BOV and other toys

[Heath]

So I was shooting the breeze with some petrol heads at work today and we got talking about their cars and the mods they make.

Got talking about my diesel turbo and what could I do to it for a bit more power etc.

A BOV for a diesel (works off the TPS wiring), boost controller, another window washer and a sprayer for the intercooler and finally finishing the dump pipe for my exhaust. Of course there is always LPG fumigation (but we wont go there )

Of course I wont be doing all of these (maybe just the dump and boost controller), but it was food for thought and wondered what the thoughts of diesel mechs would be. Lets just assume its an exercise for the mind.

[DieselBoy]

BOV is not required in a diesel, it just increases turbo lag.

There is no throttle butterfly in the intake of a diesel engine as the power is controlled soley by the amount of fuel delivered by the injectors. As a result the engine is always getting as much air as the turbo can feed it all of the time, even at idle.

By releasing the pressure in the intake manifold between gear changes it just means the turbo has to build all that pressure up again each time.

As there is no restriction in the intake manifold, keeping the pressure between gear changes has no detrimental effect on performance.

Some toyotas and nissans have a butterfly in the intake, but it's more for the EGR and soft stop functions.

[vinceparts]

water sprayer on the intercooler works pretty well but when was the last time you filled your window washer bottle let alone one for your intercooler which would last sweet bugger all

[IanB]

water sprayer on the intercooler works pretty well but when was the last time you filled your window washer bottle let alone one for your intercooler which would last sweet bugger all

Agreed, if I'm filling washer fluid jugs, it will be for a water or water/meth injection setup.

[vinceparts]

i reckon intercooler (front mount if possible) , 3 inch zorst with dump pipe and boost controller, electronic if possible

[strx7]

BOV is not required in a diesel, it just increases turbo lag.

this is partially correct, but it is also wrong.

On a standard turbo deisel running fairly standard boost levels it is correct, but when you start running significantly higher boost, or change the turbo and run significantly more CFM then a BOV does prolong the life of the turbo itself.



As far as performance increases.
A front mounted intercooler.
free flowing exhuast system.
upping the boost a fraction
water/meths injection
and you'll be cranking along close to 50% above std

[DieselBoy]

BOV is not required in a diesel, it just increases turbo lag.

this is partially correct, but it is also wrong.

On a standard turbo deisel running fairly standard boost levels it is correct, but when you start running significantly higher boost, or change the turbo and run significantly more CFM then a BOV does prolong the life of the turbo itself.

Care to elaborate on your claims????

What is significantly higher boost and CFM in you opinion???

How does BOV in a diesel prolong the life of the turbo????

I don't understand how it's of any benefit, when a diesel ideally needs full pressure all the time. Once you pump the manifold up to 20psi, why would you want to release the pressure and start having to build it up all over again each gear change????

There is no throttle butterfly in a diesel so no need for a BOV???

Keen to hear your thoughts man

[tweake]

a diesel doesn't need boost all the time.
especially when on trailing throttle (ie off the gas).
if your at full boost then take foot straight off the gas, you have no drive pressure on the turbo as fuel is at minimum. but there is still high boost in the intake which tries to push back through the turbo.

it may not be as sudden as a butterfly closing but the effect can be bad enough to snap turbo shafts even on diesels. tho thats usually on engines running seriously big boost.
have a read up on "turbo bark".

[strx7]

hit the nail on the head there tweake,

deiselboy obviously doesn't understand why a BOV is used on a petrol.
compressor stall is why BOV's are used, regardless of what the engine is using to combust, the same things still apply.

[KIWI_TERRANO]

A friend has a highly moded 1kz and he was having trouble with what he called turbo blow back but he fitted a bov and he now wishes he did it ages ago as it picks up power alot smother

[DieselBoy]

a diesel doesn't need boost all the time.
especially when on trailing throttle (ie off the gas).
if your at full boost then take foot straight off the gas, you have no drive pressure on the turbo as fuel is at minimum. but there is still high boost in the intake which tries to push back through the turbo.

.

Im no expert, just looking to learn something, but I'm not just gonna take your word for it

The pressure in the manifold during gear changes is dissipated through the intake valves into the combustion chambers.

With out writing a wordy novel on it here is the generally accepted logic. Let's take couple of givens:

Turbo produces 15psi
RPM change between gears is 500rpm

You take the motor up to 3000rpm @ 15psi and then change gear. The motor drops 500rpm because you reduced the fuel being supplied by the injectors to the combustion chamber.

The potential for the exact same volume of air that was being pumped in remains the same regardless of throttle opening as in a diesel it is related to engine RPM. No throttle butterfly remember. For example, if you were able to shove in 240CFM at 2000rpm with the accelerator open, there is nothing to stop the same volume being supplied with the accelerator closed.

So the reason that the experts say you don't need a BOV is that because there is not throttle butterfly, you do not get the surging effect can stall the turbo.

As there is no restriction to the intake valves a diesel will take all the air you can give it all the time, as a result even during gear changes with the fuel delivery at minimum, they are still hungrily taking any air they can get. This prevents the problems encountered with a petrol as the path of least resistance is still into the engine.

Also, with the full volume of air still entering into the combustion chambers, it's also still exciting through the exhaust in the same volume, which in turn keeps the turbo spooling further reducing the likely hood of stall.

There is no butterfly that snaps shut causing a stationary colum of pressurized air in the manifold that first has to stall the compressor before it can escape out the air intake like a petrol.

I Will leave it at that, as I understand how petrol heads can struggle to understand the principles under which a diesel operates

[ice4x4]

I'm with Dieselboy on this one.

I'm no expert on car engines either but I believe most have a wastegate which keeps the charge air pressure constant. If the boost is at a constant pressure then there is no need for a BOV on a TD engine.

The correct term for what you are talking about is "Surging" of the T/C. This occurs when the pressure at the charge air manifold is greater than the pressure at the compressor diffuser. This occurs in petrol engine systems when the throttle butterfly is closed and pressure builds up in the pipe before the valve. There are fewer combustion gasses passing over the turbine wheel which reduces the output from the compressor and the air pressure at the diffuser drops below the pressure at the outlet causing the "blow back" in the charge air system.

If the boost was not constant and varied with load..... Different story.

[churchill]

After a brief readup this is what I found:

When the throttle is released on a diesel at WOT the fueling is decreased. This causes less combustion thus causes less pressure on the turbine side of the turbo. If the pressure on the compressor side of the turbo is too great in comparison to the pressure on the turbine side, a stall can occur.

It looks like this only occurs very high boost applications and incorrectly sized turbos.

I can see how a BOV could fix this problem but supposedly correcty set turbos don't exhibit this problem. Don't ask me what they mean by "correctly set up".

[ice4x4]

When the throttle is released on a diesel at WOT the fueling is decreased. This causes less combustion thus causes less pressure on the turbine side of the turbo. If the pressure on the compressor side of the turbo is too great in comparison to the pressure on the turbine side, a stall can occur.

No surging of the T/C has nothing to do with pressure on the turbine side. The pressure difference is between that in the charge air manifold and at the outlet of the diffuser on the compressor side of the T/C. Basically the pressure in the charge air manifold is higher than the pressure the compressor can maintain under its current conditions.

If the charge air pressure is kept constant then this condition will never occur.

[churchill]

Compressor "stall" not "surge".

What happens to the turbo if the pressure on the turbine side drops off whilst the post compressor side stays high?

[ice4x4]

Stall is part of the whole surging process. For the rotor to stall it would have to be in an extreme scenario.

What happens to the turbo if the pressure on the turbine side drops off whilst the post compressor side stays high?

It is basically the same thing.

The turbine wheel is turned by the kinetic energy imparted by the nozzle ring and heat energy in the exhaust gas. This turns the compressor wheel which imparts kinetic energy into the air and this is turned to pressure energy by the diffuser. If the pressure in the charge air manifold is higher than the pressure that can be produced by the diffuser, surging will occur..

[churchill]

The turbine wheel is turned by the kinetic energy imparted by the nozzle ring and heat energy in the exhaust gas. This turns the compressor wheel which imparts kinetic energy into the air and this is turned to pressure energy by the diffuser. If the pressure in the charge air manifold is higher than the pressure that can be produced by the diffuser, surging will occur..

So if the turbine cannot supply enough energy to drive the compressor to produce enough pressure a stall/surge situation will occur?

[ice4x4]

To match the pressure already in the charge air manifold. Yes..

[churchill]

Interesting, we both agree that a stall/surge situation can occur on a turbo diesel but we disagree that a BOV could fix this.

I still believe that if a compressor stall/surge occurs when transitioning between WOT to closed throttle a BOV will help.

[ice4x4]

Well no, a stall/surge situation can and does occur on many turbo diesel engines and fitting BOV will definitely help/eliminate the conditions occurring.

What I am saying is in a normal car set up with a wastegate fitted the charge air manifold pressure should be the same at all operating conditions, i.e if you set your boost at 15psi it will stay at that pressure at that pressure at maximum fuel or minimum fuel. Therefore the conditions should not be able to occurr..

As clear as mud.....

If the boost is varied with the load on the engine then I suspect a BOV could well be needed.

[jakwoo39]

can somebody explain to me how a bov actually works on a diesel? i thought it was something to do with vacuum that opened petrol ones or are those electric ones needed

[churchill]

Where I'm coming from is that there is not enough energy in the exhaust gas due to the fuel being reduced to keep the turbo spinning fast enough to keep the boost up. If the boost level in the manifold is too high for the compressor a stall/surge can result as the gas pressure will overpower the compressor due to it having no drive from the turbine.

I'm thinking of it in terms of an energy system. To compress the air the turbo uses energy from the fuel, when you take the fuel away the only other place the energy can come from is the kinetic energy of the rotating engine pumping air through the turbo. This will be a lot less energy than the fuel can provide so the turbo won't be able to hold the same pressure.
If the pressure in the manifold is too great it will flow back through the compressor causing a surge.

Come to think of it I'm suprised all performance turbo diesels don't use a BOV to keep the turbo spinning fast through gear changes. It'll decrease efficiency but increase the turbo responce between gear changes.

Funny, I was answering to a DB post that I can't find anymore.

[strx7]

can somebody explain to me how a bov actually works on a diesel? i thought it was something to do with vacuum that opened petrol ones or are those electric ones needed

instead of being vacuum operated like on a petrol they are electrically controlled based on a switch off your throttle pedal.

[TD power]

i dont know much but a bov is a waste of time on a diesel with out a bitterfly it would be good on a diesel with a bitterfly. but most diesels that have a bitterfly it is just for the EGR wich most of you would block off and get rid of the bitterfly at the same time. c15 cats can run round 60psi boost and dont have a BOV and turbos last round 400000kms like a said what would i know hahahaha

[ice4x4]

Where I'm coming from is that there is not enough energy in the exhaust gas due to the fuel being reduced to keep the turbo spinning fast enough to keep the boost up. If the boost level in the manifold is too high for the compressor a stall/surge can result as the gas pressure will overpower the compressor due to it having no drive from the turbine.

I'm thinking of it in terms of an energy system. To compress the air the turbo uses energy from the fuel, when you take the fuel away the only other place the energy can come from is the kinetic energy of the rotating engine pumping air through the turbo. This will be a lot less energy than the fuel can provide so the turbo won't be able to hold the same pressure.
If the pressure in the manifold is too great it will flow back through the compressor causing a surge.

Come to think of it I'm suprised all performance turbo diesels don't use a BOV to keep the turbo spinning fast through gear changes. It'll decrease efficiency but increase the turbo responce between gear changes.

Funny, I was answering to a DB post that I can't find anymore.

Well I think we all agree now on the conditions needed for a T/C Surge.

We are talking about a diesel engine in a car and like DieselBoy said at the start if the fuel goes from max to minimum and the turbo stops working i.e between gear changes, at 20 psi the cylinders are simply going to pump the air away....... There is no butterfly valve.

[Heath]

Still got the flutterby in my playdo.

I have left it there for now (havent been assed to remove it yet) and wondered if removal would make the engine stop rough. You know ehen you switch off the engine with the butterfly out will the engine shake like shit? There is a soft stop thingee somewhere in my wagon around the butterfly (not sure where) but when the pipe was disconnected it felt like the engine shook a lot at shut down.

Been an interesting discussion though and I am learning heaps from the more experienced amoung us - Thanks.

[kbushnz]

Still got the flutterby in my playdo.

I have left it there for now (havent been assed to remove it yet) and wondered if removal would make the engine stop rough. You know ehen you switch off the engine with the butterfly out will the engine shake like shit? There is a soft stop thingee somewhere in my wagon around the butterfly (not sure where) but when the pipe was disconnected it felt like the engine shook a lot at shut down.

Been an interesting discussion though and I am learning heaps from the more experienced amoung us - Thanks.

It will shake a bit but not much.....(When I did mine) But it wont hurt it as most diesels don't have butterfly's Mr Toyota used it to quiet it down and also EGR emissions control.... I had a manual with how it worked somewhere but cant locate it

[UBZ]

There are two flutterbys in the 1KZ.
Main large one attached to the throttle cable/TPS and a second smaller one attached to two vaccumm valves just behind it.

Main one is directly related to the EGR vaccumm valve.

When engine is running smaller is open fully all the time . During stoping this closes in two stages reducing the air gradually and giving you a "soft stop" instead of the main flutterby just closing air off completely .

I have taken them both out along with the EGR. I all so removed the smaller flutterbys shaft and replaced with a bolt as it was leaking air into the manifold .

All associated electrics are disconnected with no resulting fault codes.

Stopping is not rough just a little more abrupt.

Main benefit apart from a slight reduction in boost lag is that my intake manifold pressure is now constant and does not flutter between negative and positive pressures at idle, which had started happening after I removed the EGR.

[churchill]

Well I think we all agree now on the conditions needed for a T/C Surge.

We are talking about a diesel engine in a car and like DieselBoy said at the start if the fuel goes from max to minimum and the turbo stops working i.e between gear changes, at 20 psi the cylinders are simply going to pump the air away....... There is no butterfly valve.

Yeah man, agreed there.

What I can't understand is what keeps the turbo spinning to provide to 20psi to the cylinders when the fuel is reduced. Perhaps the kinetic energy of the engine spinning and pumping air is enough? Doesn't make sense seeing as full throttle was required to do this initially so if you cut the fuel you would expect to see a reduction in boost as the turbo slows down.

I'm changing tack here and saying that a BOV on any diesel could help make power faster after a gear change becauce the turbo wouldn't slow down as much. I can't find any information to state otherwise. The only argument that has been put forward so far is that you don't need BOV's because there is no butterfly on the intake.

[chrome]

its refreshing to see some real tech being discussed on here for a change..
rather than a bunch of plonkers getting their backs up about who is right.
or wrong.
still unsure of the answer there tho as there is some persuading arguement on both sides
i toyed with putting one on the prado for a while but never looked that hard into it, it was pretty standard cept for the dumpy and exhaust
now i have a poo honda wagon