Velocity collectors in side pipes ?

[coneeng]

It all depends on the type of collector you are referring to. A "sweged" collector made from a piece of tubing will be at least 3.5", sometimes as large as 4". This isn't because that is the best flow, it's because you have to start with a big diameter in order to stretch it out to fit 4 x 2" primaries. You will actually find that there are more collectors on the market with outlets that are too large rather than too small.

On a normally aspirated motor we have found a 2" primary flows best with a 3.00" collector outlet and then a 3.50" trasition cone to promote scavenging. When space was an issue we found that it performs better without the transition, staying at 3" than increasing collector outlet to 3.50" immediately. With a turbo or supercharger, then yes, a 3.50" outlet is often called for. With the side pipes we have used a larger collector and skipped the cone if the customer prefers that look.

Originally Posted by Rare Iron

Funfer, most collectors are 3.5" OD, so are the exit spouts. I've only built mufflers for one customer that had 3" on both of these. FYI.

-Eric