Topic: Oem Honda header pipe design w/ tuned inner steel sleeve;is it necessary ?

[grcamna2]

I'm looking to build a header/front pipe for a Honda single and have an exhaust tuning question for exhaust builders on here.Do you know if the 'tuned'-length inner steel 'sleeve' inside the chrome 'outer' pipes of the original Honda oem factory headpipes is necessary/important for good mid-range and low end power ? I had thought that the factory stock Honda headpipes had double-wall steel pipes inside them to keep the outer chrome part from 'bluing' excessively.. I admit I don't really have a clue on this and need some feedback from you.
I look at aftermarket headers and none of them have the double-wall steel inner 'sleeve'.. only the oem front pipes do.
Have any of you ever built a custom exhaust for your Honda and noticed a difference in torque or performance w/o that tuned inner steel 'sleeve' ?
I cut off the first 1.5" of the inlet flange(I want to have it welded to the new diameter headpipe) and removed the inner steel 'sleeve/cone' where it begins inside the inlet of the stock headpipe on my XR200;it looks like it would give the engine more initial backpressure having that piece inside the inlet and i am contemplating whether to re-install/weld it back in or leave it out.I'm increasing the diameter of the rest of the headpipe to compensate for having a larger bore and stroke and a nice ported head w/ a better cam.I'm going from 1" i.d. up to 1 3/8+" for the XR200 high performance engine and i'll be riding it on the street in a street bike frame and using it for all-around riding including climbing hills so I'm hoping it will still have enough low end and midrange power to go along with it's much improved higher top end performance.I haven't got it on the road just yet.

I'm just guessing but that little tapered inner steel cone shaped piece that i removed from the inlet of the stock XR200 headpipe I have pictured could be what's called an "Anti-Reversion Cone" and might help broaden the powerband of the engine considering that i'm increasing the inside diameter of the pipe..
I have looked in the inside of a few different vintage oem stock Honda header pipes and noticed that the double wall design begins with the inlet flange and then slowly increases in diameter until it exits at the end of each headpipe and then it's at it's largest diameter where it pushes the exhaust into the collector or muffler;that slow tapering design is the engineered factory exhaust tuning.

[333]

I've always thought that tuned exhaust is only needed for multi cylinder engines to keep back pressure even. And with headers, the tuning promotes scavenging(or the momentum of exhaust from one cylinder helping to "pull" the exhaust of the next cylinder". So, I'm not sure how tuning helps a thumper.

[grcamna2]

By 'tuning' I mean the inner shape/taper design of the oem factory Honda header pipes;the inner steel 'tube' is a big performance factor.They engineered/designed that to work well at many different engine rpm's and throttle positions.
I'm modifying my engine and trying to keep as much flexibility in the powerband that I can.
The sohc4's also have the 'double-wall' stock oem header pipes which give the stock engines the best all-around performance,the stock header pipes are much heavier than an aftermarket 4into1 header for that reason.

[Don R]

 Most of the newer dragster headers are step tubed, they start small and increase in size one or two sizes. I'd stay close to the factory dimensions if it's a stock engine.
  The overall length of a pipe can tune the torque curve. There is a program named pipemax that can get close to optimal given the correct info.
 

[grcamna2]

Most of the newer dragster headers are step tubed, they start small and increase in size one or two sizes. I'd stay close to the factory dimensions if it's a stock engine.
  The overall length of a pipe can tune the torque curve. There is a program named pipemax that can get close to optimal given the correct info.

Many of the Honda oem header pipes are a type of 'step tube' of gradually tapering design depending on the shape of the pipe and type of engine;the Honda engineers designed them to be optimal exactly for each model bike.
I used to hate those little decals that Honda put on the bikes when i was a kid basically saying 'leave this exhaust system alone because nothing will make it run as good as it does'  , at least that was my 'take' on it..
This XR200 engine isn't stock and has excellent port work done but will be a mild version of what i call "high performance" and to start will have an oem keihin carb. and 10:1 CR oem piston and the stock camshaft and increase later.I want a good all-around street engine that can be pumped a bit more if i want to burn more fuel  .
A fun little street 'saver' mini-cycle to get me around a bit slower than warp speed so i can 'stop and smell the roses' while I'm on my rides.
I was reading on one internet search I did from an Australian Bucket Racer that a 36mm i.d. headpipe will work best so I'll shoot toward that dimension when i look for the right o.d. automotive pipe(and the i.d. will change according to the thickness of the tubing)to give me 1 3/8"+.A tubing bender dude will do a mandrel bent head pipe for me but he prefers bending thick tubing.. I'll call him on Sat. and see.
Don,Have you ever used "pipemax" for a motorcycle engine ?

[WCJonesJr]

+1 on Pipe Max

http://maxracesoftware.com/pipemax36xp2.htm

Find a copy of Scientific Design of Exhaust & Intake Systems by Philip H. Smith