Very Nice. But what they don't tell you it is fitted with a VERY Noise Ex pipe. You should not run it at your local park as you will get chucked out, and it is NOT OMRA legal.
Just install your own internmal stinger its easy and it works exellent.all you need is some tubing the same diam as the internal part of your outlet on the pipeor stinger as its sometimes called then slide it in as far as the widest part of the pipe or centre of band etc,allways good to drill a small hole in your new internal stinger tube just where the pipe converges to the stinger so as to drain out the oil ,slide it in and either fasten with a pop rivett or silver solder in place.By all accounts it will quieten any noisy pipe to legal limits and it doesnt hurt the performance in fact some say it can improve it and for an extra quiet pipe you can also add an add on muffler .
Mart
Mart, No arguments with the concept of an internal stinger. But, assuming that the pipe was correctly dimensioned in the first place, the internal diameter, of the new, internal stinger, needs to be the same as the internal diameter , of the original stinger. If the wall thickness of the internal stinger is less than the original, you may be able to drill out the i/d of the original stinger to the o/d of the internal stinger - then slide it in. If not, you need to replace the original stinger with the internal stinger. If you just make an internal stinger to slide inside the unmodified original stinger, you are significantly reducing the diameter of the stinger, and altering the characteristics of the pipe. If the pipe was previously well designed, this will cause power loss, excessive back pressure, excessive heat, and quite possibly engine damage due to detonation.
Properly implemented, an internal stinger will reduce noise significantly, and probably without power loss or other ill effects. I don't think it will reduce the noise from an open pipe down to OMRA / MPBA levels though. It may just about work for the (10dB higher), permitted levels in the US, but radiated noise, and the noise received by a measuring device depends on many other factors as well.
Hi mate i can see what your saying but the guys who have done this mod are very well respected and they say they havent had any issues doing this,Scott Schneider been one.In any case most of the noisy pipes tend to be china pipes which in my experience tend to have over large stingers anyway so reducing its diam will probably benefit its performance as seems to be the case by all accounts.Heres a cpl of links of some how to information etc.By the way funny you mention back pressure as my mate tried his rcmk with one of the better know pipes on the market in the hydro i built him and said it had so much back pressure the boat did all of 5 mph then blew the pipe clean off the header,after several attempts he gave up on it.It was a new cooper quiet pipe,he imediateley changed to a china pipe and it ran like a champ if a little noisy see vid.
Mart
china pipe on comet hydro,first test run.
http://www.youtube.com/watch?v=lLJP0PrWkxs
http://www.jrcbd.com/showthread.php?t=3569&highlight=internal+stinger
http://www.jrcbd.com/showthread.php?t=3569&highlight=internal+stinger
Hi Mart, Yes, too big a stinger will hurt performance too. As a general rule, too large will hurt top end, but is "safe". Too small will hurt torque, and is less safe. I you start off "too big" on the stinger, and get gradually smaller, power will increase to a point. One danger is that, beyond that point, the power fall off is initially quite small and therefore hard to detect, before detonation starts - potentially destroying the piston. Some of the effects of reducing stinger diameter emulate a shorter pipe. These factors can be compensated by lengthening the pipe, but there are others which can't - like the rate at which the stinger will allow the exhaust gases to escape. As stinger size is one of the easier things to change (like pipe length), it is something that can be tweaked - by those who know what they are doing. Andy Brown, for example, offers different sized stinger inserts for some of his pipes. Which one works best will depend on a fairly wide range of factors (engine, boat, fuel, environmental etc).
If you follow what someone has successfully done before - with the same pipe, engine etc, there should be a good chance of success, and I certainly wouldn't dispute people like Scott Schneider's ability, and to some extent that is the key (ie they know how to interpret the results of changes they make). I just didn't want anyone to think you could do this blindly with any pipe, and expect it to work well. If you keep the stinger diameter the same, you should be able to run quiter with less unknowns, and with a higher probability of no adverse effects. Ideally, this should really be done without changing the length of the stinger either. Lengthening the stinger also increases its flow resistance - though to a lesser extent than reducing the diameter. By sliding a pipe into the existing, unmodified stinger, you are making it longer and smaller.
The earliest reference I have seen to the internal stinger, was from the "Two Stroke Tuner's Handbook" by Gordon Jennings - written circa 1973. Jennings wrote that he stumbled across the idea - by sliding the whole length of the stinger into the baffle / converging cone - trying to make a shorter pipe. He later discovered that it had been documented a few years previously.
Sorry it's a bit of a long post again. I'm trying to avoid going into tuned pipe theory in any great depth.
Ian