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Author Topic:   Supercharging question
SteveLaRiviere
Administrator

Posts: 33371
From: Saco, Maine
Registered: May 99

posted 11-09-2002 08:49 PM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
Why aren't the throttle bodies put before a centrifical supercharger? What effect would that have on throttle response?

On Roots type blowers the throttle body assembly is put before an impeller.

Anyone have any theories?

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'70 Mustang Mach 1 - '72 Mustang Sprint - '94 F-150

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Moneymaker
Administrator

Posts: 19704
From: Lyons, IL, USA
Registered: May 99

posted 11-10-2002 01:10 AM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
Because they blow Steve.There will be too much pressure loss by trying to suck air in front of the blower charge. Roots type blowers are most effciant when they suck.
More tomorrow when I am awake.

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Alex Denysenko
Co-Administrator and Moderator

NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
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The Barry of BarrysGrrl

Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"

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Wulfgar
Gearhead

Posts: 193
From: SAn diego, CA, USA
Registered: Oct 99

posted 11-10-2002 11:41 PM     Click Here to See the Profile for Wulfgar   Click Here to Email Wulfgar     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Moneymaker:
Because they blow Steve.There will be too much pressure loss by trying to suck air in front of the blower charge. Roots type blowers are most effciant when they suck.
More tomorrow when I am awake.


so to sum things up
Superchargers blow
Blowers Suck

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Moneymaker
Administrator

Posts: 19704
From: Lyons, IL, USA
Registered: May 99

posted 11-10-2002 11:48 PM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
Well that's an oversimplification, but yes roots blowers are more effciant drawing air in.

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Alex Denysenko
Co-Administrator and Moderator

NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Professional Manwhore
The Barry of BarrysGrrl

Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"

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V8 Thumper
Gearhead

Posts: 3467
From: Orange, Ca. United States of America
Registered: Dec 2001

posted 11-11-2002 12:20 AM     Click Here to See the Profile for V8 Thumper   Click Here to Email V8 Thumper     Edit/Delete Message   Reply w/Quote
...then is a centrifugal supercharger essentially a belt-driven turbocharger?

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1965 GT coupe, 333ci aluminum headed/solid cammed stroker, four speed, 3.70:1 9"

All Blue Oval, no blue bottle
http://mustangsandmore.50megs.com/V8Thumper.html

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Wulfgar
Gearhead

Posts: 193
From: SAn diego, CA, USA
Registered: Oct 99

posted 11-11-2002 12:31 AM     Click Here to See the Profile for Wulfgar   Click Here to Email Wulfgar     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Moneymaker:
Well that's an oversimplification, but yes roots blowers are more effciant drawing air in.


I know Alex. I was just playin. hehe
Forced induction is still out of the scope of my understanding anyhow. But maybe one day.....

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SlowFord
Journeyman

Posts: 22
From: So. Cal
Registered: Dec 2001

posted 11-11-2002 11:38 AM     Click Here to See the Profile for SlowFord     Edit/Delete Message   Reply w/Quote
What is easier to do, blow air through a straw or suck air through a straw? That is why most supercharged fuel injected Mustangs that I have seen will use a very large Mass Air sensor but get away with a relatively small throttle body. It is easier to push air through a small throttle bottle than to pull air through a small Mass Air sensor.

V8 Thumper: Yes, centrifugal superchargers are like a belt driven turbo. The Powerdyne on my 1988 Mustang even has "turbo lag" and doesn't really show itself until about 2,800 RPM. It did knock over a full second off my 1/4 mile time, though, so I won't complain about a little lag time.


[This message has been edited by SlowFord (edited 11-11-2002).]

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Daniel Jones
Gearhead

Posts: 495
From: St. Louis, MO
Registered: Aug 99

posted 11-11-2002 06:28 PM     Click Here to See the Profile for Daniel Jones   Click Here to Email Daniel Jones     Edit/Delete Message   Reply w/Quote
>V8 Thumper: Yes, centrifugal superchargers are like a belt driven turbo.
>The Powerdyne on my 1988 Mustang even has "turbo lag" and doesn't really
>show itself until about 2,800 RPM.

What you're experiencing with the Powerdyne is the non-linear output of a
centrifugal compressor. Axial (Latham) and centrifugal (turbos, Vortech,
Paxton, etc.) superchargers produce flow that is proportional to the square
of the impellor speed. Double the speed and you'll quadrouple the flow.
That may seem like a good thing (more flow = more boost) but it's not
necessarily. The non-linear flow curve limits the working range of a
centrifugal supercharger. Gear one to produce meaningful boost at 2000
RPM and you'll over-boost the engine at 6000 RPM, unless the static
compression ratio is very low. The linear output of positive displacement
blowers allows them to operate over a wider RPM range without over-boosting.
Turbos get around this by using wastegates which bleed off boost above a
certain level. I suppose you could do the same with crank driven centrifugal
compressors but you'd run into drive reliability problems. There have been
various transmission schemes applied to centrifugal superchargers to extend
their RPM range but I don't know of any that have made it to market for
street vehicles. The drive system (gear, belt, and ball and race drive
systems have been employed by various manufacturers) is usually the weak
point (long term reliability) of a crank driven centrifugal system.

Turbos are exhaust driven centrifugal superchargers, so they also have the
non-linear output but turbo lag has an added dimension. Even if the engine
RPM is high enough to for the turbo to make meaningful boost, the RPM of
turbo is a function of exhaust gas flow which is a function of the throttle.
If you're cruising at 3000 RPM, the turbo will not be spinning as quickly
as if the throttle is wide open. Since the turbo has mass, it takes some
time for the turbo to spin up once the throttle has been opened. That time
to spin up is turbo lag.

Dan Jones

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V8 Thumper
Gearhead

Posts: 3467
From: Orange, Ca. United States of America
Registered: Dec 2001

posted 11-11-2002 06:36 PM     Click Here to See the Profile for V8 Thumper   Click Here to Email V8 Thumper     Edit/Delete Message   Reply w/Quote
OMG Dan, I'm going to have to insist that you post more often. Great information as always, thank you

------------------
1965 GT coupe, 333ci aluminum headed/solid cammed stroker, four speed, 3.70:1 9"

All Blue Oval, no blue bottle
http://mustangsandmore.50megs.com/V8Thumper.html

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SteveLaRiviere
Administrator

Posts: 33371
From: Saco, Maine
Registered: May 99

posted 11-12-2002 04:13 PM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
We are experimenting with a Paxton ball drive system. My friend has a theory that by moving the throttle plate to the inlet side of the compressor, he can have more control at the throttle plate and more response.

Currently, the system builds pressure on the inlet side of the throttle plate. By moving the throttle plate to in front of the compressor, the throttle plate would be at vacuum, like a normally asperated engine.

He notices that the way his system is set up now, when he backs off the throttle the pressurized air has a tendency to keep the throttle open. He had to overcome this with a stronger return spring. His view is that throttle plates are designed to operate under vacuum, not pressure.

One the things we're wondering about is will having the compressor under vacuum cause it to suck in compressor lube past the seals.

We're not trying to outthink the engineers of these systems, we're just wondering why they don't set up these systems this way.

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'70 Mustang Mach 1 - '72 Mustang Sprint - '94 F-150

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Moneymaker
Administrator

Posts: 19704
From: Lyons, IL, USA
Registered: May 99

posted 11-12-2002 07:40 PM     Click Here to See the Profile for Moneymaker   Click Here to Email Moneymaker     Edit/Delete Message   Reply w/Quote
The enclosed carb systems have a vent for just that purpose.

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Alex Denysenko
Co-Administrator and Moderator

NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Professional Manwhore
The Barry of BarrysGrrl

Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"

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BarrysGrrl
Gearhead

Posts: 1356
From: Illinois/Indiana & parts inbetween
Registered: Jan 2002

posted 11-12-2002 07:47 PM     Click Here to See the Profile for BarrysGrrl   Click Here to Email BarrysGrrl     Edit/Delete Message   Reply w/Quote
See, Alex . . . . .


(Sorry to all who were looking for actual advice. Not my area. See above or below. Have a nice day!)

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Beth
Head Cheerleader for Moneymaker Racing!
I'm so proud of Alex & Tony!

"My best friend is the one who brings out the best in me." - Henry Ford (for Alex)
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jsracingbbf
Gearhead

Posts: 1677
From: Batesville,MS. , U.S.A.
Registered: Mar 2002

posted 11-12-2002 11:10 PM     Click Here to See the Profile for jsracingbbf   Click Here to Email jsracingbbf     Edit/Delete Message   Reply w/Quote
So basically what your saying is "Injection is nice but I'd rather be blown?" personally I like injection........ as long as Im not the inject---EE

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Jerry Smith
69 Mustang Pro ET Drag
70 Mustang retired former footbrake car
"Even a blind Hog can find an acorn every now and then"

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Fastymz
Moderator

Posts: 11429
From: Reno Nv USA MEM#1240
Registered: Apr 2001

posted 11-13-2002 01:13 AM     Click Here to See the Profile for Fastymz   Click Here to Email Fastymz     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by jsracingbbf:
So basically what your saying is "Injection is nice but I'd rather be blown?" personally I like injection........ as long as Im not the inject---EE



LOL,you beat me to it,thats my favorite saying.

SCOOP

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oddly obsessed with big scoops on little Mustangs

2.26 60'S
14.9 @ 90.86MPH

65 coupe,351w,C4,Big Boss 429 hood scoop,8"3.40 TracLoc,Cragar SS,Black Suede.

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