DEZERTE

Ive drivin my car with the VDI set to open around 5500rpm and ive drivin the car with the VDI closed (and air pump removed). And I can say that the car seems to have much more pull with a force closed VDI and no air pump..
I imagine this is because my intake is really open and its already getting alot of air because i have a Streetport, with ported TB, straight intake pipe and all manifolds ported (uim, extm, lim) with the 6pi removed.
my car seems to lose torq when my vdi is functional at high rpm...
any thoughts or comments?
ps, im sorry if i worded this stupidy, im kind of in a hurry.

DEZERTE

i just took the airpump off permanently, it was goign to come off anyway after i turbo'd the car

ddub

I never really understood the whole VDI system. Seems to me that it would probably work best on a stock or near stock car, from what I understand of it, but as you mod it and port the motor etc it just seems like it'd be another restriction. My .02, but again I don't know much about the VDI system.

DEZERTE

well, its a restiction, but in a good way. When the VDI is open, it seems like there would be a shitload of turbulance in the intake. I dont know, my VDI being closed = good as far as i can tell.

Novacaine

from my little knowledge I think the reason it doesn't pulls hard is because the pressure pulses that it is set up for are not happening at the same RPMs it was designed for due to the changes you have made. If you could figure out the new correct RPM for it to flip and put an RPM switch to control it's function then you could be making more power not less. This is just a stab at it from the class I took that discussed the pressure pulse and how to tune the intake for them.

DEZERTE

you mean like, dyno it with the VDI closed, then dyno with the VDI open then set it to open where the lines cross? Good idea, but i probably wont bother with it, cuz im going turbo.

SonicRaT

iTrader: (6)

it creates a natural 'supercharging' effect, as most call it, chances are that the motors so much more efficient now that you can't even notice the differnce.

Zer0 Cylinder

from my research, the vdi does better on non modded cars......but once you've ported + such, s4 manifolds flow better.

DEZERTE

so leaving it closed = a good idea?

Zer0 Cylinder

ask icemark, or the other guy's name.....i forgot his name, but he has like a cartoon cat gremlin thing as his avatar.....they'll school you on it.

but if you're ported and ****, id see about s4 manifolds.

ddub

Weren't you going to get the turbo manifolds/tb anyway for your conversion? Then it doesn't really matter since when you do that you'll lose vdi anyways.

DEZERTE

nope, i was gonna run the NA manifold, just a s4T2 exh. manifold with the spacer/adapter

ddub

Mmmm, ok I thought you said something about it in that thread where aaron cake and hailers were explaining how it would work. Nvm then.

Either way I'd have them not functioning with turbo, not sure how though. Either wired open, wired close, ditched, but which I have no idea. Good luck.

Novacaine

the pressure pulse work by (well on a piston engine but sorta the same here I guess) when the combustion chamber opens a low pressure pulse is created and it travels up the intake tube to the plenum where it acts as an open node and sends back a high pressure pulse. The trick is to get the pulse to come back to the chamber right before it closes so you get an extra hit of A/F mix to give a sort of little forced induction, but not really. This all depends on the diameter of the tube(porting intake changed that) and the duration the chamber is open (porting motor changed that) and length of the tube (could be others but I am forgeting them right now cause it has been a while). Now you can "tune" the intake to do this right at certain RPMs, but car company usually just dyno the car and hack off length of the intake till they find the sweet spot cause all this isn't an exact science because of the variables and nothing works exactly as in theory. There are equations to predict the correct spots but those are for straight pipes and such. I am assuming mazda found the correct RPMs and made the VDI so that you get some benefit from this at below a certain RPM and then change the intake length with the VDI to get it again in the high RPMs. Now that you changed so much of the equation, it really would take a lot of experimentation to get it back to working. If you are gonna run a turbo there really isn't any need for the VDI system because you aren't gonna notice small pressure pulses when you are already hitting 10 psi.

I hope this was correct, but again I haven't done this stuff in a couple months and it wasn't covered all that indepth when I did do it.

DEZERTE

ill probably just leave the VDI closed.