Audi Quattro Turbo 5 cylinder on S80 wont start!

[stevieturbo]

Cool

[Rob Stevens]

Still curious why it didn't cough and fart into some sort of life?

[mefmotorsport]

it did, quite a lot, it seemed like it wanted to fire, just wouldn't catch! No wonder!

[mefmotorsport]

All went very well at the mapping session on a 4WD rolling road but once tthey started to map further up the revs they experienced with a waste gate problem and had to abort the session. Apparently the external waste gate wasn't big enough to control the boost and it kept trying to boost at 3 bar or more, a bigger waste gate is required or modified exhaust manifold design, or both. Watch this space!

[stevieturbo]

ensure gate and any controls used are operating correctly first, but yea, depending on build etc, a bigger gate may well be needed.

Although it would be less common on cars with external gates.

[mefmotorsport]

We wired out the Mac control valve to eliminate the electronics, piped up the waste gate directly from boost pressure and even with the very weak spring it still wanted to boost to the moon!

[stevieturbo]

We wired out the Mac control valve to eliminate the electronics, piped up the waste gate directly from boost pressure and even with the very weak spring it still wanted to boost to the moon!

And check with a mityvac to ensure the poppet valve is actually moving fully and correctly ?


Or the other option...as the yanks say..."send it" lol

3 bar is doable !

[mefmotorsport]

Yes, confirmed it was moving around 1cm do the conclusion was that either the valve curtain area was too small or that there was a problem with the manifold as the waste gate aperture flange was sitting on top of 2 of the 5 primary pipes in the merge collector, maybe the exhaust from the other 3 pipes didn’t get a chance to escape. It doesn’t look like an ideal design to me, surely the waste gate should be in the common pipe feeding the turbo after the merge? It seems that that wasn’t possible since the turbo flange was directly on the outlet of the merge collector.

Pics now added

[mefmotorsport]

Pics of manifold & wastegate
https://imageshack.com/i/plV8xsvAj
https://imageshack.com/i/pniHB9icj

[stevieturbo]

It certainly isnt ideal in terms of flow/positioning. In cases like that, moving the gate takeoff to the turbine housing is an option.

What diameter is the gate itself ? Even with bad positioning....a big gate can overcome it.

No idea what sort of turbo etc you're on. But if it was me building anything like that, I'd be using the likes of a 46mm Precision Gate ( or Turbosmart or whoever ). But in and around that size.

I would not be using smaller, and depending on build/turbo/power etc etc...may even go for a larger gate. Most gates these days use v-band connections though, old 4 bolt stuff is rare.