diff. btw. supercharger and turbocharger

The name, the way they're powered, and how long it takes between "stomp it" and "boost kicks in". Turbocharger = exhaust-powered, always "on" (but may not be producing useful boost) and takes (relatively) forever to spin up and start producing boost. Supercharger = some other (usually belt to crankshaft, possibly gears, occasionally even a separate electric motor) power source, on or off at whim, always produces at least some boost when on. Both perform exactly the same function: cramming more air (for injected engines) or air/fuel mix (for carb) into the cylinder per intake than non turbo/supercharged operation can achieve, with a resulting increase in engine power output.

Thank you.

I think you confused the two. Turbos are prone to lag but "forever" is not the correct wording.. Obviously that's a hyperbole but turbo lag can be reduced with a smaller turbo. Of course, a smaller turbo means less boost. The turbo has a wastegate which bypasses the exhaust side turbine and does not allow the turbo to spool up to produce boost.

The supercharger is the one that is always on. It's continuously pumping air but, under non-load conditions is being bypassed from the intake to the exhaust side of the supercharger. Once boost is called upon, the bypass valve is shut and the intake is pressurized.

Other differences are that turbos are usually more efficient than a supercharger. ATI (accessible technologies) tells you the installation of a supercharger will not effect gas mileage unless your driving style changes dramatically (always going into boost).

The supercharger makes a whining noise which pretty much tells anyone that you've got one if they don't assume it's a loose belt or a dying pulley bearing. A mustang pulled up next to me and the driver looked over like he wanted to race, he then rolled down his window, heard my supercharger, rolled up his window and looked straight ahead trying undo the last couple seconds of looking at me and reving the engine. It's pretty easy to notice.

Hope that helps,

-Bruce

Turbo lag can also be reduced by simply adjusting the wastegate opening rate. Lots of today's factory turbo charged cars pop the wastegate open when the throttle is engaged in order to prevent an over responsive car from causing a problem. By keeping the gate closed until boost builds, you can decrease lag.

There's always a little lag with a turbo - off the line a supercharger wins.

""Other differences are that turbos are usually more ""efficient than a ""supercharger. ATI (accessible technologies) tells you ""the installation of a ""supercharger will not effect gas mileage unless your ""driving style changes ""dramatically (always going into boost). Aren't superchargers more efficient than turbos? Another thing I've found interesting is that some Buick Pk.Ave. Ultras, w/superchargers, have a lower comp. ratio (8.0--to reduce total compression at max. boost, I assume) than the non s-chg'd ones (8.5). So, if one has enough self-control, which I lack, he could theoretically run lower octane fuel in the supercharged version--and of course GM recommeds premium fuel only in the s-charged ones. Just 2 more cents worth--and sometimes worth every dime! sdlomi

In article "sdlomi" writes: $ Aren't superchargers more efficient than turbos?

Turbos are powered by the kinetic energy of waste gases, energy which would otherwise simply be vented to the atmosphere (i.e. wasted). Internal combustion car engines are quite inefficient; the majority of the energy available from combustion is either wasted outright (e.g. heat radiated to the atmosphere, internal friction, thermal and kinetic energy that goes out the tailpipe) or is used for purposes other than propulsion (powering the air conditioner, oil pump, power steering pump, valve train, electrical system, etc.).

Superchargers are run as an accessory powered from the crankshaft (typically by way of a belt, like power steering, air conditioning, etc.) and impose a parasitic load. This energy is not free; were it not for the supercharger, this energy would be available for other purposes.

It's more efficient to recover energy that would have been wasted than to drain energy away from the engine's real purpose (i.e. propelling the car).

Turbos have another efficiency advantage - their boost is a function of the speed and volume of exhaust gases, so when the engine is under lower load (and doesn't need the turbo's help), the turbo isn't trying to force a lot of extra air into the engine. A supercharger, on the other hand, is powered solely by engine revs, so it treats (say) 2500 rpm cruising down the highway the same as 2500 rpm with the accelerator fully depressed. (A few supercharged engines actually run the supercharger through a clutch that's under the control of the engine computer; in this case, the supercharger can be entirely disconnected when not in use, which fixes these efficiency problems. But most superchargers don't run this way.)

Not to say that turbochargers are better in all ways; as has been pointed out previously, they suffer from turbo lag. When you nail the throttle, you're initially running without turbo boost, until the increased energy of the exhaust gases can get the turbo up to speed. Superchargers don't have this lag; if the engine is running, the supercharger is running, so you nail the throttle and the extra power is available immediately.

$ Another thing I've $found interesting is that some Buick Pk.Ave. Ultras, w/superchargers, have a $lower comp. ratio (8.0--to reduce total compression at max. boost, I assume) $than the non s-chg'd ones (8.5).

This is normal - though the 8.5 compression ratio for the normally aspirated engine is quite low.

Turbo/supercharged engines end up with more air in the combustion chamber; that's the whole point :-) More air in the same space equals higher pressure. To keep the peak pressure from getting ridiculously high, the compression ratio is typically reduced when compared to a similar engine without a turbo/supercharger.

But, using a turbocharger is far from "free" power. Every turbocharger raises the exhaust back-pressure AT LEAST as high as the pressure it creates in the intake manifold, quite often higher. The added back pressure saps power that would otherwise go to the wheels, not unlike the direct mechanical connection to a supercharger does.

In a "suck-through" application (throttle blades upstream of the supercharger) such as a roots blower, closing the throttle means that the blower is operating in a partial vacuum. Since its no longer compressing as much air, it "unloads" and draws less power from the mechanical drive than it does with the throttle open. The blower only draws its maximum power in wide-open throttle situations. This isn't true for "blow-thru" systems like most add-on centrifugal superchargers, but then they tend to be low-boost (5 psi typical) units anyway.

Not strictly true. See previous paragraph. At 2500 RPM with the throttle mostly closed, the supercharger is spinning in a partial vacuum and drawing very little power. Open the throttle all the way at that same

2500 rpm and dense air hits the supercharger, causing it to draw more power and produce boost. This can be easily viewed on any "suck-through" supercharged engine with a boost/vacuum guage downstream of the blower

The real benefit of a turbo is that a PORTION of the power that drives them comes from expansion and cooling of the exhaust gasses as they pass through the turbine. This recovered thermal energy *is* put to work rather than wasted. On the downside, to maintain optimum performance a portion of that recovered energy has to be thrown away AGAIN when the intake charge is passed through an aftercooler to prevent detonation and increase intake charge density.