VR4 max boost on standard turbos??

[Dom B]

http://www.clubvr4.com/forum/showthr...light=td03+map


Simple search - "TD03 map"

Not quite.

If you look at the post of that thread even kieren agrees that there is loads of td04 info available and very little or almost no td03 info available. That is exactly what i was meaning when i said i haven't been able to find any specific td03 compressor maps.

The things kieren posted are useful to some extent but they are not a real compressor maps which are needed to plot rpm and load figures across it. The plot shown is more a comparative chart to help select a turbo on some approx data. It is helpful though.

I am sure they are out there they will be found eventually.


The chat about the piping diameter, restrictions etc is very interesting, right along the lines of the sort of info that makes a real difference in turbo applications.

It is very true that without a restriction there is no measurable pressure at the exit of the turbo. However the compressor wheel and the diffuser (the circular part of the snail shell before it becomes the turbo outlet pipe) still serve to increase the pressure of the air as it passes across the centrifugal compressor. It is impossible for the air not to increase in pressure ratio from inlet to outlet (P1/P2) across the wheel itself. The airs own inertia is its own restriction. If you could measure the very edge of the compressor wheel in a totally open unconnected turbo, you would still be able to measure the pressure. However this would only be for the few mm around the edge of the wheel. The problem with measuring it any further without a restriction to build pressure against, is that the compressed flow will be diffusing back to atmospheric as it exits so by the outlet there will be no relative pressure measurable by the time it gets there.

Strangely if you uncase the compressor completely and run the turbo with no front housing at all, the pressure at the edge of the wheel will actually be less than atmospheric due to the acceleration of the air lowering the pressure on account of the bernoulli effect.

When you design a hard pipe system the temptation is to go bigger and bigger. Bigger does promote better flow and at high rpm high bhp that's great. However every part of a system introduces a pressure drop. The intercooler is a prime example. You drop several psi across a poorly designed intercooler and every intercooler will drop some amount. In a low pressure turbo application of say 3psi (perhaps an aftermarket kit for a standard compression normally aspirated engine) you are better off without an intercooler at all. At these pressures there is so little heating that there is almost nothing to intercool. Whats more the presure drop across it cancels out any pressure gain. Net result the car is not any faster then before. The 1.8t vw engine has many BHP levels and the 150bhp ones don't even have an intercooler, they have a bit of squashed pipe just to lose some heat without the pressure drop.

Big Hardpipes with a big volume and also big intercoolers with a big volume mean that there is a large mass or air to move. The bigger the space then the slower the air moves for the same pressure. So huge system at low rpm means mega lag while you wait to get the compressor to squash up that mass of air which acts like a massive spring then to get it moving as that much air has serious inertia and is at a virtual standstill at low rpm. That's why big turbo cars have big lag in a lot of cases.

There is an optimum trade off of big for flow vs small for air speed and low air mass inertia. The trade off size allows enough flow for high power but sufficient air speed for fast response. In our case peoples testing seems to show that 2.5" seems to work very well and allow sufficient scope for high BHP without trading too much drivability.

There is an interesting thing about peoples boost gauges. When air expands into a bigger space for the same flow rate either the airspeed or the pressure will change. In the real world both will change. (in fact temperature does too, this is how a refrigerator works). So if you tee your boost gauge off the snail shell you will have a different reading than if you tee off the manifold plenum volume for the same car. So comparing boost pressures depends on where you measure it. Ideally you would measure it right in the port but that is very tricky. To compare OE pressure you need to tap off as close to the OE sensor as possible, i think it is on the plenum on these cars, perhaps someone can jump in to confirm that or not.

People say why make the hard pipes bigger if the compressor outlet is so small. Well The compressor outlet is small but it is well matched to the compressor itself. You have a fixed restriction of the turbo outlet. It is generally not a good idea to mess with this size as it is carefully matched to slowly expand the air up to the larger pipe size at a rate that wont cause stagnation or flow separation which in turn would cause turbulence and choke the outlet. Polishing does help as it lowers the Reynolds number meaning that turbulence wouldn't happen until a higher speed or a more aggressive angle or the diffuser expansion. So the turbo outlet can be considered fixed and therefore so is its restriction and pressure drop.

However you still have to get the air to the point of combustion. With our intercooler too that is a long and torturous path. You get pressure drop from a length of pipe as with any part of the system and it is per unit length. i.e. the longer the pipe the higher the pressure drop. The smaller the diameter then also the higher the pressure drop.

Imagine trying to blow through a straw 1 mile long and a pipe 2" in diameter and 12" long, which would be easier?

So the engineers need to expand up the tube size to minimise the pressure drop on it's journey otherwise the engine would be choked not being able to get enough air through thin piping.

I better have a rest before i type any more

[Stevo]

impressive, sombody passed physics with a nice high score unlike me

[Turbo_Steve]

Dom.....good explanation....especially as we were having a similar discussion around intercoolers the other day! LOL

I take (very mild) issue with the term "lag" being used on the inlet side...unless we're talking 5" turbo piping, on a road car lag remains relatively confined to the exhaust side...inlet side issues are generally percieved as "throttle response" rather than lag. If you have a turbo which will flow 450cfm, then even spoolin we're talking in terms of 50-100cfm flow rate. That means it's take a minute to fill 100cubic feet of intercooler and associated pipework. As these typically have a total volume of about 3cubic feet.......we're not talking a huge amount of time. That said, it IS perceptible, esepcially on fast road / small circuit cars, but usually as "hesitation" rather than lag.

I'm nit picking here, I will admit, as good overall pipework design will offset this massively (the organ pipe design, again).

[666damned]

i'm no expert on turbo's,but have worked with compressor's(bear with me....lol...)....increase in pressure+increse in temperature ........ my cousins kwak zxzzr turbo monster record attempting bike is producing around 540 bhp at the wheel !!!!........and he uses a water/methanol internal cooling spray of the charge air....reduces temp of chagre air and therefore can increses pressure/density....he's also running a relatively small intercooler in comparison to the power the thing is producing,i'd say 300mm square..!!..............i've seen people at the shows doing 1/4 strips and 0-60 runs and they heve all been spraying the outside of the intercooler with co2 extuinghuishers to cool them down........to me its a waste of time(unless its also got a mist spray externally as well) and theres much more gain to be had when done internally.............

[Turbo_Steve]

Hardly a waste of time: If you can freeze the surface of the intercooler, it becomes a "heat sink" for the duration of the quarter mile. In theory, anything you inject into the charge means less space in the cylinder for fuel\air mix, which means less power.

Water injection allows you to run more boost or more advance, however it does so at a fractional reduction in VE.

[666damned]

Hardly a waste of time: If you can freeze the surface of the intercooler, it becomes a "heat sink" for the duration of the quarter mile. In theory, anything you inject into the charge means less space in the cylinder for fuel\air mix, which means less power.

Water injection allows you to run more boost or more advance, however it does so at a fractional reduction in VE.

does the methanol add to the charge plus a bit more power to the mix than the reduction of the fuel/air mix steve?.......also forgot to mention that he's also running quite a monster of a fuel rail under about 40psi ........

[Turbo_Steve]

adding anything to the fuel is a risky proposition at best: methanol will change the calorific value of the fuel whilst not neccesarily changing it's octane rating.
Often, aromatics will effectively surpress detonation, whilst compromising the calorific value of the fuel: this means that you'll run more advance, but get the same effective power output. Pure water seems to be the best compromise. If you're going to start changing the fuel composition, I'd consult a really good petro-chemist first. There are more benefits to be had by simply switching to C10 and a dedicated map.

[666damned]

adding anything to the fuel is a risky proposition at best: methanol will change the calorific value of the fuel whilst not neccesarily changing it's octane rating.
Often, aromatics will effectively surpress detonation, whilst compromising the calorific value of the fuel: this means that you'll run more advance, but get the same effective power output. Pure water seems to be the best compromise. If you're going to start changing the fuel composition, I'd consult a really good petro-chemist first. There are more benefits to be had by simply switching to C10 and a dedicated map.

you got me now Steve...............

[Turbo_Steve]

Just to add, this does rather depend where you're injecting: I am working on the assumption that you're planning to tap the inlet manifold, or just before the throttle body (which, notably, has a bloody heater in it!).

If you're injecting prior to, or into the intercooler, then the methanol will evapourate prior to reaching the cylinder. This severely negates it's impact on the combustion process...though it still displaces a little air/fuel mix.

[Davezj]

What would happen if you used a second set of injectors to spray a little more fuel in to the inlet manifold to cool the air and compensate for fuel cut. well it is not really fuel cut it is fuel starvation and the ecu cuts the ignition to stop lean burning doesn't.

[Turbo_Steve]

er.....unless you change the ECU software, the ECU doesn't know about the extra fuel, so still fuel cuts.
Essentially, the ECU cuts fuel cos it doesn't know what to do with an airflow number that big.

[Davezj]

In closed loop running at a constant speed, doesn't the O2 sesor read the fuel mix and relay that back to the ECU which backs off the primary injectors beacuse it is running rich with the added fuel from the second injector, i didn't think the ECU used maps when running closed loop mode only when in open loop, when at WOT.

i don't know this just thinking about it.

[Eurospec]

All the O2 feed back does is move a trim. The trim has 18% iirc range +/- outside this the ecu cannot compensate.

So the ecu is using the 2 fuel maps in cruise and uses the trims to adjust the pulse width outputs do the injectors based upon O2 volt.

In Open loop, the trims are not used.

cheers,

Ben.

[Davezj]

excellent info thanks for putting me right on that.

this obviously would work in the real world, and very simple theory, i know there is a lot more to consider but at a basic level am i thinking along the right lines.
So in theory i could add 18% more fuel with a second injector (an a bit of electronic gadgetry) and this would fool the standard ECU into using the max negative trim on the fuel map to decrease the primary injector pulse, all the way up to the point when normal fuel cut is reached. However the ECU still has that -18% trim set. so the ecu can still happily add the extra +18% fuel trim to utilise some extra boost. asuming it has been turn up.

but that would only be closed loop operation, but when you want the extra fuel to stop fuel cut and use the extra boost, it will be at WOT so the ecu will delivery a fixed amount of fuel anyway.

is that about right.

[Turbo_Steve]

No: fuel cut is an absoloute: The ECU looks at the number coming from the MAF and cuts the fuel: it's that simple. Sorry: I really like your thinking, but one of the reasons fuel cut is so hard to defeat is that it's fairly primitive in it's operation: It takes one of the primary sensor signals that the ECU requires to be accurate (that you don't want to mess with) and then uses it to stop thefun

I'm generally of the belief that manufacturers know what they are doing with fuel cut: it's pretty much chosen at the point where the factory injectors can't be guaranteed to do the job. You MAY get more (most will) without any problems if you subvert the ECU. But 1 in 1000 (or whatever) will not.

I generally take the view that if you're up against fuel cut, it's time to be looking at mapping anyway.

[Nutter_John]

I have been beefing up on the Evo 8 maps and if you look at those you can see where and when the fuel cut will be hit

there is a table that is rpm based and as a load cell value

so for instance if the engine is at 4000 rpm and in the 230 load cell you have a fuel cut match so it will cut fuel

Now I would iamgine there will be a similar table in the vr4 maps

[Turbo_Steve]

That's interesting: I didn't know that it was RPM dependant: figured it was just the limit of the normal map table.

[Nutter_John]

here is the table from a evo 8

[Eurospec]

Yeah, thats exactly how it works. Its a load vs rpm dependant cut.

see there on the evo how the cut is higher in the assesed load scale right in the spool range? thats beacuse they know thats the most likely place that the turbo will overshoot.

In Vr4's its always around 4 to 4.5k. Whilst this is outside the spool area for a stock car it may be that they were more concerned with limiting peak torque there for some reason.

Cheers,

Ben.

[Eurospec]

PS, nutter, that must be a 260 table right? 230 is pretty damn low.

Cheers,

Ben.