Avanti Supercharger!

[mfg]

Regarding a Paxton Supercharger's impeller, volumetric efficiency goes up the higher the impeller's tip speed....True?

[brad]

The boost goes up as a square of the RPM. double the RPM get 4 times the boost. Up to a point when the tips of the impeller reach speeds where there are shockwaves, the boost stops. (The tips can actually break the sound barrier).

[mfg]

12 hours ago, brad said:

" Up to a point when the tips of the impeller reach speeds where there are shockwaves, the boost stops. (The tips can actually break the sound barrier)."

 Answer....FALSE!.....and Brad said it better than I could!

.

 

[Dwight FitzSimons]

Do y'all know the formula for boost as a function of RPM, or can you point me to a source?

--Dwight

Edited July 5, 2023 by Dwight FitzSimons

[mfg]

1 hour ago, Dwight FitzSimons said:

Do y'all know the formula for boost as a function of RPM, or can you point me to a source?

--Dwight

Not quite sure, but I think Brad's first sentence answers that question.

[Geoff]

Dwight, I found on auto.howstuffworks.com that a compressor spinning at 50k RPM is going to give somewhere between 6 and 9 PSI of boost. It also stated that centrifugal supercharger impellers can spin about 55k RPM, give or take.

They mustn't know about https://www.rotrex.com/ superchargers though, a company which produces four supercharger models. Their two largest models spin at 90k RPM, their mid-size model spins at 120k RPM, and their smallest spins faster than 200k RPM. Those impeller speeds are closing in on some turbocharger impeller speeds, which Garrett claims can spin up to 350k RPM.

I've also heard this expression before, "boost is a measurement of restriction." Thinking about that more, that makes sense. One won't be 'filling' anything if there's a way out, and the cleaner/larger the way out the faster the escape and the lower the built up pressure.

I read an interview with a Vortech engineer who suggested 115-119 LSA or else boost escapes out the back, and I recall 1025's engine, RS1021 had quite a bit of valve overlap, pressurizing the exhaust. That car accomplished what it did with 2" diameter exhaust pipes, but with boost pressure forcing out the exhaust, the pipe diameter variable for power becomes somewhat moot.

https://ateupwithmotor.com/terms-technology-definitions/turbocharging-and-supercharging/
https://auto.howstuffworks.com/how-much-horsepower-does-supercharger-add.htm
https://auto.howstuffworks.com/supercharger.htm
https://www.motortrend.com/how-to/torqstorm-offers-a-great-supercharger-for-mild-mannered-engines/