auditunerb5

I'm tired of boost going down in cold weather. Also want to run a little more boost than 15psi. I know the K03 isn't going to flow that much....But I'm going to run mechanical mbc up to a set rpm then switching over to ecu controlled n75 via a comparator circuit triggered by rpm.

Plan on dialing in 18 psi. At what rpm should i switch over to ecu controlled n75 so I don't fry the little k03? According to the compressor map I'm not really supposed to run 15 psi much past 3500 rpm but everyone does that. Chip tapers at 5k on my GIAC chip. Would it do any good to stretch that to 5500 or 5700? Any info would be appreciated?

Audi2ptzero

First off your going to find that your boost sensor is going to see a much higher boost level then what your chip is requesting, this does become some what of a problem when it starts putting your car into a limp mode.

Other problem is that the K03 cant make a set boost past 5K rpms no matter what you do, that is unless you plan on down grading your motor to a 1.5 liter so that there is less exhaust flow going past the turbo exhaust wheel. See the things is there is "boost" and there is "air flow", boost means nothing while air flow is what makes power. The turbo can only push so much air flow and when you push the turbo harder with more boost you end up reaching that limit of air flow much soon and the boost level drops off.

Mike O.

...because the engine management system doesn't care as much about "boost" as it does about "g/s" of airflow. Cooler air means a denser air charge and therefore less boost required to achieve the requested "g/s".

Mike O.

JAFO

having a set boost at low speed may cause drivablity problems.

auditunerb5

This setup acts more like stock. I might add a pressure relief valve for quicker spool up but the k03 spools fast already so no a priority mod to add!

auditunerb5

My car goes into limp mode around 21 psi. So running 18 or 19psi should work. I will let you know. The DBW wire should compensate for the added airflow. I'll get Vag Logs to make sure I'm not running lean!!

On the flow thanks that was what I thought. I will switch over to the stock n75 at 5000. I probably not going to get more HP but torque should be up quite a bit going from 15 to 18 psi.

I would like to do a stage III but I got a 14month old and a 1 week old so no money now!!!

ModifiedA4

plus as Mike O. stated, the engine cares about the mass of air entering it. not boost. its part of a basic concept of thermodynamics.

pv=nrt.

cuatrokoop

Not only the ideal gas law (that fixes the relation ship between the cooler temps and the more dense air), but also the mass conservation law (that fixes the mass of air entering the engine)...

But definately not a good idea to try and keep the boost at 18psi when its cold out. The ECU decreases boost for a reason (safety of the motor).

auditunerb5

I understand what you are saying. This would be true if all other parameters where static. However I was under the impression that the motronic m7 monitored maf,iat,ho2,knock and charge pressure. The m7 can add the appropriate fuel, and adjust timeing as long as it is within the map tables of the GIAC chip and there was suffiecient duty cycle of the injectors?

Audi2ptzero

the barometric pressure changes and adjusted alt lowers. When this happens your car makes more vacuum so when you get into boost it looks like there is less since your measuring boost levels inside the manifold and not directly at the turbo.

There is an easy test for this. When it is warm outside just log what your vacuum is at idle and when your driving let off the throttle and log what your vacuum is under load. Do this again when it is very cold out side, you can also do this test when at sea level and then at high alt. You might see about 1-4 inHG changes with weather tems and alt changes.