jahwerx

Does anyone know how much HP is required to drive the centifugal-style superchargers throughout their operating range or as a function of boost?

Thanks in advance,
Josh

jerrypeterson

Much less than it makes.

Which Centrifical charger? What configuration? What use is this information?

jahwerx

"Much less" - thanks I'm not trying to ignite the SC v. turbo war here

To answer the question of "which"; Logically, either the Comptech or Vortech - although I'd assume their respective efficiencies are pretty similar . . .

Here's the reason for the question - has anyone given any serious thought to equipping one with a variator-based transmission (Of course it would eat some power too) but you might be able to have your cake and eat it too.

Bottom line - you may not be limited to a "fixed" pully ratio. Since these variators are based on rpm, you would be able to dial-in more boost at lower rpms and taper it off at the top of the rev range.

I was doing some poking around and these things exist for applications anywhere down to "moped-level" i.e. a couple of horse power, up to "car-sized" (Audi CVT for one), with plenty of options in between.

I think it comes down to three things:
1) Function (Could one get THAT much more boost at 2-3k revs to make a diff?)
2) Packaging (This is why the power question is important)
3) Reliability (They make some pretty bad-ass kevlar reinforced belts out there primarily for variator applications, but this is new ground)

This is total "what if" stuff here - no product development is even being considered. Shoot, I'm still running NA.

ultimate lurker

Its been tried in one way or another for decades. Back in WWII some aircraft engines would use multispeed transmissions on their superchargers.

In reality, the reason that these sorts of developments have largely gone by the wayside for SCs, particularly centrifugal SCs is, of course, turbos.

However, that doesn't have to stop us from hypothesizing.

First, let's look at the ratios available in CVT type applications. Typically you aren't going to see a ratio spread of greater than 6:1. That means that the ratio of the tightest gear to the tallest gear isn't more than 6:1. How does this impact us? First of all, let's look at existing S2K superchargers. They produce around 6- 7 psi of manifold pressure, or about 21 psi of absolute pressure. This pressure is produced at 9000 rpm and steadily drops off as you go lower in the rpm range. Lets say that we wanted to produce approximately the same amount of boost at 3000 rpm. We'd probably need to spin the SC about twice as fast as it would spin normally at that rpm to make the boost desired. Thus, there would be no issue with the ratios available.

The second issue is, of course, power. A centrifugal supercharger of the size and configuration used in S2000s probably consumes 25-45 hp at peak rpm/boost. I base this on Roots blower power consumption curves (assuming the centri should consume less power due to better effficiency). A CVT setup would be unlikely to consume much more power.

Then there is packaging. While there is lots of room available in the S2K setups, integration probably wouldn't be too easy unless you got the SC manufacturers involved (Vortech or Paxton).

Finally, cost is a problem. Would it really be worth it? Depends on your needs, but frankly given all the trouble involved, I'd be more inclined to do a positive displacement blower or a turbo.

UL

jahwerx

Thanks, UL.

If the hp estimate is on the lower side (i.e. 25 hp) then there appears to be an application out there for a scooter:
http://www.taffspeed.co.uk/technic/burgman.htm

If feasibility makes sense (i.e. boosting to 6 psi at 3k - who wouldn't like that ??), the one limitation, must be the unit itself - like you mentioned; integrating one end of the variator into the SC unit. . .I suppose another solution may be to add a tensioning pully into the system and leave the SC bone stock, OR have the transmission function as a self contained unit (with add'l input and output drives).

Hypothesising much further than this is difficult without starting to get hands on.

.. but still I wonder why no one HAS released a positive displacement application yet ..