Exhaust pipe size after headers

[super vw]

Hey guys, i need to start thinking about what size pipe i need to get in order to make my exhaust. I have a Kymco 1 5/8 header im using for my 1914cc N/A motor.

I will be useing two glass pack style mufflers (dynomax, flowmaster... not sure yet) in series (one after another, single outlet). Whats the best size to use keeping in mind im looking for the most torq.

Thanks!
Jonathan

[zenjoe]

After the header, a good size would be 2.5 inches. 3 inches is a little large and will kill exhaust velocity and your low end torque. 2 inch is a little small, your EGT's will be a little higher (because of the restriction), but you will produce better low end power, while sacrificing your top end.

I would reccomend going with a dynomax ultraflow or magnaflow brand mufflers (or anything using a perforated core [louvered is acceptable, but the louvers themselves make the air turbulent, which restrict air flow.])
The Dynomax superturbo mufflers (aka "phat-boy") flow ok and are queiter. I would not reccomend going with any flowmaster, they are restictive for their size. My buddy Jim Ratto ran some tests on his 2276cc engine by using the same header (1 3/4" primary) and changing only the exhaust, he said that the magnaflow 2.5 inch muffler produced more power, while having 20 degree lower cylinder head and oil temps than a 3 inch flowmaster.

Everyone wants madrel bent this and that to straighten out the flow of the exhaust, why would you want a muffler that makes the exhaust split up and go all over the place? Totally defeats the purpose.

This is a picture of a flowmaster, see all the baffles that are in the direct path of the exhaust? not good for flow.

compare to magnaflow



Hope this helps.