Banks experiment - altitude and hp

valhalla360 wrote:
I stand corrected that there are supercharged production vehicles...of course, none listed look like typical tow vehicles. Most aren't even typical passenger vehicles but specialized performance vehicles sold in tiny numbers. So while technically true, you aren't likely to see many of these towing a 30' TT.

Out of curiosity are they permanently on and at max boost? If not, you might see a similar effect to turbos.
- Cruising at highway speeds on level ground at sea level, my assumption is they turn off the supercharger as it's simply not needed...similar to a turbo charger not boosting under light load. Only it's worse as superchargers eat up some of the HP to power them.
- Under heavy load climbing at altitude, a supercharged engine intended for towing would be putting out max boost.

It would probably be a little more choppy in terms of effect (on vs off rather than a more smooth matching of boost to needs) but the general effect would still be there. Or as someone suggested, they may have some sort of gearing (or equivalent function) to adjust boost to need...but again, none of the examples are intended for serious towing.

To the second part of your comment: it's nice to see the math but nothing beats actual testing as unexpected issues can come into play.

Now that you've mentioned it, I believe the Range Rover 3.0 V6 and 5.0 V8 supercharged engines have a "boost bypass" function, which allows the blower rotors to freewheel.

But even on a normal supercharger, you're not putting how max boost constantly, because the throttle body is in front of the blower. So at partial throttle, you're feeding the blower a vacuum, and getting slightly less vacuum out of it. That's why I made up that simplified 50% throttle example.

I agree they're not ideal for towing - you have a lot of parasitic loss, and heat rejection (roots and screws not as efficient as a centrifugal compressor, and OEM only use roots/screw).