Another exaust thread with ?

[Scorpio1963]

Ok heres what I want to know if you are still running the standard 2 header pipes with the hpipe before the muffler,if you move the hpipe forward say about a 1/2ft closer to the engine what affect will have on your torque and rpm range,will I notice any difference and if so how much?
Once again thanks all for your help.

 

[drewpy]

I doubt you'll notice anything different, but maybe you won't be able to access the sump plug anymore

 

[Scorpio1963]

Thanks Drewpy for letting me know this,I`ll have to check and see if its going to cover it when I put the pipes back on.
OK what about if I moved it a foot closer to the engine would that make any difference?

 

[drewpy]

I doubt it!

 

[16VGTIDave]

Exhaust tuning is a science. Pipe diameter, pipe length, bends in the pipes, initial exhaust gas temperature, rate of gas cooling in the pipes, velocity of the exhaust pulses, restriction caused by the mufflers, and desired performance change all determine where a crossover pipe should be placed.

Unless you are able to measure these factors and run complicated computer simulations, then it is all down to guess work. That said, a crossover pipe will generally improve mid-range torque while making the exhaust noise quieter. One can usually use more restrictive mufflers without loosing top end power as both mufflers are used by each cylinder.

Dave

 

[Scorpio1963]

Exhaust tuning is a science. Pipe diameter, pipe length, bends in the pipes, initial exhaust gas temperature, rate of gas cooling in the pipes, velocity of the exhaust pulses, restriction caused by the mufflers, and desired performance change all determine where a crossover pipe should be placed.

Unless you are able to measure these factors and run complicated computer simulations, then it is all down to guess work. That said, a crossover pipe will generally improve mid-range torque while making the exhaust noise quieter. One can usually use more restrictive mufflers without loosing top end power as both mufflers are used by each cylinder.

Dave

Thanks Dave well I have my stock exaust sytem completed for now.Im not sure how far I moved the crossover pipe cause before it was pieced together with auto exuast reducer pipes and looked like crap especialy with all the muffler clamps.It probaly wont look like much cause I didnt take a before picThat will be posted below.

 

[Scorpio1963]

My stock exaust system after I fixed it,when I first got the bike there was great big gaping hole where the crossover pipe connected to the headers.I found another one from another bike and pieced together.Then I had cut the mufflers off cause they were all rusted.So now that I have this part completed not sure what Im going to use for the rest of the exaust system.Im thinking of a homemade baffled piece of pipe on each side or straight pipes.$ is tight so it doesnt look like Im going to be able to come with the 2 in 1 I wanted.

 

[Scorpio1963]

Ok heres something strange I found this exaust system from yamaha 400xj with 2 hpipes on it.So what would be the purpose of having 2 of them?

 

[bentwrench]

Are you sure they both flow through? Could be for support only.

Bear in mind that these bikes were Yamaha's first forays into twin cam motorcycles. Could also just be an experiment (like YICS)

 

[xschris]

Yamaha started making twin over head cam bikes back in the early 70's. Two I can think of off the top of my head where the tx/xs500 and the tx750 I still see a bunch of the xs500's around but not much of the tx750's I think they only made them for one year 1973 or 74.

 

[16VGTIDave]

Did I mention weird science is involved with exhaust tuning? I'd guess that the dual crossover pipes have something to do with pulse tuning.

Dave

 

[drewpy]

it won't be for tuning but lengthening the pipe means it will be quieter.

in effect, each exhaust pulse has further to go thus its quieter to meet the more stringent noise emission legislation in the models life.

 

[Scorpio1963]

Well I know Im talking 2 different breeds here but on dual exaust for autos the hpipe is to equalize exaust pressure which gives the engine more horsepower.Could this be the case with dual hpipes on the motorcycle exaust also?

 

[drewpy]

any exhaust barring 2 strokes need to scavenge the spent exhaust quickly.

Tuning the exhaust requires a megaphone type to send pulses back to block the valve overlap on highly tuned exhausts ( keeping the fresh charge from exiting the chamber) and that is only at certain RPMs.

I've never seen any H pipes on drag cars for instance!

 

[16VGTIDave]

it won't be for tuning but lengthening the pipe means it will be quieter.

in effect, each exhaust pulse has further to go thus its quieter to meet the more stringent noise emission legislation in the models life.

Umm, I believe that you contradicted your self. Lengthening = Tuning. Any change to the exhaust will have an effect on the tuning of the system.

If the Harley-Davidson's (and V8 trucks, School buses, etc.) around here can be used as an example, long small diameter pipes can be louder than a short, large diameter pipes. Like I said before, exhaust tuning is a science with many variables. Many books have been written on the subject. I don't claim to be an expert, I just know how ignorant I am on the subject...

Dave

 

[Lou Ranger]

Ok heres something strange I found this exaust system from yamaha 400xj with 2 hpipes on it. So what would be the purpose of having 2 of them?

With one fore and one aft, it would give you unfettered access to that sump plug

 

[Scorpio1963]

With one fore and one aft, it would give you unfettered access to that sump plug

Probaly not according to the pic because the 1st crossover is up on the bend of the header pipe.The 2cnd one is far enough back to where access is not a problem.

 

[OG-Rider]

All of post #5 is true. However, it's also true that when our bikes were built the japs always hung about 20 pounds of muffler on each cylinder, and used ridiculously restrictive intake systems. Most old jap bikes perform better if you open things up so they can breath, and then re-jet the carbs appropriately. Straight pipes do not have sufficient back pressure to get peak performance throughout the rpm range. Steal baffles of various lengths are cheap and readily available. I figure that when I get that far on my current bike, I'll use some of those baffles, the stock head pipes, and my seat of the pants dyno to get it sorted.

 

[16VGTIDave]

Make sure that you wear ear plugs while running your "dyno". You don't want to be fooled by thinking noise = power.

Better yet, perform rolling timed runs in 1000 RPM increments and document the results.

Dave

 

[bentwrench]

What I love about the butt dyno is that truly, the number doesn't matter. How the bike makes you feel is what matters. So if your awesome home brewed exhaust is louder, makes you proud of your bike, and you lose 2 hp but never notice because of the grin on your face, have you really lost anything?

All that vs. $100 for a run at the local speed shop to show you a line on a piece of paper (one that inevitably even LOOKS like a frowny face!)