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posted November 06, 2003 05:52 PM
Edited By: redelk on 6 Nov 2003 17:53
undertail exhaust?
A poorly edited version, but HEY! I wasn't going to spend all night making it "perfect"!
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There are only three sports: bullfighting, motor racing, and mountaineering; all the rest are merely games.
-Ernest Hemingway
posted November 06, 2003 08:50 PM
Your "artist concept" certainly looks clean. I still want to know and nobody has ventured forth with an opinion yet, but, which type of system works the best in terms of performance? It seems like the undertail exhaust makes for a much longer system. I don't know how that effects performance. Obviously, an undertail exhaust will probably weigh more. It seems like the motorcycle manufacturers who are using undertail exhausts on race bikes where style is not a factor, are primarily "V" engines. The important question is, which system makes the best and most HP over the widest range. In the showroom, style is important. When I go head to head with someone, I would rather have the power. If undertail is the best in both catagories, I'll take it. Otherwise give me the best performing system, whatever it is.
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posted November 07, 2003 10:20 AM
Bottom line is that it ain't ever gonna happen. At least I doubt it from the bigger manufacturers. THe swingarm isn't really set up for it and tuning one that goes to the outside of the swingarm, but still exits from under the seat wouldn't be worth the R&D. I'm guessing that the canister would be a lot shorter, but could just as easily be a lot wider.
Way too much work and R&D for even the "big guys". Plus, it'd would likely be in excess of $2K. If I could get the same kind of performance from a side mount, I'd save the extra $$. I ain't looking at my pipe when I'm riding and if I drag my OEM canister... I've already lowsided.
____________
There are only three sports: bullfighting, motor racing, and mountaineering; all the rest are merely games.
-Ernest Hemingway
posted November 08, 2003 05:27 PM
I like it. And honestly, it was on my wish list. But I need to inspect the swingarm more closely to see if we can work it in there without compromising the power. It may require a 2" diameter S-Bend, and that's on the small side when using a single muffler on an inline four.
When we designed the one on the Honda 600RR, we had to completely change the perameters from the port on back, because the S-Bend section needed to be so long. We're doing the same on the 1000 (oops, I couldn't have one because none of the new 1000's have been released....). Without giving away the specs on the 600 exhaust, we did indeed have to shorten the muffler, which caused additional power headaches that took a month to overcome. The problem with making a shorter (than 18") muffler for a street bike is sound. On the ZX10, we'd probably be looking at a 16" muffler. And that's going to be a little on the loud side (100 dbA or so).
I can promise you this, if I make one for my ZX10, they will be available to everyone.
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posted November 09, 2003 12:35 AM
Of course, I've been known to speak about stuff I know nothing about.
kb, is it possible that such a system designed for a bike that did not originally come with a undertail exhaust cost quite a bit more than the average side mounted aftermarket system? Since the aspects and effects of pipe length, diameter, and bends are way over my head (not to mention the effects of canister configurations)... is there any MAJOR benefits of an undertail system that couldn't be acomplished with a side mount (besides looking "cool")?
It seems that the focus of aftermarket systems is both weight and fncreases in top end HP numbers. I would gladly sacrific top end numbers for a strong 6K to 9K (or 10K) rpm range. Sure, most pipes help in that area, but it seems the most dramatic improvements are at redline. What does it take to make such a system? Am I offbase on my belief on aftermarket systems?
____________
There are only three sports: bullfighting, motor racing, and mountaineering; all the rest are merely games.
-Ernest Hemingway
posted November 09, 2003 12:02 PM
The benefits on a modern sportbike are mostly emotional. It looks very cool. Other than that, there is no practical reason. And yes, costs definetly go up. Ground clearance just is not an issue anymore, so scratch that benefit. Your weight center of gravity is definetly much higher. So unless your using ti, carbon, or inconel, it's going to affect handling because the weight is at the highest point.
From a manufacturing standpoint, it's way harder and the liability factor goes way up. Your now running exhaust through/over the swingarm and tire. If a bracket fails on the muffler or S-Bend, it's going to drop on the tire or bind up the swingarm. Big issue... If the customer does not pay attention to repacking the core, heat can radiate exceedingly and cause problems in the rear cowling area and/or tire. So on and so forth. You can use your imagination. This configuration runs much hotter, because airflow is cut way back to cool those way high temps that are hot enough to blow through an aluminum cannister that has little packing in it. That would be in the 700 + degree area. I've seen issues with guys running them on the dyno, and not placing fans on the tailsection area and burning the rear cowling, turn signals, etc. It gets very little air flow at conventional speeds.
Then we start talking about the dynamics of snaking the S-bend from the header pipes through this area and supporting it. Not that it can't be done, but your tooling costs go way up, the production pipes cost goes up, and your +/- error must be really tightened up because you have very little space to work with. So on a bike that does not come standard with a high mount, the aftermarket does/should look at it much more carefully.
posted November 17, 2003 07:05 PM
Another benefit for undertail exhaust!!!!??????????
The chief (?) engineer for the new R1 remarked to a British magazine (TWO) on the undertail exhaust. He said something to the effect of the undertail exhaust is mostly for style but there might be some aerodydnamic advantage and there is an improvement in handling due to improved mass centralization.
Let me get this right..... the center of mass on the new R1 is very high on the bike and behind the rear axle. I think the currently trendy "mass centralization" catch phrase is getting stretched pretty thin here. Seems like PR Bovine excrement.
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posted November 18, 2003 05:33 PM
Edited By: redelk on 18 Nov 2003 17:40
ROTFLMFAO, zx!
Mass Centralization, eh? So, let's make the whole exhaust system, from header to canister, weigh less then a gallon of milk, stuff a 1/3 of it under the seat and call it, Mass Centralization! PR spin doctors on crack. On the other hand, we could DOUBLE the weight of the canister(s) and there might actually be some validity to it!
As for the aerodynamics... well since most school buses (and bricks) have a similar drag Cx as the average sportbike and the "top speed" war is over, I doubt if an undertail set up will be cutting any lower lap times.
Ya notice that "improves engine performance" isn't a common phrase with tose types of systems? It's not that I am "against" them, I actually like them a lot better than the "standard" configuration. It just that to claim that it's for anything else but appearance is laughable.
posted November 19, 2003 11:05 AM
why dont manufacturers jsut turn the engines the other way round? that handbuilt "tularis" bike did it. it was a straight shot from the exhaust ports to the undertail. seems u'd save alot of weight and the exhaust routing has got to be better. it it simply harder to package the intake out front? seems it would still be possible and likely benefitial overall.
posted November 19, 2003 01:44 PM
It's been done many times. Especially on the 500 GP 2 strokes. I believe even some of the Top Fuel or Funny Bike cylinder heads were turned around.
The general concept was to have a "ram-air" type affect on the intake. And a straight shot out of the exhaust. The 2 strokes were a little more sensitive to this, than the 4 strokes. I would think the benefits of forcing more air/fuel would be slightly more critical than a straight route for the exhaust. Though if you did both, well, you'd have an awesome potential to make big power.
posted November 19, 2003 08:53 PM
so that begs the question... why aint it done? what's the big drawback? obviosuly the ram effect wont work nearly as well on the 4stroke since ur looking for narrow included angle, so cant have the intake comin off the side of the cylinder, but so what? i'd lean the engine back towards the top so the exhaust has less of an arc to go thru past the valve, and jsut have the intake point more or less straight up into an airbox. granted, leaning the engine backwards is liekly less efficient for packaging and weight distribution (CG will be farther back). but u'd prolly also have better cooling performance. the rad aint next to such a hot part of the engine (the exhaust), and u could route the air past the engine but within the bodywork, letting it work it's way past the exhaust to wick away heat, and exit out the back, filling in the vacuum behind the bike. i imagine this may make for better aero's cuase of filling in the vacuum and not making as much air go around the bike (when u make it exit out the side). of course, i may be full of crap or a bit naive about the laws of physics
posted November 20, 2003 02:54 PM
The ram air issue has been resolved with all the different snorkles and such.
Exhaust wise, I think on a street bike, you'd have so many issues routing the exhaust from the reverse position, not to mention a major heat issue with a 4 stroke. Take a look at a Ducati, RC51, or V4 Interceptor. It's dam ugly and tight. And that's with only 1 or 2 exhaust ports!
posted November 20, 2003 07:05 PM
i'm not sure i understand why it would be tight when all u have to do is route it more or less straight out the back, with just a bit of curvature along the way. but i can understand the heat issue. without fresh air being forced right against the exhaust side of the engine, that hot air may sit there somewhat stagnant.
posted November 20, 2003 11:46 PM
There are couple main "issues" why not to turn the engine other way. And as a side note the MV Agusta was first engineerd like that but then they abannoed it. The main reasons are that it won't have a big advantage on the intake side, because if the carbs(FI) would be on the front it would be very difficult to get proper airbox volume. And if the volume would be sacrified it would hurt much more than the straighter airpath would help. And in fact if You look the now common layout the path is allready quite straight, because the intake path is almost vertical - wich is the the straightist way. You remember that the valves work almost vertical too. So in the old days when carbs were positioned almost horizontal it seemed like it would benefit to have the carbs in front of the engine. But this airboxes and straight intake path work much better. Another drawback would be where to put the exhaust, because it needs a certain amount of volume to work properly - ie power, noiselimits etc. Look at the V-twin engines backcylinders exhaust it is routed with many loops (Ok one reason for that is also to get the same volume for both cylinders). And the maybe biggest drawback would be if You were to change the engine position - ie more back, that would ruin the weight balance and mamke it even more difficult to build these long swingarms. There's also couple of other little issues and You may want to also look Cevin Camerons superb book: Sportbike performance hand book - there's more. Allthoug I think You may have read it - but if not I think there's a lot of good information.
posted November 21, 2003 01:22 PM
thanks for the info tuusinii! i suspected most of those things were issues, so now they are confirmed. i'll have to look for that book.
posted November 23, 2003 08:02 AM
Edited By: berzerker on 23 Nov 2003 08:05
As far as Performance differences between different exaust lengths. It's somewhat like Changing the diamiter. The farther away from the motor you get, The cooler the exaust gas and the more it "shrinks".
A longer exaust Would increase the pressure and the gain would be in Torque and low end.
A Shorter exaust would be for a High RPM HP gain.
To make undertail exaust work properly for the 10R you would just need to reduce the pipe diamiter to compensate for the added length. As compaired to side exit exaust for the same setup.
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posted November 06, 2003 05:52 PM
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posted November 06, 2003 08:36 PM
