1.9 Boost Issues

[polo_spec_d]

Hello all,

Ive noticed since I have got my 2.5 turbo back exhaust my 1.9 doesnt peak at 19psi as it did before and now im lucky if I get 12 or 14psi peak.

I have a Oettinger tune, Seat intake, provent and the exhaust are the only engine mods I have made. Could this be the tune not using the exhaust to full effect? Would I need to look at a custom tune to get full effect from the exhaust?

Thanks in advance

[Jarred]

I'd look for a boost leak first, before I started worrying about the tune.

can you put it down to an exact time you noticed the boost missing? was it after you picked the car up from the exhaust shop, or 'sometime' after that?

[polo_spec_d]

Well it still goes as hard as it did before and have done a search on the car but cant find anything, Ive had the exhaust on for about 8 weeks now.

[Tim]

Is your boost gauge a mechanical one? If the car still goes just as hard it may be the tube for that leaking?

[polo_spec_d]

Yeah mechanical VDO, yeah ill give that a look, cheers fellas

[polo_spec_d]

Gave the boost gauge piping a pressure test, No leaks on the pipework. hmm now im stumped.

[geoff_gti]

It's a fair bit cooler today, see if that make a difference?

As the engine output is still the same, could it just be the exhaust pressure will be a bit less now that you've change the system? That's just a random guess...I could be way off being non-tech :|

[gldgti]

hey mate.

if you are only making 14psi now, theres almost no way the car is going as fast as before.... are you sure your butt dyno is calibrated properly???

as suggested, very important to know for sure that your boost reading is accurate.....i would suspect a leak somewhere still. if the boost reading your getting really is accurate, is it possible that there is a sensor in the exhaust (exhaust gas recirculation) that was disturbed when the exhaust was fitted?

hope to help - i wish i had more experience on the newer oilers and their systems....

**edit** 2000 posts for me

[h100vw]

I think you need to log it with VAG-COM and see what boost it is producing, as far as the ECU is concerned.

Gavin

[Greg Roles]

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.

[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.