Trek 4500/ GP460 now Staton 18.75 Drive

[DetonatorTuning]

It is not about "pipes" filling up, that is an erroneous notion, it has to do with the time it takes for the (negative) pressure wave to be reflected back to the exhaust port to aid in scavenging,the shorter the pipe the quicker this occurs,which means at higher frequencies,that is at higher rpm.

thank you, but in the case of the 2 stroke doesn't the reversion wave help promote and contain cylinder filling ?

this doesn't sem to help answer the question of what amount of decline in low-midrange shoul dbe expected.

could you explain further please.

thanks,
steve

 

[kerf]

For what it's worth, that may not be a bad thing unless you plan on running WOT all the time. When I installed my expansion chamber muffler, I expected to loose top end and I did. The bike now tops out at 40 but the torque curve also seems to have moved down. The bike has a noticeable improvement in bottom end and is much stronger from 5-8K, my normal operating range. As a 30-35 mph cruise is what I want along with a much quieter machine, I'm happy. If I drop to idle at 25-30 mph, I can't hear my engine over the wind.

 

[DetonatorTuning]

well now ,this is getting real interesting because more and more options are surfacing as we go along.

with the original mounting bracket removed my Dom. is very close to fitting as is. i can take some material off the drive box casing ( not my first choice because someone else might want to use it someday ) or dent the expansion chamber to have it fit. ( not my second choice as there is no way to know what will happen to the characteristics of the pipe. )

i can cut the head pipe by 1/2" and loose some low-midrange and gain the height to clear the drive box. ( not my 3rd choice because i'd rather not go to the trouble, even though i have a very good welder available ) or i can add an x-port which will move the pipe forward away from the drive box causing the more upswept area of the pipe to be over the areas needing clearance and POSSIBLY pick up some lowend.

x-port it is. unless of course someone can find fault with my reasoning.

thanks,
steve

 

[DetonatorTuning]

For what it's worth, that may not be a bad thing unless you plan on running WOT all the time. When I installed my expansion chamber muffler, I expected to loose top end and I did. The bike now tops out at 40 but the torque curve also seems to have moved down. The bike has a noticeable improvement in bottom end and is much stronger from 5-8K, my normal operating range. As a 30-35 mph cruise is what I want along with a much quieter machine, I'm happy. If I drop to idle at 25-30 mph, I can't hear my engine over the wind.

kerf, do i understand you to be saying your new giant muffler alone gained you some bottom -midrange AND cost you 5mph at 11,000rpm ?

hmm, maybe increasing the volume of my pipe by adding the x-port is NOT what i want. i want a 40 cruise with reserve rpm's and speed.

Craig, can you put that x-port on your Dom. and tell me what happens ?

thanks,
steve

 

[kerf]

New WOT 9600, I'm on the dark side of normal in plug color, could go 1/16 leaner, could pick up some but just went 32/1 mix????? The bike and I topping out at 320#. Leaving well enough alone.

 

[duivendyk]

The physics underlying these exhaust tuning devices is quite complex because there are multiple reflexion points in the exhaust tract.These are deliberately introduced to shape the torque characteristic of the engine.The other day I ran across an article on line on this subject which was quite interesting.It was written by an expert on the subject (he had written computer programs to optimise such a system),but at the moment I can't recall how I got to it. My comment was of a general nature,at the high end it is difficult to expell the burnt gasses fast enough out of the combustion chamber,a negative pressure at the time the exhaust port opens can speed things up.At the low end a positive back pressure could help in pushing escaped new micture back in, improving cylinder filling.I will try to track down this article.

 

[kawasaki999]

Sorry I cant put x port on dom because it will move the mounting holes too far foward. you will gain some low end with x port and lose a little on the top.

 

[DetonatorTuning]

hmmm, maybe the answer is cut the pipe to gain the clearance and use the X-port to get the power bands back inline then.

thanks,
steve

 

[DetonatorTuning]

well,

i decided not to grind the box or cut the pipe or buy a X-port. since i already cut the bracket off the pipe to get it close sooo.......

i went ahead and dented the underside of the chamber approach throat and the lower rear reduction taper of the chamber itself.

it took awhile working progressively and i was concerned for awhile, (but i know where i can find at least one Dom. that might not get used ) the deeper i went the more i wondered how it was going to affect the powerband.

GOOD NEWS, it softened the bottom end VERY slightly but it GREATLY IMPROVED the 25-55mph range and the 35-45 range is CRAZY STRONG.

i'm adding a pic, it is not as clear as i hoped but you can see the 2 dents and kind of judge how big and deep they ended up. in the 2 critical spots i have 3/16" clearance.

steve

 

[appye]

How Do You Know It Will Fit Without Attaching The Gear Box? That Sure Looks A Lot Like A GEBE On There!