Hey all,
Thought Id help muddy the waters here!
Flow numbers are used for standardization and comparison between products.
I picked 25" of water due to Hughes's use of 25" of water. Thats how much
pressure is required to move a column of water 25" against gravity. Sooo,
You put the TB on a flow bench and crank up the fan! The flow rate is
measured by an inclined manometer and the pressure by a standard manometer.
As I increase the speed of the fan, the air flow through the throttle body
increases AND the negative pressure increases at the bottom of the TB
(sucking through the TB). I can take flow numbers at any negative pressure
up to the maximum of the flow bench! The higher the flow, the higher the
pressure! The more restrictive the throttle body, the higher the pressure
for any given flow rate! Higher pressure= more restriction! or, you want
the maximum flow rate at any given pressure... You can go too far.. a
manhole flows pretty good, but wont work on your truck...
If you test a product at a lower pressure (with a lower associated flow
rate, like 454 CFM @ 10"H20, you can "do the math" and figure out what it
will flow at 25" H20... The flow regime is turbulent all the way, so its
pretty straightforward!
Bruce
----- Original Message -----
From: <bernd@texas.net>
To: <dakota-truck@buffnet.net>
Cc: <Dakotausa@yahoogroups.com>
Sent: Monday, March 12, 2001 6:19 AM
Subject: DML: Re: [Dakotausa] FW: Final flow numbers, 4.7L 68mm Stage I TB
>
> Straight from Holley:
>
> "In the United States, most carburetors are rated in flow capacity at a
test
> pressure of 20.4" of water."
>
> (A 650CFM carb does NOT flow 1000+CFM.)
>
> - Bernd
>
> > I posted this on the DML, but for those who may not be on the DML list,
here
> > it is.
> > Matt
> >
> > > -----Original Message-----
> > > From: Barret, Matt
> > > Sent: Monday, March 12, 2001 10:17 AM
> > > To: 'matt@aol'
> > > Subject: Final flow numbers, 4.7L 68mm Stage I TB
> > >
> > > I've got the FINAL flow numbers for the 68mm Stage I TB, I talked to
> > > Hughes Engines again this morning and Dave was able to squeeze about
30
> > > more cfm out of it! I have listed below flow data at 10" and at 25",
> > > just for you Bernd! ;)
> > > I asked Dave about the 10" test results, he says most Carburetors you
see
> > > are done at 10", so a 650 cfm Carb would be approx. 1025 cfm at 25".
> > > Dave's opinion is, we're not even close to max out on air flow!! So
that
> > > means, a Billet unit from Bruce is going to be the way to go, for
major
> > > air flow! Since I am the test mule for Hughes engines, Its only
costing
> > > me 75 bucks (normal $150) for their service, plus I bought the 68mm
TB.
> > > Total investment about 225 bucks (300 @ normal price), for a 17%
increase
> > > over stock. Not bad, but not GREAT.
> > > I bet 300 bucks will put a nice dent in the cost of Bruce's Billet
unit.
> > > ;) Hey Bruce, can I get one that flows about 1000 cfm??? :)
> <snip>
>
>
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