Having said that I was happy with my current exhaust insert (see earlier Venturi 2 thread), I started to question what had transpired, and how to take things to another level………..or back to where they should be!
‘V2’ as I shall now refer to, was producing a pleasing sense of ‘get you there’ urgency at all revs and at only part throttle. It’s as if the combustion process was constantly being ‘advanced’ in some way. There was a sweet spot between 3600 and 4200 or so and as you rode through this region of midrange (in spite of a healthy engine pick up) the exhaust note became a subdued thrumming. A bit like taking a freshly run in Honda above 5-6000 rpm for the first time……..NICE…….
, but absent was the bad ass ‘BOOM’ we know and love in our Evo-X motor Buells. This alone suggests to me that the pressure wave, or wave pulse within the exhaust had shifted one way or another. Above 4200 and going open loop, the motor pulled harder and harder as you wound open the throttle to an addictive sort of beat from each power pulse, but there was no escaping the fact it all felt a bit ‘metered’.
In the above scenario the V2 sleeve insert when measured at regular internal diameters through its 62mm length from entry to exit was; 46 – 43 – 43 – 44.5 – 46mm. That’s a regular sided inlet cone, a parallel choke and a regular sided shallow angled exit cone. What I thought was needed was to open out the rear of the 43mm choke to increase the low pressure area in the exit. I decided on something nearer 46 – 43 – 43.5 – 45 – 46mm. This makes the exit cone more ‘bell shaped’ with greater volume (flared), but it is still an incredibly subtle change.
30 minutes later with an abrasive flap wheel and you would be hard pressed to see the difference, but by drawing the tube walls between a pinched finger and thumb you can definitely feel the shape. Once installed and after the magic 26.4 mile warm up, after which I can only guess that the air temp sender is nicely cooked, I was able to see the differences.
I was initially worried that I had opened things out too far and would throw away all that low rpm part throttle advantage, but nothing of the sort. The most important change was that the Buell’s characteristic ‘boom’ was back! It seems to combine all the power pulses into one homogeneous sound as if each exhaust pulse is complementing the other (in tune?). Whatever, the power surge when overtaking was more instant or explosive. It reminded me of watching and hearing the boom of a 6.5 litre V8 McLaren M6B blitzing the Silverstone Club circuit when I was a lad. That sort of thing stays with you, and maybe that’s why I love Buells.
I can only conclude that I had caught the 'wave' again!
I was also starting to become concerned about directional stability as I passed cars winding it on in the oncoming lane. Maybe the tyres were under inflated, or maybe I am just getting old and infirm?