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

Anyone have any theories?

------------------
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:

---

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

------------------
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

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

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.....

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.

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.

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

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.

------------------
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

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

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

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

------------------
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.