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Why are some carbs ported? #2310053
05/23/17 10:59 PM
05/23/17 10:59 PM
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Hot 340 Offline OP
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Hot 340  Offline OP
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Why not just use a bigger venturi main body from the get-go?

Re: Why are some carbs ported? [Re: Hot 340] #2310075
05/23/17 11:45 PM
05/23/17 11:45 PM
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Charlotte, North Carolina
sgcuda Offline
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Because castings and flow are not always the same between venturi's. Porting them equalizes the flow, just like with cylinder heads.


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Re: Why are some carbs ported? [Re: sgcuda] #2310108
05/24/17 12:18 AM
05/24/17 12:18 AM
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Hot 340 Offline OP
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Originally Posted By sgcuda
Because castings and flow are not always the same between venturi's. Porting them equalizes the flow, just like with cylinder heads.
Hard to imagine it would be worth the effort, if that's the only reason. Castings are pretty accurate these days and if you get after a set of hand ported heads with good measuring tools youll be amazed how innacurate the human hand is. But it doesnt seem to make a notable difference to the engine.

Re: Why are some carbs ported? [Re: Hot 340] #2310126
05/24/17 12:42 AM
05/24/17 12:42 AM
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sgcuda Offline
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Modern castings and billet pieces aren't the ones that need the port work. Although sometimes, you just want a higher flow carb without the full price of a new one.


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Re: Why are some carbs ported? [Re: Hot 340] #2310158
05/24/17 02:34 AM
05/24/17 02:34 AM
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jwb123 Offline
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Flowing the throttle body and increasing air flow is just part of it. Measuring the pressure drop on each venturi and getting all of them to pull on the jets the same is more important in my experience. this is a good article of some of the stuff you can do on the bench. http://www.hotrod.com/articles/carburetor-tuning-bench-flow-testing/

Re: Why are some carbs ported? [Re: Hot 340] #2310470
05/24/17 05:35 PM
05/24/17 05:35 PM
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PorkyPig Offline
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Originally Posted By Hot 340
Why not just use a bigger venturi main body from the get-go?

Carb shops like AED and BLP start with smaller venturi bodies and run their own CNC programs to open them up with the radii and tapers they want, not what Holley or whatever carb company uses when they cast a big venturi. It lets them use in between sizes that aren't a common cast size too.

Re: Why are some carbs ported? [Re: Hot 340] #2310873
05/25/17 12:43 PM
05/25/17 12:43 PM
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Mark Whitener Offline
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It was more common to open up stock castings in the past, there was a big jump in venturi size from 1.375 to 1.56, 950 HP to a 1000 HP. Now Quick Fuel has a 1.40, 1.45, 1.50, and 1.59 venturi sizes for a 1.75 throttle blade. BLP can machine billet any size up to 1.63. I will usually open a 950 to around 1.42 to give it some flow, clean the step in the casting. I'll occasionally open a 1050 when the owner wants to stay with their carb, and engine dictates a larger carb. New builds I just get the right casting or billet size correctly.


Mark Whitener
[url=www.racingfuelsystems.com[/url]






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