engineering question

[rcmatt007]

I realize that no matter what there is a lot of "It Depends" to the answer... However.... on the M3W forum there is a lot of discussion about knocking out the cats and/or baffles hoping to get more power out the engine.

However, there are others that feel having better airflow into the engine is the way to increase power.

Feel free to add your thoughts....

[ericheath]

Another cat dies

[CYBORG]

Your right,"it depends". But old school always taught that the more flow, the more power.

[Oldewing]

engines are pumps, easy in easy out is always faster.....


forced in, blasted out better.

forced in , sucked out better yet

forced in, compressed, up boom capacity(Nitro) blast out....best..

[low-side]

If the cats are sized properly, they aren't hurting anything. If the engine has been modified, they might be too restrictive. Another thing to consider is that too little backpressure from the exhaust results in decreased effective compression which causes a loss of power and greater hydrocarbon emissions (gas out the tail pipe instead of burning to make power). Most "mods" like that just make something louder and frequently cause performance issues somewhere in the powerband.

[Track T 2411]

It's been often posited that Harley purposely restricts the stock exhaust on their engines so they can sell more 'upgrades' for instant power increases. Find a REAL Harley tuner and get more power without blowing out your eardrums...

[rcmatt007]

I did find that on my M3W I gained acceleration by simply replacing the stock air filter cover with one that has a slightly larger diameter and also has a built in scoop which helps at speed.

I have no intention of knocking out the baffles... which is why I added the third option

[robin1731]

I did find that on my M3W I gained acceleration by simply replacing the stock air filter cover with one that has a slightly larger diameter and also has a built in scoop which helps at speed.

I have no intention of knocking out the baffles... which is why I added the third option

So you set up timers and a measured distance to verify this?

.

[rcmatt007]

no... but the difference accelerating up the on-ramp onto I81 was significantly different as before I changed the cover it would flatten out

but that is an idea.... a la mythbusters

[dontwantapickle]

Another thing to consider is that too little backpressure from the exhaust results in decreased effective compression which causes a loss of power and greater hydrocarbon emissions (gas out the tail pipe instead of burning to make power).

this is incorrect

[low-side]

Another thing to consider is that too little backpressure from the exhaust results in decreased effective compression which causes a loss of power and greater hydrocarbon emissions (gas out the tail pipe instead of burning to make power).

this is incorrect

Too much back pressure slows the evacuation of gasses from the cylinder. A properly tuned exhaust scavenges exhaust gasses at just the right rate for a given set of operating parameters (rpm, etc.) to ensure optimum performance. A poorly designed system with too little backpressure can run into a number of issues, including reversion and in extreme cases exhaust of fresh mixture. In any event, there's a reason grandma's grocery getter isn't running 3" duals so just be careful that you don't accidentally ruin a good exhaust system. BTW, the stock Morgan cats do appear to be excessively restrictive if the pipe is otherwise sized properly.

[gltriker]

Another thing to consider is that too little backpressure from the exhaust results in decreased effective compression which causes a loss of power and greater hydrocarbon emissions (gas out the tail pipe instead of burning to make power).

this is incorrect

Too much back pressure slows the evacuation of gasses from the cylinder. A properly tuned exhaust scavenges exhaust gasses at just the right rate for a given set of operating parameters (rpm, etc.) to ensure optimum performance. A poorly designed system with too little backpressure can run into a number of issues, including reversion and in extreme cases exhaust of fresh mixture. In any event, there's a reason grandma's grocery getter isn't running 3" duals so just be careful that you don't accidentally ruin a good exhaust system. BTW, the stock Morgan cats do appear to be excessively restrictive if the pipe is otherwise sized properly.

Sounds more like, old time 2 stroke engine exhaust tuning theory. A "tuned pipe".

[Old Fogey]

To a much lesser extent on a four stroke and mainly the gains are found on competition machines, but the theory still applies.

[Sidecar Bob]

Some years ago Lang Hindle (Hindle Exhaust Systems) said in a magazine interview that the exhaust system that produces the most power is almost never the one that makes the most noise....

As for cats, it has long been known that poorly engineered ones can do more harm than good. When they first became required some models of car needed to burn so much more fuel for the distance travelled that, while pollution per volume of fuel burned decreased pollution per distance travelled increased. I'm sure the engineers have learned how to prevent that now but if the system isn't designed by an engineer that specializes in exhaust systems all bets are off.

[rcmatt007]

That is the "it depends" part of the question. How well the whole system is engineered. One advantage of newer ECU engines (over carbs) is the ability of the engine to adapt to conditions. Or, of course at a large price, installing a truly mappable ECU.