Do I require to vary the boost pressure with respect to an increase or decrease of throttle (engine rpm)?

*Note: The supercharger is electrically driven (motor) and not by engine crankshaft.

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    An electric supercharger? You mean like those leaf blower motors? What did you put that in? – race fever Mar 30 '16 at 13:27
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    That "supercharger" is more of a air flow restrictor than anything. – race fever Mar 30 '16 at 13:29
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    Supercharging adds restrictions?! – user16006 Mar 30 '16 at 13:31
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    @racefever, Related if you missed it: mechanics.stackexchange.com/q/27626/12030 – JPhi1618 Mar 30 '16 at 14:22
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    @user16006 Also, edit your question to clarify what you are trying to do. A lot of it has been addressed in the comments but really should be in the question so other users don't have to read all the comments to figure out what you are trying to do. Otherwise your question will likely get closed as too broad. – Move More Comments Link To Top Mar 30 '16 at 16:26

I gotta first apologize to user16006. I was looking for ways to stop you from modifying your motorcycle because the idea seemed silly. But who am I to do that? I mean, modding cars is one of my passions. I'm gonna stop being a dumbass and try to help you.

On your motorcycle, you want to limit boost pressure to when the throttle is fully open. The reason is that the engine is tuned to provide the most fuel and timing under those conditions. If you are not going full throttle, the engine is tuned to save fuel. When you boost an engine you need more fuel. To limit damaging the engine, just turn on the supercharger during full throttle with a microswitch.

Now, you are going to be putting more air into the engine. You need to balance out the ratio between air/fuel. A fuel injected engine means you will either need a bigger injector from a bigger CC engine, or put another injector that only works when the supercharger does.

You are also going to need to tune the engine in order to get the most performance out of it. It depends on how much boost you can get out of it. Get yourself a boost gauge from a diesel vehicle (you can find those in scrap yards) and hook it to the intake manifold. For every .3 bar of boost you are going to want to test removing one degree of timing.

Now, to directly answer your question:

Do I require to vary boost pressure with respect to increase or decrease of throttle (engine rpm)?

In your case the answer is yes.

Good luck OP! :)

  • Pretty cool answer. – DucatiKiller Mar 31 '16 at 0:50
  • You are saying 3° of timing per bar (or 14 psi) of boost? That's good to know. – Pᴀᴜʟsᴛᴇʀ2 Mar 31 '16 at 1:16
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  • @Pᴀᴜʟsᴛᴇʀ2 That is just a very safe approach since I don't have a clue as to what timing the OP's motor runs. In turbo Porsches I actually add timing at the top if the cams will take it. – race fever Mar 31 '16 at 12:26
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    @Zaid I do love some Roadkill. :D – race fever Mar 31 '16 at 12:26

I'm going to say it's not necessary here.

An "electric supercharger" like a leaf blower is more a pump than a compressor. The amount of extra air that isn't that much; it should be quite readily compensated for by the fuel injection management.

  • Someone remind me to post up calculations when I have some time – Zaid Mar 31 '16 at 6:00
  • How do you know how big is the supercharger? If someone would disconnect Mercedes compressor from the belt and installed suitably powerful electric motor to drive it - would you still call it a leaf blower? – Agent_L Mar 31 '16 at 9:33
  • @Agent_L The 'powerful electric motor' only has 12.6volts. How powerful of an electric motor can you have? Additionally it's a very small motorcycle. Do you think the tiny stator in that can drive a 'powerful electric motor'? – DucatiKiller Mar 31 '16 at 19:06
  • @Agent_L it takes a lot of energy to compress gas. It's why air-con compressors in cars remain belt-driven. If you want to run a supercharger off electricity I suspect you'd need something in the kW range to get it to work. With just 12-13 V on hand, the current demand would be huge. – Zaid Mar 31 '16 at 19:11
  • @DucatiKiller You're making another assumption out of the blue. He never said it's 12V, he never said it's powered from the engine. – Agent_L Apr 1 '16 at 7:59

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