Outer Limits 4x4 Board

the standard inlet pipe going to the inlet manifold on a gu 4.2 td starts off at 45mm at turbo and goes to 60mm. is there an advantage in making it the same 60mm right through from the turbo to the inlet manifold?

looks cooler. normally stuff like that is done for a reason. give it a shot and hit us back with the result. im sure there would be several people interested if it does improve stuff

If you have a smaller inlet hole going to a wider outlet hole it'll force the air to rush thru faster than the normal rate.

If you stick to the same size all the way through you'll only push thru what can be pushed thru, it might be slightly more only because the inlet opening is larger but the sped of the air will be what ever your turbo can push thru.

If you have a large inlet going to a smaller outlet you'll reduce the speed at which air passes thru the pipe, before the oulet pipe after the outlet pipe hole it can speed speed again due to the force created from the smaller oulet and the force of the incoming air.


This is what the steam train designers did to speed up steam or slow it down, while passing thru injectors and stuff.

It's the opposite way around but yes that's the case.

I'm not sure of the exact name (i think it's the venturi effect) but when all other parameters are equal (pressure, volume) then the flow (speed)rate will increase and temps will rise marginally as the volume is forced into a smaller aperature and friction increases. would be the opposite way round if the aperture got larger. Don't quote me but depending on which fluid laws the air abides by (newtonian etc.) forcing air past a restriction would increase the likelihood of the air going from a laminar to turbulent (and therefore less efficient) model.

Like i said don't quote me, i work more with fluids than gases

MILO

ok, going on the idea that air coming from small hole to large hole speeds up. then the way it is now is hole at turbo 40-45mm going to inlet manifold 50-55mm a gradual tapper, this then speeds the air up. so if i go 45mm to 55mm in 100mm distance then the other 500mm in 55mm is this the same?

numbnuts wrote:ok, going on the idea that air coming from small hole to large hole speeds up. then the way it is now is hole at turbo 40-45mm going to inlet manifold 50-55mm a gradual tapper, this then speeds the air up. so if i go 45mm to 55mm in 100mm distance then the other 500mm in 55mm is this the same?

the air would slow down if it was coming out of the turbo (intake housing outlet) at 40-45mm to the intake manifold 50-55,
i'd tip that if you increased the pipe dia to the intake manifold size (50-55) all the way to the turbo (intake housing outlet) and then step it sown to the 40-45mm at the turbo, youd achieve 2 things
1, create a larger plenum volume meaning that it would take longer get boost (you have to compress the air in the extra pipe volume) wouldn't be much at a guess.
2, cause more turbulence(and therefore probably restriction) with an abrupt taper (going from the sizes you mention above)

All things being equal a gradual taper should provide better airflow than steps and ideally you'd want to not increase the volume of the piping - unless of course it stepped down at the turbo outlet as that would be a restriction - im assuming it doesn't.

By all means try it and let us know, but i personally wouldn't unless you put on a new turbo with a larger outlet..

good luck

rockcrawler31 wrote:It's the opposite way around but yes that's the case.

I'm not sure of the exact name (i think it's the venturi effect) but when all other parameters are equal (pressure, volume) then the flow (speed)rate will increase and temps will rise marginally as the volume is forced into a smaller aperature and friction increases. would be the opposite way round if the aperture got larger. Don't quote me but depending on which fluid laws the air abides by (newtonian etc.) forcing air past a restriction would increase the likelihood of the air going from a laminar to turbulent (and therefore less efficient) model.

Like i said don't quote me, i work more with fluids than gases

MILO

I think Zagan actually has things the right way around.

If you have a divergent passage, and air passes into the inlet at high pressure and exits at a lower pressure and no external work is done by the air, then there is a decrease in kinetic energy of the air (pressure drop) and an increase in potential energy (velocity).

Mr Gustaf de Laval relied heavily on this fact back in 1883 when he developed the first purely 'reaction' steam turbine, as briefly touched upon by Zagan.

You want a gradual taper from the turbo outlet up to the normal pipe size. 6 deg total angle is the rule of thumb for keeping flow attached.

Angles bigger than 6 deg, the air stream can detach from the wall, causing a lot of turbulence which restricts the flow.

Milo and zagan are proberly both corect as steam is forced through the oriface and a venturi is drawn through from a preasure indifference ie; vacuum.
Negative preasure vs posative preasure could have a different affect on the restriction as the high preasure zone would be on different sides of the restriction.
I could be wrong but its my understanding of the principal.
Someone feel free to correct me as I'm interested to know if this is correct.