Drag Racing Discussions > Front Engine Dragsters

Zoomie size?

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glofria:
Because doing so will have adverse affect of what is intended. You want to keep the velocity at a constant rate throughout the header. Otherwise you have air that will get trapped before the bend and a reversion affect (reversal of air flow) will happen when both valves are off the seat and will go back into the cylinder. That is also why the opening of the header does not match the exhaust port runner; it acts like an air dam. Once the air exits the header there is a slight back-draft that goes back into the header.

I asked dad that question this morning on the way to breakfast and he also stated that air does not like to change directions. On the manifold side you want it to be as straight as possible because the air is heavier (mixed with fuel) and relies on the piston cycle to draw air in. On the exhaust side the air is obviously hotter and thinner, thus bends help with the exit velocity.

There are other benefits to bending zoomies as oppose to straight weed burners like propulsion and so on, but you can learn all that by watching the NHRA big show.

There is a lot more that can be explain, but I not going to type this all out. However, you get the gist of it.

THE FRENCHTOWN FLYER:
Air would only get "trapped " before the bend if the cross sectional area is reduced at the bend, like cheap muffler shop pipe benders. But suppose the D shape does not have a smaller cross section by design. Then the advantages of a flat radius floor and resultant laminar flow (or at least reduced turbulence from the bend / change in direction of flow) from the D-shaped bend might actually help to maintain gas velocity, no?

Mismatch at the exhaust port / pipe juncture is a whole nuther discussion and is probably straying far afield of the original topic.

cad500justin:
Guys thanks for the detailed responses!
Flyer, that was my next question! You should line up the top of the pipe with the top of the port right?

THE FRENCHTOWN FLYER:
Generally speaking, yes.

If the ports are well designed I do not think pipe misalignment / mismatch is necessary or useful. My experience is with non-supercharged applications so others with blower experience may know better.

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