Monday 12th May 2003

Negative Supercharging

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[ChrisD]

To me, this sounds like complete bullshit. They're even blaming catalytic convertors for AIDS on that page... And, well, what has one got to think of a page that describes every kit they sell as consisting of "major hi-performance/hi-tech parts"... reminds me of certain other car-related onlineshops.

[deltaf]

Called pulse tuning. Theyve been doing it for years, but, it only works at one engine speed and to lesser degrees at harmonics of that engine speed.
It does make a difference, but nowhere anything like the effects youd get from a supercharger.

[ATG]

Certainly very hard to see how a small additional pressure drop in the cylinder prior to the intake stroke commencing could make more than a fractional difference to the toal mass of air/fuel in the cylinder after the intake stroke has finished.

It's also very dodgey talking about creating a partial vacuum behind a moving charge of gas, unless the bulk velocity of the "charge" is pretty close to the speed at which the individual molecules are winging around in the hot gas (which I guesstimate is about 600ms-1 or 1500mph). If you've got exhaust gas velocities of 1500mph, surely your engine is wasting a lot of energy?

p.s. the pulse tuning sounds interesting. Given the resonances bit, I assume it is using the exhaust manifold like an organ pipe, getting a standing wave going so that the pressure in the cylinder rises and falls as the sound waves bounce up and down the manifold. Trick would be to shut the valve when the cylinder was rarified.

>> Edited by ATG on Tuesday 13th May 10:51

[GreenV8S]

Yes it seems to me they're describing perfectly conventional engine tuning. Didn't understand their bit about charge/water temperatures though. Along the lines of a hot charge burned faster/better/something and produced a power gain, more than enough to compensate for the loss in charge density. I would expect exactly the opposite, and if there *is* a significant difference in burn speed don't you just adjust the ignition timing to compensate? Not at all convinced.