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Manual Boost Controllers-not the typical question (i hope)

Prawn Jan 11, 2007

  1. Prawn

    Prawn My other car is a MINI!!!!

    Afternoon guys,

    ive been meaning to post this for a while, but have only just got around to finding the time to think about it properly.

    before i start, i hope this doesnt come across as the typical 'can i fit this to my car and get 30bhp' question.

    ive heard an awful lot of bad things about mbc's, and was wondering why they are thought of so badly....

    i know on many non VAG cars its possible to turn the boost too far up, causing the engine to run lean, things to get hot, and things to start melting....

    from what ive been able to find out so far:

    The 1.8 T standard ECU is able to maintain factory Air/Fuel ratios up to 15psi of boost (im assuming this is through sensors in the MAF and the Lambda)

    i also believe the ECU will go into soft limp mode at 14.7psi (1 Bar) if what i have read is correct.

    now, are mbc's so frowned upon because people tend to increase boost too much, causing continous hitting of limp mode? or is there another reason?

    i ask, because a friend of mine has recently fitted an mbc to his mk4 golf gti T.

    he has fitted the mbc, in place of the N75 completely, leaving the n75 doing nothing, and increased the boost to a mild 13psi, clearly well below the limp mode at 14.7.

    he has been running the car like this for around 2 months now, with no problems whatso ever.

    the car is a fair bit faster than it was, whilst still being totally driveable, and still very smooth, and if what ive read about the ECU's ability to maintain air/fuel ratios is correct, it wont be running lean at all, and thus will be completely safe.

    so- in this case, running only a small increase, and seeming to be able to hold boost for longer, what is the problem with running an mbc?

    ive noticed many people over in the USA are now fitting mbc's to the 20vt engines, with seemingly good results, provided the boost isnt upped to a silly level.

    ive read all the articles about fitting the zenner diode to clamp the volate the ecu reads, and im not too fussed about that stuff, im just talking about adding an mbc alone, and upping the boost a small amount, like my friend bill has.

    so-whats so bad about it?
  2. ChriS3

    ChriS3 hud at ye bam

    Don't believe everything you read. First rule of internet forums. If you use a manual boost controller in place of your N75 you will still need the mapping done to suit as the requested and actual boost levels will be different, causing you to run too rich/lean.

    I'm using the Apexi AVC-R on my S3 and it works brilliantly. Took a lot of mapping to get it right, and the guy that did it still wants to try another map to get a cleaner top end (should be done by saturday). I have it set to maintain 1.45bar with the option to change the duty cycle and give a low rev spike to get a lot more torque.

    My original remap with the K04 was running at 1.55bar. There are those on here that spike a fair bit higher than that without hitting limp mode.

    The advantage of the MBC over the N75 is it's ability to keep the boost levels up higher in the rev range. With the N75 I could only keep 1.3 bar at 6500rpm. I keep it at 1.45bar with the apexi.

    The best way to get your boost levels up is to get a remap. far safer than hoping the ECU can compensate. Boost controllers are a waste of time on a normal S3.
  3. PocketRocket

    PocketRocket Member

    I have ECU remapped and I use an MBC replacing N75, on my A3 (AGU).

    When I had standard N75, boost peak(in 3rd gear) was 18psi and dropped quite fast.
    After fitting MBC, I set it to peak 21psi and drops pressure a bit slower.

    I think remap has a lot to do with it. Where I live, many people remap and fit MBCs and I have never seen a problem in years. Though a guy once fitted an MBC without remapping and got lots of problems in less than a week.

    You could also install MBC in line with the N75. It wont let you full MBC usage but will keep acceleration smooth as standard. MBC alone will always force you to be more careful and tricky playing your foot/throttle, and from time to time monitor pressure with a boost gauge.

    I did feel a big difference in car response, and pushing more at high revs.
  4. simch

    simch Active Member

    If you have a car worth say 8-10k, why try to "tune it" for £40quid.....!!

    Tread carefully is my advise!!
  5. Prawn

    Prawn My other car is a MINI!!!!

    if it makes any odds, i was talking about an A3 1.8t, not the S3 (clearly wouldnt consider something like that on a car worth 10k!)

    sorry guys, i wasnt planning on fitting an mbc, i was just interested in the reasons why people are so against them, when initial impressions suggested they could be good.

    i know very well that a remap is the best way, i simply dont have the £400 needed, and wont do any time soon!

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