ramyar

If I'm understanding the comparison link in my earlier post correctly, it looks like with a root supercharger, the compression occurs in the engine (as in between the supercharger and the cams/top end). Woth the centrifigal, though, it sounds like it compresses it internally and then passes it to the engine.

Not exactly sure how this can be though, but it could be that since the centrifigal does this internally, it acts as a buffer and relieves some stress/pressure off the cams.

iversonm

The centrifugal will compress "in the engine" as well. All it does is push air. A positive displacement supercharger does produce more boost at low rpm, as air cannot flow backwards through it. A centrifugal unit is not efficient at low rpm. The part that does not make sense is the camshaft. All it does is open and close the valves. Pressure an the back side of the valves would tend to open them, easing pressure on the cam. I might be missing something, but this doesn't seem to pass the smell test.

sirch

On a turbo and centrifical superchanger the air is compressed outside the engine and then put into the engine. A root style superchanger the air is compressed on the inside. I hope that makes sense. I can try to make it clearer I just do not want to put in a whole bunch of tech stuff up, and prefer to explain it in simple terms.

iversonm

No, that makes no sense whatsoever. The supercharger pumps air into the intake plenum faster than the engine consumes it. Whether the supercharger is bolted to the intake manifold, bolted to the alternator bracket, or connected by a long hose 100 yards from the engine won't change this fact. (That's 92.3 meters for those outside the USA.) All a supercharger is an air pump. If you think it is an issue with charge cooling, positive displacement blowers can be plumbed into aftercoolers in the same manner as the other varieties.

Please feel free to post technical jargon as to why one model is rather more adept at eating cams than the other. I feel I have a sufficient number of postgraduate degrees in engineering to absorb it.

ramyar

It doesn't completely sink in with me either, but what I can infer from the explanations I've read are:
1. forced induction does indeed "blow air" into the engine, regardless of whether it is a root, screw, or centrifugal (or even a turbo)
2. regardless of the type, there is pressure on the engine side of the forced induction device

I think the difference is how that pressure is delivered. It sounds like with centrifugal, it is pressurized within the supercharger and then delivered/pumped/blown (whatever word we'd prefer to use) into the engine. Whereas, with the root it is delivered directly to the engine. This difference seems to mean that with the centrifugal, there is a buffer (the supercharger itself is the primary pressurizing chamber) and therefore the boost is more regulated than if it is just dumped directly into the engine (as with root the lead between the supercharge and the engine is the primary and only pressurizing chamber). This would suggest the overall delivery of the air is smoother with the centrifugal.

Either way, I don't really see how the cams will undergo much more stress at a measly 6-9psi. Perhaps this is more of an issue with very high boost as in racing/towing/hauling applications.

asickmf

i'm more worried about paying for 20" p-zero neros at $435 a whack than camshafts.

iversonm

Thanks for trying to clarify argument, but it still does not hold water in my mind. The "pressurizing chamber" is the space between the supercharger and intake valves. The air is not pressurized in the supercharger, it is pumped from one chamber to another. Pressure is created by the fact that the engine uses air slower than the supercharger is moving it into the intake.

The argument about the large plenum is also irrelevant. It indeed may be good to have such a plenum. However, there are centrifugal setups that have but a short pipe to the intake, and there are positive displacement superchargers with extensive aftercooler plumbing, so plenum size is not a related to supercharger type. There's also no real reason you couldn't fit a centrifugal unit in the valley of a V-8 engine for that matter. I suspect such a large plenum would tend to create significant throttle lag, As it would take more time to pressurize a larger volume.

Centrifugal units are inefficient at low rpm, so they generate comparatively less boost at low speeds. Perhaps this is what the poster that brought up the topic was referring to.

However, all of this discussion is waste, as I was asking for a reasoned argument on how any of this is bad for the camshafts. I'm still waiting, and I suspect that won't change anytime soon.

keynon

I need this for my 530I 2004 E60. Will it work?

Thanks,

Ken

AlexFW

Search for messages by this member :
http://forums.e60.net/index.php?showuser=2635