports. This part is true. The S4 manifold is also tuned for stock ports. The S5 manifold when in "long" mode is 400mm longer than the S4 intake runners and when in "short" mode are 200mm shorter than the S4 intake runners. What this means is that the runners are really tuned on the S4 to give a nice powerband between 5000-6000 rpm on a stock port engine whereas the VDI activation and dual length system on the S5 manifold allows a better overall powerband from 4000-7000 rpm. This is shown in an SAE paper by Mazda. The S4 manifold is no different than the S5 manifold in that it is tuned for stock ports. The benefit that it gives with the dual runner system still still applies with a streetported engine. It still tunes better above and below the S4 manifold. The actual tuning points may have shifted slightly due to the porting but this is no different than the S4 manifold where the tuning point has also shifted. Alot of people wrongly assume that the S5 manifold isn't good for a streetported engine but an S4 is because the tuning is for a stock port engine. Wrong. Both are tuned for a stock port engine and both are tuned to do a specific job. The S5 just does it better.

I have a streetported engine in my car. I swapped over to the S5 intake after I had driven it ported. I assure you it is faster with the S5 intake than the S4. The top end is much nicer. Now that I have a standalone ecu and can tune anything I do, the car drives great.

Jaguarx7

wtfdidusay82:
Yes, you can use the air pump to power just the 6PI. You're referring to Viperdude152, he has a website, I believe it's www.racingrotary.com he has a lot of writeups on that site, including that one, i believe.