i just replaced the diverter valve on my a4. i am till losing boost. the car will hold 10lbs under normal acceleration, but when i put it on the mat it will peak to about 15 then fall to 5 and surge back and forth. this continues until i let off. any ideas or suggestions?

 

What year is your car are you running a chip and what are you using to control boost?

 

its an 01' and its bone stock. i just put a new k03 on it the ald one was shot. i installed a boost gauge when i felt the surge so i could see what was going on.

 

Well there is your problem right there. If you are bone stock your boost should only be hitting 11-12psi, when you hit 15psi the ecu closes the throttle and this causes surging, this is why the 2000+ cars have a map(boost) sensor and it uses it as a safety to keep the car from over boosting. So either your wg on the new K03 is too tight causing the boost to hit higher then it should or you have a leak on the hose going from the N75 valve to the wg actuator.


The actual boost can not be more then 300mbar over requested, this is why people cant just throw on a MBC to bump the boost up. Even the race N75 valve which just bumps boost 2-3psi over stock causes ECU on the 2000-2001 to close the throttle causing the surging issue.

 

So tell me about this N75 valve. I keep hearing about it. What's its purpose? I have a 98 so if I replaced mine with the race spec would I see an increase in boost?

(BTW mike, thanks for all the previous help. Unfortunately most shops want $700 for labor and that bumps up my quote two $1600, which I cant afford. If I only upgrade to a KO4, Southbend Stage II would be fine right? I was researching the Elim kits and they're a lot less plug and play than I thought. Its not the install that worries me, but the weekends spent wrenching to get it back right or the hours spent on the side of a road, awaiting the pickup truck. I need something more relaible since this is my DD and I'm taking it snowboarding.)

 

okay, that actually helps alot. how do i go about solving this problem. i am new to the turbo thing. i build big block ford racing motors. so turbo's and audi's are on the other side of the spectrum. what is a n75 valve?

 

Yes you would see an increase in boost. Each N75 valve is designed to allow a set amount of pressure thru it when it sees a set signal. This means if you put in a N75 valve that allows less pressure thru at the same signal you will get more boost since the wg is not being opened up as much.

You might be ok with a Stage 2 if you get one from me since mine come modified for more clamping pressure which means its tq rating is slightly higher. It might be ok if you dont ever plan on launching the car with the K04 setup. But just so you know your talking about a difference of $15 between the SB stage 2 and SB stage 3 for the 1.8t.

 

niiiiiice. good to see another ford guy here. The First engine I ever built was a carbed 302 for my thunderbird when I was back in high school.


Audis are pretty new to me too, though I've learned a lot from this forum. To answer your question the N75 is a valve near the front of the engine that tells the wastegate on the turbo when to open/close, thus controlling the amount of boost pressure. (or lack thereof in my case).

 

Well whats the price for a Stage two with flywheel vs without flywheel?

 

So how do I fix it