BOV venting to exhaust(pre turbo)

[barryogen]

I was just reading about using a BOV to vent into the exhaust prior to the turbo to keep it spinning, as a sort of antilag without the harshness of a true anti-lag system...

I've been trying to think of a reason why this would be bad, but this is not even close to my area of expertise. So I throw the idea to the floor... what do you guys think?

[RedMist]

The ST205 WRC runs this. However you'll note that on the rally cars they also run stock mode one, bang bang, antilag.
I'll be running it on my ST205 in conjunction with mode 1. I would have to concur in regards to it being the least distructive verion of antilag.

The ST205 has very small stainless pipes that dont flow a tonne. I would suspect that this is by design and that big ports allow exhaust pressure to backflow and force open the antilag (BOV) valve. Hence allowing exhaust gasses into the intake.

Still I'm yet to play with it. I have however managed to make the ST205 WRC antilag valve function. Its got a single weld that stops the valve from functioning.... I whacked the shyte out of it.

[JustinSpiderholden]

Also the early z18et did something similar with the blow off value dumping into the exhuast housing of the turbo

[barryogen]

so basically it just helps keep the turbo spooled up between shifts?

How would one go about adding this to a normal/oem style turbo syste?
Just plumb up a suitable pipe(size?), presumably metal/heat proof until at a safe/cool distance from the headers, and plumb the BOV into it?
I guess a one way valve in there couldn't hurt either, to further keep heat away from the BOV/intake.

Is this sort of system used in other motorsport? or just rallying?

[RedMist]

It's supposed to keep the turbo spooled between shifts. However I dont know how effective it is. As stated earlier the WRC rally cars still used bang bang antilag on top of the throttle bypass antilag.

The ST205 system uses a VSV to open a dedicated antilag valve. This valve then bleads boost pressure into two ports that further split into four stainless lines. These stainless lines are banjo bolted to the exhaust manifold approximately 5 cm or so from the manifold face.

Its a bloody good point re other motorsports using bang bang antilag. I have no idea as to why they dont. Noise regs perhaps?

[method]

Evos have this too, think all models still have it and it is used in conjunction with bang bang antilag.

[xsspeed]

anyone got links or can explain true (bang bang) anti lag to a turbo n00b?

[method]

It goes bang bang then your exhaust falls off. You put a new one on then your turbo breaks.

I understand it pretty much puts fuel through the engine and ignites on the exhaust stroke and keeps it spooled kinda like how a single stage centrifugal gas turbine works.

Computer keeps throttle partially opened and timing is pulled right back, so air and fuel is going through, but just no power is coming out because of timing..

I shoulda been a mechanical engineer eh

[xsspeed]

nah cos then you'd have air con in your car, building services whut!

thanks tho bro, I get that, apart from the timing bit, but I can work that out. so its basically just burning more fuel on exhaust stroke to keep the turbo spinning, I assume this feature if properly controlled shuts off at higher rpm?

[method]

nah cos then you'd have air con in your car, building services whut!

thanks tho bro, I get that, apart from the timing bit, but I can work that out. so its basically just burning more fuel on exhaust stroke to keep the turbo spinning, I assume this feature if properly controlled shuts off at higher rpm?

The pulling of timing means the spark ignites the fuel after the compression stroke, near the point where the exhaust valves are open. that means all the energy goes rushing out the exhaust at great velocity and spins the turbo.

And say the fuel is ignited at the bottom of the down stroke, no power would be made at all, so with aggressive antilag you can boost 1.5bar and be idling.

[xsspeed]

get it now, for some reason i was thinking of the timing for the compression stroke but i see what you mean

[barryogen]

I'm currently reading "Forced Induction Performance Tuning" and came across a bit that went into describing how this sort of setup sends up being mildly like usual bang bang anti-lag.

If the car is running MAF, adding air into the exhaust manifold pre turbo would provide air... with the heat of the manifold and/or turbine we have "spark" which would spool the turbo.

Interesting, and I'd like to know how harsh it is when compared to the traditional bang bang anti-lag... and so we enter into testing phase.

A mate of mine has a 4age with a cheap as chips turbo* on it, running maf, so we'll try it and I'll get back to you.

* ~$400 trademe item, so we went halves, and bought him another one just in case we royally fcuk it with the trial.

[ChaosAD]

Wont you still need some sort of ignition cut/retard to provide fuel?

[matt dunn]

Is this sort of system used in other motorsport? or just rallying?

Just rallying really, as you have no engine braking which is better for circuit racing,
With anit lag on the circuit you would have to brake too early, and would cook the brakes,

Also on a circuit you are usually in the right gear and keep the revs up anyway, where rally cars need a much wider torque band.

If you want a really crude version of anti-lag,

crank the throttle open as far as it will go on the throttle stop,
and the adjust tghe TPS so that the idle contacts are closed.

The ECU will cut the spark at 1500 rpm with the contacts closed, so the car will have a high surge idle,
but as soo as you crack the throttle and open the contacts, it will take off.

Only works on cars that have TPS switch that cuts on overrun,
and works, but only a very little.

[samlloyd]

How is true 'bang bang' anti lag bad for a turbo?

[barryogen]

Happy to be corrected, but, from what I've read, over heats the turbine/exhaust causing excessive wear, can overspin the turbine quite a lot too, meaning even more wear, and worse if the oil is already cooked due to the over heating.

And if you have a CAT, melts it into a much lower flowing item.

All in all it seems to be fine if you intend to replace the turbo fairly regularly.

As for still needing fueling, from what I understand of turbo'd cars running MAF, the air that has already gone passed the MAF is accounted for, and fuel provided, so when the BOV vents to the manifold(pre turbo) as opposed to the intake(post MAF), there should be "some" unburnt fuel... I am still reading though.

[method]

what ive always wondered is what the pressure in the exhaust manifold is.

All the antilag systems ive seen that have a valve going to the exhaust manifold have quite small piping. I wondered if this is to keep the pressure up so you dont have exhaust flowing into the intake piping.

Most piping ive seen seems too small to flow any decent ammounts of air too.. would say you are much better off using proper antilag.. retard timing, open throttle, add fuel and have the air going through the engine rather than a bypass valve.

[barryogen]

I have no doubt that you are correct, that true anti-lag would be better, but it is also a lot harder on gear. If this works as described in what I've read, I'd be keen to use it on a car of my own.

think of it as poor mans, not quite as good as the real thing anti-lag.

[method]

Good luck with it, be good to see what kind of results you can get.

Ill try clearing up my last post;

My worry is this:
If you use a BOV sized valve i think there may not be enough pressure created by the turbo to force air into the exhaust manifold and through the turbos ehaust wheel.

If you use a too small sized valve you will just get compresser surge and it would completely defeat the point in putting air into the exhaust manifold.

The alternate hypothesis is that there will actually be a vaccume - or less pressure than in the intake pipes, than in the exhaust manifold because the exhaust wheel on the turbo is trying to suck air through after the flow of gas has stopped from the engine.. in this case it would work prefectly as wanted.

Be interesting to see what happenes. But there must be a reason why the air bypas systems on cars use such a small diameter pipes from factory..

[RedMist]

A couple of things you may not have thought of.

You loose almost all of your engine braking as the throttle is open.
You loose brake assist, as you are no longer pulling a vacume when off throttle.
You loose vacume assisted steering.

So change gear, throttle off and you have to work harder to steer or brake. Not really acceptable in any car.. but tollerable in a rally car.