intake ports and solenoid bridging.

Any form of normally aspirated power mods.
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intake ports and solenoid bridging.

Post by Project-RX8 » Wed Jul 04, 2018 11:18 am

It's worth me starting by saying this is a bridgeported motor and fuel consumption i'm not too bothered about.

I experienced the car feeling sluggish up to the secondary ports opening.

Took it apart and there was a vacuum leak on the solenoid stopping the first ports opening.

With a better understanding how it all worked it got me thinking.

How does it exactly work?

two theories.

1) Primary port opens at the given RPM range and closes when the secondary opens at the higher rpm. (this is the unlikely option and would mean the secondary would have to be bigger or different.)

2) Primary port opens at the given RPM and remains open when the secondary also opens.


I'm assuming it's the second?


With that in mind...

I have two ideas that could net a nice little power gain mid range or possibly low and mid range.

a) Has anyone made both the ports open with the first solenoid? This would be very easy to do.

b) What about gutting the butterflies and have them both constantly open? This would mean even more flow without the butterfly disks and shaft.

What are people's thoughts? option b) may result in a loss in low end power, with my nsx removing the vvis system results in a slight low end loss but upper rpm range gain. However on a bridge ported rotary engine this may not be relevant and result in gains throughout the whole rev range.

option a) will at least make the fuel consumption conservative on a drive but make it more lively mid range and could result in a great gain.

This could be very useful on track, more mid range power meaning wider usable rpm range.


In terms of the bridging you wouldn't bother with wiring, just plumb the vacuums differently using a Y piece or two.

This means when the first solenoid kicks in both ports open resulting in lowering the 6k rpm kick to 3.5k (i'm not entirely sure at what rpm they kick in.)

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Re: intake ports and solenoid bridging.

Post by Phil Bate » Wed Jul 04, 2018 11:45 am

I think you may be misunderstanding how the intake air system operates. As a club member you have privileged access to the FAQ - Technical section of the forum, where you will find the Multimedia Training material. This is a downloadable presentation that will show you (amongst other things) exactly how and when the various ports operate :thumleft:
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Re: intake ports and solenoid bridging.

Post by Project-RX8 » Wed Jul 04, 2018 12:29 pm

Got it thanks.

I'm pretty sure i don't have the VFAD, never saw it when removing the front bumper and i have a aftermarket induction kit.

SSV - 3250rpm - vacuum
VFAD - 5500rpm - vacuum (believe it has been removed as i have a aftermarket induction kit)
APV - 6250rpm - Electric motor (will be complicated to open at lower revs) (Do you know how the signal to the motor works?)
VDI - 7500rpm - Shortens length of intake tubes, like a solenoid on a exhaust system

It's interesting that the VDI opens at 7250 close to redline,

How about T piecing the VDI to open with the SSV solnoid? surely a shorter route will always be beneficial for power?

APV I might be able to open earlier, depending on how the signal to the electric motor works. The solenoid to the SSV has two wires, guessing live and ground. Would it be as simple as taking the live from the SSV solenoid to the APV?

Would be keen to have a spare APV out of the car to experiment with.

The air pump i hear guys say its for cold starts but i have heard a couple of people suggest it gives more power and comes in additional to cold start. Not sure how true that is.

for reference:

Image

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Re: intake ports and solenoid bridging.

Post by 13Black » Wed Jul 04, 2018 12:31 pm

Basically the intake operation goes like this:

-Low rpm
Primary only open (and always is, no valves)

-Mid rpm
Primary still open
Secondary opens

-High rpm
Primary still open
Secondary still open
Auxiliary opens

-Very top end rpm
Primary still open
Secondary still open
Auxiliary still open
VDI acoustic tuning valve opens
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Re: intake ports and solenoid bridging.

Post by PeteH » Wed Jul 04, 2018 12:48 pm

Mazda tuned all that lots to give the engine enough breathing potential at very high revs, but without compromising low rev torque ( :shock: I know, I know!). They chose the opening points specifically to optimise the torque at every point in the rev range. If you open all the valves at low revs the consequences for low rev torque would be dramatically bad. The speed of the air flow through the intake would be very low, and the filling ability of the chambers would be terrible.

Feel free to do what you want. But when I had my race car mapped by RR we adjusted the opening points by just a few hundred revs, and we really struggled to improve on Mazda's tuning.

Bridging will give you more air flow potential at very high revs, but the basic tuning parameters at lower revs really won't be much different. If you do want to fiddle with the valve tuning then it's all possible via normal ecu tuning. You don't have to start messing with the hardware.

vFAD: we think it's mainly there to reduce low rev resonance through the intake system. It doesn't seem to be a significant tuning mechanism.
Air pump: Purely a cold start system for heating the cat quickly. The load it puts on the alternator is significant, and will draw net power from the engine. How does anyone think that injecting air into the exhaust can actually improve power...?? Also, if you ran the air pump while the engine was warm it would just add to the exhaust back pressure, and mess up the mixture tuning, so it would be doubly bad for power. I love the internet. [-X

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Re: intake ports and solenoid bridging.

Post by 13Black » Wed Jul 04, 2018 2:32 pm

It will have been designed by some quite clever folk with powerful software.

Tested and refined no doubt.

And those with the tools to mess with it now currently don't really change anything about it.


Without sounding abrasive, I don't think you understand the system or the physics behind it enough, so if there are any inroads, I suspect they'll be small and out of your reach - free dyno time being fairly essential also :(
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Re: intake ports and solenoid bridging.

Post by Ryan Rotary Performance » Wed Jul 04, 2018 4:09 pm

just putting my two pence in.

If you have a standard engine then changing anything will do very little and most likely reduce performance.

However, if you have a street, half bridge or full bridge then the port timings WILL need adjusting to make the most of the modifications, especially the SSV which is the most sensitive to these modifications.

so nutshell, if the engine is standard leave them alone, if the engine is anything than other then yes have a play

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Re: intake ports and solenoid bridging.

Post by Project-RX8 » Mon Jul 09, 2018 11:44 am

Great thanks for the info guys.

I know Mazda did a very good job with the Renesis engine but they also have to take in to consideration driveability and fuel economy so it's always interesting to discuss from a performance point of view.

With a modified engine as Ryan mentioned things change, i might have a little play. I have a local dyno, i might book a before and after power run as seat bhp always adds 10bhp including stickers ;)

If i see a gain i might even remove the VDI entirely for the weight saving as it looks bulky in images. It's basically a huge cylinder with a square cut out in opposite ends that rotates to open the air flow.

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Re: intake ports and solenoid bridging.

Post by 13Black » Mon Jul 09, 2018 11:49 am

It's aluminium and mostly hollow.

I can weigh one if you like.
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Re: intake ports and solenoid bridging.

Post by 13Black » Mon Jul 09, 2018 3:40 pm

The valve, gasket, actuator, basically the whole thing.
Less than 400g
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Re: intake ports and solenoid bridging.

Post by Lemon » Mon Jul 09, 2018 4:35 pm

13Black wrote:
Mon Jul 09, 2018 3:40 pm
The valve, gasket, actuator, basically the whole thing.
Less than 400g
now you need to use Pete's "Spinnermajig" (patent pending) to test it for spinneryness.
Thanks, Stu

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Re: intake ports and solenoid bridging.

Post by 13Black » Mon Jul 09, 2018 5:10 pm

Trifilar rig wasn't it. Witchcraft and Microsoft Excel had a baby and this stringy thing was the result.
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Re: intake ports and solenoid bridging.

Post by PeteH » Mon Jul 09, 2018 5:57 pm

Hmmm. It's not a question of rotational inertia. I'm not sure the ports have rotated with the entire engine since Felix built his original prototype.... ;) :lol:

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Re: intake ports and solenoid bridging.

Post by ChrisHolmes » Mon Jul 09, 2018 10:27 pm

The intake valve system is designed so that when the ports open there is a high pressure wave arriving at the port opening which increases the size of the intake charge going into the chamber. Therefore when an engine is ported and the rotor opens the port earlier does this upset the pressure waves as less pressure will be built up by the time the port opens thus lessening the charge effect, but then the port is open longer so does it balance out the lesser pressure or am I talking blx?
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Re: intake ports and solenoid bridging.

Post by 13Black » Mon Jul 09, 2018 10:38 pm

I think a street port doesn't affect the port opening times (at least not by that much), mainly delay the closing time. A bridge certainly would affect port opening times.

Can't answer the main point of your question though I'm afraid - it's probably hard to say exactly what's going on fundamentally with much certainty. A friend of mine has some intake/exhaust/engine modelling software we wanted to use for an RX-8 but we suspected it's far too refined for piston engines to accurately be of use for what we have. It would be great to get it working for these though. Maybe one day.
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Re: intake ports and solenoid bridging.

Post by ChrisHolmes » Mon Jul 09, 2018 10:55 pm

I suppose the principle is the same Nick, opening degree point, degrees duration, closing degree point, overlap with exhaust. Not to mention gas velocity and port shapes so it gets a bit complex.
Someone must have done some flow bench work to see the effect of port shapes and how the air flow through the opening as the port opens. A classic case in the good old days was the Ford Pinto where the exhaust port was a similar shape to the RX-8 and a large bore circular manifold mismatched interface was found to produce more power than a matched shape that flared out to the circular section. I hope that description was clear enough. I suppose it's a similar scenario with a tubular manifold on the Renesis.
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Re: intake ports and solenoid bridging.

Post by 13Black » Mon Jul 09, 2018 11:12 pm

Yes a small step on the exhaust can stop reversion back into the cylinder leading to less exhaust gas contaminating the next intake charge and freeing up available clean air volume. That may be why the block doesn't like up perfectly with the manifold primaries but I don't have proof of it.

I would assume that uniform circular valves that open/close in a smooth fashion thanks to lobe shapes are easier to model than fairly jittery ports ... whether there is scope for this in that software I have no idea. It's not the end of the world to calculate port surface area for a given crank angle but that may not get us all the way there due to the path the airflow takes in the runners.

Oh to be clever and able to do such things! :(
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