Turbo upgrade for TDI?

[dammfool]

With the DP chip my polo screams all the way to red line

[Volvo Driver]

That intercooler kit has a long way for the air to travel, wouldn't it be best to find or make an intercooler that has the intakes on the one side to keep it nice and short so you get less turbo lag?

Though it might not have much loss due to the intercooler being more efficient.

Your exhaust should only be as big as the exhaust of the turbocharger is, nothing to gain from going bigger.

Changing injectors on a PD motor is easy compared to fitting an intercooler, it's just riskier.

[Preen59]

Your exhaust should only be as big as the exhaust of the turbocharger is, nothing to gain from going bigger.

Wha??

[Volvo Driver]

I thought that made sense, the exhaust side of the turbo where the downpipe goes, there isn't any need to make it bigger then the housing hole is, well maybe a little bit bigger, but not much, as that's the restriction in the system.

Unless somone can show something that proves me wrong to that as that's how I understand it.

[Preen59]

Unless somone can show something that proves me wrong to that as that's how I understand it.

You need it to be larger to form a pressure drop on the exhaust side to reduce lag. There, done.

[Jarred]

That intercooler kit has a long way for the air to travel, ....

air weighs bugger all. hence 'moves' very quickly, esp under pressure/vaccum.

mk 3 central locking system uses a vacumm pump in the boot (i believe in the boot]. how come all the doors lock at the same time? cause air weighs bugger all, hence distance isn't an issue.

edit: also, have you ever changed injectors on a polo TDI? just out of curiosity

[Greg Roles]

What you most certainly gain by going bigger, is bigger muffler internals, and bigger bends absolutely flow better. If you do some reseach on autoweb, or any other source you have faith in, you'll see plenty of tests that show, on a turbo car, you can't go big enough. Naturally aspirated needs a tuned length to get optimal cylinder scavenging, but again after this tuned length, you can't go big enough. Donaldson, a truck muffler company from the states recommends much much larger exhaust sizes that is usually considered necessary, they recommend 2" for up to 75kw, 2.5" for up to 120kw, 3" for up to 165kw, etc etc.

Fraid I'm also a believer of the big arse exhaust, and am glad my 2.0 125kw diesel has a 2.5" stock, which according to the above is quite borderline.

What a smaller diameter DOES do is increase back pressure and that dramatically reduces NOISE.

[Greg Roles]

That intercooler kit has a long way for the air to travel, wouldn't it be best to find or make an intercooler that has the intakes on the one side to keep it nice and short so you get less turbo lag?

Though it might not have much loss due to the intercooler being more efficient.

Your exhaust should only be as big as the exhaust of the turbocharger is, nothing to gain from going bigger.

Changing injectors on a PD motor is easy compared to fitting an intercooler, it's just riskier.

Again, do a search on autoweb, and you'll find the way an intercooler "looks" has little to do with how well it actually flows. E-bay is a minefield, and you often get what you pay for. Intercooling is one area I'd pay the extra to get a decent, serious core, such as a PWR or Plazmaman, or similar big name unit.

[gldgti]

I thought that made sense, the exhaust side of the turbo where the downpipe goes, there isn't any need to make it bigger then the housing hole is, well maybe a little bit bigger, but not much, as that's the restriction in the system.

Unless somone can show something that proves me wrong to that as that's how I understand it.

GAS FLOW THROUGH PIPES.

when you apply a pressure difference across a length of pipe, the gas will want to move along the pipe from the high pressure area to the low pressure area.

lets assume that p2 (low pressure) is at atmospheric (outside your tailpipe) and p1 is the pressure at the exit of the turbine. for now, p1 does not need a value, we just know its greater than p2.

once the gasses in the pipe are moving (not stationary) and turbulent (exit flow from a turbine will be turbulent flow) a boundary layer will begin to form at the wall of the pipe, between the actually moving gasses and the gas that is in partial contact with the pipe walls. in turbulent flow, this boundary layer thickness is restricted to a roughly constant thickness for a given gas volumetric flow rate and velocity... and the boundary layer thickness, and its effect, changes most dramatically with velocity

this boundary layer is effectively what is responsible for most of the "drag" on the pipe from the moving gasses; and conversely, the pressure drop required to move the gasses through the pipe and any given volumetric flow rate and velocity INCREASES as the pipeline "drag" increases.

the best way to decrease "drag" is to reduce velocity - we all know this, because we know its takes much more horse power to drive a car at 180km/h than it does to drive at 80km/hr. infact, drag goes UP by the square of the velocity.

therefore, for a given volumetric flow rate in a pipeline, it produces less "drag" when gas velocities are LOW instead of HIGH.

now - if you increase the diameter of the pipeline, the velocity must necessarily DECREASE for any given volumetric flow rate, and thus the pipeline drag will decrease significantly. this amounts to lower pumping losses through the system, and as such, if less pressure drop is required to pump the exhaust gas from the tailpipe, then that amounts to a larger pressure drop across the turbine, which allows a more efficient spool-up.

[Volvo Driver]

Again, do a search on autoweb, and you'll find the way an intercooler "looks" has little to do with how well it actually flows. E-bay is a minefield, and you often get what you pay for. Intercooling is one area I'd pay the extra to get a decent, serious core, such as a PWR or Plazmaman, or similar big name unit.

I know plenty of people that have had good success with them and they have been tested on autospeed or one of those sites as being more then efficient enough, tube and fin isn't that hard to do.

Ones like this: ebay

I don't see why they wouldn't be any different to one made here that costs a lot more considering there have been flowtests on Autospeed I think it was?

No I haven't taken injectors out of a polo, but I have done work on my Dad's mk3 tdi with the same basic motor, not PD but still TDi and at work the MAN's I work on are PD too.

Everyone else: Thanks, I was wrong clearly and now I have learnt something today