Motronic Mp 3.2 / 2.0 Turbo Boost Control

[Henry Yorke 269 3 Cars]

By disconnecting the pipes to the boost control solenoid and putting them to a turbo 3 way bleed valve, you can adjust how much boost the turbo runs.

 

I believe the standard ECU's Map sensor is good for 1 bar (14 psi)

I believe the standard t25 turbo is good for 1 bar too.

 

If I was to run 0.8 bar to 1 bar instead of the standard 0.5, is there anything you particularly need to be worried about? Obviously above 1 bar is asking for problems!

 

Fuelling is controlled by the lambda and the MAP sensor, ignition by the knock sensor, inlet temp is monitored by the err... inlet temp sensor! Anything else?

 

(a fiver says sonofsam answers this first!! )

[sonofsam 5]

By disconnecting the pipes to the boost control solenoid and putting them to a turbo 3 way bleed valve, you can adjust how much boost the turbo runs.

Yes correct. although my MBC was plumbed into wategate and throttle body.

 

I believe the standard ECU's Map sensor is good for 1 bar (14 psi)

Yes.

 

I believe the standard t25 turbo is good for 1 bar too.

No, not really, it will run out of puff up the rev range quickly, thats why Im chucking a T3 on

 

If I was to run 0.8 bar to 1 bar instead of the standard 0.5, is there anything you particularly need to be worried about? Obviously above 1 bar is asking for problems!

Yes, under fuelling = detonation. knock sensor is a sensor to determine knock. ie detonation! or rather pre detonation..

 

But above all as I've said before, a bleed valve or a mechanical boost controller are not 'boost control' as in

the boost regulator solenoid wich is controlled via the ECU and rev/wheel speed dependant.

 

Trust me mate, I have used an MBC and its rubbish compared, even though it will 'up' the boost you lose

that element of control that the solenoid gives and you get wheelspin plus nasty spikes wich in time will damage your turbo.

 

You can play with one if you like, but I'll doubt you will be happy with the results especially if your engine goes bang.

 

Now, where's my Lady Godiva

Edited February 25, 2007 by sonofsam

[bales 1]

But surely if you put the bleed valve in after the solenoid between the actuator and solenoid, then you are still getting the pulsed boost signal but a specific amount of this is bled off. Therefore the actuator still see's a varying degree of boost but just slightly less than it would of without the bleed valve?

 

I mean the amal valve is pretty simple it just cycles on and off at a certain frequency to allow the wastegate to be progessively opened rather than being "blown" open at a certain boost level, hence why Sam has said that with a mbc you get a very on-off boost transition.

 

I can't see how by putting a bleed valve after the solenoid that you would lose this progressive control, it would just be fooled into runnig slightly higher boost before the wastegate is opened.

 

And the whole undefuelling side of things depends on the whether the ecu actually has the load sites for fuelling and spark at those map sensor levels. It is all well and good if the map sensor can detect the amount of boost at 1 bar but if it has no values in its map for these boost values then it can't fuel/spark correctly.

 

Even if it does have a knock sensor surely all it will do is retard the spark so that you lose performance anyway and therefore have gained no advantage from running the higher boost anyway.

 

I think the only way you can have a definitive answer to this is if someone has seen the standard map and can verify that it has load sites for map sensor values much above 7-10psi ish....or whatever that equates to in volts.

[sonofsam 5]

You can't use a bleed valve/MBC and a solenoid together!

[bales 1]

You can't use a bleed valve/MBC and a solenoid together!

 

why?

[bales 1]

Just to kind of answer my own question the I don't know in depth how the boost controller works but I would have only thought a bleed valve couldn't be used afterwards if it was a fully closed loop system. As in that there is a feedback loop between the ecu and solenoid, so that the solenoid constantly changes frequency depending on MAP sensor output. If the solenoid runs at a built in cycle (this could be lots of different cycles still) but if it doesn't change in relationship to the boost signal to the ecu then I cant see a problem?

[tom_m 0]

bleed vaves are a very quick way of melting pistons, and not the best manual boost control method either. they are prone to spikes which can be very expensive.

 

a dawes device is kinder to spool up because you do not get actuator creep

 

as sam says though you lose the ecu control of the turbo, and risk it throwing woblies because the engine is not behaving how the ecu thinks it should be.

 

another thing i would be worried about is intake temps, pushing the small turbo out of its envelope you will start generating a lot of heat.

 

if you are going to have an ecu 'chipped' i'd ask the chipper to up the boost that way and keep the boost control solonid

[Henry Yorke 269 3 Cars]

as sam says though you lose the ecu control of the turbo, and risk it throwing woblies because the engine is not behaving how the ecu thinks it should be.

The main risk being the fuelling map for higher levels of boost is not there? Does anyone know for sure whether it is there or not?

 

another thing i would be worried about is intake temps, pushing the small turbo out of its envelope you will start generating a lot of heat.

Does anyone have the tech specs of the T25 turbo as used on the XU10J2TE so we know at what boost pressure there is a drop in performance, i.e. Intake charge to Boost ratio increases prior to the intercooler? PSA will not run the turbo on its max capacity for longevity reasons.

 

if you are going to have an ecu 'chipped' i'd ask the chipper to up the boost that way and keep the boost control soleniod

 

The map of a Superchip or the likes will surely address the optimum boost levels before negative returns.

 

I know I am asking a lot of questions I sort of know the answers to, but I was wondering if anyone had any hard, referencable facts as opposed to applied logic! The truth is out there!!!

[bales 1]

Does anyone have the tech specs of the T25 turbo as used on the XU10J2TE so we know at what boost pressure there is a drop in performance, i.e. Intake charge to Boost ratio increases prior to the intercooler?

 

Compressor AR 0.48

Turbine AR 0.64

 

Pressure ratio 1.47 (@ standard boost - 7psi) Pr = turbo + atmos / atmos

 

Compressor outlet temp rise = dimensionless factor from table - for Pressure ratio x (ambient temp in C + 273K) x 100 / compressor effciency %

 

 

Can get effciency off compressor map but i dont have one for this turbo but it will be well below 70% at one bar, so if you assume 70% at 7 psi and 60% at 14.7 psi

 

Then @ 7 psi (assuming no intercooling)

 

Temp rise = 0.110 x (25 +273) x 100 / 70

= 46.8 deg C

 

So 25 + 46.8 = charge temp of 71 deg C

 

@ 1 bar - 14.7 psi

 

New Pressure ratio of 2

 

Temp rise = 0.217 x (25 + 273) x 100 / 60

= 107 deg C

 

So 25 + 107 = charge temp of 132 deg C!!!!!

 

That is just a complete guess with the efficiencies but you can see how much difference it makes, in reality the difference will be less than that probably but you can see how much effect it has on charge temp, so thats why you need to pretty good intercooling when you increase the boost with these i would guess.

 

All the temps are without intercooling aswell so you can assume intercooling is 70% effcient and recalculate for that but i cant be arsed now.

 

 

The factors i got from the forced induction book by alexander graham bell

[Henry Yorke 269 3 Cars]

That is the sort of data I was looking for. Basically you can plot a graph across 0.5 to one bar and see if it is an exponential curve or a linear one. I am guessing exponential.

 

The factors i got from the forced induction book by alexander graham bell

 

Was Alexander Graham Bell into turbo's just before he invented the telephone!!

 

I think you mean Corky Bell!

[bales 1]

Nope!

 

a.graham bell

[sonofsam 5]

T25 a 1bar will tail off @ 4500rpm when it slowly falls down to 0.8-0.7bar...

 

A TT doesnt even run 1bar Henry.

[Ant 2]

The derv doctor will remap the ECU to one bar for about £250

 

But you still have the issue of a restrictive manifold. I am thinking of looking at making my own exhaust manifold, getting a remap and upgrading the injectors. That should see a healthy 190-200 bhp for not stupid money

 

regards

 

Ant

[kyepan 291]

Compressor AR 0.48

Turbine AR 0.64

 

Pressure ratio 1.47 (@ standard boost - 7psi) Pr = turbo + atmos / atmos

 

Compressor outlet temp rise = dimensionless factor from table - for Pressure ratio x (ambient temp in C + 273K) x 100 / compressor effciency %

Can get effciency off compressor map but i dont have one for this turbo but it will be well below 70% at one bar, so if you assume 70% at 7 psi and 60% at 14.7 psi

 

Then @ 7 psi (assuming no intercooling)

 

Temp rise = 0.110 x (25 +273) x 100 / 70

= 46.8 deg C

 

So 25 + 46.8 = charge temp of 71 deg C

 

@ 1 bar - 14.7 psi

 

New Pressure ratio of 2

 

Temp rise = 0.217 x (25 + 273) x 100 / 60

= 107 deg C

 

So 25 + 107 = charge temp of 132 deg C!!!!!

 

That is just a complete guess with the efficiencies but you can see how much difference it makes, in reality the difference will be less than that probably but you can see how much effect it has on charge temp, so thats why you need to pretty good intercooling when you increase the boost with these i would guess.

 

All the temps are without intercooling aswell so you can assume intercooling is 70% effcient and recalculate for that but i cant be arsed now.

The factors i got from the forced induction book by alexander graham bell

what an excellent post, never seen that equation before,

 

If you want more go out of your turbo, try better intercooling (not sure what options there are), or perhaps according to puma racing some headwork turbo tuning from dave baker

 

You could probably pop for a slightly larger turbo and run lower boost, depending on the blade pitch it may spool as quickly as your small one, some even have the same manifold so they are a direct replacement, you could run lower boost and generate less heat.

[adrian_gti 0]

T25 a 1bar will tail off @ 4500rpm when it slowly falls down to 0.8-0.7bar...

 

A TT doesnt even run 1bar Henry.

 

mine was.. then it blew up

 

how about getting something like an APEXI boost controller Henry? Thats pretty good at controlling spikes.

[Henry Yorke 269 3 Cars]

Nope!

 

a.graham bell

 

I stand corrected!!

Not this handsome devil then!

 

This is Corky Bell's book, which Gerben recommended

http://www.amazon.co.uk/Maximum-Boost-Turb...TF8&s=books

 

It appears you have to be a bit of a Bell to be into your blowers!

[Henry Yorke 269 3 Cars]

So to conclude, running more boost via a bleed valve gives more power but gives boost spikes that can damage your turbo and melt pistons.

 

The correct way to do it is via a remap / chip that retains the boost control solenoid.

 

However running more boost through a T25 gives more heat and that needs more intercooling, but is not good for turbo's

 

Therefore boost bleed valves are dangerous, even if running at standard boost due to spikes.

[Grez4 2]

Henry

 

I have managed to safely run with a bleed valve with no problems as Iam sure many other people do, obviously there are better more expensive methods.

 

 

They serve a purpose and providing the fueling is there all should be good.

[tom_m 0]

if you're going to run an MBC a dawes device would be far superior to a bleed valve and no more expensive.

[sonofsam 5]

The MBC I had looks near on the same as that Dawes device, its just a ball and spring mechanism

and still spiked on occoasion, does say it needs 200 miles or so of running in though.

http://www.gb-ent.com/products/boost.htm

 

Im sticking the solenoid back on, so really it was a bit of a waste of money imo.

[inferno 1]

i didnt realise what this was u was playing with sam!!! is it really that bad when the boost limits reached? i was planning to do something similar myself when im running higher boost, to stop creep.

[sonofsam 5]

It was more aggresive coming on boost also wich led to wheelspin

[inferno 1]

hehe i like the sound of that... coupled with a gear/speed related boost control of course...

[bales 1]

So to conclude, running more boost via a bleed valve gives more power but gives boost spikes that can damage your turbo and melt pistons.

 

The correct way to do it is via a remap / chip that retains the boost control solenoid.

 

However running more boost through a T25 gives more heat and that needs more intercooling, but is not good for turbo's

 

Therefore boost bleed valves are dangerous, even if running at standard boost due to spikes.

 

I don't really agree with most of that, I don't think you can conclude that running a bleed valve is dangerous, I think it is dangerous if the fuelling is not adjusted and the engine runs lean, but in itself with proper fuelling I don't think a bleed valve is a bad thing.

 

I personally don't feel that anyone has explained adequately about boost "spikes" and what this is caused by and how it is detrimental to a turbo.

 

Thinking back about the whole boost control and the point of it is not quite that straight forward, as I think there is two aspects here rather than one. What I said in my previous post about the boost solenoid allowing a smoother boost transition as the wastegate doesn't get slammed open but progessively opened I think is wrong.

 

One aspect of solenoid control is to stop actuator creep as tom_m mentioned, which is where the actuator starts to bypass some of the exhaust gases before it should because of the sustained presssure against the actuator diaphragm. So the solenoid bleeds off a progressive amount of the boost signal until just before full boost is reached so that the wastegate only opens just at the last minute. However this contradicts what I thought about having a smooth transition between on and off boost? but then again this isnt the transition between on and off boost, it is the transition between the boost rising and the boost being capped

 

 

In my eyes the other aspect is in effect trying to mask the true characteristics of a turbo engines power delivery, in most basic terms its a centrifugal compressor so the boost is related to the square of the speed which is why you get nothing at the bottom and too much at the top hence boost control being needed in the first place. So I suppose the solenoid is just trying to make the car perform as an n/a car and mask the swelling of torque, but I guess with proper turbo matching to an engine this isnt necessarily as much of a problem, which is why peugeot probably used such a small housing anyway on both sides of the turbo.

 

But I would appreciate it if someone could explain why bleed valves give boost spikes as that is one aspect I dont really understand fully. Is the boost just not going to rise at its natural rate that is related to the charcteristics of the compressor, I can understand that this may in itself be spiky and that boost modulation smooths this curve, so are we saying that the boost spikes are actually the natural pressure curve given by the compressor i.e if we plotted a graph of speed vs boost we would see a spiky risng line, not a smooth exponentially rising curve?

 

And all that the solenoid does is vary the boost signal to smooth this curve out?

 

Sorry for the long post but I am trying to understand this myself as I like to fully get my head around the basic principles of these things. I hope the tone of this doesnt come across as me telling people what happens, cos I really dont know much and I am trying to learn so please correct anybits where I am wrong about things. I am explaining each aspect out more for my benefit as when I write things it hepls me understand them better.

 

Cheers

 

Alex

[inferno 1]

The only spikes i knew of were the pulsing from an unequal lenth manifold, which is myth so doesnt count:P