morning,

very simply what is the science in choosing the right length of velocity stacks... is it purely as a result of testing on the dyno, are there formulas which one could use to figure out gains vs losses of different length stacks, etc...

i've been searching around on the web and while i did find places selling them, i didn't find much explained about the science of picking the right ones...

someone here care to help?

-e

EricB,

Typically, shorter stacks produce better high RPM HP and longer ones at lower RPM. This pretty much holds true on header length as well. As you mentioned, the only true way to see what results have transpired with these changes is to put it on the dyno.

Just one man's opinion. Hope this at least gives you a basic guide line.

It would be kinda of a grey area considering how many factors would go into the correct, or best performing ones....

Carbs, carb modifications, intake runner lenght, valve size, valve placement in the head and shrouding,valve angle, port size, port matching, combustion chamber volume and shape, etc. etc. etc....

To tune it to the "nth" degree, it would have to be done on a dyno, so that all the other criteria can be taken into account.

A few year ago Scott Bruning of Z-Therapy fame had a MIT engineering student do a study of 240Z factory velocity stacks VS all other aftermarket stacks.....the factory stack flowed more air at a higher velocity than all the others....just food for thought.