Toymods Car Club Inc: Tech & Conversions => Toyota SC14 Supercharger pros/cons on small diesel

Toymods Car Club
www.toymods.org.au

F.A.Q.

Home

Members

Toymods » Tech & Conversions » Toyota SC14 Supercharger pros/cons on small diesel Show: Today's Posts :: Show Polls Email to friend

Author

Topic

oldcorollas
Forums Junkie

Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003

Re: Toyota SC14 Supercharger pros/cons on small diesel

Wed, 03 November 2004 01:29

wagonist wrote on Wed, 03 November 2004 12:13

Sorry, I don't quite get that.
If the boost reponds linearly to the SC revs (which is relative to the engine revs) then you're going to have max boost at max engine revs.

How do you get max boost at near idle then?
Is it is function of the supercharger design?
or does it vent the excess pressure after a point?

well...
it is a positive displacement pump. it is a function of the SC's design...
that means that for each revolution, a certain amount of air is moved, regardless of rpm. look at the pics below... the air actually moves around the OUTSIDE of the casing, and the inside part where the lobes mesh SEALS the center of the SC...

unlike a turbo, at idle rpm, the SC will move 1.4L of air per SCrevolution. at high rpm, the SC will move 1.4L of air per SCrevolution. the boost is then just a result of how much air doesn't get into the engine! or more simply, if the engine capacity is less than the SC's capacity x the drive ratio, then there will be intake pressure.

http://www.fefcholden.org.au/techinfo/supercharge/images/rootes.jpg

http://www.ic.sunysb.edu/Stu/rrupnick/Supercharger_files/image013.jpg

a turbo on the other hand requires exhaust energy to get the turbine and thus compressor spinning.. you have to wait until there is enough exhaust to move enough intake charge, to make enough exhaust to make enough intake charge to make boost Wink

the downside of an SC is that the losses increase by the square of rpm, ie the power required to drive it increases with rpm. the heat generated will also increase with rpm...
if you are driving the SC at 'normal' SC speeds, then the losses will not be huge (maybe 10hp? at most).

an SC is less efficient at compressing air (i think) since the compression only happens when the room pressure air contained by the lobes, hits the already pressurised air in the intake... causing heat to be generated..

twisted lobe SC's like:

http://us1.webpublications.com.au/static/images/articles/i11/1102_4mg.jpg

have less of a pressure pulsation, and thus less heat generated, and are more efficient...

so anyway, the amount of air moved by the SC is linear with rpm. if the amount of air consumed by the engine is linear with rpm, then the resulting boost will also be linear. there will be fluctations due to engine efficiency and cam profiles, but compared to a turbo? linear boost with RPM..

[Report message to a moderator]

[Message index]

-=] Back to Top [=-

Current Time: Thu Aug 14 11:05:44 UTC 2025

Total time taken to generate the page: 0.004741907119751 seconds

.:: Contact :: Home ::.