I have a 1835 non-stroker engine with 40 idf webers.
Are velocity stacks worth the trouble ?
I certainly like how they look, and I like the idea of more air being pushed into the engine, but... ?
Not sure it is appropriate or worth the trouble for this size engine / carb.
Has anyone done anything similar? How high are the stacks? Noticeable difference? Re-jetting the carbs?
Humm?
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If you watch an engine on a dyno (especially during acceleration) you can see a sort of "fog" Just over the carbs where the velocity stacks would be. This is called fuel stand-off. The stacks help to direct this fuel fog down the throat of the carb thus allowing all the fuel intended to be going into the engine to do so. I don't know if the jetting would need to be changed if you added stacks. I do know that I had to build a set of stacks for some Weber DCNF 40's I was using and it did eliminate a slight "cough" at the beginning of throttle opening. It wasn't necessary to re-jet them though. The stacks on my current 44's are flared at the top as usual and are 2.25" high. They fit nicely under my CB paper air cleaners which are about 4 " high...Bruce
IF YO DO THE WORK YOUSELF ITS WORTH IT, THE RULE IS SHORTER LENGTH MAKES TORQUE LONGER LENGTH MAKES HORSE POWER, ITS TRUE ABOUT FUEL STAN OFF. IF YOU RUN AIR CLEANERS MAKE SURE YOU HAVE AT LEAST 1 AND 1/2 INCHES OF CLEARANCE TO THE TOP OF THE AIR CLEANER. BILL
Thanks Bruce, I had no idea about the fog of fumes. I always thought the stacks simply increased the air flow - kind of a Helmholtz flute effect - ie squeezing the garden hose... They do not cost a lot, so I might simply play with it and see what I get.
I'll use the little filters that fit on the ends. I like how they look... But hiding them under the original filter is something I had not thought of.
Buckwheat - good food for thought. It seems 3" is the standard.
They do both things, Carlos- improve airflow into the carb (as much as about 5% iIrc) and help contain fuel standoff so the engine makes more power. I have read that "25% above the diameter of the intake will feed the carburetor, and there's no point in the filter being taller than 50% of the intake diameter. A 40mm carb needs 10 mm clearance from the velocity stack to to the underside of the aircleaner top."
Here's a series of "tests" Kaddie Shack did w/Kadron/Solex. Tests used the following set-up:
82mm crankshaft x 92mm pistons/cylinders
9.1 compression ratio
Norris 408S camshaft, 1.1:1 rockers
KSR-4000 ported cylinder heads, 40mm x 35.5mm valves
1-5/8" AA Sidewinder Exhaust
Kaddie Shack EMPI Kadron-style 44mm dual carbs
Thanks Al big help!
Art interesting graph, thanks for posting.
