OR, The scavenging affect of the hot spent gas leaving the cylinder helps draw more charge into the combustion chamber? Like drinking through a straw.
The reduction of backpressure can increase this affect.

 

Spark arrestor?, " I dont need no stinking " ahhh.... spark arrestor. [img]i/expressions/face-icon-small-tongue.gif[/img]

 

I'm trying to figure out why we lose HP at the low-end when we run open pipes. A lot of guys say you have to have backpressure to run right. Then you read the stuff from exhaust manufacturers that say its a myth, backpressure is bad all the time. Ok, ok, so we take the baffle out of our bikes n sure enough, we lost some low-end torque. But, then again we watch on tv all the drag bikes running open pipes and they don't seem to have any problem. What gives???

I can only think of 2 ways it could be.

1) Running an open pipe actually increases backpressure at low rpms by some law of thermodynamics or whatever.
2) Low rpms need to see the backpressure after the exhaust valve opens AND before the piston gets to the bottom or else the power of the expanding gases will just go out the exhaust pipe instead of pushing the piston down. Everything changes at high rpms and its actually better for the gases to blow themselves out the pipe rather than having the piston force them out. But at low rpms that's not such a good thing.

Everything would be easy if we had variable cam timing, lol. Just run open pipes for the most HP at all rpms.

I wonder if there is a way to hook some baffle up to the throttle cable. As you open the carb up, you also open the exhaust up. Backpressure at the bottom and none at the top. Instead of the way we have it now, plenty of backpressure at the top and none at the bottom, lol.

 

<div class="FTQUOTE"><begin quote>Originally posted by: BigMc

Spark arrestor?, " I dont need no stinking " ahhh.... spark arrestor. [img][/img]</end quote></div>

Dont know how it is in AL, but in GA.... well, not sure really about GA either, but since they regulate everything else we do I'm sure spark arrestors are mandatory in state parks. Especially with all the drought we've been enjoying lately.

We went from rivers overflowing to not being able to water the grass certain days of the week to never being able to water the grass and now I just seen in the paper they are saying we have to cut back on baths n washing clothes!

 

Could it be a lean mixture condition at part throttle? If the fuel mixture is off due to a lack of flow, then hp would suffer.

 

Arrestor's are required in Bama as well. Oh, and since you said something about it. What do you think about AL and FL arguing with GA over water rights? "Cant we all just get along?" [img]i/expressions/face-icon-small-confused.gif[/img]

 

<div class="FTQUOTE"><begin quote>Originally posted by: BigMc

Could it be a lean mixture condition at part throttle? If the fuel mixture is off due to a lack of flow, then hp would suffer.</end quote></div>


Could be.... If there is a small backpressure, then flow out will have a big scavenging effect. A big scavenging will increase vacuum in front of the carb. The increase in vacuum should try to equalize itself by sucking harder on the pilot jet and the air filter. I think it would be easier to suck more air than to suck more gas from the small pilot. So, the mixture would probably be leaner, I guess.

I think it is the other way around at WOT though. At least if there is a big carb involved. My 28mm carb was so starved of vacuum, it ran way too lean with the 180 main jet that it came with. I must have drilled that thing out 6 or 7 times before I got it right. Now, since I took out a baffle, I got a black plug, too rich. So, decreased backpressure is fouling my plugs. I had to go down 3 or 4 sizes of drill bits and drill more jets.

 

<div class="FTQUOTE"><begin quote>Originally posted by: BigMc

Arrestor's are required in Bama as well. Oh, and since you said something about it. What do you think about AL and FL arguing with GA over water rights? "Cant we all just get along?" [img][/img]</end quote></div>


I actually don't know that much about it.,, but I know GA wants to control everybody if that's any help to understanding. At least that's the impression I get. Its nothing out of the ordinary to have the government put restrictions on water use, and I guess Florida is no exception, lol.

 

71 mm is my piston size. Im ordering rings from total seal getting gapless top ring[img]i/expressions/face-icon-small-smile.gif[/img]

 

Well got new pictures up of my pipe, rear grab bar, chain tensioner etc, well I think the pictures are up depends on how fast the moderators approve.

Almost forgot also have my new Mikuni 28mm Flatslide carb installed to.