Ok but if I put my foot flat right....you get a wooooooOOOOOOOOSSSSSSH (as the boost builds) then it starts going SHHH SHHH SHH SHH SHH SHHH with my foot still flat. Then obviously the dump noise when you lift.

Im just wondering about the SHH SHH SHH SHH part.

EDIT. In the vid you dont hear it that well. I'll do another this wekend.

Huh - Wastegates bleed off excess exhaust gases from what I can recall?

You weren't on your way to Beyers Naude on the N1 this morning?

Nope. Not me hey. Car is in to get the Matrix system installed and stuff.

My friggin rear plate fell off yesterday (silicone on the big black bit at the back is not conducive to sticking stuff to), and I already got pulled over by the dudes patroling the M1 yesterday for not having plates but they let me off after i showed them the license docs showing that I only just got the car. So I had to take back roads from killarney to Wynberg this morning to avoid them!
DOH!

Ok ya thats kinda what I meant. Indirectly it's controlling the boost though.

Indirectly, yes...

Is that not the intake ?

No - directly. The boost controller opens the wastegate when it senses the required number in the intake manifold. The BOV has nothing whatsoever to do with controlling boost pressure.

We'll have to disagree then, as I view the wastegate as controlling the amount of exhaust gas flow through the turbo which affects it's rpm which affects the boost generated, so in my opinion not directly at all...

Yeah but when it opens it redirects exhaust around the turbo, which causes the boost to drop, or stay the same and not increase.

It doesn't actually get rid of boost that's already been made.

Don't kill yourself, Stu.

McF

I'm not that guy. Seriously. I've never even seen 200km/h in a car.

Me neither. I've only ever seen 292km/h on the 10.

Disclaimer: This was on my private testing strip A.K.A N14

My S3 make the exactly the same same noise, usually more so when accelerating from low RPM, I always just thought it was excess boost bleeding off...

Awesome Stuart! Congratulations, you've got your "STi" now.

Can we rally in it?

Wuss - You could barely speed at Gerotek in the Jetta

Welcome to the club. Now change your nick to something more appropriate - and remember, I'm watching you!

Congrats Cupra Stu




Golf too

I had that same effect on the Uno with the TD04.Some people call it cavitation,some call it surge,doesnt matter,its irritating ne,because its holding back there.

Thing is,the turbo moers into boost so quickly,that it actually runs out of air to compress.You can counter that by turning boost down.....or by going bigger turbo.

A smart electronic boost controller could most likely sort this.But you must sort it....impellers and shafts doesnt like that sort of thing.

That's exactly what I was trying to say. Boost is coming in too early

I would say surge. Cavitation would be at higher rpm. A small turbo with a big intake is unlikely to run out of air at low to midrange rpm. The way I understand it.

Weird...I actually found some videos of cupras on youtube...they also make that sound so Im not too worried. It stops doing it at higher RPM. Its just more noticeable in the higher gears where you sit i THAT rpm range for longer when floring it.

This one does the exact same thing on the second pull http://www.youtube.com/watch?v=Emp6mZG5 ... re=related

Doesnt matter if they all do it,its not right,and you are killing that turbo.For now try and drive around it by feeding power in at 3k and floor it as soon as you see stable boost.

Garron,i had this problem for years....and yes,cavitation is apparently at high rpm,i have never experienced it.

But this "surge" thing....On my Uno the problem with the 13G wheel i had,was that it used the same exducer size as the std 13G,but with a bigger inducer,which actually caused the fucker to produce more air at that rpm than what the engine could take.I even tried a bigger throttle body..nada...still did it.

I changed to a 15G and it was gone,but i had massive lag.And seeing that i now had a cut compressor housing...i was fucked.Cos the 15G had a bigger inducer,i had to open the housing.

Sooo,i got a used housing from Rudi and retried the whole thing,because with the 15G the car made more power....ummmm and cut the powerband in half....which made for a stronger BUT very much slower car.

And at the end,with a ported and polished head,it was nearly gone.Very faint,and apparently the new owner solved it completely by driving through a t-junction at 200kmh.....

So,i think whats happening here,is like we have said above....when the turbo goes into boost it actually boosts more than what the engine needs at that rpm,causing reverse flow to the turbo.What i actually still wanted to try back then,was to fit a restrictor in the boost pipe,which is like fucking a tight teenager with 3 inches of your dick...defies the bigger turbo.Unless you can find a restrictor that still allows enough air through up top to not change power too much.

Camtiming should also cure it....ma dis n fokken wereld van pyn.Getting the head to flow more will cure it.Doesnt these things have that variable inlet tract fokken besigheid?