Noob Question - Variable Valve Timing Equivalent?
04-29-06, 05:56 PM
#1
Noob Question - Variable Valve Timing Equivalent?
I posted this question up in the General Rotary Tech section (https://www.rx7club.com/general-rotary-tech-support-11/noob-question-variable-valve-timing-equivalent-535016/), and someone made a very interesting point, but I'm not sure what the possibility/implications of it were on a 13B-REW. Thought I'd pick some of your guys' brains, esp. since we have a lot of very knowledgeable guys here who don't visit the General Rotary Tech section all too often 
And the response:
Marek's right...I remember hearing about the 5th and 6th ports on the 13Bs. But as he mentioned, those were the NA's. Is there a specific reason why Mazda ditched that design on the 13B-REW? Is it something that could still be used in a FI application?
Thanks
~Ramy
Originally Posted by FDNewbie
I know rotaries don't have pistons and valves (duh), but I'm curious if there's anything in a rotary motor (or anything that could be done to or added to one) to have the same effect of variable valve timing?
While I was aware that VVT is used to keep the engine at optimal performance throughout the rev range, I was watching a Best Motoring video on the HKS R-34 GT-R (http://videos.streetfire.net/search/...B545DC5535.htm), and it was interesting b/c HKS developed an electonic variable valve timing system for the RB26, advertising that:
1) Low to mid-range power and speed is retained while still increasing power with cams and bigger turbines.
2) Even with high profile cams the engine maintains smooth idle and good emissions.
I guess I never thought of VVT being used to compensate for loss of low-end power/torque when using a large single turbo etc. So I'm wondering if there's anything we can do on a rotary that would have the same effect...help salvage some low end power/torque in the face of a large single? (Other than the "run a properly sized turbo" answer)
Thanks
~Ramy
While I was aware that VVT is used to keep the engine at optimal performance throughout the rev range, I was watching a Best Motoring video on the HKS R-34 GT-R (http://videos.streetfire.net/search/...B545DC5535.htm), and it was interesting b/c HKS developed an electonic variable valve timing system for the RB26, advertising that:
1) Low to mid-range power and speed is retained while still increasing power with cams and bigger turbines.
2) Even with high profile cams the engine maintains smooth idle and good emissions.
I guess I never thought of VVT being used to compensate for loss of low-end power/torque when using a large single turbo etc. So I'm wondering if there's anything we can do on a rotary that would have the same effect...help salvage some low end power/torque in the face of a large single? (Other than the "run a properly sized turbo" answer
)Thanks
~Ramy
Originally Posted by Marek
Actually the rotary community used variable "valve" timing before the piston community. On the N/A 13bs the 5th and 6th ports are controled by a pnumaticly actuated sleeve At about 3500+ RPM. When this sleeve rotates this opens up the larger (size and timing) ports. By doing this it accomplishes the same as the V-Tech. Increase of charge velocity, more overlap: which all equates to a phrase coined as enertial supercharing. Long story short more power over high RPM Range and more torque down low.
Thanks
~Ramy
04-29-06, 06:09 PM
#3
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yeah I saw this post and thought "why is he posting this".... then I realized that as an FC guy, I might have a step up on some info. The 5th and 6th ports are basically the VTEC part of the rotary, but most people end up wiring them open anyways. It seems that the only way to get VVT would be to have some kind of contraption like that, but with the Rx7, why would you want to limit the lower rpm for more mpg? Most of the VVT systems are for making better mpg at lower rpm, but when you get on it, the equivalent of the 5th and 6th ports would open and give more flow = more power. I'd much rather have the engine designed as the TT is with the flow going through at all points. I don't want to have to worry about turbo lag AND VVT lag!
04-29-06, 06:21 PM
#4
MontegoRx, oh it's nothing against you. I'm an FD guy, and I def. wanted some FD-specific input too. Plus, I know like half the guys on here 
I dunno enough about the 5th and 6th ports, how they work, etc, but if you wire them open, do you make or lose low end? Cuz again, the VVT I'm talking about specifically (the HKS one for the RB26) is being used to *increase* low end torqe to *compensate* for them throwing on a HUGE single, and thus having laggy low end. That's what I'm trying to see if there's a counterpart to it on rotaries...a way to achieve that.
~Ramy
I dunno enough about the 5th and 6th ports, how they work, etc, but if you wire them open, do you make or lose low end? Cuz again, the VVT I'm talking about specifically (the HKS one for the RB26) is being used to *increase* low end torqe to *compensate* for them throwing on a HUGE single, and thus having laggy low end. That's what I'm trying to see if there's a counterpart to it on rotaries...a way to achieve that.
~Ramy
04-29-06, 07:01 PM
#5
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Originally Posted by FDNewbie
Cuz again, the VVT I'm talking about specifically (the HKS one for the RB26) is being used to *increase* low end torqe to *compensate* for them throwing on a HUGE single, and thus having laggy low end. That's what I'm trying to see if there's a counterpart to it on rotaries...a way to achieve that.
~Ramy
~Ramy
PS the RX8 has secondary intake ports that open at higher rpms, too.
04-30-06, 12:18 AM
#7
aren't the secondary ports the same? first the primaries then at a certain rpm or load the secondaries. It doesn't matter if it's n/a or not.
The tertiary ports (5th and 6th) are beneficial on n/a to be able to breath more, since the turbo already forces air in the engine then they aren't used in turbo applications.
SO it could be said that the turbo 13b's have 2-stage intake timing while the rx-8 has 3-stage timing (actually there are more stages due to the variable dynamic resonance thingy intake)
The tertiary ports (5th and 6th) are beneficial on n/a to be able to breath more, since the turbo already forces air in the engine then they aren't used in turbo applications.
SO it could be said that the turbo 13b's have 2-stage intake timing while the rx-8 has 3-stage timing (actually there are more stages due to the variable dynamic resonance thingy intake)
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04-30-06, 07:44 AM
#8
Constant threat
One would think it not too difficult to employ some sort of 'shutter valve' on the intake side of things that would incorporate a variable diameter that was computer controlled for optimal engine response. Think of a camera aperture, for example.
On a similar note, how exactly did the variable intakes on the 787B 3-rotor work? My (rough) understanding of it is that the intake 'trumpets' could change length....
On a similar note, how exactly did the variable intakes on the 787B 3-rotor work? My (rough) understanding of it is that the intake 'trumpets' could change length....
04-30-06, 08:10 AM
#9
development
one way I plan to pick up some low end, is to re-install the double throttle plates (coolant operated ones in the UIM)
but have Haltech control them...via rpm and boost. Theory is it will increase velocity thru the primary runners/ports...I don't inject fuel into the secondaries until 3psi of boost, so why should I give them air?? Tuning will be required
but have Haltech control them...via rpm and boost. Theory is it will increase velocity thru the primary runners/ports...I don't inject fuel into the secondaries until 3psi of boost, so why should I give them air?? Tuning will be required
05-16-06, 10:25 AM
#10
Originally Posted by bajaman
On a similar note, how exactly did the variable intakes on the 787B 3-rotor work? My (rough) understanding of it is that the intake 'trumpets' could change length....
~Ramy
05-16-06, 11:34 AM
#11
VVT controls timing and duration of the valves and airflow in a piston engine, the same thing we accomplish through size/shape/location of stationary ports. When we do a streetport, we do the same thing as changing the cam profile and timing for greater flow at higher rpms. Without 1) using butterflies to open and shut those larger ports at low throttle (the stock throttlebody already does this to some degree) or 2) using several staged ports the engine and intake (similar to FC 13b NA 6 port engines and the renesis) there's no way to change a rotary's stationary port size on the fly.
The reason mazda went away from it on all the turbo motors is because the turbo moves enough air to compensate for the lack of flow that a nonturbo would otherwise have. The FC 6 port setup is basicaly like an REW secondary port divided in half along it's length, with a sleeve in the top half to open and close it. Looking at it that way, the division and sleeve are a restriction in a turbo environment.
There's also the problem of actually fitting the variable port hardware on a turbo intake manifold, as mazda lays theirs out in stock form...there's a rod and actuator that are used to turn the variable port sleeve on the nonturbo setups, and there's NO room for that in the slimline turbo intake manifolds because the turbo sits right beside them on both FC and FD models. The only way to effectively do it is using butterflies in the runners further upstream where there is more room (similar to what dubulup is fooling with) but then you create another airflow restriction for yourself and just add complexity to an engine that's already difficult to maintain and work on.
The reason mazda went away from it on all the turbo motors is because the turbo moves enough air to compensate for the lack of flow that a nonturbo would otherwise have. The FC 6 port setup is basicaly like an REW secondary port divided in half along it's length, with a sleeve in the top half to open and close it. Looking at it that way, the division and sleeve are a restriction in a turbo environment.
There's also the problem of actually fitting the variable port hardware on a turbo intake manifold, as mazda lays theirs out in stock form...there's a rod and actuator that are used to turn the variable port sleeve on the nonturbo setups, and there's NO room for that in the slimline turbo intake manifolds because the turbo sits right beside them on both FC and FD models. The only way to effectively do it is using butterflies in the runners further upstream where there is more room (similar to what dubulup is fooling with) but then you create another airflow restriction for yourself and just add complexity to an engine that's already difficult to maintain and work on.
05-16-06, 02:28 PM
#12
development
Originally Posted by RotaryResurrection
The only way to effectively do it is using butterflies in the runners further upstream where there is more room (similar to what dubulup is fooling with) but then you create another airflow restriction for yourself and just add complexity to an engine that's already difficult to maintain and work on.
05-16-06, 05:07 PM
#14
I'm not a stock purist type, but these sort of endeavors leave me wondering if they are worthwhile. Do we seriously think that some guy in a garage is going to think of something that factory engineers overlooked while being backed by years of research and thousands of dollars in R&D funds?
At some point down the line when the REW was developed, somebody had to play around and find the optimal point for opening the secondary intake runners. The throttle body linkage is set to automatically do so at that point. Unless we're talking about a radical change like a bridgeport, I can't see that there's much to be gained here.
I of course look forward to any results that might be posted in the future, but as usual with these projects I will not hold my breath.
At some point down the line when the REW was developed, somebody had to play around and find the optimal point for opening the secondary intake runners. The throttle body linkage is set to automatically do so at that point. Unless we're talking about a radical change like a bridgeport, I can't see that there's much to be gained here.
I of course look forward to any results that might be posted in the future, but as usual with these projects I will not hold my breath.
05-16-06, 05:13 PM
#15
Kevin, I agree w/ you, but my usual mental field trips (lol) are within the context of significant changes in power. In this case, a considerable port (aggressive street or race, or even a half bridge as you mentioned).
~Ramy
PS: I also kinda hope that while the technology our cars was built upon is fixed, it may be possible that new technology can give us an advantage or leg up on getting more out of our cars, that's all.
~Ramy
PS: I also kinda hope that while the technology our cars was built upon is fixed, it may be possible that new technology can give us an advantage or leg up on getting more out of our cars, that's all.
05-16-06, 10:12 PM
#16
Originally Posted by FDNewbie
....so I'm wondering if there's anything we can do on a rotary that would have the same effect...help salvage some low end power/torque in the face of a large single?....
05-16-06, 11:24 PM
#17
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Mazda has already done this with the Renesis. The timing on the six ports (3 per rotor) of the Renesis engine is controlled through the intake manifold system, not the sleeves found on the older 6-port motors. That was one of the contributing factors in being able to produce an emissions friendly side-port motor with more (or less) power. Now, if you could take the intake and control system of the RX-8 and somehow adapt it to the 3rd gen motor, then that could have some type of effect. Maybe good, maybe bad. Just a guess.
05-16-06, 11:28 PM
#18
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Originally Posted by FDNewbie
....so I'm wondering if there's anything we can do on a rotary that would have the same effect...help salvage some low end power/torque in the face of a large single?....
05-17-06, 07:30 AM
#20
development
Originally Posted by RotaryResurrection
At some point down the line when the REW was developed, somebody had to play around and find the optimal point for opening the secondary intake runners.
how about something radical like twice the stock boost pressure on a turbo that moves serious air...and of course we aren't talking stock port timing.
05-17-06, 11:31 PM
#21
The 5th and 6th ports are still opened and closed by sleeves, but are controlled electronically by the PCM and atuated by servo motors.
What the intake manifold system does is change the length of the runners depending on RPM with a series of valves.
What the intake manifold system does is change the length of the runners depending on RPM with a series of valves.
Originally Posted by quicksilver_rx7
Mazda has already done this with the Renesis. The timing on the six ports (3 per rotor) of the Renesis engine is controlled through the intake manifold system, not the sleeves found on the older 6-port motors. That was one of the contributing factors in being able to produce an emissions friendly side-port motor with more (or less) power. Now, if you could take the intake and control system of the RX-8 and somehow adapt it to the 3rd gen motor, then that could have some type of effect. Maybe good, maybe bad. Just a guess.
Last edited by neit_jnf; 05-17-06 at 11:34 PM.
05-18-06, 11:32 PM
#22
Originally Posted by neit_jnf
The 5th and 6th ports are still opened and closed by sleeves, but are controlled electronically by the PCM and atuated by servo motors.
What the intake manifold system does is change the length of the runners depending on RPM with a series of valves.
What the intake manifold system does is change the length of the runners depending on RPM with a series of valves.
really? i never knew that? point me to where i can see this...i was only aware of the 3 stage fuel system
05-19-06, 09:30 PM
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05-20-06, 02:37 AM
#25
No it's not Turbo'd
I thought I saw the trumpets on the 787 or some of the older star mazda motors moove up and down, I asked a guy a while back, and he said it was to lengthen or shorten the intake tract to accelerate or decelerate the intake air. Based on throttle or ecu or something. Kind of like a longer chimney tends to draw better... ???
-DC
-DC