ORIGINAL: jdoug
I just wanted to start a thread on how people tune and find the right pipe length. One question I have is if your engine isn't revving up like it should, then how does one know if the pipe length is the culprit or it just needs some tuning. On my WT .18 I just put my pipe length to 8.5 in. to the convergent cone and tuned from there. I got that measurement from Ron O.
Yes, it screams, but, how do I know that's all I'll get? I suppose I could buy another header and start over with an engine that seems to be tuned in. Another question would be...If I change my pipe length wether its longer or shorter, on an engine that's tuned, would I have to retune with the new pipe length?
Do you own a GPS you can run in the boat?? If so, do you have a little room between your header and pipe?? Mark the pipes length in some way, so you know where it is now. Run the boat a couple times and write down the speeds you are getting. Now lengthen the pipe just a little (quarter inch or so), and run it again. See if the boat sped up or slowed down. If it slowed down, go the other direction (shorter) and run it again. I would think that different props, hull styles, etc, would tune in at different pipe lengths (need a different balance between the RPMs you get with a shorter tune, and the power you get with a longer tune). I am running a little shorter tuned length than you are with my .18 CVRM. Not saying my pipe length is optimal, or would work for you, but you might want to try it a little shorter. When possible, I cut the header instead of the pipe, because headers are cheaper than tuned pipes. So if I do mess it up (go too short) it is just a matter of buying another header.
EDIT: By tuned length, I am talking about measuring from the center of the glow plug down the center of the header and pipe, to the widest part of the pipe. I know I have seen at least one other person refer to the physical length of the pipe by itself. I don't think you can go by this because...as an example, the MV has at least 3 different header lengths I have seen. The version 1, Version 2, and one you buy by itself.
Sean