Bud exhaust mods

[abx131]

I thought I heard somewhere that you could trim off part of the 1/12 bud's tail pipe for improved performance. Any one know how much and where the cutting is done? How much improvement is made in performance?

[BoatDoc]

if you want to shorten the pipe you should cut the header pipe. as little as 1/8" can make a difference. it's wise to only do a little at a time. the alternative is to push the pipe into the coupler which effectively shortens it. you will also need to bend the rear pipe brace or make a new one that will hold the shorter pipe.

[Watercadet]

I double zip tie my cuppler and flair both the end of the headder and the pipe and don't run a hanger on my bud. It is held steady by the cowl in mine. And ditto on what BD said.
Adam

[abx131]

Is the performance gain noticeable?

[Watercadet]

I have never run the stock headder but it is way too long to be effective. I would thint that an otherwise well set up boat would benifit from shortening it maybe by 1-3 mph on the top end. Seat of the pants gain prolly won't be noticable but you will see it when the boat starts to get flighty:D
Adam

[abx131]

Do these engines rely on back pressure?? I would think you would want to trim the end of the pipe to open up the diameter and reduce back pressure.

[BoatDoc]

don't trim the end of the pipe. it's best to trim the header pipe. remember, a tuned pipe works because of the distance from the cylinder to the peak of the cone on the pipe. people with a lot more knowledge than most of us worry about the rest of it! cutting the tail end of the pipe can likely ruin the pipe.

[Chris LaPanse]

Yes- they rely on a pulse of backpressure coming at just the right time to force the extra fuel that comes out the exhaust port back in the engine. If you enlarge the opening, it will ruin the pipe. If you shorten the pipe, it will cause the pulse to arrive at the engine sooner, therefor causing the HP gain at higher rpm. This would give it more top speed, but less acceleration. On the other hand, you could lengthen it, for more low rpm gains, resulting in more acceleration with a reduced top speed. However, all of this depends on the shape, so only lengthen or shorten it at the header, where it will not severely affect the general shape of the pipe.

[abx131]

I cut off almost a 1/4 and it had a noticeable gain. How much can you cut off before things become counter productive? Has anyone taken off an inch.???

[Hydro Junkie]

It's not when things get counter productive, it's when the engine won't get "on the pipe". As someone so bluntly put it in another thread, the shorter the pipe, the higher the RPM needed to match up with the pipe's tuned frequency. Each time you shorten the pipe or header, you raise the top end by sacrificing the bottom end. What you need to look for is a balance that suites your style of driving. If you are looking for blinding top end speed, keep going shorter, while if you want more torque coming out of a corner, leave it longer. While you are adjusting lengths, keep a record of how the boat performs after each mod. When you get past where you find the performance is "optimal" for your style, get another header/pipe and set it to the length that gave the best performance and, after that, LEAVE IT ALONE!!!!!!!!!!!!!!!!!!!!!!!!!!!!! UNLESS YOU MAKE A CHANGE TO SOMETHING ELSE(LIKE CHANGING NITRO CONTENTS OR MAJOR PROP CHANGES)IT WILL BE WHERE YOU NEED/WANT IT.