40mm vs 44mm

QRP · Posted: Wed Dec 24, 2008 10:34 pm Post subject: 40mm vs 44mm

Would a 40mm idf flow the same amount of air as a 44 idf if they both
had the same size venturies ? Confused

Eric_S · Posted: Thu Dec 25, 2008 1:04 am Post subject:

I'll say, no. The butterfly is still different. A 44 choked down will have more pull on the fuel.
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Eric_S

What are all these extra parts?

mharney · Samba Member Joined: June 01, 2002 Posts: 8353

The venturi is the limiting factor. For a given THROTTLE POSITION, the 44 will flow more, but at WOT conditions, the vent will limit the airflow, not the throttle bore size, so long as the vents are in the reasonable range of vents available for the smaller carb.

Art Thraen · Posted: Thu Dec 25, 2008 7:37 am Post subject:

keep in mind that the 40mm IDF/HPMX/DCNF/DRLA /whatever/ will run better on most 1835 and smaller and most 1915s too.

Easy to tune, ETC.. So many times I have experienced installing smaller carbs and the engine picks up power..

Even on 2000cc engines with mild cam and heads.. the 40mms work better.

Eric_S · Posted: Thu Dec 25, 2008 9:41 am Post subject:

mharney · Samba Member Joined: June 01, 2002 Posts: 8353

Yeah, it's the difference between choked flow and loss per unit length of a specified pipe, but the venturi wins hands down in the case of air flow and the length of the "pipe" with air being the fluid.

Ken Taber · Samba Member Joined: October 17, 2006 Posts: 123

I have flowed both carbs on Gene Bergs flow bench and at wide open throttle both with 36mm venturies the 30 flowes 2.67" and the 44idf flowes 4.57"

Ken Taber · Samba Member Joined: October 17, 2006 Posts: 123

Sorry I just posted 30 and it should have been 40 idf flows 2.67 " and the 44 isdf flows 4.57"

Eric_S · Posted: Thu Dec 25, 2008 9:01 pm Post subject:

Hi Ken,

Have you flowed the 48IDF like we spoke of at Superior Machine?
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Eric_S

What are all these extra parts?

QRP · Posted: Thu Dec 25, 2008 9:24 pm Post subject:

I am running a single 40 with 32 vents now.

if the 44 with 32 vents flows more at WOT will I loose some of my lower rpm torque ? Confused

ERIC_S
do you have the results from the 48 test ?

Ken Taber · Samba Member Joined: October 17, 2006 Posts: 123

Yes I have flowed the 48 idf and stock with 45mm velosit stack and 40 mm venturi it flows 7.3 . After modifing the whole carb I can get it to flow 10.81 with a 43mm vent.

Eric_S · Posted: Thu Dec 25, 2008 10:39 pm Post subject:

Ken,

You were telling me about your mods to the 48IDFs. Can you do that to mine? Have you flowed any CB update kitted carbs? I have a set of 44s with updates to try. Check your PM.
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Eric_S

What are all these extra parts?

mharney · Samba Member Joined: June 01, 2002 Posts: 8353

Ken Taber · Samba Member Joined: October 17, 2006 Posts: 123

Mark you asked about 48 ida. Doug Berg on their bench flowed the stock 48 IDA with 42 mm vents. It flows 8.6. A fully profiled 48 IDA with 42 mm vents and custom Berg velosity stack flowes 10.86 . Doug Berg is the one that showed me how to profile the Webers. and Eric I can do your 48 IDF's. and no I have not flowed the 44 idfs with the CB update yet.

vwairheads · Posted: Tue Nov 29, 2011 12:42 am Post subject:


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