Well the mod engine is finally broken in, time to tweak for speed! Full take of fuel carb leaned by 1/16 of a turn, pipe set at 12 1/4 inch. after 12 laps 58 mph top end. Came in for a check and all seamed good even the Cooper Muffler stayed on.Back in the water,after 4 laps the boat came alive top speed 64 mph but sounded like the Cooper was coming loose. Brought it back in only to find out the water nipple on top of the rudder had broken off. the motor was still getting cooling but not the pipe! NP drilled out and replaced the fitting and all four O-rings. Another 6 laps and top speed of only 58mph???? What am I doing wrong?? :dash:

If you are looking for more speed, you might get rid of that leaky alum pipe, replace it with a no leak flange 0 or 1" band steel pipe.

Not sure what u mean by leaky pipe? The reason the noise went up is that the pipe got so hot it melted the o-rings! I had pressure tested the setup with smoke before I ran it and it was tight! My question is why the big top end and torque gain when it was not being water cooled.

In my case, the alum pipe is always leaking water for me when the boat runs, I ran a few of them on my boats when I was new but not any more now, I'm not the pipe expert but I know lots of the high speed boats would use hot pipe system, someone might chime in to explain why hot pipe gain more speed than the alum pipe.

Thx for the input Ken ! Was the water leaking inside the pipe? I did notice a very small amount of moisture and fuel mixed dripping out of the Cooper muffler. I was not sure if it was coming in when I was bringing the boat in, cause my exhaust runs thru the hull and is low to the water line.

Without your cooling the pipe would have heated up & changed the tuning effect of your pipe length. Try shortenning your pipe by small amounts (1/8" ) at a time until you notice it pick up speed. When it starts to bog down in turns you have shortened it too far.

Will taking off the Cooper Muffler also change the effect? I was getting better torque without it?

Just to clear the air on a previous post .... the "Hot Pipe" is nothing more than a sales name for Quick Draws latest steel pipe.

** That said, HEAT within the exhaust system could very well have made the power difference while your o-rings were having the meltdown.
Hotter the gas's within a pipe become, faster the sonic wave activity is. A hotter pipe acts like a shorter pipe and visa versa when cooled down.

Generally the aluminum pipes are slightly milder it there tuning having broad power and run cooler because of the thermal conductivity that aluminum possesses. Steel pipes on the other hand because of there hardness for one, resonate crisper and have slightly better power capabilities. They also run a LOT hotter generally.

So too answer your question, Higher heat within the pipe equals greater BTU's within the engine. It is the expansion of hot gas's that drives the piston down in the first place !
Greater the BTU's at time of combustion, greater the force against the piston, higher the power produced :dance4:


** This is the basic process, and many tuning parameters are at work in the final process. As suggested, try running pipe at a shorter OAL 1/4" at a time and see what it does for your power.

A pipes internal "Back Pressure" also effects it's tune.
Adding or removing a muffler, stingering up or down the outlet size of a pipe are ALL tuning tricks used by advanced tuners.

Reason ALUMINUM pipes are water cooled is because aluminum will anneal under the high heat while becoming softer while hot.
This makes for a pipe that would quicky fail after a few heat cycles. So they cool the coupler which cools the whole system.

Steel pipes run HOT and because steel does not measurably change it characteristics within the heat range it is subjected too.
When used in a pipe it can be allowed to run as hot as it wants.

Down fall of steel pipes is when used in tight quarters or under decks it burns up anything close by !!
They also in some designs suffer cracking caused by the heat cycling, vibration and flex causing the steel to work harden then crack at stress points.


I know .... more than you asked :dash:

What Scott said. And I would bet your water cooling was going inside the pipe. Either at the pipe flange (at engine) or at the coupler (between header and pipe chamber). It is common thing with those setups. You can eliminate the first (the flange leak) by using "no-leak" flanges. With this type of flange, even if the Orings get damaged, there is no possibility of water getting inside the header and pipe. The second problem (the coupler) can be taken care of by using good Orings and ensuring that the pipe sits in it's stinger support without forcing the pipe in any direction. The pipe should fall right into the bracket and the bracket then tightened without forcing the pipe.