bill shurvinton

Drago:



You are being a bit silly here with your claims as you are quoting a paper without having thought about what is going on and why. The key thing that has escaped your quote fest is that the tuning mazda is talking about is for a STOCK engine with a restictive exhaust that causes significant back pressure and has had to be optimised not for high power but for broadest power band.



For a performance application, which would be the only reason for going to an IR setup (well that and bling value) you would not accept anything like the back pressure that the mazda factory system gives.



Go here :http://www.yawpower.com/techindx.html and read those articles to see the other side of the tuning story and then have a think. Also the plaigurised Dave vizard articles on the grape ape racing site give some useful pointers.

j9fd3s

the 20b and 13b-re intakes work the same way as a t2, even though it looks like an open plenum its not.

mazdaspeed7

Reading one paper hardly makes you an expert. Quoting that one paper and claiming to be an expert makes you look bad. And arguing for your point after that is brought up makes you look even worse. My point was that while you may have a little fundamental knowledge, you dont have enough working knowledge of whats going on to be very helpful. Anyone can read that SAE paper, and understand the basic principle behind the VDI manifold.



One thing needs to be clarified. ITB's dont make more power. The intake manifold that goes with ITB's does. Moving the throttle close to the engine makes the throttle response quicker.



With a single TB, it only has to flow enough to feed one rotor at a time in our case. With ITB's, each throttle body has to flow enough for the corresponding port(s) its feeding. That is why ITB's have more area on the throttle body.

Drago86

My point was that MS7's assertion that "The pulse from opening of the chamber is ALWAYS negative" was wrong. there is a positive and negative pulse associated with the opening of the intake, the tunned length ITB setup uses the negative wave, most of the stock mazda units use the positive wave.



Also while i agree that this may work better for stock applications, it is still not to be disregarded. No one has created a pefectly scavenging header yet(which you would need to negate this effect), and on turbo applications there is allways some back pressure (if there was no pressure change between before and after the turbine it you wouldnt have a turbine would you?) there is also allways some back pressure no matter how free flowing you exhaust, thus there will allways be a positive pulse. this can be seen in a real world sense in dyno's done of FC NA's with free flowing exhaust, the vdi still adds ~20 HP after about 6500 rpm versus the 88 manifold or a closed vdi valve. There will allways be some residual chamber pressure after the exhaust cycle.



Also it must speak something for the system if mazda has choosen it for both of there latest engines, the 13b-rew and the Renesis.



Besides all that the VDI system also uses the pressure wave from intake closing, which is uneffected by exhaust back pressure (the opening pulse is little effected aswell as i just discussed) Mazda saw pressure increases up to ~2 psi when they discoverd the interaction between rotors on a 2-rotor motor.



I am not saying this is the only way, only that it is a valid way, and that MS7's statment that all intakes use the negative wave was false, proof of which can be seen in numerous stock intakes from mazda. Tunned length ITB systems, or plenum stylse systems may vary well make as much, or more power then the stock system, however i have yet to see proof of that fact.



Also many of the aviation guys are currently designing there own tunned DEI style systems, which lower BSFC and provide more power, and they all have fairly free flowing exhaust aswell.

Dysfnctnl85

I'm in way over my head here.



So this is what I gather:



- ITBs have a place on a turbo or NA motor.

- Moving the TBs closer to the intake makes for faster throttle response. (Is there no CON to this? There must be!)

- The rotary engine does not like plenum designs...?

Drago86

1. yes



2. yes, no down side, except the 4x throttle plate shafts extra area but thats negligable. The closer the plate to the port, the better the responce.



3. Plenum designs do work on the rotary, as shown by the 20b, 13b-RE, and 13b-T(i think) the R26b uses ITB's with no plenum but the pricipal is the same, both used tunned intake runners and a volume change to reflect the negative pressure wave, so you could count the R26b for the non vdi style aswell. Both ways work, which one works better for what application is currently being disscussed.

mazdaspeed7

You just wont quit, will you? You obviously dont even understand manifold tuning well enough to understand my argument.



The pulse from the *opening* of the port is always negative. The positive pulse the VDI manifold uses is from the *closing* of the port. With an ITB setup, there IS NO positive wave. The negative wave from the opening of the port is inverted at the end of the runner, which is usually terminated in a bell mouth, and returns back down the runner as a positive pulse. The manifold is considered tuned for the rpm where this positive pressure pulse is trapped in the chamber by the closing of the port.



Even with the VDI manifold, there is still a negative pulse from the opening of the chamber. But the VDI doesnt use this as the primary method of tuning. But it is still present.







Just for future reference, the problem with the stock intake manifolds isnt the runner length, its the runner cross-section. Its optomized for a stock engine. All of Mazda's careful design starts to go down the ******* when you start modifying other parts.

mazdaspeed7

Youre making assumptions, and youve already proven you dont know enough about this to offer a knowledgable conjecture, let alone real knowledge.



1. ITB's do have a place on both turbos and n/a's, but its more common on n/a's because the throttle response of a turbo car is more dependent on the turbo than the location of the TB. The gains less likely to be worth the extra complexity.



2: Its a two edged sword. You can have too sharp of throttle response. It makes the car hard to drive. Drive a modded n/a, esp one that has a ported engine. The first bit of pedal travel is an on-off switch thanks to the shitty stock ecu. Not one of my friends have ever been able to drive my car smoothly. I cant even drive it smoothly 100% of the time, and I have driven the car for nearly 5 years.



3. Plenums have their place, they are just harder to tune. I dont understand enough about plenum tuning to give a good answer, but to my knowledge, no production, fuel-injected rotary used a plenum for the secondary ports, while most used it on the primaries.

Drago86

Are you even reading my posts? I know very well that the ITB setup uses the negative pulse reflected and inverted off the bell mouth, in fact ive stated that in my previous posts.



My point is, the VDI uses the positive wave from the closing AND opening of the port. this fact is stated in BOTH of the SAE papers i posted, read this quote:





(2) As shown in the bottom of Fig. 9 the residual exhaust gas, which still has high pressure, is blown up through one of the intake ports and puishes against the intake air momentarily, thus raising the pressure. As a result, a (****) high pressure wave (****) is sent down the other intake pipe cramming more air into the other intake port."



^^^^that is at intake OPENING, there is a positive wave issued FIRST, then the negative wave. Dont believe me? look at figure 9. Read It in the other SAE paper, and look at it's figures.

Drago86

Also the 13b-re, the 20b and tha 13b-t are all stock motors that use a plenum style intake (though a fairly small volume plenum). Plenums are only complex when you start getting into helmholtz resonators, other wise the plenum just provides the cross seconal change to reflect the wave. It is kind of a waste to make a plenum intake without using a helmholtz resonator though.