The "Boost Machine"

[Marky]

Sauce here: http://www.autospeed.com/cms/article.html?&title=The-Audis-DIY-Boost-Control-Part-1&A=111348

Just passing on something useful - results may vary

Years back I used to have a *lot* of V6 VR4\'s. Downfall of them is that the turbos are too small - twin td025s - and while you can have 20psi at 2500 (yay) it falls away to normally around 12psi by redline (boo). I\'m not sure if it was a wastegate issue with them all - simply because if freeboosted OR controlled by an avcr they could hold over 20psi to over 8000rpm

So I hunted high and low for something to "force" them to hold boost, and I\'m a cheapskate and refused to use an AVCR which used to be one of the only genuine "closed loop" boost controllers, most of them used to be overpriced crap to be blunt

Solution was found in the above link - a generic pneumatic relief valve - when I used it, it would hold whatever pressure I wanted, dead steady.

Theory is - as soon as you bring a car on boost, there is pressure being applied to the wastegate. You can bleed off more and more (through either MBC or EBC) but it\'s still "dulling" response a tiny bit - the idea is that a relief valve set to say 75% of your target boost will not let any pressure through to the WG until you reach whatever PSI you\'ve set it to. They are the thingy you hear go "PSHTpftpftpftpft" on a truck etc when it\'s idling and the brakes have reached full pressure I think?

Effectively - the car drives around freeboosted up until the limit you have set, the wastegate is held closed by the spring tension and there is 0 boost being applied to the diaphragm

On a normal car this has the result of a "livelier" feeling car - it will bring on full boost with part throttle rather than just at full noise like you normally see. Takes a little bit to get used to at first as small throttle openings start to mean a lot more boost than before, and it does wake up quicker. Some don\'t like it - some love it - I\'m in the second camp. Makes it feel a bit more like a big N/A motor rather than a peaky 2L turbo one.

On the TT legacy it also has the added bonus of as soon as the VOD hits, the wastegate gets snapped closed and it helps to wake up the secondary a bit faster. I\'m not talking OMG it\'s a different car, but it is something I notice improved - and when removed, the car feels quite "doughy" if that makes sense - just lazy to come on boost.

What I\'ve done on mine is leave out the regulator, I just have turbo --> relief valve set to around 14psi --> small bleed to atmo --> wastegate. You could still use this with an EBC, all this valve is doing is helping with part-throttle and transition response.

The small bleed off is needed partly I guess to smooth things out and eliminate spiking over what I want, and also there needs to be an outlet between the valve and gate - or else when you back off the loud pedal and the valve shuts off, the pressure gets "held" in the small length of pipe and keeps the WG open (found that out the confuse-myself way).

Takes a bit of trial and error to get things juuust right, and there\'s still a tiny bit of wander (like 1psi up & down) at full boost (I\'ll work on that, it can get dialled out so to speak), but for the small cost involved it\'s well worth the trouble if you can be bothered with it

p.s yes if you have uber fancy boost control already then disregard - and yes in theory it would be fine with factory boost control systems, though would be defeating the purpose somewhat

[Stoffa]

Same way a GFB turbo fuse works i think

[ADIKT]

Interesting read!

[Marky]

 Stoffa said:

Same way a GFB turbo fuse works i think

Sort of, but... the exact opposite haha

A 3 port solenoid works in the same way as this does - basically blocking signal or letting it through

After a couple weeks of having it in it 100% makes the car feel much much nicer to drive, much much more responsive on part throttle and VOD drastically reduced, definately spools up quicker

You can make a version of this using a factory boost solenoid and a boost activated switch - even a boost gauge with a warning light will work - just run the WG feed in one port and out the other, have it trigger at target boost, bam you have semi closed loop boost control

Probably a bit hard on the WG diapraghm but meh, never heard of one failling due to rapid cycling as such

Yes I am a tightarse but it works

[DacerX]

i think you are still the only person that i know to have gone to such lenghts to improve the twin turbo system

[Marky]

That\'s the thing though - it\'s not just something for the TT motors - (if anything they\'re not the best place for it cause if I want 18psi on twin, I have to have it on primary as well) - they\'re magic on anything where boost falls away up top and people resort to electronic control to make it hold instead (say, early legacy/wrx, late model evos, you name it) - if boost starts to fall under target, the gate just gets closed off again - same as a closed loop EBC does (just in a more crude form, you get what you pay for)

[johnny5]

interesting

[DacerX]

i would love to go for a drive in that gtb of yours, ive had a standard one and then a single turbo and there was a noticeable difference.