I have been playing with my auxillary ports lately, and in the process wired open the VCI as well. I understand a very basic idea of how and why it works, but I just need someone to REALLY explain it. I left it working, and have had it not working back and forth for a week now, trying to decide which I like better. Thanks for helping the moron out!!

 

Hey, Rico5 - I haven't been around here too much lately like in the past, but I could almost swear you've asked this question in the past, but no worries mate.

Heres the general low-down. In the VDI manifold, there are 2 sets of intake runners, a longer set and a shorter set. The VDI manifold has a canister inside that rotates when the actuator arm is pushed up. This canister has holes in it that rotate with the canister to switch which intake runners your intake charge is going through on its way down to the lower intake manifold. I believe that before 5600rpms the shorter intake runners are used(I haven't seen my RX-7 since I moved here to Canada for school, so I can't go outside to check), and then the longer runners are used for above 5600rpms. The VDI is just a way of adjusting the distance your intake charge has to travel on its way into the engine to optimize Hp/torque at a broader rpm range.

The VDI arm is actuated from air pressure supplied from the airpump. The airpump supplies the pressure, and the VDI solenoid which is connected to the computer is activated at 5600rpms. This allows the air to goto the air control valve(ACV)where it is routed to the VDI manifold actuator.

Hope this helps.

 

SR: That was mostly correct, except you got the "order" wrong - longer runners result in higher flow velocity (and thus more torque), while the shorter runners allow higher absolute flow at the expense of flow velocity. Thus, at low RPM the longer runners are used, while at high RPM, the shorter ones are added (air still flows through the longer runners, IIRC).

Brandon

 

It's lower... 5200 rpm's I beleive...
The VDI doesn't stop at utilizing standad air velocity from incoming air in the vaious length runners...
It also uses the pressure wave that is generated when the intake port is covered. (the same kind of pressure wave that a blow off valve relieves). It uses this sudden surge, and directs it to the opposite rotor, thus driving the intake charge in harder!
Pretty damn cool if you ask me!

 

This was discussed recently in this thread.

 

Here, it's the change of positive manifold pressure due to the route that the ariflow takes.

 

Damn, Mazda is cool!! Well, since my air pump is not working, it is always locked in low since there is no vacuum to open it. I am glad I kept my air pump, bc I think I am going to attempt Samp's method of actuation.

Sepped, yea, I have asked this question before, but it was never really answered as well as this one was. Thanks guys!!

 

An intake is efficient in a narrow RPM range. In reality, an intake is perfect at only one minisule RPM point and everywhere else in the powerband is a compromise. Because the rotary doesn't have torque, Mazda gifted the NA with a 2-stage intake(3 if you include the switchover from 4 to 6 ports). This helps provide the lowend without killing the topend or vice versa---provides topend without killing lowend. Some of the german automakers use a 3-stage intake. I believe that the Renesis is going to a 3+ stage intake(not sure is Mazda is counting port actuation as a stage). It is more than the pressure wave and the intake flow velocity, or the use of the former to increase the latter. The purpose is to provide the highest average VE over the widest possible RPM range. Mazda calls it VDI and Nissan calls it VI and Porsche calls it Varioram and VW has the Shrick.......And the ancient domestic boys had the predator variable venturi/flow carb........A continuosly variable length and diameter intake would be perfect. All we would need is a "shape shifter" to want to spend its life as an intake/exhaust. My only problem with Mazda is how complex the rotary intake is. There are numerous single points of failure. But, that was the risk for being the first to use variable intake. I don't remember any other automaker with regular production(affordable) VIM before 1986. Mazda started an engineering trend.

Exhaust systems also suffer the same fate. Perfect at only one single RPM point and a compromise everywhere else. Some of the motorcyles have exhaust tuning valves. Backpressure exhaust control is a bandaid(that works) compared to variable exhaust runner length/diameter. Anyone want to murder their RacingBeat/Mindtrain header and add a couple of Yamaha Exup valves?????
Eventually(never), we will see fully infinite variable intake and possibly variable exhaust. Right now, the automakers are IMO wasting money(????) on variable infinite gear transmissions. I believe that it is cheaper for the automaker to tune the engine at two points; one for max power and the other for max economy. This way, the CVT picks the RPM point needed and does all the work.

Several features of a dyno pull(other than HP and torque), are to measure BFSC, VE, BSAC, BMEP, ET, ......something that noone ever mentions. The web has plenty of info on the above mentioned acronyms used by automakers when tuning engines/intakes/exhaust for economy/emissions/power......

Read and learn:

http://www.howstuffworks.com/question517.htm
http://personal.riverusers.com/~yawpower/techindx.html
http://www.auto-ware.com/combust_bytes/eng_sci.htm
http://www.engr.colostate.edu/~allan...ge7/page7.html
http://autozine.kyul.net/technical_s...h_engine_2.htm
http://www.sae.org/servlets/index (do a search for variable intake)

The only moron is one that does not ask questions.

 

Thanks so much guys for expalining why and how this works. deadRX7Convertable, that was a VERY insightful bit of info!! Thanks a lot!!

 

Just a slight correction Rico, the VDI AND 6-ports of a series 5 FC run of air PRESSURE and not VACUUM.

DEFINENTLY check out deadRX7Conv's second link he posted. Paul Yaw's technical articles are the best ever. Great info about intake and exhaust cycles, and its stuff that can be applied to piston engines as well.