Holley venturi sizes
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Le Mans Master
Joined: Apr 2006
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Holley venturi sizes
So on holley 4150 carbs as you go from 650, 750, 850 the venturi sizes increase and on the 850 the throttle bore increases to 1.75. So was looking at holleys own web site out of curiosoty on dominator carbs they have now a 750, 950, 1050 all have the common 2 inch throttle bore size, but all three list the same venturi size of 1.690. How the hell does that work.
Thread Starter
Le Mans Master
Joined: Apr 2006
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They were all using annular boosters and the same 2 inch throttle blades. Must be just the specs listed wrong. Going from 750 to 1050 without different venturi size not happening. If you look at there monster dominator"s up to 1475 at 1250 they change to 2.125 throttle plate then even bigger then that along with changes in venturi sizes.
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Le Mans Master
Joined: Apr 2006
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Sure but it's misprinted different sizes of boosters only have small effects on cfm capability of carbs. Id like to make an IR manifold and everything I can find out shows they need big throttle plates to work best.
Le Mans Master
Joined: May 2007
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From: North tonawanda NY
From what ive read on this topic, the advertised CFM of carbs doesnt always match realistically though... I know when I had an avenger 670 cfm carb I read it was the same size base plate as the I believe the 600cfm model I have a QF 680 carb now and the throttle blades are bigger even though its only 10 cfm advertised difference.
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Le Mans Master
Joined: Apr 2006
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Holley base plates stay at 1.688 with venturi changes making cfm differences. Until you get to the 850 then the base plate goes to 1.75. Been that way forever even back to the 1970s when I had an 850dp carb. I happen to have 2 800 dp. The way they came up with that in comparison to the 750 dp the back 2 barrels have a bit bigger venturi then the front. You can easily see it with your eyes looking down into the carb. That's not to say that if you went from a regular booster to the bigger annular booster that it could effect the flow cfm a bit if the venturi is not changed in size to compensate for the restriction it causes.
Last edited by Little Mouse; Jun 20, 2022 at 09:38 PM.
Le Mans Master
Joined: May 2007
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From: North tonawanda NY
Your right except but the holley 650 (at least some of them) and 670 street avenger has a 1.563 bore. The quickfuel 680 has the 1.688 bore. The newer holley "ultra 670 has the 1.688 bore though and its possible some of the 650 cfm series has it too. I see the brawler 650 has the larger bore.
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Thread Starter
Le Mans Master
Joined: Apr 2006
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The three dominator 750,950 1050. That's correct not a misprint all have the 1.690 venturi size. Same 2.0 throttle blades. The old king demon carbs they made some smaller ones by using a 1.850 throttle blade different venturi. I remember some of them had changeable venturi sizes you could do. Webber
made at least a 55 mm throttle bore side draft carb, you could change the choke/venturi on them. From what I can find out IR systems need really big throttle blades even bigger then 2 inch preferred.
made at least a 55 mm throttle bore side draft carb, you could change the choke/venturi on them. From what I can find out IR systems need really big throttle blades even bigger then 2 inch preferred.
Le Mans Master
Joined: Mar 2008
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From: Oxford MA-----You just lost the game!!!!
My brother is a motorcycle/snowmobile mechanic, so I see these Mikuni side-draft carbs laying around all over the place in his shop. I can't help but wonder if you could hook up 8 of the things to a small block Chevy. In my mind, I envision a heavily modified TPI manifold and a bunch of re-purposed motorcycle parts making the whole mess work, and it looks glorious!
Scotty
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Le Mans Master
Joined: Apr 2006
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Jim englease after selling his company years ago came back into business now calling the company " Jim englease 8 stack " he will make a webber setup with four 55mm dcoe side draft carbs. But I'd bet it's at a minimum 5 grand on up in cost.