twincharging prototypes needing constructive critisism (SC14 + turbo)

[brett_celicacoupe]

Depending on turbo selection, I have honestly thought that the bypass may never need to shut completely at all...? Just a thought... It could be very bloody close to closed between say -5psi to +5psi. Under that, slightly more open, over that WO.

you mean like wastegate creep?


thats what a boost controller is for

same problem,
same principle,
smae solution

[Ben Wilson]

That looks very similar to the idea I've had for years now.

You don't have to disable the supercharger, if you've got atmospheric pressure at both sides of it, it will be doing bugger all work and drawing bugger all power.

The two throttle bodies should be working on a common cable so they are synchronised (getting the idle right will be tricky).

[brett_celicacoupe]

yucky yucky!

one way valves FTL!!

[Ben Wilson]

OK then, grab a throttle body and a vacuum modulator. Use the vacuum modulator to open the valve whenever there is any vacuum behind it and close the valve whenever there is pressure.

Or - you can use closed loop electronic actuation and use a map sensor between the SC and the turbo, modulate the TB so that whenever there is pressure between the two, the TB is closed then progressively open the TB to ensure there is never any vacuum.

You could call either of them a one way valve......

[2JZR31]

Ben. I think your idea inspired my idea ages ago Did you make a thread on PF where we affectionately named your one-way valve a "Ben valve" I agree that one way valves seem good in theory but seem to not work in practice. So in my model the bypass TB is mechanically opened at the same time the one way valve would start to open. (when the pressure behind it falls to atmospheric). Which is exactly what you said here.

OK then, grab a throttle body and a vacuum modulator. Use the vacuum modulator to open the valve whenever there is any vacuum behind it and close the valve whenever there is pressure.

You are right that the SC won't draw much power when pressure on both sides of it is equal. But the SC will most likely overspend which can't be good..

Why do you have a TB in of your SC? Is this just to get around fitting another type of SC bypass to prevent boost buildup between the SC and main TB?

[Ben Wilson]

Yeah, that was me - one of the advantages of not changing user names...

It sounds like we're on the same wavelength. You could get away with a BOV as a supercharger bypass (I've got one on my car at the moment), but it doesn't work 100% perfectly on the transition on to boost. If I was going to the effort of building a twincharger, I'd want it to work just like a factory car (but with a bit more power )....

[mic*]

...And to further explain what i said Brett;

My bypass is the standard ABV (very small). Only thing is, its no longer controlled by the factory VSV. I have just plumbed a inlet manifold pressure reference to it. So it acts as a bypass (OPEN) under vac. If you put your foot down, the SC builds pressure in the manifold quicker than it is bypassed, so the vac disappears, then at ATM the pressure reference closes the ABV and we boost away ->

**At this point i will note again that having a driven SC under vac MASSIVELY improved the driveability & response of my (low standard compression) car. And no jolt, so i can take people for a drive without them thinking i have inept control of the throttle...***

If it were twin charged, i have thought that depending on how i sized the turbo, it would be starting to flow pretty hard by ATM manifold pressure. Which the point where turbo flow exceeds SC flow is the point that the vavle would start to need to open. So would it need to completly close???

My theorectical prob is, no matter what the opening point is, it is the point where the air demand will drop.

To put it simply, when the turbo is blowing the SC14 you effectively have a 2.8L (four stroke) motor demanding air from, & spooling the thing. As soon as the SC is bypassed, you are back to the 2.0L 1G.

The turbo is already flowing enough air at this point to start making boost against the "2.8L". Surely to translate this into the same flow at a higher pressure, (ie the actual 2.0L + boost as the valve opens) the exhaust turbine will need more energy. Where will this come from since exhaust has momentarily dropped as the whole intake is now equalizing in pressure at the expense of a little bit of intake... This is my hiccup.

And its also why i thought that creeping the valve around for smoothness at the expense of a tiny bit of efficiency might be the way to go...

Ie, if the valve was open the tiniest bit at the point where turbo starts exceeding flow, this would allow air pressure to try and maintain balance through the transistion period. I imagine the boosted air would try to bleed back initially, then would see a slowing then reversal of air flow through the valve as the turbo flow power takes over. The valve would then be WO after this.

[mic*]

I have also thought many times;

Fark the complexity, just blow the turbo straight through it and get the cooling right...

There might be slightly less outright potential, but more than enough to investigate my curiousity, gain some experience, and come up with EDUCATED new and better ways.

[Ben Wilson]

My design was all about removing the transitional problem. There may be a few potential issues, but the basic concept is:

Low revs - Supercharger blows straight through the turbo, no problem right?

As revs come up - The turbocharger begins to spool. As it spins up, it will start to reduce the load on the supercharger by lowering the pressure in the pipe between the two.

Once the turbocharger 'outruns' the supercharger, it will be demanding more air than the supercharger can supply. This is when the 'Ben valve' opens and supplies more air.

There shouldn't be a 'step' in the boost or power delivery.

I am a little worried about possible compressor surge with such low pressure ratios, but if that wasn't an issue, it could be a good thing.

[mic*]

Yeah it does sound good Ben. Its basically the same as a couple of ideas referenced in the thread. Have you got the patent for the BenValve yet? How were you gonna do it?

What engine was this design intended for? As in did you think into detail about physically mounting it all onto an engine in a particular bay?

I am thinkin a bit tricky on the 1G, but you ave a 4A right?

[brett_celicacoupe]

Once the turbocharger 'outruns' the supercharger, it will be demanding more air than the supercharger can supply. This is when the 'Ben valve' opens and supplies more air.

id be warey of allowing the turbo to do this.... if you think about it, you might get strange presssure waves in the pipe between the SC and turbo. like if the turbo begins to move all the air from volume between the SC and turbo, a vacuum may begin to be made that the turbo wont be able to hold forever. shortly after this vacuum is made, the turbine blades may surge to a really high RPM(becuase no load).....then all the sudden the air might come back through the turbine and smash blades?


i think the turbo will do funny things if there is a big restriction placed in front of it. read the thread regarding "TB before turbo" some of these ideas or put foward there .

also, if there is ever a vacuum, a carbon seal may be required for the turbo?

[2JZR31]

mic*. Bens way is pretty much exactly the same as what I am suggesting and the VW golf. So if all the posts I have made a relevant. Only thing is the one way valve is crap, simply because there aren't any valves that will be very suitable. So all you need to do is use a TB that opens at the same time the one way valve would. Which is piss easy and we have already talked about....

The whole idea is you can use a turbo with a large exhaust housing to keep back pressure low. This will stop surge anyway.

[2JZR31]

id be warey of allowing the turbo to do this.... if you think about it, you might get strange presssure waves in the pipe between the SC and turbo. like if the turbo begins to move all the air from volume between the SC and turbo, a vacuum may begin to be made that the turbo wont be able to hold forever. shortly after this vacuum is made, the turbine blades may surge to a really high RPM(becuase no load).....then all the sudden the air might come back through the turbine and smash blades?

There wont be a vacuum. The bypass TB/Ben valve opens when the pressure between the SC and turbo reaches atmospheric. So the pressure ratio across the turbo will be exactly the same as if the SC wasn't even there at all.

[Ben Wilson]

The plan was for a 4AG, the mr2 has the advantage of the space over the gearbox for plumbing.

I was thinking about using a throttle body for the valve with some sort of vacuum actuator, I found a reference for an actuator that is used to open the vacuum secondaries on Holley carbs which might do the job.

I doubt I'll ever try it, I'm starting to lose interest in the whole big power thing...

[Ben Wilson]

The whole idea is you can use a turbo with a large exhaust housing to keep back pressure low. This will stop surge anyway.

Hence the S5 RX-7 turbo I've got sitting on the shelf at home...