Well, it's not taking me long to find subtile ways of "uncorking" some flow potential with the X18 . Many years ago a wise old man schooled me on the advantages and dangers of "backyard performance". My performance mentor commented further that a combustion engine is simply an air pump. As for performance gains generally speaking when you "let more air in, you need to let more air out". So if you add a huge 22 mikuni carb , but you have the stock choked exhaust your not gaining anything. Adversely when you add a performance larger diameter exhaust, and the engine is sucking through the stock carb and intake valves... again your not going to gain much flow. A wise tuner will know how and when to modify flow, and also when to STOP modifying for reasons of loosing hp beyond a certain point of modifications. My performace mentor has a famous comment with respect to backyard performance junkies : "I'ts far easier to loose 3 hp trying to gain 1 hp.. "
So with the X-18' exhaust, and after drilling some rivets and removing the end cap I clearly found my first "choke" point within the stock X18's exhaust :
This partition restriction must be the "governor" to the limited top end on the engine. Most of the exhaust piping measures about 1" and that restrictive tube only measured 5/8". So it had to be removed. I've read other posts about cutting the canister open and re-welding, but my peticular mod only requires drilling and grinding. So those of you without a welder can do this mod.
Step 1) For future ease of assembly index the end caps and the body with a marker:
Step 2) drill out the 8 rivets at both ends using a #20 (.170") drill.
Step 3) Now lay the muffler vertical with the 3 bolt flange facing up. Place just the aluminum canister OD on top of your vice jaws. Now use a wood block and rap the top of the flange and the core will start to exit out the bottom (spray a little WD40 at the joint if its being stubborn). :
Now you will need to drill out the inner restrictor tube. You will need about a 3/4" drill minimum. I have the luxury of being able to stuff a 2-3/8 behemoth drill at my work. After you drill out the tube you can just grind out the remainder of the partition. :
At this point you're probably asking "why not just gut the whole muffler for better flow " ? Reason being is 4 stroke engines need a certain amount of exhaust gas flow restriction. This slight restriction creates better exhaust scavenging, and the created backpressure also cools your exhaust valve(s). If you have zero restriction you are actually hurting performance and possibly doing harm to your engine. If you look at the next pic you can see there is another offset "chamber" that IMO will not hinder exhuast flow, and modifying any further simply won't yield any further gains but just increase noise.
Next step is to grind and clean up the hagged snot welds on the inlet side of the muffler core for better unobstructed flow :
last step is to line up your previously marked index lines, and re-rivet the muffler back together ! Granted this mod is not going to produce earth shattering performance gains such as a big bore kit, but for a "cheap" mod that most anyone can perform it will certainly help! Cheers,
Rich
So with the X-18' exhaust, and after drilling some rivets and removing the end cap I clearly found my first "choke" point within the stock X18's exhaust :
This partition restriction must be the "governor" to the limited top end on the engine. Most of the exhaust piping measures about 1" and that restrictive tube only measured 5/8". So it had to be removed. I've read other posts about cutting the canister open and re-welding, but my peticular mod only requires drilling and grinding. So those of you without a welder can do this mod.
Step 1) For future ease of assembly index the end caps and the body with a marker:
Step 2) drill out the 8 rivets at both ends using a #20 (.170") drill.
Step 3) Now lay the muffler vertical with the 3 bolt flange facing up. Place just the aluminum canister OD on top of your vice jaws. Now use a wood block and rap the top of the flange and the core will start to exit out the bottom (spray a little WD40 at the joint if its being stubborn). :
Now you will need to drill out the inner restrictor tube. You will need about a 3/4" drill minimum. I have the luxury of being able to stuff a 2-3/8 behemoth drill at my work. After you drill out the tube you can just grind out the remainder of the partition. :
At this point you're probably asking "why not just gut the whole muffler for better flow " ? Reason being is 4 stroke engines need a certain amount of exhaust gas flow restriction. This slight restriction creates better exhaust scavenging, and the created backpressure also cools your exhaust valve(s). If you have zero restriction you are actually hurting performance and possibly doing harm to your engine. If you look at the next pic you can see there is another offset "chamber" that IMO will not hinder exhuast flow, and modifying any further simply won't yield any further gains but just increase noise.
Next step is to grind and clean up the hagged snot welds on the inlet side of the muffler core for better unobstructed flow :
last step is to line up your previously marked index lines, and re-rivet the muffler back together ! Granted this mod is not going to produce earth shattering performance gains such as a big bore kit, but for a "cheap" mod that most anyone can perform it will certainly help! Cheers,
Rich
