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Discussion Starter · #1 ·
Every now and again we get questions about ram pipes on here. And one questioned mentioned fuel stand off.

Take a look at this link


This is a good design.
It has a very generous top radius - this enables air to flow in without any shearing or vortex generation.

It has a gentle taper which helps accelerate the air as it goes in and deaccelrate the air if there is any blow back or if a constant rev range causes stand off. Stand off is caused when a full harmonic of a fixed frequency occurs and the wave length has a node at the closed valve and the reflection carries the fuel and air to a second node just above the carb outlet. The taper help stop the second node from forming.

These ram pipes are short enough to fit under a filter - well the ones I have anyhow.

Whilst not long enough to give any boost to torque in a beetle rev range - their efficiency in getting air in is well worth having.

A correctly designed ram pipe gives the most effective air flow, better than a flat plate (ie a filter housing on a Weber carb) or a simple open pipe.

Someone mentioned air boxes - these help by providing a large area of still air for the ram pipe to work in. A German company produced a large box that fitted across the engine - you needed a Porsche fan I think - with an biggish blob on top of the carb throats. My guess is that this would also help - but it was big and ugly - probably find a home only in German lookers.

As the air inside a beetle engine compartment is probably fairly calm my guess is that the volume inside the filters produces a workable space for ram pipes to work. I chose the largest filters I could for this reason.

BTW - some of the above is why pancake filters are rubbish and the standard filter is so good - now there is a surprise.

I hope that answers some questions.
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