![]() The oil bath air cleaner stack acted to contain fuel fog stand-off at high RPM's. It was approx four inches tall, and it wasn't there just to keep the oil out of the carb. The VW oil bath air cleaner had one inside. There is a trick velocity stack question that many VW guys never think about, even though they know the answer.ĭid the VW Bug come equipped with a velocity stack as standard equipment? Plenum carbs don't need the same size venturis as non-plenums to give equal performance.įirst, yes, the airhorn design of a velocity stack smooths airflow due to its tapering. And, a last oddity between plenum and non-plenum carbs is there is no direct comparison between performance and venturi sizes. Shorter runners lengths give more power at high RPMS, longer lengths give more power at lower RPM's.īy the way, the Solex carb design sold by Kadron is a plenum type and needs no VS, even though you can buy them. For variable RPM road racing, a 1.6 engine redlined at 6000 needs about a 16" runner length, meaning the total measurement from carb mouth to intake valve. The short Weber manifolds most kits have work just fine with the appox 3" high VS in the same kit. For racing, you can change this by just changing VS!įor the street, you have to compromise. Race tuners know there is a specific length from the carb mouth to the intake valve that produces the best power at a specific RPM. VS stack height is related to manifold lengtht. and this is why many old time Weber tuners think of air filters as fire safety devices. Just let a high-rev valve float on an intake valve allow a manifold backfire. If there is no VS, the air/fuel mix gets messed up, and a carb fire is a good possibility with aerated gas now being ejected into the engine compartment. The velocity stack (sort of a misnomer) is just an extension of the carb to contain that air/fuel revulsion. Webers are forced to have velocity stacks, because at certain RPM ranges, the return shock wave from the intake valve literally forces air/fuel out of the top of the carb. The disadvantage of the plenum system is it is not as tunable as the Weber type system. Plenum designs are much easier to tune than nonplenum systems, which covers the Weber, Dellorto, and similar designs. The force of this "reversion" can be made worse by some cams.Ī plenum design gives that shock wave a place to dissipate. The intake valve slams shut as the air is flowing, and a shock wave created by the sudden halting of flow shoots straight back up the manifold into the carb. The air coming into a carb and intake manifold is not just on a one-way trip. The plenum space allows a common area from which the cylinders draw an air fuel charge, and the plenum acts as a cushion to dampen the violent reversals of air velocity that occur between the carb throat and the intake valve. V8 builders have a plenum area under their big 4bbl carb manifolds. They correct an airflow problem non-plenum carbs have at certain engine speeds.Ī "plenum" is just a space or area. ![]() All the average tuner sees is ads that sell them.įirst, VS are not for looks. ![]() That's probably because good info on them is lacking. Since I am in the middle of my carb rebuild.I find the velocity stack to be one of the most misunderstood pieces of tuning equipment. Would cutting down a K&N filter and somehow fitting it into a velocity stack allow enough airflow? Are there any velocity stacks available for my carbs that have a quality filter builtin? So my questions to all of you knowledgable folks are: It appears that unless I make something myself I am left with 2 options.ġ) Velocity Stacks which = poor filtering I did some searching on this site and the interwebs and couldn't find anything on this. Ideally I would want the filters recessed into the stacks if possible so they are not visible.so basically I want form & function if at all possible I have been toying with the idea of taking a K&N filter and trying to cut it down and retro fit the pieces into a velocity stack, however since most K&N pods are huge compared to a velocity stack I'm not sure if the little pieces of filter would allow enough air flow, as well as I am still unsure on exactly how I would accomplish this either way. Every velocity stack I've seen for sale looks like someone just glued a screen onto the end of which while great for keeping sticks and small animals out of my engine, doesn't look like they will do much for keeping dirt out. I am in the process of rebuilding my carbs and I love the look of velocity stacks on a bike, however I am concerned with the air filtering ability of velocity stacks.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |