I had a thought- turbos and spool up times

[ausubaru92]

I was reading somewhere that the inlet on the turbo dertimines how fast it will spool up, small inlet = spool up at low rpm/ sacrifice high rpm boost and vise versa for the large inlet.

 

So... if a turbo was to have a variable aperture at the inlet, where it could be restricted at low rpm and provide fast moving exhaust air and be opened up at high rpm to provide little restriction.

 

I know very little about turbos but this just crossed my mind

 

Anybody got any opinions???

[Syonyk]

So, something like this?

 

http://www.technologie-entwicklung.de/Gasturbines/VNT15-Turbo/body_vnt15-turbo.html

 

The vanes open & close (watch the animated .gif at the end for a good feel of how it works) to adjust the effective exhaust pressure. They close at lower RPM to tighten up the inlet slits and increase the velocity of the exhaust. At higher RPM, they open up to let the full exhaust flow through.

 

-=Russ=-

[erik litchy]

I was reading somewhere that the inlet on the turbo dertimines how fast it will spool up, small inlet = spool up at low rpm/ sacrifice high rpm boost and vise versa for the large inlet.

 

So... if a turbo was to have a variable aperture at the inlet, where it could be restricted at low rpm and provide fast moving exhaust air and be opened up at high rpm to provide little restriction.

 

I know very little about turbos but this just crossed my mind

 

Anybody got any opinions???

 

you mean the inlet on the compressor side? i would guess any restriction would make it worse. lag is made worse by exhaust restriction more than anything, then the volume of air between the turbo and the engine inside the piping. huge intercoolers and sutch definalty make turbo lag worse.

 

I think that every engine that i have driven with a variable vane turbo had worse lag than normal turbos. like the ford 6.0 wow it doesnt even kick in until 2nd gear.

[calebz]

any restriction would make it worse. lag is made worse by exhaust restriction more than anything, then the volume of air between the turbo and the engine inside the piping. huge intercoolers and sutch definalty make turbo lag worse.

 

Actually, quite the opposite. The size of the exhaust pipe (uppipe) going to the inlet makes probably the biggest difference in turbo spool times. A smaller diameter pipe forces higher exhaust velocity/quicker pulses, which results in quicker spool up. If that pipe is too large, the exhaust pulses can not build the speeds then require to spool the turbo effectively.

 

As far as lag from larger intercoolers, you gotta have a friggin huge intercooler coupled with a itty bitty turbo before that will really become a factor in spool times.

[ausubaru92]

I actually thought that a restriction on the exhaust inlet (something that works similar to the apeture on the lens of a camera)

 

The origional idea aroused when we dimantled our fireplace and i saw the gate at the top for restricting the smoke out the chimney

[NorthWet]

I actually thought that a restriction on the exhaust inlet (something that works similar to the apeture on the lens of a camera)

 

The origional idea aroused when we dimantled our fireplace and i saw the gate at the top for restricting the smoke out the chimney

Having recently looked at this, I have a little insight here... especially as I wanted to do something similar.

 

Due to the design of the turbo on our cars, doing a variable inlet nozzle is difficult. An iris doesn't do much good, at least as I envision from your description, basically being perpendicular to the flow as a slide-throttle plate would be; this would merely act as an obstruction. Other mountings wouldn't work well with the turbo design.

 

The inlet scroll decreases in cross section as it wraps around the housing, and the gas passage to the turbine blades is a slot on the inside of the scroll and along most of its length. The best way that I can see to provide any variable nozzle is to have a flexible "tongue" that can be extended into the scroll and pressed up against the slot, obstructing all but the end under low-flow conditions and retracting and exposing more of the slot as the flow increases. It would have to be thin to conform to the curvature of the scroll, but tough enough to handle the temperatures.

 

As far as maintaining exhaust velocities prior to the turbo, I think that this is relatively unimportant, as the scroll provides the gas acceleration, relying on the heat and pressure to produce this acceleration. In fact the right side exhaust stub on the EA82T actually points back a little towards the left side port. Large pipes on the exhaust inlet side would promote lag by increasing volume which would take longer to be brought up to pressure needed by the turbo scroll. It would be nice to maintain velocities, but everything is made moot by half of the exhaust flow pointing backwards...

 

$.02

[Vanislru]

It would be nice to maintain velocities, but everything is made moot by half of the exhaust flow pointing backwards...$.02

Definately, the best way to go IMO is to have better header coupled to a ball bearing turbo. Fast spool ups and higher effiency.

[erik litchy]

Actually, quite the opposite. The size of the exhaust pipe (uppipe) going to the inlet makes probably the biggest difference in turbo spool times. A smaller diameter pipe forces higher exhaust velocity/quicker pulses, which results in quicker spool up. If that pipe is too large, the exhaust pulses can not build the speeds then require to spool the turbo effectively.

 

As far as lag from larger intercoolers, you gotta have a friggin huge intercooler coupled with a itty bitty turbo before that will really become a factor in spool times.

 

i figure the best size for the pre turbo exhaust is around the same size as the hole for the turbine?

 

i wasnt thinking of the pre turbo exhaust in my post at all!