# switchable supercharger? **URL:** \ **Category:** Factual Questions\ **Created:** [April 17, 2008, 10:08pm UTC](https://boards.straightdope.com/t/switchable-supercharger/445794 "2008-04-17T22:08:21Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![Running\_with\_Scissors](https://avatars.discourse-cdn.com/v4/letter/r/a183cd/32.png) [@Running\_with\_Scissors](https://boards.straightdope.com/u/Running_with_Scissors)\ **Post date:** [April 17, 2008, 10:08pm UTC](https://boards.straightdope.com/t/switchable-supercharger/445794/1 "2008-04-17T22:08:21Z")
Why is it that nobody has made a car with a supercharger that can be turned off? Seems to me that 95% of the time you’re driving you wouldn’t need the extra power, yet the supercharger is sapping power from the engine whether you need it or not… ---
**Author:** ![Cardinal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cardinal/32/4000_2.png) [@Cardinal](https://boards.straightdope.com/u/Cardinal)\ **Post date:** [April 17, 2008, 10:23pm UTC](https://boards.straightdope.com/t/switchable-supercharger/445794/2 "2008-04-17T22:23:20Z")
I asked this here, and IIRC, the answer is that you’re pretty much describing a turbocharger, which doesn’t have a significant effect until the rpm get high enough, which is a sign you’re really trying to gun it. So a switchable supercharger becomes R&D that’s not really worth a competent company’s time. ---
**Author:** ![yoyodyne](https://avatars.discourse-cdn.com/v4/letter/y/a9a28c/32.png) [@yoyodyne](https://boards.straightdope.com/u/yoyodyne)\ **Post date:** [April 17, 2008, 11:17pm UTC](https://boards.straightdope.com/t/switchable-supercharger/445794/3 "2008-04-17T23:17:07Z")
There are superchargers with electric clutches. The problem is that there must also be a way for intake air to bypass the supercharger when it’s off, because air won’t flow through it when it isn’t turning. It’s kind of a messy way to do something without much benefit. ---
**Author:** ![cornflakes](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@cornflakes](https://boards.straightdope.com/u/cornflakes)\ **Post date:** [April 18, 2008, 3:23am UTC](https://boards.straightdope.com/t/switchable-supercharger/445794/4 "2008-04-18T03:23:08Z")
Stock supercharged gas engines usually have a bypass gate for low load conditions. The supercharger still turns, but it doesn’t take as much power to turn it. ---
**Author:** ![Khampelf](https://avatars.discourse-cdn.com/v4/letter/k/8e7dd6/32.png) [@Khampelf](https://boards.straightdope.com/u/Khampelf)\ **Post date:** [April 18, 2008, 3:32am UTC](https://boards.straightdope.com/t/switchable-supercharger/445794/5 "2008-04-18T03:32:31Z")
So, the nifty pull switch on the stick shift of the V-8 interceptor in _Mad Max_ and _The Road Warrior_ was just Australian Film Industry nonsense? ---
**Author:** ![dynamitedave](https://avatars.discourse-cdn.com/v4/letter/d/ed655f/32.png) [@dynamitedave](https://boards.straightdope.com/u/dynamitedave)\ **Post date:** [April 18, 2008, 6:44am UTC](https://boards.straightdope.com/t/switchable-supercharger/445794/6 "2008-04-18T06:44:53Z")
[QUOTE=The Sonoran Lizard King] So, the nifty pull switch on the stick shift of the V-8 interceptor in _Mad Max_ and _The Road Warrior_ was just Australian Film Industry nonsense? [/QUOTE] Don’t you disillusion me now! Fingers in ears, la la la… ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [April 18, 2008, 2:34pm UTC](https://boards.straightdope.com/t/switchable-supercharger/445794/7 "2008-04-18T14:34:18Z")
[QUOTE=Running with Scissors] Why is it that nobody has made a car with a supercharger that can be turned off? Seems to me that 95% of the time you’re driving you wouldn’t need the extra power, yet the supercharger is sapping power from the engine whether you need it or not… [/QUOTE] Because nitrous oxide systems would do this sort of thing better and already exist. Seriously…if you want your ‘turbo boost’ button-style power you see in movies, it’s already been mastered by nitrous oxide systems. You can also set it up so that when the throttle is fully opened, it triggers the system to inject N02 with the driver needing to do nothing more than mash the pedal. The whole engine could be stock and carry nothing more than the bottle’s extra weight and it would never interfere with normal operation, economy, rotating mass, etc. N02 systems just lay around waiting for you to switch it on and/or mash the throttle. ---
**Author:** ![Madd\_Maxx](https://avatars.discourse-cdn.com/v4/letter/m/5f9b8f/32.png) [@Madd\_Maxx](https://boards.straightdope.com/u/Madd_Maxx)\ **Post date:** [April 18, 2008, 4:39pm UTC](https://boards.straightdope.com/t/switchable-supercharger/445794/8 "2008-04-18T16:39:31Z")
[QUOTE=The Sonoran Lizard King] So, the nifty pull switch on the stick shift of the V-8 interceptor in _Mad Max_ and _The Road Warrior_ was just Australian Film Industry nonsense? [/QUOTE] The switch was for the AC. It gets hot in the desert. ---
**Author:** ![Cardinal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cardinal/32/4000_2.png) [@Cardinal](https://boards.straightdope.com/u/Cardinal)\ **Post date:** [April 18, 2008, 5:08pm UTC](https://boards.straightdope.com/t/switchable-supercharger/445794/9 "2008-04-18T17:08:11Z")
[QUOTE=Philster] N02 systems just lay around waiting for you to switch it on and/or mash the throttle. [/QUOTE] If you inject NO2, don’t you also need to inject more gasoline? Isn’t that the point? I thought you needed some system to take care of that too. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [April 18, 2008, 6:19pm UTC](https://boards.straightdope.com/t/switchable-supercharger/445794/10 "2008-04-18T18:19:34Z")
[QUOTE=Cardinal] If you inject NO2, don’t you also need to inject more gasoline? Isn’t that the point? I thought you needed some system to take care of that too. [/QUOTE] The same system does both, injects more fuel and NO2. If you want to talk about boats, you can get switchable superchargers. Penta makes a 3.5L and 4.5L turbo/supercharged engines. Yep both a turbo and a supercharger. the supercharger is on a electric clutch and come on from idle to about 1800 RPM where the turbo takes over. Why both? So you can water ski behind your 35’ cabin cruiser was the answer I was given. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [April 18, 2008, 8:00pm UTC](https://boards.straightdope.com/t/switchable-supercharger/445794/11 "2008-04-18T20:00:07Z")
[QUOTE=Cardinal] If you inject NO2, don’t you also need to inject more gasoline? Isn’t that the point? I thought you needed some system to take care of that too. [/QUOTE] No. You can put a bottle in the trunk, run the lines to the throttle/intake where the NO2 jets are installed and install a switch that is activated by the throttle position. If you have the system “on” and the throttle hits a predetermined point (usually full throttle or close to it), then you’ve got boost. You don’t need to hook up any special fuel delivery supplement. Some guys who are being quite aggressive anyway might opt for high flow injectors or hi-po pumps, but you can take a stock car and give it an NO2 upgrade. ---
**Author:** ![Balthisar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/balthisar/32/2825_2.png) [@Balthisar](https://boards.straightdope.com/u/Balthisar)\ **Post date:** [April 19, 2008, 1:15am UTC](https://boards.straightdope.com/t/switchable-supercharger/445794/12 "2008-04-19T01:15:32Z")
Nitrous only injects more oxygen, in the form of the nitrous oxide. In a modern car, the fuel injection system already keeps things as lean as possible. So, on a modern car, are you sure you don’t need to inject extra gasoline (leave the injectors open longer) so that the extra oxygen has something to actually oxidize? ---
**Author:** ![Pork\_Rind](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pork_rind/32/111_2.png) [@Pork\_Rind](https://boards.straightdope.com/u/Pork_Rind)\ **Post date:** [April 19, 2008, 1:26am UTC](https://boards.straightdope.com/t/switchable-supercharger/445794/13 "2008-04-19T01:26:16Z")
All the guys I know with a nitrous setup spray fuel as well as the NO2. Otherwise you’d just go mega-lean. From [here](http://www.go-fast.org/z28/new_to_nitrous.html). > [@](#): > > I’m sure you’ve heard the terms “wet kit” and “dry kit.” … > A “wet system” is a nitrous system which mixes nitrous and fuel, and feeds it (in a “fog”) into the intake. A “dry system” only feeds nitrous into the intake, and tricks the existing fuel system to add the fuel. ---
**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\ **Post date:** [April 19, 2008, 7:56pm UTC](https://boards.straightdope.com/t/switchable-supercharger/445794/14 "2008-04-19T19:56:36Z")
[QUOTE=Cardinal] I asked this here, and IIRC, the answer is that you’re pretty much describing a turbocharger, which doesn’t have a significant effect until the rpm get high enough, which is a sign you’re really trying to gun it. [/QUOTE] Not only RPMs but throttle/load, too. My two previous cars had intercooled turbos and my current car is supercharged. It is pretty easy to drive around in the supercharged car without even blipping the boost gauge (though the supercharger is obviously spinnign). The turbo cars are boosting anytime I pull away from a stopsign, merge, pass, etc. ---
**Author:** ![Cardinal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cardinal/32/4000_2.png) [@Cardinal](https://boards.straightdope.com/u/Cardinal)\ **Post date:** [April 19, 2008, 8:06pm UTC](https://boards.straightdope.com/t/switchable-supercharger/445794/15 "2008-04-19T20:06:16Z")
OK, I need an explanation for that, because it seems backwards to me. A turbo would have insignificant boost at low rpm, but a supercharger, being on a belt from the crankshaft, would be boosting all the time (right?). ---
**Author:** ![drachillix](https://avatars.discourse-cdn.com/v4/letter/d/48db29/32.png) [@drachillix](https://boards.straightdope.com/u/drachillix)\ **Post date:** [April 19, 2008, 8:41pm UTC](https://boards.straightdope.com/t/switchable-supercharger/445794/16 "2008-04-19T20:41:48Z")
[QUOTE=Cardinal] OK, I need an explanation for that, because it seems backwards to me. A turbo would have insignificant boost at low rpm, but a supercharger, being on a belt from the crankshaft, would be boosting all the time (right?). [/QUOTE] Correct, significant low speed turbo effects can be found when you are operating in low gears at high RPM’s since its how fast the engine is turning that matters, not how fast you are going.