Gramma_Benz

Courtesy of Waldig from the SRT6 Forum:

http://youtu.be/h9Exe2rxYgc

chris.bachman

That's interesting because I was under the impression it cut out while cruising under certain RPM's. Is it possible that this is different than a C32's programming?

Autotechnica

That would explain why our cars drink so much gas. They're pretty much always engauged unless you're at a dead stop.

I have a boost gauge on my DashDAQ. Throughout my daily commute to work I rarely hit boost, just vaccum. It makes me wonder why these things are such gas guzzlers.

Beaker

Yeah I'm with you on this one! Always vacuuming especially in traffic/city driving.. ah well.

AMGFTW

There is parasitic loss whenever the supercharger clutch is engaged. Just because you are not making any boost has nothing to do with it. When the supercharger is spinning there is more rotational mass for your engine to overcome. Hence the shatty gas mileage.

Autotechnica

Good to know. That was the next question I was going to ask. Whether or not the S/C kicks in even though you're just making vaccum. So I guess the S/C engaugement is based on RPM and not load or throttle position. There must be quite a big parasitic drain, because without boost there's no need to run more fuel. What's the point of having a S/C clutch if it kicks in at just 1300RPM? It doesn't really save you any fuel, basically just another part to go bad. I wonder if there's a way just to keep it on all the time. IHI is crap IMO, wished they had used a more common roots type or something.

Newzchspy

Jerry and I played with a switch to turn off the Mag Clutch off the SC. Car ran like a C36 and mileage was not that great either. Better to just leave it on.........

Autotechnica

My car already consumes more gas than a Yukon truck, so gas mileage isn't really an issue for me. If it takes away the low RPM jerkiness then I'm fine with the increased consumption. I rarely do any stop and go driving. I'm always on the highway anyways.

What do you mean it ran like a C36, can you elaborate? I've never driven a C36, but from what I recall they weren't very fast. I can't see this affecting normal driving too much as it really only shuts down when you come to a stop.

thanks,

Bry

Newzchspy

You lose about 100 HP, so thats about what a C36 is??

gt4awd

My assumption is the clutch has variable amperage, and what we see in this video is a low amperage applied to spin the rotors allowing better air flow. There is no boost for a reason... Technically the supercharger is never disengaged completely. I still consider no boost to be disengaged, and a little led light isn't going to change my mind on that.

mikekuriger

your assumption would be wrong. The supercharger engages at approx 1800 rpm. It completely disengages under 1800 rpm. (unless you're in park of course)

You wouldn't want to leave the SC disengaged all the time, not only would you get no boost but now you have a large restriction in your intake airflow.

There is no "low amperage" feature on the sc clutch. It's on or off.

gt4awd

So when I'm at 6k RPM naturally aspirated when the supercharger should be boosting 18PSI where is that boost going? Why can't I hear any boost being produced and bypassed? Why does my boost gauge remain at 0 PSI?

Lenin

What gauge do you have? Maybe it's not setup correctly. Only shows vacuum?

gt4awd

It doesn't show vacuum at all. Boost only gauge. I can run through the gears without any boost by applying less throttle... Basically you work the throttle up as RPM's rise. You're only applying enough throttle for a naturally aspirated burn. Boost line is tapped into coupler for y-pipe. Sunpro Analog boost 0-30PSI. I see an average max boost of 20PSI on this gauge.

Lenin

I see. Under low load you can get to 6K RPM and not get the SC generate any boost. The zero boost may have to do with how the SC clutch gets engaged.

gt4awd

Exactly what I'm trying to say here... AFIK, our supercharger doesn't have a bypass. The reason of course being that it has the electromagnetic clutch. If my boost gauge shows 0 PSI the supercharger is not engaged. I still think what we see here is more of a standby mode, or as previously thought to spin the rotors slightly allowing better air flow while the engine is operating as naturally aspirated.

Dingleberry

Sorry bud, you have no idea what you're talking about.

If your boost gauge is showing 0 PSI and you are above 1300RPM in drive, then your supercharger is engaged and you are in vacuum. Boost is a function of load and RPM.

Lenin

The bold statement is not correct. The SC works in the vacuum (minus) and boost (plus) territory. Somehow you have to get from vacuum to zero (and then to boost). Maybe if you had a vaccum/boost gauge vs. just boost it would be clearer.

gt4awd

No, I understand that... What are you trying to say though? That because my gauge doesn't show vacuum I can't see the changes in vacuum pressure. There's still no boost..?

Autotechnica

I don't fully understand how superchargers work. However, I think the confusion is the following. If boost is produced by the S/C, and the speed at which the supercharger spins is directly related to the crank speed, then why is it at high RPM it's possible to create 0psi of boost. Where is that air going? If you're at 6000RPM and the S/C is engauged, where is that boost generated going? IMO the S/C engauges when there is enough load. I still don't think it engauges 100% simply because you're over 1800RPM. As gt4awd mentioned, there is no dump valve and there is also no bypass or recirculation valve, a S/C doesn't need one (unless you want variable boost at the same RPM). Perhaps it's something related to the way our S/C's are designed. A turbo works by recirculating exhaust gas to spool the turbo, therefore it would make sense that boost is based on load. However, explain how a S/C can create a different amount of boost based on load at the same RPM. A S/C isn't based on exhaust gas, it's directly proportional to crank speed (this is what I understand). If not, please educate me.

BTW, I just want to learn how this works like many people here. Not looking for an argument. This is a really interesting thread, keep it going.

Bry

mikekuriger

it seems like some of you may be a bit confused as to how an engine works. the vacuum you see is a result of the pistons attempting to pump air through a closed (almost) throttle plate. Since air is pumping out at a faster rate then it's being let in, you get vacuum.

Once you open the throttle, more air is allowed in, motor can pump more air, rpms rise, etc. Once your SC is spinning fast enough it will begin to force more air in. When the sc begins pumping in air faster than the motor can pump it out, you see boost.

If you make the engine more efficient (cams headers, headwork, etc), you will get more power and see less boost on your gauge. You will be pumping more air through the engine which is where the power is actually coming from. that explanation is for another thread though.

hope this helps!

mikekuriger

I'm not sure how the MB supercharger is plumbed, but usually if there is NO dump valve then instead they simply place the throttle body before the supercharger. Under light load, the supercharger itself is in a vacuum and has no air to pump, creates no drag, creates no heat. It's still spinning at the same rpm however. Once you open the throttle and let the air in, the SC has something to pump and boost is made immediately.

You can see this behavior with your own home vacuum cleaner. Ever been using the vacuum hose and plugged it up completely? What happens to the motor RPM? It spins faster right? But why? Seems like it should slow down. But in fact, once you block the airflow there is no more air for the vacuum to pump. The pump is spinning in a vacuum so it spins faster.

Autotechnica

That makes perfect sense. Thanks.

gt4awd

+1, agreed... So, basically the supercharger is engaged, and is spinning relevant to the crank RPM. However, there is no boost as air is simply passing through the charger?

splinter

^ mikekuriger nailed it.

Know you’ve achieved increased output on your 318i with a roots blower.

The C32’s Lysholm is far more efficient. :)

http://kennebell.net/KBWebsite/Commo...romcatalog.pdf
http://kennebell.net/KBWebsite/Commo...efficiency.pdf