backpressure mythos

[jimn235]

if i understand correctly, it is posted in many, many places that stock dual exhaust is somehow less performant than 4-2-1 replacement single cans...

I have to say I have a blast with my stock 4-2-2 on my 96 600 kat. if in fact this is overkill exhaust on a stock bike wouldn't it be more exciting to fix the CAM profiles and/or jet richer than to stuff a tennis ball in the tailpipe?

[91_gsx600F katana]

You always want alittle back pressure in an exhaust system... too much can limit performance and become a restriction.

not sure i agree with your statement. The fact is that stock bikes can benifit from aftermarket higher flowing exhausts. More is gained when you increase the output of the motor with a jet kit,filter,ignition advancer (all those would be pointless if you couldnt get exhaust gases out more efficiently without a performance exhaust). Aftermarket systems allow exhaust velocties to stay higher and help with scavenging, allowing more exhaust to exit faster/more efficently and reduce restrictions. Adding another turn (or path to follow) like a dual can setup will reduce velocties compared to a single can setup. Of course higher flowing dividers or HEII even an X pipe of some design could help even out the exhaust pulses and help more with scavaging in a dual exhaust setup. But that would also mean running a 2 primary into a single pipe then into an X pipe into dual cans. Works on race cars, increases the RPM range alittle and mellows the exhaust tone out too! Proof and experience on my 521cuin big block race car.

[boomer_95]

You always want alittle back pressure in an exhaust system... too much can limit performance and become a restriction.

sort of... if you look at a race application, they have little to NO back pressure. for example, moto GP bikes and drag cars (top fuel being one with NO back pressure)

little to no back pressure will KILL any low end performance. you have to rev to red line just to get the huge boost of performance they do give. in other words it is one of the many factors that moves the power curve or "power-band". the less back pressure the higher (in relation to RPM's) the power-band is, the less low end you have. the more back pressure you have the lower (in relation to RPM's) and longer the power-band is, but less top-end you have.

This is all true ONLY if the bike is jetted and setup for that exhaust system. if its not properly setup, any exhaust you put on that isn't OEM will run like crap regardless of RPM

[jimn235]

This is all true ONLY if the bike is jetted and setup for that exhaust system. if its not properly setup, any exhaust you put on that isn't OEM will run like crap regardless of RPM

what are the stock dual characteristics that might seem flawed as mufflers and pipes go?

I look and I don't see anything goofy with regards to flow, and the mufflers do seem generous, if not excessively throaty; dual setups tend to be quieter than single setups in my experience given the increased surface area challenging the output.

wikipedia "scavenging" includes
(i.e. modifying the exhaust gas velocity by changing exhaust tube diameters) can detract from the "ideal" scavenging effects, and reduce fuel efficiency and power if not properly planned out and executed.

did suzuki use the wrong measuring stick with the katana exhaust?

[scottynoface]

did suzuki use the wrong measuring stick with the katana exhaust?

No, they just didnt care about the performance because the Katana isn't a performance-dedicated bike.

Switch to a 4-1, you'll notice the difference.

[boomer_95]

There's more to exhaust than backpressure. That's just one of the many factor in building exhausts. And also as Scotty said, the Kat is not a performance bike in any form

[GSXFJim]

There's more to exhaust than backpressure. That's just one of the many factor in building exhausts.

+1

Other exhaust related things to consider.. while not considering getting the A/F mixture into the cylinder and getting it to ignite... thats another subject, as related as they are.

Longer header tubes tend to increase power below the engine’s torque peak and shorter header tubes tend to increase power above the torque peak.

Large diameter headers and collectors tend to limit low-range power and increase high range power. Conversely, small diameter headers and collectors tend to increase low-range power and limit high-range power.

"Balance" or "equalizer" tubes between the header tubes tend to flatten the torque peak(s) or widen the power band.

Stainless headers do not transfer heat to the ambient air as fast as mild steel headers. Keeping more of that heat "inside" the header pipes aids exhaust flow because the hot exhaust gas is more energetic and it reduces the amount of heat flowing across the engine.

[boomer_95]

and the collector configuration also needs to be considered as well... if its a 4-2, 4-1, or 4-2-1, they all have different effects. also which cylinders are joined at which point has an effect as well. everything mentioned will change the characteristics of an engine slightly, even tho they may still have the same back-pressure's. its a very delicate subject that can-not be simplified by one simple thing like back-pressure, even tho that has a large effect

[H-2 CHARLIE]

Some pipes are just loud and the other ones a bust .

[KatKrak]

^^ threads been reduced to fart cans