Engineering question

[Arkaign]

I was thinking of how turbochargers and superchargers enable engines to make more power, at the expense of added heat/fuel usage/moving parts. Also in my considerations were the reality that for most daily driving, grinding through rush hour traffic jams, the excess power is unnecessary for the most part.

From what I can tell, having owned N/A, Turbo, and SC vehicles, is that on many turbo setups, if you shift early and don't accelerate too hard, you can keep the boost from hitting, and thus achieve about the same fuel economy as a NA version of the same setup. This might be more difficult to achieve with low-rpm turbos like the setup in the 335i, but I'm not sure. I also know that when I put a SC on my 5g Prelude, my fuel economy took a big dive no matter which way I drove it. Before the SC kit, I could get about 23/30mpg, and after, it was more like 18-24.

My question is this : how hard would it be to engineer a dual-intake system for a motor, one side for N/A, and one side for F/I, or some other manner of having the ability to enable/disable the forced induction apparatus by the flip of a switch. I know with the belt-driver SC systems, this might get confusing, but could it be done like how the A/C compressor doesn't put drag on the motor when it's not on?

Thanks for any and all input!

 

[vi edit]

Subaru has the "SI" drive dial in their turbo cars that dials back the boost for economy.

It's a "soft" fix because it's a computer controlled setting rather than a physical shutdown of the turbo.

 

[LTC8K6]

Supercharger clutch.

Mad Max had one.

 

[Demon-Xanth]

Wouldn't be hard at all. Just have a solenoid open and close a butterfly valve that bypasses the turbo. Possibly just use the wastegate to regulate boost to "0". (though you'll still have some parasitic drag). With superchargers you'd need to replace the exhaust valve with a clutch, much like what are on cooling fans and A/C compressors already.

 

[Vic]

With a turbo it's really not necessary. Just keep your foot out of the boost.

 

[GoatMonkey]

You would probably want some way of changing your compression ratio when the boost is turned off. Many factory boosted cars run a lower compression ratio. You would want to have a way to increase that since your fuel's octane rating hasn't changed.

 

[exdeath]

The problem is the engine internals and compression ratio. If you boost obviously you make more power and eat more fuel. But if you don't boost, the low compression ratio isn't as efficient and still gets worse mpg than the same engine would N/A with higher compression ratio. Also misc assorted other things involved with forced induction: added weight of the intercooler and plumbing, blower/turbos, etc, bigger injectors to flow under maximum power conditions that are less accurate and cause poor MPG at lower flow rates, etc.

With turbos, it doesn't matter what their boost threshold is or how early they spool, you can control their influence entirely through wastegate size and opening behavior.

With a supercharger, many have an internal butterfly situated just at the inlet, known as a boost bypass. Under idle and cruise conditions this butterfly stays open allowing air to bypass the rotor pack and allowing the supercharger to freewheel in vacuum and consume no more than maybe 5-10 HP of parasitic loss. The Eaton M62 is an example of a clutched blower that activates this internal bypass and the pulley clutch simultaneously to eliminate even that loss.

So it can and has been done; most all superchargers have some kind internal or external bypass that allows the air to come in through a single induction path and meter while bypassing the blower. Turbos can be controled by the wastegate.

The Mad Max setup (even though it was fake in the movie) doesn't work for several reasons:

1) no bypass for when the blower is off. With the Scott Injection throttle plate up top, and no internal bypass provision in the 6-71 type blowers, there would actually have to be a second throttle opening and linkage somewhere on the lower intake. And since the injectors are up top, there would also have to be a second set of injectors behind the blower as well. A bypass system can only work if it is designed to use a common induction and metering path and common point of fuel delivery. This means the forced induction and naturally aspirated paths must run parallel and split only after the filter and meter, and merge before fuel injection; something which a modern supercharger with a boost bypass valve achieves, as does any turbo system.

2) The Scott Injection system was merely an intake hat and throttle/injector plate. There is no air cleaner/filter... Remember all that red clay and dirt on the car in the second movie... that engine would have been destroyed in days.

3) The sudden engaging of a stationary supercharger rotor pack at RPM and under load, especially the size of a 6-71, would at the very least throw a belt, and with a cog drive most likely break your crank and/or bearings, shear the crank key, rip off the supercharger snout, etc. The electromagnetic clutch would need a timer to engage slowly and slip for several seconds to overcome the blowers stationary inertia before engaging. Or it would be an automatic system that engages the blower only at appropriate RPM and load (ie: always in use beyond a certain load-RPM and integrated into the engine control package seamlessly; not user switchable)

 

[The Boston Dangler]

a few years ago, mercedes had a sc engine that used a clutch on the blower and a butterfly valve on the intake.

 

[exdeath]

Originally posted by: The Boston Dangler
a few years ago, mercedes had a sc engine that used a clutch on the blower and a butterfly valve on the intake.

Eaton M62

 

[Arkaign]

Interesting guys, I'm happy I asked I learned a lot!

 

[T2urtle]

My SER pretty much has a little best of both worlds. stock SR20DE motor with a T3/T4 turbo, Its a rather average sized turbo. bigger then most factory turboed cars but average in the aftermarket world.

I have a stock motor up untill 3 grand and then after that i go boosting. now driving and shift under 3 grand is easily done and best for MPG in ANY car. I like the setup a lot, its similiar to having a switch for the turbo. actually i almost have exact control over the turbo

 

[compman25]

Originally posted by: exdeath
2) The Scott Injection system was merely an intake hat and throttle/injector plate. There is no air cleaner/filter... Remember all that red clay and dirt on the car in the second movie... that engine would have been destroyed in days.

Not if they employed the super high tech zanejohnson air filter.

 

[LordMorpheus]

Originally posted by: LTC8K6
Supercharger clutch.

Mad Max had one.

That's the first thing in my mind when i read this thread's title.

 

[Colt45]

Could open the wastegate on a turbo.. then no boost. Or you could just not hammer on the gas pedal.