exhaust headers?

[jchristy456]

Hey fellas


So i picked up some new stock pipes to day from a guy. As we were discussing my plans for the pipes he told me something interesting. I am planning on running just the headers. He informed me that that wasnt wise. The muffler serves a "pressure" service for the valves. I asked him to elaborate but he couldn't. any ideas why running just the header is a bad idea? and if so what are my options.



thanks doods!

 

[RatyXS]

You can run just drag style pipes. Not going to affect valves. Drag pipes will hurt a touch of low end. 2 into one pipes or pipes with a x over tend to keep it because of increased scavenging effect from the chambers . But your not hurting anything by running drag pipes. You can make lollipops to put in the pipes that will get your low end back. Again as long as you have pipes of some sort it will not damage valves.

 

[NONclow]

Without getting too involved..... it has alot to do with: Midrange torque


"Backpressure": the muffler restricts flow enough so the outgoing exhaust pulse fills the headpipe. Too much flow and the pulse exits so rapid the next pulse cannot be scavenged by hot escaping gases unless you're high in the powerband/RPM

Pulse timing: Each 4-stroke cycle produces 1 exhaust pulse. Spent gas volume is determined by displacement, air/fuel metering, and valve timing. The pulse size also varies from small (small throttle openings), to large (WFO). For optimum tuning, the length of the primary headpipe should match the length of the pulse.

Most manufacturers, not aftermarket companies, are looking for the best balance. If you want to run short pipes you can make or buy baffles that should retain the power, unless you want to run at 6500rpm all day log (not recommended for these bikes)

On the other hand there are countless muffler options out there

 

[jchristy456]

xs650.com does it again! thanks guys for all of your help. NONclow and ratyXS thnaks for taking the time to explain this for me.

 

[hoffman900]

Your only issue about burning the exhaust valves is if the pipe is way too short. I doubt anyone is running a pipe that short however.

If back pressure increases power, then your pipes are too big.

Most people put too large of pipes on the XS. Even successful LSR 650 Triumph racers are using 1 3/8" head pipes for engines that peak in the mid 7000 range.

Tune length is about getting the proper length for a given rev range.

2-1 will certainly have more mid range than 2-2. This has been hashed out by the Harley guys with MANY examples. Can't say this will hold true with a rephase however.

A few successful tuners build exhausts this way:
Primary pipe / diameter for the given engine combination. Sharp step up at the primary tune length coinciding with peak power. Megaphone / muffler is extended to the corresponding torque peak length.

You can figure all the above mathmatically, and it will get you 98% of the way of an ideal combination as figured on the dyno.