stock header question
 

Sunday, 9:30 a.m., cup of coffee in hand, when a question re-hit me. I'm in the process of getting my BCP headers and Z-Tek up pipe ceramic coated (no plug for the company), and on removal, I wondered what function the cross-over pipe served in the exhaust design of the stock bike. Just curious.

That's a very good question....the easy answer to which I would normally have spouted off about. However, given recent things we've seen, none of them explain in my mind why we see such diversity. Take the R1200S for instance. Stock header has cross-over. Replacement Remus does not. The R12S HP we saw race at LeMans has two. So what does this mean? Is this just fine tuning for the application? Is one method wrong? I don't know.

Bob certainly knows more about this than me;but, I've been told that it's a sudo two into one adaptation that allows for improved evacuation of the exhaust plus reduced back pressure because the exhaust gas has the use of both pipes to get sucked out and therefore a boost in HP. Only a dino could prove/disprove this assumption. I've always heard that two into one systems produce more HP. The crossover does simplify the pluming problem and gives balance to the look of the boxer engine.:confused:

I found this blurb on the website

Hi Pro motorcycles have one pipe because the entire exhaust system is
tuned to the upper power band. Bike engines have to be small and light
and powerful, and the faster you can spin the crank the more explosions
per second you can get, thus the more power, so designers can only meet
the power demands on a small engine by spinning them faster and designing
everything accordingly. At these higher RPM's the exhaust system can
scavenge if the system is tuned for it, in short not only is there no back
pressure
there's actually a negative pressure there in part of the exhaust cycle that
literally sucks the exhaust right out.


Maybe this makes a case for not messing with the factory stuff unless you install the entire tuned after market system. I admit that I'm not the expert here but it does make me think.

Noise does not= more power. It's just that NOISE.

More than just a simple cross-over pipe, if you look inside there is a restrictor, which presumably tunes the pipe to improve evacuation, although I'd expect that it's effective only at certain rpm's. When thinking about racing exhaust designs it's useful to remember that those bikes spend most of their time running flat out and so it might not matter if exhaust scavaging is not efficient at lower rpm's where us street riders spend a lot of time. If you really want to speed the exhaust on out & away then install the SJ exhaust inserts. They really, really work and yes that's an endorsement.

I would guess the restrictor (haven't looked personally) would set up a venturi effect to assist in the evacuation at high revs much the same as the SJ inserts.

The SJBMW exhaust inserts are already inside the headers. The ceramic coating from there to the can should also help exhaust scavenging significantly, not to mention great looks on the headers. I also used Ultralux teflon coating inside my SJBMW power filter from the nozzle back thru the whole plastic housing. Got some from a boating buddy on Lake Texoma, he uses the Ultralux to reduce drag on water on his V-drive racing boat. Definite increase in intake noise, performance, who knows?

Post the pictures of what you have please.:cool:

Do a search on the subject and you'll find some comments have been made in the past. I know Nate Kern clipped the cross-over the other year, on his 1100S, and welded up the hole and got a touch more power on the top end. Some have stated that the restrictor in the 1100S cross-over was designed to add peak HP. Opening up the restrictor a bit gives more mid-range grunt. This past winter I hogged out the cross-over restrictor to 7/16th and I feel a difference.

As for the twin cross-overs on the 1200S HP motor, that is just one of many details we'd all like to get a better explaination of.

Let me get the coated headers on, will shoot back a pic. For the air system, the PTFE was a clear coating, it just looks shiny and is very, very slippery. He said the stuff is $190 per gallon, a tad more than enough for the bottom of a 21' fiberglass hull. Part of the price of being competitive, for him anyway.

Wait, a slick coating makes more noise on an air system now?
I can't keep up with today's science.

:)

Never said or implied the "slick coating" created noise. The noise comes from air passing through the SJBMW "cold air" induct/airbox system into the engine intake with less restriction and more velocity. A FTPE (Teflon) surface is also electrically and chemically inert. Air passes more efficiently across or through a smooth surface, even moreso where there is no static electricy generated to attract dust particles. Less friction. Ever wonder why they put Teflon on skillets? Or coat industrial pipes with Teflon to increase flow efficiency? Or why turbos and blowers seem to be such a popular way to increase horsepower?

Answer; so eggs won't stick? But I still wind up spraying the darn pan with Pam.

All I know is that if on stroke 4 when your engine doesn't have to waste energy pushing against the out route that unwasted power goes to the rear wheel. Friction free suction is a new arena. We've now moved from the rear end to the front end.

Actually, where that stuff works really well is on the nose of my bike and the Cee Bailey. The bugs come off with nothing more than couple of swipes with a wet towel, even grasshopper guts that seem to turn into an organic cement.

I removed the crossover tube at @15K made the exhaust note a little more raspy, I now have 43k on the bike with no problems!