Torque/Power on Boost

[rodpaslow]

Simple question -I've got a vnt that spools rather quickly and pulls hard till boost hits about 16 psi and then seems to back off or surge just a wee bit; very little to no smoke out the tail pipe on boost.  Will turning up the fuel screw reduce or eliminate this (it's a Giles superpump)?

[R.O.R-2.0]

mine only pulls till about 17 psi.. then levels out, then might gain 1 or 2 psi thru the rest of the powerband..

it gets to 17 quick, flattens out, then pulls maybe 1 or 2 more psi before redline..

[rodpaslow]

Thats pretty much what mine does.  I was just wondering if increasing fuel would help that?  I'm not looking for more boost, just to keep pulling as hard as it does at a slightly less boost.

[R.O.R-2.0]

im turned up as far as you can go on a stock pump.. any more fuel and i need giles..

i POUR COALS off boost.. i have lots of fuel. but that turbo cleans it up great, and doesnt take much boost to clean it up.

i think its just the nature of the beast..

[rodpaslow]

Thanks!

[RabbitJockey]

my guess is above a certain rpm the compressor is no longer efficient at maintaining 16psi.  so its spinning much faster and putting out more hot air, and also creates more back pressure.  lowering boost may delay this but inevitably every compressor can only flow a certain amount of air efficiently.

[745 turbogreasel]

What are the vanes doing?

[R.O.R-2.0]

my guess is above a certain rpm the compressor is no longer efficient at maintaining 16psi.  so its spinning much faster and putting out more hot air, and also creates more back pressure.  lowering boost may delay this but inevitably every compressor can only flow a certain amount of air efficiently.

these little buggers will make ~40 psi.. they start to scream like a supercharger around 30 psi.

ive blown the head off a 1.5D with a stock VNT15 before 

[rodpaslow]

I agree with ROR they can just screem.  I only tired it once-don't want to blow my fairly new 1.6.  My vane are controlled by a cable and I'd say at 3/4"pedal for my car would be 3/4 closed at 18-20 psi.  Mine maxes at 22 before the boost can starts opening things back up.  I can hold 18-20 psi just by throttle movement and that's when it seem to reduce pulling power.  Below 16 or 17 psi its awesome.  I'm going to add more fuel and see if it helps.  I'm amazed at this little turbo though, right from 1400-1500 rpm to as high as I want to go it's producing  boost!

[RabbitJockey]

my guess is above a certain rpm the compressor is no longer efficient at maintaining 16psi.  so its spinning much faster and putting out more hot air, and also creates more back pressure.  lowering boost may delay this but inevitably every compressor can only flow a certain amount of air efficiently.

these little buggers will make ~40 psi.. they start to scream like a supercharger around 30 psi.

ive blown the head off a 1.5D with a stock VNT15 before 

im sure they do, but thats some hot ass air with some crazy exhaust manifold pressures i'm sure.

[8v-of-fury]

Rodpaslow you seem like you have the perfect setup, pulling boost all the way through the rpm band.

[rodpaslow]

I turned fuelling up a bit and it seems to have helped things.  It boosts just a week bit higher with the fueling increase, but pulls hard throughout now.  I have a water to air intercooler to help with the heat at higher boosts levels.  This thing is awesome now!  Now I just have to work out if the tires are the problem as I have a fair vibration over about 70 mph....

[8v-of-fury]

If the vibration happens at a certain speed as opposed to a certain rpm, the engine and trans can pretty much be ruled out. Which leaves being out of alignment, tires out of balance, or possibly something to do with outer cv joints/bearings.

[R.O.R-2.0]

my guess is above a certain rpm the compressor is no longer efficient at maintaining 16psi.  so its spinning much faster and putting out more hot air, and also creates more back pressure.  lowering boost may delay this but inevitably every compressor can only flow a certain amount of air efficiently.

these little buggers will make ~40 psi.. they start to scream like a supercharger around 30 psi.

ive blown the head off a 1.5D with a stock VNT15 before 

im sure they do, but thats some hot ass air with some crazy exhaust manifold pressures i'm sure.

im sure it was more the EMP that blew the head off the engine, rather than the boost.