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What's the largest venturi available for 40 Dells ?

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Craig Torrens 6 times Australian, 7 times State Hillclimb Class Champion

8,040 posts · joined Jan 2003 ·

#642924
As the title says..................

can I get 36mm for them ?


hellbugged 48's and straight cuts

5,080 posts · joined Apr 2003 ·

#642999
good luck finding vents for them Craig..............what are the chances of you having a mate with a CNC machine, i have heaps of vents to copy?

dangerous 23 Windows of Awesome

5,901 posts · joined Jan 2005 ·

#643010
apparently 38s will fit from a 48dell?

When in doubt, bore it out.
westi wrote:That's mad Alan.

Craig Torrens 6 times Australian, 7 times State Hillclimb Class Champion

8,040 posts · joined Jan 2003 ·

#643153
dumone wrote:good luck finding vents for them Craig..............what are the chances of you having a mate with a CNC machine, i have heaps of vents to copy?
More than happy to make them up.

I will be up your way in a couple of weeks, so I can bring the k bar kit and pick up some vents to copy!


mactaylor Custom Title Time!

1,005 posts · joined Aug 2007 ·

#643306
does venturi size matter? as in is bigger better? will the carb become less responsive with less of a flow differential when the step between bore and venturi increases? all i know is when the hole your draging from is unrestricted there is a vortex that initiates and itis hard to counteract
EVERLAST CONCRETE TANKS
1800 552 123

hellbugged 48's and straight cuts

5,080 posts · joined Apr 2003 ·

#643334
fark yeah they matter!

completely change the drivabilty of an engine and effect the range in which a motor is in it's "sweet spot".........

basically the pressure drop and air speed changes associated with changing the sizes effect when the mains come in and total amount of air available.

there is no way i would be running 48s on a 1776 without the small vents. (34 35 36 38 )

i could open the throttle wide and all the engine would get was a gut full of air..............unless i "choked" them down with the vents, thus providing the vacumm (at the top of the carb) to pull the fuel up thru the main circuit and out the secondary venturis............... which my small "air pump" would not do otherwise until very high rpm.

a change of 1mm smaller vent lowered the driving range of my motor by close to 600rpm...........the difference between getting the best response at 6400 instead of 7000, which is a desireable thing for a street car with my 309 cam..................Jeffs eventually ran 46mm vents and ran at 9000 rpm which suited it's capacity, heads and cams designs.

i might come back explain a little better when i feel like typing some more............anyone else?

matberry Moderator Go hard or go home

8,114 posts · joined Mar 2006 ·

#643336
No need Daimo, you said it, its all about compromise, hp vs. driveability
Matt Berry Motorsports...air cooled advice, repairs and mods Ph 0408 704 662
OFF-ROAD,CIRCUIT,DRAG,STREET,ENDURANCE

colin Fahrvergnugen

984 posts · joined Mar 2007 ·

#643339
Hey mactaylor here is some food for thought.
Was running 40mm vents 48 ida 1916 cc motor. Engine made 123rwhp at 7000rpm.
Changed to 37mm vents, came down 1 main jet size. Engine made 121.9 rwhp but gained 18 rwhp at 4500 rpm .
Torque curve flattened out and engine became more responsive.

Cheers Col

bat69 There is no status

791 posts · joined Apr 2005 ·

#643439
Vents sizes can make a massive difference. I spent a significate amount of time (nearly 6 hrs) on the dyno last month doing back to back tests trying every possible vent size as well as trying differnt carb sizes as well. I, like Colin made a few top end hp's with bigger vents but lost a fair amount of mid range torque. So dispite what the misses tells you. BIG is not always better.
White Knuckle Racing Team [/i]
"Drive it like dirt"

mactaylor Custom Title Time!

1,005 posts · joined Aug 2007 ·

#643447
thats the stuff! real people talking about real cars, havnt spent much time playing with carbs mainly with efi forced induction stuff. keep these sort of threads going cause its the only thing keeping me sane.
EVERLAST CONCRETE TANKS
1800 552 123

lugnuts Custom Title Time!

1,070 posts · joined Aug 2002 ·

#649437
colin wrote:Hey mactaylor here is some food for thought.
Was running 40mm vents 48 ida 1916 cc motor. Engine made 123rwhp at 7000rpm.
Changed to 37mm vents, came down 1 main jet size. Engine made 121.9 rwhp but gained 18 rwhp at 4500 rpm .
Torque curve flattened out and engine became more responsive.

Cheers Col
See i love stuff like this,out of curiosity i plugged colins specs into a carb and vent calculator they have at CSPs website,i put in 1916 and 7000 and got 46.6 for carbs and then i got 36.6 for vents so there pretty dam close eh,later Mick.For those that feel the need to play the calculator is at customspeedparts then click check out our other sites then tech then engine tech then carb calcs,somthin like that anyway.
Dont listen to what they say,just watch what they do.Oh yeah ive NEVER finished anything ive started.:o