Hi Dean & All,
Well, after much analysis - I DID IT. The new 3" round ID cores went on yesterday and I cranked it up yesterday for the first time. They are back off now for painting. I went with 20.5" (.5" longer) and cut off my old muffler cans and reused my header-collector, tailpipe tip, and mounting brackets.
Observations and Conclusions:
- Sounds nothing like my original 2.5" ID ERA exhaust pipes. Totally different.
- Much deeper and less crackle sounding; More deep pop, sound pressure.
- At least 25% more air coming out at idle by a quick hand check.
- The new muffler cores weigh about HALF. Those old ones are heavy.
- LOUDER at low frequency exhaust note range (more DB)
- QUIETER at high frequency exhaust note range (less DB, less annoying)
- More noticeable torque response at midrange for sure, a nice suprise.
- I think I need to rejet, checking on this now. Need to measure. 2-3 up?
- To me, Its maybe 20% louder but only at low frequency which is nice.
- Seems easier to talk with a passenger now with mid/high frequency gone.
- Exhaust note/type is more similar to a factory SPF sidepipe than ERA, KMP.
After looking at this muffler setup a bit more all said and done, there is actually some engineering to it; and more than I originally thought. The shorter ID glasspack inside a larger center section creates a chamber expansion-contraction-expansion effect which completely changes the exhaust note; it cuts out almost all of the high frequency note. This is very similar to some expermintation I did with my Harley Fat Boy exhaust a few years back with the exact same type results. Once I get the sidepipes painted up, decide on what carb rejetting is actually required, I'll have a better idea on performance gains. Overall, I'm really glad I had my factory ERA pipes on there for a while first to make a real hands-on comparison. Its fun to try something different. There are about 10 guys around here waiting to hear the results. Pun intended. Can't wait to get them back on again. See Ya.
