Tom, Dave
Back when I ran my top gas dragster with Hilborn blower injectors we had our
best runs with the scoop on backwards, A lot of the top gas cars ran this
way.
Glen
----- Original Message -----
From: "Marge and/or Dave Thomssen" <mdthom@radiks.net>
To: "Land-speed Racers" <land-speed@autox.team.net>
Sent: Monday, December 31, 2001 3:47 PM
Subject: Fw: Air Scoops
> Hey Tom
> If the scoop opening is so large that flow is larger than the needs of the
> engine, then you could be getting circulation in part of the opening and
out
> part of it, thus creating a negative pressure from the velocity. The rule
of
> thumb for carburetor hood scoop is 10% more area than the venturi area.
> Don't ask me how I know, but if the opening is too big you can actually
> siphon fuel out of the carburetor from the circulation air movement and
> create a fire hazard and lean out the engine. A 5X5 inch opening sounds
> large. Take a look at Al Teague's scoop opening. It might be half that
> area.
> Just a thought
> Dave the Hayseed
>
> ----- Original Message -----
> From: "Thomas E. Bryant" <saltracer@awwwsome.com>
> To: "Land Speed" <land-speed@autox.team.net>
> Sent: Monday, December 31, 2001 4:01 PM
> Subject: Air Scoops
>
>
> > List:
> >
> > I would like to start a new thread discussing air scoops. Many of you
> > know that I have been experimenting with a variety of scoops for the
> > last few years with questionable success.
> >
> > The last meet at Bonneville (the World Finals) I had installed a new
> > RacePak data collection system. When ordering the system, the sales
> > person attempted to discourage me from using a scoop pressure measuring
> > sensor. He gave several good reasons why it was difficult to attain
> > reliable information. I still was not convinced to leave this
> > information to chance, so it was included in the package.
> >
> > The scoop pressure system consists of a tube out the front of the nose
> > of the car (a reference pressure) and a tube going to the scoop. The
> > reading should be zero or a bit positive if the scoop is working as
> > designed. The results were as follows: Once the car was put in gear and
> > started to pull, the scoop pressure went negative. The higher the RPM
> > the more negative until it reached 9.6-9.7 in. water, then it leveled
> > out for the remainder of the run. (It reached 9.6 @ 6400 RPM in low gear
> > and @ 6200 RPM in high gear.)
> >
> > This didn't seem right to me, but I didn't fully understand what might
> > be going on. Before going to the Lakes in November, I did two
> > things...First, with the car running and the computer recording, I blew
> > into the scoop tube by mouth and registered a positive reading, so now I
> > knew what pressure should look like on the readout. I also move the
> > scoop pressure pickup from the side of the scoop to the center rear just
> > below the stacks so that movement of air into the stacks would have less
> > effect on the reading.
> >
> > At the Lakes, on the first two runs, I repeated the same readings that I
> > was getting at the World Finals. The 3rd and 4th runs at the lakes were
> > made after cutting the nose off the scoop, giving about a 5"X5" opening.
> > With that modification the pressures went a maximum of 0.1 inches
> > negative in low, 2nd and the bottom of high gear. Above 5000 RPM in high
> > gear the readings were from 0 to 0.5 inches positive.
> >
> > I don't know how much this was hurting our top speeds (according to my
> > calculations, we were pulling about 3 inches of vacuum in the scoop),
> > nor do I know why the scoop wasn't delivering the air needed. The
> > opening was actually larger than the calculations called for, almost
> > five square inches. Possibly, for some reason, the air was being
> > deflected away from the scoop opening. What do you think?
> >
> > I also have a couple of question for the engineers on the list. (1) What
> > is the conversion of inches of water to psi?
> > (2) What is the conversion of inches of water to inches of mercury?
> >
> > Tom, Redding CA - #216 D/GCC
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