exhaust duration

Bump

Was reading in "Performance Tuning by Graham Bell" and ran across this formula

"The formula we use to determine the tuned length of the exhaust is:-

L = (ED*42545)/rpm

where L= tuned length in mm
ED = exhaust duration in degrees
rpm = engine speed exhaust is tuned to work best at"

Holy thread revival

jjm86m said:

Bump

Was reading in "Performance Tuning by Graham Bell" and ran across this formula

"The formula we use to determine the tuned length of the exhaust is:-

L = (ED*42545)/rpm

where L= tuned length in mm
ED = exhaust duration in degrees
rpm = engine speed exhaust is tuned to work best at"

Click to expand...

That looks almost like the equation used for making an expansion chamber. (which he was probably trying to do)

Foureasy got 172 to 178 degrees on the exhaust before any port work.
http://motorbicycling.com/showthread.php?t=12490

From what I've heard, every ht engine is a little different. So it's probably best to measure it with a degree wheel to be certain, which is also done by scott83 in the thread mentioned above. It sounds like his measurements were a little off though...