SAI and N249 Removal

[noone]

On a turbo car, this would be true during off boost conditions and very small throttle openings. When you open the throttle, boost rises and you have positive pressure in the manifold.

Thanks mate, thats what I expeced, but was not sure. I assume that bypassing the N249 would make the vacuum control on the diverter obsolete as well...

[noone]

I bypassed my N249 today, I had tried it ages ago, but did not notice any improvement.

Big difference today, boost comes on earlier and stronger. I'm going to keep it like this for a while to see if the ECU adapts to the difference and tries to compensate by bleeding my boost somewhere else or delaying when it comes in (altering the N75 use).

[break]

noone, did you just do the typical method of looping the N249 onto itself, then running the diverter valve straight off the plenum, or did you go to the trouble of removing the N249 entirely with resistors etc?

[noone]

Just taking the diverter vac feed from the manifold tubing (using the first T piece) and looping the pipe for the N249 back on itself.

No codes, etc.

I am interested in getting rid of the rest, but don't want codes coming up all the time. Maybe if I get a retune down the track and they can remove this function I will do ii all...

[Catfish]

Just taking the diverter vac feed from the manifold tubing (using the first T piece) and looping the pipe for the N249 back on itself

I've just done this as well. Do small cable ties (2.5mm) work ok as permanent replacements for the single use metal clamps on the vacuum lines? Or do you use something else?

[noone]

Cable ties work fine. I was very scheptical about these previously, but all my original ones are as new and I've seen too many pics of other cars with them to worry now.

[Plautos]

I'm using transistors in the solenoids place's they have 30ohms and 5w. Small and good looking.

[noone]

I've ordered the SAI blanking plate, but not sure if i'm going to be able to get rid of all the VAC stuff without removing the N75...

Can this be done?

[ssman]

I'm doing the boost controller for the n75, and running it into the car, so I can make adjustments next to the gauge. I used 330 ohm 5 watt ceramic resistors and I have a improper flow code after 4-500ks but that's the only one that's thrown a code out of three. (it was a cold and rainy day) have left the code on to see if there's any other issues, nothing yet.

Fingers crossed

Cheers

[Plautos]

Don't waste time... remove the n75.

I've ordered the SAI blanking plate, but not sure if i'm going to be able to get rid of all the VAC stuff without removing the N75...

Can this be done?

[noone]

I'll trust you on that one...

Any recommendations? I want to keep the power delivery smooth for suburban / city driving

[Catfish]

I'm following this with morbid interest. What is the advantage of replacing the N75 with a MBC and then having to constantly fiddle with settings, depending on external conditions (temp etc) and driving style (road, track, etc)? I know it gets rid of a fair bit of plumbing, and I'm all in favour of ditching the SAI system, but pretty nervous about removing the N75.

ps - I've done the n249 bypass as per noone and it worked well.

[noone]

The idea is that the car is designed with safety in mind rather than power.

an MBC generally speaking holds boost until it hits a determined level. For the purpose of this, lets say the level is 18psi.

On the normal setup, the N75 controlls the vacum to the turbo wastgate and the N249 Controls the diverter valve (then controlling the boost between the turbo and the throttle body. By removing the N249, you have made the control of the wategate manual (controlled by the vacuum created from closing the throttle body. The ECU is likely trying to smooth out this action and bleed the boost occasionally.

The N75 is programmed to control the boost for: Smooth power delivery, remove boost spikes and at times, reduce the boost if it decides the boost is too high.

My concern is that an MBC may make backing off the throttle whilst under boost jerky or uncomfortable.

I'm thinking that if I do these changes without removing all the gear, I can gauge the difference and revert without too much work if I don't like the changes...

[insanekiwi]

so what sort of boost are you hitting now with N249 removed noone? interesting... any down sides?

[noone]

I'm not currently using a gauge, but last vag com had me at about 17 peak. I don't really know as the boost pressure is a sum of some other info from memory...

I don't think the N249 would change the peak boost much, it seems to stop the pressure being bled off which means it boosts a little earlier and faster. This probably also means the boost spike happens earlier and drops off earlier.

Flat road, was playing with my new iPhone more than wanting to show off, taken in 2nd gear. Didn't redline it, only the dump pipe done.