Free ride vs freestyle vs race engine

[tntsuperjet]

Wax don't confuse low blowdown backwash with bad pipe tuning.
28 deg of blowdown timing is enough to pull any cylinder to a negative state if the pipe is correct.
But look at the pipe tune lengths of watercraft wet pipes vs a hot dry pipe of other two strokes.
We have the pipes so dang short in most cases we are causing that pressure wave to recharge the cylinder and needing exessive blowdown to allow the transfers to do part of the pipes job.
Nuke, you are right the difference between 180 and 200 will be noticed right off idle. But it will only be noticed at 3/8 throttle or less.
Once your inlet volume exceeds your trapping loss the motor will actually hit harder as you will have cold I burnt fuel in the exhaust on your reverb wave that is still in a warm state from mixing into expansion dwell of the pipe and when it recharges it will give faster burn rate.
But the motor will def lag much more at 1/8-1/4 throttle under 4000 rpm.
My best advice is to break your power into three3rd.
First third is low end second third is mid and last third being top end.
Because we are direct drive anything at 1/4 or less the motor cannot get past mid range power.
But look at the rpm difference between the first third of throttle and last third of throttle. There is 3500 rpm plus difference in engine rpm to that throttle positions
But now look at the difference between 1/2 throttle and full throttle it's maybe 1,000 rpm.
Why is the rpm not linear between thirds of throttle??
How can you say that 1/4 throttle isn't oat affected by engines low end ability when 0to 1/4 throttle the engine is in the lower quadrant of its available RPM's???

 

[waxhead]

Wax don't confuse low blowdown backwash with bad pipe tuning.
28 deg of blowdown timing is enough to pull any cylinder to a negative state if the pipe is correct.
But look at the pipe tune lengths of watercraft wet pipes vs a hot dry pipe of other two strokes.
We have the pipes so dang short in most cases we are causing that pressure wave to recharge the cylinder and needing exessive blowdown to allow the transfers to do part of the pipes job.

I understand what your saying there but if the pressure wave was coming back fast enough to push the spent gases down the transfers after only 28-30 degrees of crankshaft rotation you would have to have such a short exhaust I'm not sure how you could even make it. I agree that we have really short pipes due to them running cooler than a normal two stroke dry pipe. Most engines I port I normally run and anti reversion step in the pipe to cylinder area to help avoid the hot gases coming back into the cylinder. I learnt the hard way when porting an rs125 that grinding the anti reversion step out loses about 3hp.

 

[tntsuperjet]

I am finding that the sharp bends in the exhaust manifold are a big ga use of transfer back wash and contaminating clean I take charge with spent gasses from exhaust below 3000 rpm.

 

[tntsuperjet]

Another big cause of the transfer charge back wash is inconsistent exhaust pressure caused by water loading the exhaust outlet.
Example landing hard on the tail of the boat will cause hard pressure wave back at the engine and leave exh residue all the way back to reed pedals.
So if you want to do trace debris analysis you really need to start with clean cyl and cases and run the boat in clean water and never back load the exhaust then do a tear down.
Other wide there to many variables in riding any standup that can cause the exhaust blow back contaminants.
Just a little food for thought.
I have done 30-40 dyno runs on a motor and had no carbon traces in the intake track and after couple hrs running had quite a bit.
This is what made me redesign a water box to help eliminate exhaust back loading and help improve exh flow and jetting inconsistencies do to inconsistent exh flow.
If your not catching what I am saying try this little truck.
With your boat on the stand start it and rev it up three times good and hard, then have someone cover the exhaust outlet with two finger and rev it three more times you will hear the boat go log rich. Specially if you don't have a water box.

 

[holeshot]

Agreeing with TNT, Blowdown period and pipe design go hand in hand. Ive worked with motors that make power up to 20k with just 30 degrees of blowdown. Blowdown is not just the degrees of crank rotation its also the area of the port, more area even without more time is still more blowdown. If youre blackening transfer passages you should be having serious charge dilution problems effecting power at that rpm. To me those black transfers sound like the effects of extremely retarded ignition timing during rev limit.

 

[tntsuperjet]

So many racers make this mistake it's mind boggling.
They will get on there knees and go from a idle and stab the throttle. Then they will tune the carbs to pull what feels the best from that same on the knees idle in the water.
The. At the start they lift the boat out of the water and rev it clean and dry eliminating all the water and drop the boat back into the water just before the band drops and then stab the throttle and it lean bogs or dies. Well hello. You just blower all the water out of the exhaust and then didn't give it time to get wet so your pipe is hot and short and your exhaust is open and free the boat goes lean and your start sucks.
Why?? Do you do this over and over yr after yr and never learn why u bog out on the line??

 

[tntsuperjet]

Agreeing with TNT, Blowdown period and pipe design go hand in hand. Ive worked with motors that make power up to 20k with just 30 degrees of blowdown. Blowdown is not just the degrees of crank rotation its also the area of the port, more area even without more time is still more blowdown. If youre blackening transfer passages you should be having serious charge dilution problems effecting power at that rpm. To me those black transfers sound like the effects of extremely retarded ignition timing during rev limit.

To many watercraft guys to confused on port timing vs timed port area!

 

[holeshot]

We all have the same interest just different theories. its all for fun. Enjoyed everyones post. Have a good night.

 

[waxhead]

Agreeing with TNT, Blowdown period and pipe design go hand in hand. Ive worked with motors that make power up to 20k with just 30 degrees of blowdown. Blowdown is not just the degrees of crank rotation its also the area of the port, more area even without more time is still more blowdown. If youre blackening transfer passages you should be having serious charge dilution problems effecting power at that rpm. To me those black transfers sound like the effects of extremely retarded ignition timing during rev limit.

I agree with you that's why I always say time/area so as not to confuse
I guess each to their own op as to what causes blackening of transfers.
But if you were running the timing that retarded I would think the pipe would melt off pretty quick. I would agree you would be having charge issues. As far as I'm concerned if the pressure in the cylinder is to high enough to push back down the transfers the pressure has not dropped enough so either you have a major blockage in the exhaust which would have more likey melted a piston and that's why you are looking at the transfers or the exhaust is not dropping the pressure enough and its pushing at the transfers( a badly designed pipe that's crap at scavenging could cause this )If the pressure has not dropped enough then increasing the blow down by raising the exhaust or lowering the transfers will help fix it. In the crap 62t platform decreasing the transfers is not something you really want to be doing so it's up with the exhaust

Kinda think we are saying the same thing just saying it different ways. Always good to hear the op from some one else whose work you respect. Every day is a school day

 

[MADMAT]

Good reading! I think :/

 

[DAG]

All this awesome info and no one has said anything about the speed of the return wave and how its directly related to the pipes temperature.

 

[holeshot]

All this awesome info and no one has said anything about the speed of the return wave and how its directly related to the pipes temperature.

Pipe temp has a dramatic effect on powerband characteristics. But so does port time area. Different people have different preferences. Some like power to come on hard early and slowly fade, some like it to come on smooth and pull harder as it revs. In another industry i noticed novice to expert riders went fast having as much power as they could get with an early hit, while expert to pro riders rode above that style of powerband. They wanted a later hit that pulled high into the rpm range.
I think in the stand up world these two powerband preferences may also apply to the different preferences of the surf/freeride/freestyle rider and the closed course/high speed corner rider.
having the right pipe for the motors design is a big plus for sure.

 

[OCD Solutions]

Can we add chamber composition to one of these conversations? Mild Steel vs SS vs Carbon? Effects of Ceramic coating?

 

[holeshot]

Can we add chamber composition to one of these conversations? Mild Steel vs SS vs Carbon? Effects of Ceramic coating?

Mild steel and stainless have the best accoustic characteristics. Aluminum not quite as good and carbon would be my last choice because it would dampen the sound wave making it less effective. Thats my opinion anyway.

 

[WILKEY]

Lololololol

 

[tntsuperjet]

Having built all the above pipe materials in the same pipe design I have found there differences in power curve.
Mild steel transfers heat well and at a good speed for exhaust systems
Stainless isolates heat quite well and allows for high inner and outer pipe temp differences.
Carbon is quite slow in hearing up and has inconsistent heat transfer causing hot and cold spots.
Alum transfers heat so fast it quite difficult to get a high surface heat.
That being said here the results with my given tune dimension on same engine with different materials

Mild steel has most Consistant hp, and the ability to control temps with more accuracy.
Stainless you get a high temp variation inside pipe vs outside pipe and quite easy to get inside surface hot quickly and Gears great for ECWI to hqve large affects on tune length.
Alum, I found difficult to tune as it dispersed heat so quickly the pipe actually was to long in tune length.
Carbon, was not possible to get the inner pipe surface hot enough and high rpm hp suffered much like the alum pipe. But with the carbon once you got the pipe hot it was quite slow to cool making boat hard hitting then soft soft soft,
If you have a carbon pipe it's critical you keep the temps cold and keep your setup tuned to perform with a cold pipe.
Personally I find bare mild steel to be the best all around and ease to tune.
For racers who are looking for hard pull off the line and the ability to soften the power and gain rev stainless really helps that.

From my testing the vibration resonance theory had little affect on wet pipes.
As 18-20-22 gauge steel pipes all performed vertually identical.
But in stainless they do not perform the same. 20 gauge out performed 18.

That being said I do not have a way to actually test the affects of air speed under different vibration conditions. So that leaves the door wide open for several theory's as to why the different thickness of stainless have diff affect.
But also keep in mind the dif thickness of mild steel vertually no affect.
So there is plenty of room there for debate.
Guys I can't see very well up close anymore so please excuse my typos as it's really hard to proof read on my phone without my glasses. So I don't!!

 

[Quinc]

Is there an average chamber temp that one should try and achieve to get the most power out of pipe?

 

[tntsuperjet]

Well there is a average pipe pressure every motor needs but pipe temp all dependent on port spec, prop, timing water routing and desires eng rpm vs what ever pipe tune dimension you have.

Sorry I won't post pipe pressures required as that's yrs of testing and finding gauges to measure pipe pressures.
That one is saved for TNT customers who have our engine packages

 

[tntsuperjet]

I also will be working with Eric on a TPE cyl. building that motor for Rob Flores for his twin cyl Yamaha for next yr.
we will have a 860cc twin and a 1200cc triple Yamaha in his new hulls.
Then something speciall for 2015 finals.

 

[waxhead]

I'm very much looking forward to seeing the pipe for the triple. When do you expect that to be on the dyno