chuntington101

ok, straight to the point, what limits the rpm of any given centrifugal compresor? is there any way of increasing this figure by using diffrent materials? is there a relationship between the CFM potential and the physical size of the housing, or, if you just increased the speed would that make up for it?

i know these are VERY vague questions but any help would be great

thanks Chris.

WIPLSH

Turbos spin up in the 100,000 rpms (im not sure the max limit)

I know there is a relationship between the CFM and the physical size of the housing. The turbine speed can only be increased to a point. (too much heat/turbine or bearings brake apart)

chuntington101

thanks wiplsh.

you see thats the thing, i know some turbos can spin to 100K rpm but what about the REALLY big stuff???? is that still doing 100Krpm peak??? also with centri. SCs, whats the limiting factor to the CFM they can produce??

i was thinking about altitude. we all know that once you get in thin air your turbo/SC system finds it hard to cope. i know there are turbo designed to run at altitude (for use in the pikes peak stuff) but what the diffrence between them and normal units?? also if your pulling in less air then cant you just spin the turbo/SC harder???

one restriction i can see is the matterial of the compressor blades/bering etc. but then you look at jet engines and they spin at 60,000rpm!

thanks CHris.

Skunkworks

The biggest limitation is gearing first followed by bearings and seals. Then one has to factor in inertia (things at rest want to stay at rest and same goes for things in motion). What I’m getting at is with an extreme gearing stepup ratio a modest engine step change (up or down shift) will result in a very large change to impeller speed. Power takeoff (belt drive) can/will become problematic.

Mike

chuntington101

Thanks Skunk. its a shame there no way of building in some kind of cltuch to help take some of this shock out the system. then im guessing you could run harder setups with more stepup???

i hear Rotex SC's have constant slip built in. does this help???

also from what you where syaing, does that menas its better to design a SC compressor to operate more like a turbo blade (ie high rpm to help efficent) rather than just going physicaly bigger???

thanks Chris.

Skunkworks

It’s a tough question as turbos by nature are designed to operate at higher RPM or tip speeds. This is also to put turbine in more efficient range… So turbo compressor wheel has slightly different design criteria.

Centrifugal compressor wheels can be efficient at lower tip speeds as long as pressure ratio is kept reasonable. Also look at inducer (impeller eye) and exducer (wheel diameter) of both turbo and superchargers and you will find tip speeds (ft/sec or m/sec) is not that much off especially when looking ATI products.

The Rotrex traction drive can slip and absorb shock loads, but it is my understanding it cannot handle high loads that are required in high HP LSx applications.

The accessory belt can and by design slip under shock loads. The problem is as tension is increased inorder to drive supercharger that slip becomes almost non existent. In my experience I try to get just enough tension to hold power.

As far as gearing I’m currently working on a planetary stile gearbox that has some crazy stepup potential, but it’s far from cheap or simple. So I can’t tell you how feasible it is at this time, as I’m waiting on prototypes.

Mike