Carb sizing

[MTT3107]

Is there a rule of thumb for what size of carburator(s) to use ?

My current combo is :

1835 cc, all new parts from CBperformance
CB 2239 camshaft
Steve Tim's Super stock heads
Dual HPMX 40's

I'm quite happy with it, but wondering, are these carbs a good fit?
Too big ? Too small?

Also, if I ever go ahead and build another, maybe bigger engine, how does one determine the best size of carburator for it ?

[bedlamite]

Carbs are good, depending on the venturis, use 32-34mm

Srtarting with intake valve size, carb throat should be 10% bigger, and venturi should be 10% smaller.

[Dale M.]

I have always thought less the 2000cc use 40 IDF's or clones, above 2000cc Use 44 IDF's or clones.....
_________________
“Fear The Government That Wants To Take Your Guns"
"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
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All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ...

[oprn]

Depends on if you are going for function or bragging rights... I met a fellow once that claimed a pair of 48 IDF's was just the right size for his 1600!

I wonder if it is more related to individual cylinder displacement than overall engine size. For the 1500 to 1700 engines VW used 30 to 34mm single or dual carb. We use 32 to 40 single, dual or quad throat carbs on that same range.

Just an observation... seems to me that the pressure drop on each intake stroke individually is the key not so much all 4 pulses combined. Single cylinder motorcycle carbs sizes are similar to ours if I am not mistaken...
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Our cars get old, we get old but driving an old VW never gets old!

[Dale M.]

I had a 2180 in my auto-x car with a pair of true WEBER 48IDF's on it , the carbs were loaner's, and although it ran pretty fair it never was quite up to expectations, owner of carbs wanted them back, so I got a pair of first generation HPMX 44's and it ran so much better.....
_________________
“Fear The Government That Wants To Take Your Guns"
"Kellison Sand Piper Roadster" For Street & Show.
"Joe Pody Sandrover" Buggy with 2180 for Autocross (Sold)
============================================================
All suggestions and advice are purely my own opinion. You are free to ignore them if you wish ...

[bedlamite]

[jpaull]

There is no rule of thumb that can interpret CC/Cam/Headwork all together.

You can have a 1835 that works best with 48idf's if it has a aggressive cam and heads to the point that 44's restrict flow. If you put 44 idf's on that engine that was taylored for high rpms, the 44's wont fix the cam down low and wont flow enough up high.
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[email protected] MPH 1/4 Mile & 8.1 @ 83.7MPH in 1/8 Mile with Mild Type 1 VW Mag Case 2234cc commuter engine in stock weight bug w/only .491 total lift(CB2292 Cam), 42x37 heads, 48idf's, Street tires, Belt on, Mufflers, Pump gas, video of the run here: https://youtu.be/M3SPqMOKAOg

Transmission by MCMScott:
Rhino case, Klinkenberg 4.12, Superdiff, 002 mainshaft with 091 first idler. Weddle 1.48 Third & 1.14 Fourth.

[b-man]