Can the VDI be "wired open"? Benefits/Disadvantages?
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Can the VDI be "wired open"? Benefits/Disadvantages?
Can the VDI be wired open so that it is active all the time? Would the low RPM flow be any better? I assume the torque would drop slightly at lower RPMs. What about in a forced induction situation? Would it be more beneficial then? Also, should my dyno dip in power as it does when the VDI opens? What is causing the dip?
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Yes it can be wired open. Benefits? none. Draw backs I guess the speed of the intake would not be optimal otherwise the mazda techs would not have created two positions for it. If the VDI running open was the best in all the rpm ranges it would have just been designed without the valve. Atleast thats mo.
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Originally Posted by 1987RX7guy
Yes it can be wired open. Benefits? none. Draw backs I guess the speed of the intake would not be optimal otherwise the mazda techs would not have created two positions for it. If the VDI running open was the best in all the rpm ranges it would have just been designed without the valve. Atleast thats mo.
Also, what about the dip in my dyno chart? Is that normal?
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Originally Posted by pianoprodigy
Ok. What about in a forced induction situation? Any benefits then?
Also, what about the dip in my dyno chart? Is that normal?
Also, what about the dip in my dyno chart? Is that normal?
On forced induction, among many things, i'm not an expert. I would think that if you are running a turbo, once it spools it should be open. If you are using a blower setup, just leave it open because if its doing anything towards positive pressure its moving faster than an N/a would be pulling the air.
I have seen that dip in other charts but I would think its because of the velocity change and fuel changes that occure there. Its probably not a very nice looking transition looking at it from those stand points, killing power.
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Originally Posted by 1987RX7guy
On forced induction, among many things, i'm not an expert. I would think that if you are running a turbo, once it spools it should be open. If you are using a blower setup, just leave it open because if its doing anything towards positive pressure its moving faster than an N/a would be pulling the air.
I have seen that dip in other charts but I would think its because of the velocity change and fuel changes that occure there. Its probably not a very nice looking transition looking at it from those stand points, killing power.
I have seen that dip in other charts but I would think its because of the velocity change and fuel changes that occure there. Its probably not a very nice looking transition looking at it from those stand points, killing power.
I'll talk to my tuner/mechanic about it and see what he thinks. In the meantime, any other opinions?
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Originally Posted by pianoprodigy
Can the VDI be wired open so that it is active all the time?
Would the low RPM flow be any better?
I assume the torque would drop slightly at lower RPMs.
The VDI system is basically used to swap between two different torque curves, one that peaks later than the other. By being able to utilise both torque curves, average power (and hence overall performance) is increased.
Here's a dyno graph from Mazda's development of the VDI system, taken from the SAE paper on the S5. It shows the torque curve of the S4 13B compared to manifolds with different "communicating" lengths, which is the length the pressure waves travel from port to port. The chosen lengths for the S5 manifold were "d" (400mm longer) when the VDI valve is closed at low rpm and "a" (200mm shorter) when the valve is opened high rpm. The two curves cross at 5200rpm, which is when the ECU opens the valve. The resulting torque curve is higher than the S4's at nearly all points in the rev range.
What about in a forced induction situation? Would it be more beneficial then?
Also, should my dyno dip in power as it does when the VDI opens?
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it may be good to give the VDI actuator an inspection, and to make sure it is getting the correct amount of pressure (or is that vacuum...) in the line. opening too slowly or incompletely may cause the hesitation.
you could also try hooking up the solenoid to an rpm switch, and then experimenting with different opening RPMs. i think 5200 will still be best, but there may be a different RPM that is better to open at because of the changes caused by the forced induced intake...
you could also try hooking up the solenoid to an rpm switch, and then experimenting with different opening RPMs. i think 5200 will still be best, but there may be a different RPM that is better to open at because of the changes caused by the forced induced intake...
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Originally Posted by coldfire
it may be good to give the VDI actuator an inspection, and to make sure it is getting the correct amount of pressure (or is that vacuum...) in the line. opening too slowly or incompletely may cause the hesitation.
you could also try hooking up the solenoid to an rpm switch, and then experimenting with different opening RPMs. i think 5200 will still be best, but there may be a different RPM that is better to open at because of the changes caused by the forced induced intake...
you could also try hooking up the solenoid to an rpm switch, and then experimenting with different opening RPMs. i think 5200 will still be best, but there may be a different RPM that is better to open at because of the changes caused by the forced induced intake...
If you look at this guys dyno (also a 6 port with VDI) he has no dip in power:
Originally posted in this thread: https://www.rx7club.com/time-slips-dyno-128/na-6-port-177-rwhp-363329/
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The benefit is almost non-existent on a forced induction car. It's pretty much the same as aux ports being used in an FI setup, you're flowing so much air by that time anyway that the best flow is generally the best bet.
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Originally Posted by SonicRaT
The benefit is almost non-existent on a forced induction car. It's pretty much the same as aux ports being used in an FI setup, you're flowing so much air by that time anyway that the best flow is generally the best bet.
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Basically in my turbo charged setups, with the aux ports it only helps the turbo spool a hair quicker, which isn't too big of a deal, and they hinder top-end by creating turbulance, so I prefer removing them. As for VDI, i just leave it in the open position. There was little to any change when playing with the VDI on the dyno. For an N/a setup however, these are all crucial, and I do believe changing the timing of the vdi after mods would prove to be a benefit.
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Originally Posted by SonicRaT
Basically in my turbo charged setups, with the aux ports it only helps the turbo spool a hair quicker, which isn't too big of a deal, and they hinder top-end by creating turbulance, so I prefer removing them. As for VDI, i just leave it in the open position. There was little to any change when playing with the VDI on the dyno. For an N/a setup however, these are all crucial, and I do believe changing the timing of the vdi after mods would prove to be a benefit.
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I would personally leave it working. It's there for a purpose and it still does it's job regardless of what the pressure in the intake manifold is. If this wasn't so then it might work better at sea level than at the top of Pike's Peak. It takes of the pressure waves that travel back and forth inside the manifold at the speed of sound from the ports opening and closing. It doesn't concern the amount of boost.
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Theres only one positive outcome to wiring open ports on any NA, whether its the 6port system or VDI.
The only advantage is that you don't have to worry about the ports in the first place.
The negatives outwiegh that pro tho, heavily IMO.
The only advantage is that you don't have to worry about the ports in the first place.
The negatives outwiegh that pro tho, heavily IMO.
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Originally Posted by rotarygod
I would personally leave it working. It's there for a purpose and it still does it's job regardless of what the pressure in the intake manifold is. If this wasn't so then it might work better at sea level than at the top of Pike's Peak. It takes of the pressure waves that travel back and forth inside the manifold at the speed of sound from the ports opening and closing. It doesn't concern the amount of boost.
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Originally Posted by SonicRaT
What charger are you going to be using? And yeah, that should be an OK setup.
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Originally Posted by pianoprodigy
I don't want to get a header because I'm afraid it will get too loud.
I read somewhere that modifying the exhaust creates problems with backpressure and doesn't allow the 6 ports and VDI to work properly.
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Originally Posted by NZConvertible
I'm pretty sure a stock exhaust manifold will be a significant restriction with forced induction, but i guess it depends on how far you plan to go. If you're worried about noise then get a dual muffler system with decent-sized quality mufflers (not shiney little eBay cans). You should be seriously considering a new "turbo-sized" exhaust system anyway.
Exhaust backpressure has nothing to do with the S5's 6PI and VDI systems, they operate from air pressure switched in by the ECU. Exhaust changes have zero effects on them. You're thinking of the S4's 6PI system.
Exhaust backpressure has nothing to do with the S5's 6PI and VDI systems, they operate from air pressure switched in by the ECU. Exhaust changes have zero effects on them. You're thinking of the S4's 6PI system.
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So, I've been doing some thinking about using a header. As I looked at the Racing Beat site, it seems that they offer two different headers. The first one is the "streetable" header that collects, and I think that would just replace my stock manifold and the Racing Beat "down pipe." Cost is $200. Below is a picture:
Racing Beat also offers a "Road Race" header that does not collect. I'm sure it flows much better since it is a "true dual" setup; however, I would have to replace several components of my exhaust and the cost would go up significantly (over $600). Below is a picture:
It seems that the "Road Race" setup would be considerably louder, and, of course, would flow much better. It would also be much more expensive. I think if I do go with a header, I would go with the collected "streetable" design. Would the performance gains be worth the $200? I've done a lot of searching and reading, and it seems that many don't get a very significant gain in an NA setup; however, I think in a Forced Induction setup such as mine, I would benefit more. Any more opinions?
Racing Beat also offers a "Road Race" header that does not collect. I'm sure it flows much better since it is a "true dual" setup; however, I would have to replace several components of my exhaust and the cost would go up significantly (over $600). Below is a picture:
It seems that the "Road Race" setup would be considerably louder, and, of course, would flow much better. It would also be much more expensive. I think if I do go with a header, I would go with the collected "streetable" design. Would the performance gains be worth the $200? I've done a lot of searching and reading, and it seems that many don't get a very significant gain in an NA setup; however, I think in a Forced Induction setup such as mine, I would benefit more. Any more opinions?
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I don't think I ever got a response about the VDI actuation. I saw that NZConvertible has said that backpressure did not influence the actuation; however, coldfire mentioned an "RPM switch" to activate the VDI. Is this a fairly simple device that can be adjusted on the fly (OK, let's try 4k, how about 4200?).
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Originally Posted by pianoprodigy
I don't think I ever got a response about the VDI actuation. I saw that NZConvertible has said that backpressure did not influence the actuation; however, coldfire mentioned an "RPM switch" to activate the VDI. Is this a fairly simple device that can be adjusted on the fly (OK, let's try 4k, how about 4200?).
check out summit racing, they have one that isn't too expensive.