Whats your Header size.

[Buda]

Hi Guys, I recently installed a set of Staintune header pipes to my R12s and quickly noted the diameter of the original headers is much larger. I measured both sets at a spot roughly 100mm from the flange. The BMW pipe has OD size 20mm or about1 inch larger than the staintune header. I'm a bit confused over why the staintune pipes are smaller and would really like to ask folk with aftermarket headers like AKA, laser. to post the header pipe size.

[Martin Glasser]

The photos are showing Circumference. Diameter=Circumference/3.1412

[1100s nut]

Buda, it looks like 2 cm larger circumference and that is about 1 cm Or less difference in dia. As to why staintune would make it smaller than oem is Interesting...the HQ being in your country, I am looking forward to what they have to say.

Lane

[GotRoad?]

Originally Posted by Martin Glasser

The photos are showing Circumference. Diameter=Circumference/3.1412

close, but C = 2πr, not C= 2πd so the cross sectional area; A= πr(exp2)


For C =14, A~15.6 and C=16 A~20 or a difference of ~25%. Since I'm not a engine guy I can't speak to the question of what that difference might mean.

[shreddr]

The gas velocity in a smaller diameter pipe is greater. If bigger was better, then the best setup would be nothing at all, which of course is not true. The Akra on my HP has a slightly smaller header diameter than stock, I am sure that is not by accident.

[1100s nut]

Why the oem Is not spot on in order to get best HP....wonder why?

[roger albert]

Since approximately NEVER has the OEM been spot on for max power, so that´s not even vaguely a wonder.

OEM has to do a ton of things, like be cheap, and durable, and damp out sound, and last the length of the fuel system - emission system´s

All of those are aided by relatively large diameter, and, more importantly, high wall thicknesses.

Which leads me to the point being missed, that measuring the OD vs the ID doesn´t say much, and that further, that sort of thick cloth tape is very inaccurate for such small diameters anyway.

Just because the outside is, for example, 2mm smaller, doesn´t mean the ID, is that much smaller. In fact, in aftermarket stuff, you can be sure it´s thinner, so, the difference is probably smaller than was calculated here. Also, even then, shreddr´s point about velocity is relevant too.

Good question for the curious, so not knocking it by any means, but I´d definitely file under teapot based tempests.

[1%er]

Shreddr, having seen your thread about installing a big bore kit to increase the displacement, you have altered your torque curve and moved higher. You have kept the primary pipe area constant on while increasing the cylinder displacement. If the size is too small you will create peak exhaust gas velocity too early in the rpm curve and limit you top end hp. You may want to discuss this with Akra and see what they would suggest as the optimum size for your current displacement.

Roger is right. Area= Pi x id radius x id radius

[Kernel K]

I suspect part of the difference is in the wall thickness. Is the Staintune significantly lighter than OEM?

[1100s nut]

Hahahahahahahahahahahahahahhahahahahahahahha! Roger you are a trip!

[twodear]

+1 Roger

The stock pipes are compromised for the majority of the target market; I'll put my neck out and say the target market are mainly in stop and go traffic and go for the occasional blast on the highway.

Those wanting the greatest amount of power for sport riding look for an exhaust that gives the most efficient extraction at a certain rev range - lots of science there as Shreddr alludes to.

in car circles, or better yet, truck pulling circles in the early days - smaller diameter meant higher low end torque at the expense of top end HP.

Nothing to add about differences in paper tape readings though - I be quiet now.

[chewie]

Average

[PFFOG]

What they said, lots of tricks with velocity's can change the characteristic of a power curve. But then again, maybe they just buy a boat load of that diameter for other applications, so it is economical to use it.

Either way the sound of the Staintunes will make the ride more fun, as you can turn off the ipod and listen to the sweet internal combustion music.

[darstardly]

My laser headers are also smaller dia I questioned this and was told higher velocity open pipes no cat means more power

[shreddr]

Originally Posted by 1%er

Shreddr, having seen your thread about installing a big bore kit to increase the displacement, you have altered your torque curve and moved higher. You have kept the primary pipe area constant on while increasing the cylinder displacement. If the size is too small you will create peak exhaust gas velocity too early in the rpm curve and limit you top end hp. You may want to discuss this with Akra and see what they would suggest as the optimum size for your current displacement.

Roger is right. Area= Pi x id radius x id radius

interesting point, although I doubt I would purchase another exhaust. The HP2S Akra is pricey enough, I can't imagine what a one off would cost!

as I have the Rexxer at my disposal I may try something else if I am not happy with the final result, but SOP dyno is telling me that the big bore is a fricking rocket and I have certainly not limited the top end rush in anyway.

gasses are interesting things, being compressable and all (try that with a liquid!) I may reach out to Akra and see what they say, perhaps I can do something with the crossover tube if necessary.

[1100s nut]

I can honestly say I have never felt an appreciable gain on any of the after market exhaust systems I have installed....including the staintune I installed on my boxer-cup. I like staintune because it sounds better and looks better. Even it helps 4 HP I not sure I would notice....if I did I would not notice it after one week.

Back to my oringal question...I still dont understand why the MFG would not do a little dyno work and get the best HP based on a given back pressure and spec. that to the vender.

lane

[roger albert]

Actually, it was pretty much answered

Since approximately NEVER has the OEM been spot on for max power, so that´s not even vaguely a wonder.

OEM has to do a ton of things, like be cheap, and durable, and damp out sound, and last the length of the fuel system - emission system´s

All of those are aided by relatively large diameter, and, more importantly, high wall thicknesses.

Seriously, that the real, and fairly obvious deal. Unless you're a well budgeted top fuel drag racer engine builder, things are pretty much never shipped tuned for peak power. Too many other real world (be that physics or bureaucracy) constraints and design inputs.

[1100s nut]

Roger, I am not doubting you...just puzzled that most mfg`s would not take something that is so important and not do their very best. But if getting peak HP from from the pipe throws emissions or sound out of limits then I guess I understand. But cool...it s all good.

Lane

[wswartzwel]

and lets not forget the styling dept, has a say in what looks best..

[bradzdotcom]

wahoo! i'm throwing down a semi-rant:

i think maybe some of you guys are missing the point when it comes to a manufacturer's attitude and goals in regards to producing a production motorcycle.

no manufacturer i've ever been involved with for the past 40 years is interested in making every single component the best it can be to deliver the most horsepower. that's just not going to happen.

the focus is on making a bike that's finance-feasable, reasonably reliable, won't come back and bite them in the butt with warranty repairs, won't embarass them by grenading, etc, etc, etc...

the goal to deliver the utmost available horsepower from a production-based motorcycle is the job of the race team, not the team that produces the production motorcycle in the first place. those two teams aren't even in the same building, much less the same country.

the team that produces a production bike has (among other things) a goal to produce a reliable and consistently replicable bike that's ball peen hammer safe.
a bike that the way-way-way-below-average, ignorant, irresponsible, abusive and clue-less owner can ride it like he raped it...without the bike exploding and tearing off his leg from mid-shin down...or some other variation of a gruesome outcome.

not tuning to the ultimate capabilities of the assembled components has more to do with being financially sensible and less to do with the dyno enthusist or track day ricky racer who, most times, if he blows it up, probably knows deep down inside that he caused it himself.

does anyone think that if shreddr goes out and grenades his modded hp2Spurt, that he's going to file a claim with bmw?
by all appearances, he's probably built the bike that the guys at bmw's R&D group wanted to make in the first place, but they had to tone down, based on massive meeting with those other guys at bmw who represent the warranty dept., legal group, financial nerds, spare parts division, mr. top dog bmw himself (whoever that is), who plans to put that indoor pool into his next house and damn sure wants to make sure nothing gets in they way of that, because his wife wants it, etc.

they'll never do it. don't hold your breath, you'll just pass out and when you come to, it will all be the same.

this week's favorite: i read an article that compared boeing's most popular aircraft's fuel consumption, pitting continental us flights against european flights of the same time/distance over a long period of time (i think it was 5 years).
the us based carriers spent an average of 340+ million dollars more per year on fuel than identical flights in europe because americans are fatter.
matter of "f", boeing's specs for fuel consumption is based on a particular plane that has very few (if any) coats of paint on it. i think it's silver.
that article prompted me to harass one of my sisters, her being part of boeing's lawyer team (good for her) yet still my sister (not often good for her).

her response was "yea, you wouldn't believe the reams of legal documents pertaining specifically to how many coats of paint are put on an an ordered aircraft, and how much each coat weighs. there appears to be a developing situation where aircraft purchasers are now positioning themselves to sue us and the paint manufacturers for falsifying the amount of weight that each particular layer adds, from primer to clear coat. we're good, the numbers are solid, the whole thing is stupid but it's job security."

i'll acknowledge that the aerospace industry is way ahead of the motorcycle world, but if nothing else, it's refreshing to see that we're not (yet) that incredibly anal. i guess we're too small to attract the bigger legal sharks.
give us time, we'll get there.


ps: love the measurements with the cloth rulers.
epic fail.
thank god none of us are brain surgeons.

any of you guys ever heard of very near calipers?
snap on sells 'em.
stalk a commercial industrial complex long enough (cnc machine shops make for a good location), then throw yourself in front of the snap on truck.
after he screeches to a halt, ask him about 'em.
last i heard, they even offer financing.