If that's the one that went on ebay a couple of weeks ago you got it for a good price . I thought about bidding on it but I've already got one and a lovely engine it is too. I've got a chart for pipe lengths for various port timings/revs and it indicates that, for the 61VF with 150 degrees total timing, the pipe should be about 15 1/2" from plug to first baffle at 14,000 revs. For best effect the pipe should have an internal volume suited for the engine size but you should still get boost from a smaller pipe so long as the stinger size doesn't choke it down too much. I've only run mine on the bench so far with an Eather CF pipe meant for a 45 but set very long so it only acted as a muffler. Just one tip though, because it's ABN I'll only run mine with 20-25% all castor which seems to stop that horrid peeling problem .