What's the largest venturi available for 40 Dells ?

As the title says..................

can I get 36mm for them ?

i know weber 40's go to 36

http://cgi3.ebay.com/ws/eBayISAPI.dll?ViewUserPage&userid=alfa1750

If you look here they only go to 34.

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?

What ever you can machine them out to

apparently 38s will fit from a 48dell?

When in doubt, bore it out.

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!

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

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?

No need Daimo, you said it, its all about compromise, hp vs. driveability

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

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.

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.

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.