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From: davew@shark.UUCP (Dave Williams)
Newsgroups: net.auto
Subject: Re: Superchargers
Message-ID: <1354@shark.UUCP>
Date: Thu, 25-Apr-85 12:43:12 EST
Article-I.D.: shark.1354
Posted: Thu Apr 25 12:43:12 1985
Date-Received: Sat, 27-Apr-85 04:42:13 EST
References: <337@ttidcb.UUCP>
Reply-To: davew@shark.UUCP (Dave Williams)
Organization: Tektronix, Inc., Engineering Computing Systems
Lines: 50
Summary: 


(Referring to superchargers vs turbochargers):
>>Well, they sort of do the same thing but the major difference is that
>>a supercharger forces outside air down the engine's throat (in a carburated
>>engine, the supercharger sits above the carb),

(Referring to a GMC roots type supercharger):
>Not on a "jimmy" I've ever seen.  The blower bolts almost directly to the
>head via a small adapter manafold.  Ones that use carbs have them mounted
>right on top of the blower, as if it were a manifold.  Since carbs require
>vacuum to meter fuel, I don't see how it could be any other way.

The relative position or type of fuel induction system has nothing to do
with whether a system is a turbocharger or a supercharger. (see reprint
of Popular Science article elsewhere in this newsgroup). 
Most drag racing engines using roots type blowers inject some or all of
the fuel ahead of the supercharger as the denser fuel/air mixture helps
seal the clearances in the blower and make it run more efficiently.
The Paxton supercharger, which is an after market unit blows air
through the existing carburetor on an engine. The carburetor must be
placed inside a pressurized box or the carburetors rebuilt so that the
carb doesn't leak from the increased internal pressure.
Turbocharger systems can have the fuel inducted ahead of the unit
or use port injection.
In an earlier item I said that a roots type blower on a drag engine
would eat up 35-50 HP just to drive it. Someone wrote me to ask if
this figure was correct for a Honda V65 motorcycle conversion a company
in Calif. is now selling. I was referring to a 400+ CI V8 running
12-15 lbs. boost. On a 65 CI engine intended for street use (~8-10
lbs boost), the power used to drive the unit would be substantially
less.
Finally, I was questioned by the same party as to my statement about
turbo lag and rotor design, I will say that placing the turbo as
close to the intake valves as possible and using the exhaust gases
as close to the exhaust valves as possible will result in some
improvement in turbo lag, the greatest improvements have come
as the result of improved rotor and wastegate designs.
design 


-- 


                                    Dave Williams
                                    Tektronix, Inc.
                                    Engineering Computing Systems

    "The 6000 Family"
"The workstations that made
Wilsonville famous."