1.9 Boost Issues

[h100vw]

Oops, I didn't read that very well. I thought that you had the exhaust fitted and lost the boost sometime after.

I agree with Greg. I think of boost as a measure of restriction. Remove any restriction and the boost will drop. What won't drop though is the volume of flow.

10PSI off a K03 is very different to 10PSI off a K04. The volume of air being produced is much higher on the K04.

2 ways you can look at it, there's more power to be had with a retune or you are not working the turbo so hard.

Gavin

[gldgti]

A larger exhaust will decrease backpressure, which is what you want. I don't care what anyone says, in a boosted engine there is no such thing as good back pressure. No scavenging effect with a turbo / blower in place! You should have "felt" quicker spool / response times when it was fitted, now the pumping efficiency of the engine has been raised. Since there is less restriction to pump against, the turbo doesn't have to boost as hard to develop the ECU determined power level. Remember the ECU is simply pushing the boost as hard as it needs to, given the throttle, load, temps etc. I'd expect the less restrictive exhaust I have planned for my TDI to drop the boost pressure, but the overall power output to be the same. Your drop is a bit bigger than I'd expect, but if the power "feels" the same, and your 0-100 times etc feel the same, then start looking for ways to make the most of the additional boost you can now run!

Allows more ceiling in the turbo, and thus more room for a more aggressive tune.

Cog, i dont think what you've suggested here is possible. heres why: -

the ECU cant measure the power output of the engine. all the ecu does is send timing commands, fuel metering and turbocharger vane control commands (and some emission control stuff). theres no other actuators on hte engine. the ecu does not try to make the engine produce a certain amount of torque - rather, if everything works well, the engine will produce a certain amount (at full throttle).

the technology required to actively measure the torque output of an engine is not yet developed well enough to be applied to a car. basically, you would need to measure the amount of strain in a shaft at some point in the drivetrain, and log this data, then use knowledge of the shaft dimentions and material properties to infer a shaft torque. IF, and when this technology one day comes on the scene, it will mean big changes to engine management as we know it - but its a way to go yet

there is no reason other than a malfunction of some kind for the boost to have decreased. i hope this helps a bit.

[polo_spec_d]

Ill get a scan on asap, Thanks for the feedback fella's, Ill let you all know what happens.

[Greg Roles]

I see your point Aydan, and I agree with the logic for a full power effort. What I was referring to was more a "street" effort, where the driver and situation calls for say 60kw, and the new exhaust allows the turbo to boost at a lower rate to achieve this. This is about all you can generally achieve on the street with the bummometer, a quarter mile or a dyno would be ideal!

Interesting concepts all the same

[gldgti]

indeed- in that case we are both correct. i concur that for a given "effort" the boost may now be lower.... but how much lower is dependant on so many factors... impossible to say really.

[polo_spec_d]

The Pogo is going to be dynoed and ill get a vagcom scan next week to find whats up with it, Speaking to the Fella today he has seen cases of this in 320D that have had exhaust, tune and intake work and run at 25% lower boost due to the ECU "learning" but wasnt able to tell me the tune they had used.

[h100vw]

No need to dyno really. You can check it with VAG-COM. Guy will know what a chipped Polo should show on the MAF. If it is flowing in the ball park it must be making the power.

Gavin