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What Size Carb for what size VW engine formula

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The question is put many ways, but comes down to: how big of a carb can I put on my VW air cooled engine or what size carb can go on my engine?

This is a mathematical equation formula that you can use to see if you are planning the right carb(s) for your engine.

Keep in mind this formula DOES NOT take into consideration your:
cam choice
heads or their flow or valve size
driving style
desired BLING factor
your willingness to either believe it or not

VW used a 28mm venturie in a 34 pict (34mm throat) carb for a 1600 (1584cc) engine.
That means they accounted for the engine running fine with 56.57cc for every mm of venturie (1584 div by 28 = 56.57).
If that rule of thumb worked for many years for many cars, then the same rule of thumb COULD WORK for you.

So, let's say that you have a 1915cc engine and you want to know what size throat carb you should use on it.
Here's the math for that situation: 1915 div by 56.57 = 33.85mm or a 34mm throat size carb.

Now, most people would run a 40mm 2 barrel like an hpmx, idf or a drla. But doing so means you are running 2 x 40 or 80mm of throat. So you can see that that is more than double what the math calls for.

However true the math is, remember that it does NOT take into consideration your engines capability with regard to SUCK & PUSH: cam choice, valve size choice, head flow characteristics, exhaust size & driving style.

Doghouse recently broke-in a 2387cc engine that had dual 40's on it. Initially, we told the customer we would not recommend those small carbs on that big engine.
Boy did we eat crow when we were done with the break-in. The engine not only ran fine, it ran great.

Here's why: 2387 div by 56.57 = 42.20mm throat called for. - throat provided was 160mm (4x40)= more than enough for this engine.
Lesson learned.

On the other hand things can change: for example I just attached a 4 barrel Holley 750 (shown) to my 2387cc shown and it runs fine. Ok, so I left out that it ALSO has a turbo blowing the gases into the engine!

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