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Author Topic: Questions for Ace / Bob and other gear heads.  (Read 1097 times)

chinoy

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Questions for Ace / Bob and other gear heads.
« on: January 30, 2010, 05:47:59 AM »
Guys I keep looking at pictures like this one.

http://www.enfieldmotorcycles.com/forum/index.php?action=gallery;sa=view;id=2321

Notice the shape of the exhaust pipe. Its curved.
now look at the shape of the bend pipe on the C5 and the new up-swept.
It has two 90 deg bends that Im not happy with.

Both the stock UCE and the upswept UCE use a 30mm dia pipe for the bend pipe.

My questions are
a. Am I just being stupid and curved or two 90 deg bends it hardlly matters.
b. The curve is better. In which case which modell comes with a curved exhaust with the largest diameter. So I can pop down to the dealers and buy it.

ScooterBob

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Re: Questions for Ace / Bob and other gear heads.
« Reply #1 on: January 30, 2010, 07:47:28 AM »
Well, Chinoy - I think it's intuitive that the gentler a pipe bends, the better it'll flow. The IDM pipe on the C5 doesn't have the O2 sensor placement problem, so I'm guessing that the improvement CAN be had for your bike. Again - You'll have to watch the fuel curve tho - I'm not certain that the mapping is wide enough on the IDM bikes for the MAP to compensate for the added flow - but I'd wager an even bet that it would. My knowledge of the way the IDM bikes are set up is almost anecdotal, as I've only read about them a bit and talked to the engineers at the Factory even less. I find it interesting that the IDM bikes don't incorporate the O2 sensor and all the trappings .... I suppose that it IS cheaper to produce and repair in India - and that it works well enough .... but I can't help but think the feedback system would work SO much better ..... I'll have something ELSE to make me lose sleep thinking about it .... Hahaha!!
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RGT

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Re: Questions for Ace / Bob and other gear heads.
« Reply #2 on: January 30, 2010, 10:09:02 AM »
I saw a sport exhaust that had a very sharp bend,(Afairly tight radiused 90) similar to what I have seen on some of the cafe bike exhausts, it was reported to have significant flow improvements at higher rpm's than the stock long sweeping curve. I wonder if the sharper bend might offer some anti-reversionary characteristics???It does seem counterintuitive.

ScooterBob

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Re: Questions for Ace / Bob and other gear heads.
« Reply #3 on: January 30, 2010, 04:35:30 PM »
You know, RGT - You are probably right .... The Factory spent a kabillion hours to place the O2 sensor where it is, just past a "kink" in the headpipe on the UCE engine just because of this phenomenon. The sensor gets the hottest, "sweetest" part of the outgoing gas to precisely regulate the mixture. If you look at the backside of one of these bikes' pipes after its been ridden, there will be a perfect "V" shape at the sensor .... right at the resonant pressure (heat!) wave .... it's pretty amazing when you think about it - MOST manufacturers would just jam the sensor in anywhere in the gas stream and call it good ..... OUR beloved RE boys THOUGHT about it! Hahaha! Gotta love 'em!
« Last Edit: January 30, 2010, 04:37:52 PM by ScooterBob »
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chinoy

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Re: Questions for Ace / Bob and other gear heads.
« Reply #4 on: January 30, 2010, 10:25:29 PM »
My Theory is that the bend has a drastic effect on flow.
WHich is why when the pipe gets hot. And start to glow its allways from the start to the first bend. After the first bend the heat is way lower.

The factory boys put the O2 after the first bend for one simple reason.
If they hadnt. It would burn out from the excesive heat.

If you have a 4 wire heated O2 sensor. You pick a point which is not too hot to effect sensor life.

If you have a 1 wire sensor. Then you have to be really picky about where you put it.
With a heated sensor you only need to make sure it doesnt over heat.
You could have it at the end of the ex. too.

The bends could reduce flow thus increasing back pressure. Which boosts low and midrange power.

One racer got a team mate to bang him from the rear. Bending his tail pipe allmost to the point where it was closed. The guys saw a huge boost in low and mid. Peak power was in the toilet but on a tight track its low and mid that wins races.

I have a product Idea Im working on. First implemented on my Honda 750 a decade ago.

If you have a performance exhaust. Which is loud and your scared of the cops or the next door guys making a noise.
In effect this is something you bolt onto the end of your pipe.
It has a spring loaded flaper.
At low and Mid RPM the spring holds the flap closed.

As you go faster the air flow pushes the flap open.
Beyond a certain point / angle the spring pressure forcing it closed goes to zero.
So you have no back pressure from the flap past 4000 RPM.
But under that gravity and the spring drop the flap closing the Exhaust exit.

This is like the Yamaha Variable Exhaust. Except this is mechanical.
And Yamaha system is electronic.

ace.cafe

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Re: Questions for Ace / Bob and other gear heads.
« Reply #5 on: January 30, 2010, 11:23:46 PM »
The bend in the pipe causes the exhaust gas to flow toward the outside of the bend, thereby simulating a slightly smaller diameter pipe at the bend area.

This can assist in keeping exhaust speeds up, and helping to improve extraction performance, which can help with torque and hp, as long as it doesn't restrict the overall flow rate. Generally this is a compromise between lower rpm performance and higher rpm performance, and really needs to be looked at as a whole system, to see what the overall effects are going to be on the motor over the full rpm band.

Regarding your "flapper", it's an interesting concept, but I would make it so that it never goes "closed". Closed is no good.
The reason why Yamaha does theirs up by the head outlet, is because that is where they can best affect the extraction performance of the exhaust system on the port flow, by changing effective pipe diameter.
It's much less effective out at the back end of the muffler.
They aren't really working on "back-pressure", but they are working on exhaust speeds, which are most important on extraction effects within the first 6-10" of exhaust pipe outside the head. After that, it's not really affecting extraction.
At the back end, it's just a variable restrictor.
I'd be interested to hear how it does.

Vince

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Re: Questions for Ace / Bob and other gear heads.
« Reply #6 on: January 31, 2010, 12:19:26 AM »
       The trouble with talking about exhaust is that everybody knows that "back pressure" is bad. Modern exhaust engineering  passed this stage a  long time ago. To understand exhaust flow dynamics you must forget "back pressure".
     Start with the engine. The intake valve opens. The combustion chamber fills.The  mixture ignites. Then the exhaust valve opens to let out the burned mixture. This is how it worked in the Ford Model T. In these circumstances you controlled exhaust flow with the length and diameter of the exhaust pipe. The aim was to let out (scavenge) the right amount of exhaust so as to empty all of it from the chamber. This makes room for the incoming charge.
     In a more modern engine there is valve overlap. To some degree the intake and exhaust valve timing overlap. Now exhaust flow management becomes more complex. You have to scavenge the chamber, but intake is occurring during exhaust so some of the intake charge dumps out the still open exhaust valve. Now you need an exhaust that will accelerate scavenging so it is over at the time the intake valve starts to open. Then the exhaust system must utilize the exhaust gases to form a vapor barrier, at the still open exhaust valve,  to stop the intake charge from flowing out the still open exhaust valve. You can do this with vapor or resonance waves, or a restriction that will stack or slow the exhaust gases for the period the exhaust valve is still open. The next step is to adjust all these factors to achieve maximum efficiency at the maximum flow capacity at the maximum  RPM of the engine, or where ever else the engine will be most used.
     Modern exhaust systems are designed to form a low pressure area at the exhaust valve when it opens. This low pressure accelerates flow from the chamber. The reverse wave vapor barrier is formed at the still open valve to optimize filling the chamber. One problem is that what works at 10,000 RPM doesn't work at 5.000 RPM, and vice-versa.  Also, the closer the exhaust system gets to maximum power potential, the narrower the  RPM band it will work in.  
     Stock exhaust systems are tuned to give a wide range of usable power. Can it be improved? Certainly, but it almost always involves a compromise that robs power and/or ride-ability from one RPM band to get more in another RPM band. Adding complexity (and expense!) in the form of a variable valve in the exhaust system can overcome a lot of this. Combined with fuel injection/management systems you can get a tractable motor with more power than with a non-variable valve equipped exhaust system.
     In a 5,000 RPM motor this is overkill. The engineering costs can't be justified for the little bit of extra power an otherwise stock RE engine can produce. The stock RE system works fine for the performance parameters of the engine.
     Things like the flapper valve that was suggested have a certain amount of theoretical attraction, but in practice are problematical. I had a similar device on a muffler I used on my dirt bike in the '80's. It simply disrupted flow. The engine felt torque-y, but it was God-awful slow until I was waaaay up in the RPM band. Acceleration sucked. I suppose a variable spring/ramped actuator might have helped, but then it would have been more complex. I changed gearing to accommodate my torque application needs and went back to my older, more efficient exhaust.
    Remember, it is not about "back pressure". Modern exhaust utilize flow dynamics and wave theory to give good power over a wide range of use.  
      

ScooterBob

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Re: Questions for Ace / Bob and other gear heads.
« Reply #7 on: January 31, 2010, 09:24:04 PM »
Brilliant, Vince! You are SO right on the "5000rpm motor" part. A fellow COULD make a hundred horsepower out of an Enfield engine - and it'd be WAY cool .... but you'll only do it once .... Hahaha!! Good tuning to add a bit more "meatballs" in the mid-range and not kill the economy is what this little mill begs for. WE are begging for affordable mods to compliment that scheme ..... It's the ESSENCE of Enfield!
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chinoy

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Re: Questions for Ace / Bob and other gear heads.
« Reply #8 on: February 03, 2010, 09:31:23 AM »
Wow great posts but my original question goes unanswered
Which was

a. Which RE bike came with that nice shaped Ex. without the 90 De bends. Or are all these gentelly sweaping exhausts I see again and again after market exhausts.
If they are all after market let me know I will stop looking and just build one. If this C shaped header did come on a particular Bullet was it a 350 or a 500.
The 500 uses a 30mm inside dia pipe. What did the C shaped one come with. What did the 350s come with or is the 350 and 500 use the same Exhaust dia. no matter how absurd it may sound. They did run the same cams on the 500 as they did on the 350 right ?

b. Ace. Its up to you if you want the flaper to be fully closed or semi closed. The reason for doing it at the back was as everybody keeps saying. Cheap and effective.
I could buy a R1 setup off ebay with a servo motor and splice it in but then we are talking over 40$ for the servo and controller. This way it all gets done for less than 10$ and anybody can copy the idea / do their own system. You can also add it to the end of what ever exhaust you have so its easy to put on and off.
The problem Vince had with his setup is caused when your spring is not setup right i.e. its allways trying to shut. Getting it to just go to fully open without trying to shut is not that complex.
Again I would only do this if your next door guy is giving you greif about your loud Exhaust and has called the cops on you a few times. And you want to keep your exhaust.


c. In my engine simulator I really dont bother even seeing what happens after 5500 RPM. All Im interested in is how the engine behaves from 1000-5500 RPM.
And in these numbers. There is a difference off 5-10% in the VE of the engine.
With the two 90 deg bends vs no bend on a smooth C bend.

What Vince is talking about is the same as two stroke chamber design where in your can have a very short wave which kicks in over a very narrow RPM band but will give you a stuffing pulse of 2 ATMs or you can have a wave from a shallower angle pipe which will give you a less strong wave action but over a wider RPM band.
This kind of wave action will only start to happen with tapered headers. With the kinda heders we get on the Bullet where its just a pipe with zero taper. You have only one wave action happening each time the internal section diameter of the pipe changes. And its based on the length of the pipe.
So this whole concept does not apply. Instead you can just pick which RPm you want this to happen at based on the length of your pipe.

The 90 Deg bends are hampering flow. And causing over heating of the first section of the pipe. On this score there can be no doubt.

As of now plan is to take a print out of the picture I posted in the first post and take it to my dealer and ask him if he has something similar he can sell me.

I was hoping for an answer that goes. Oh that exhaust came on this model between this year and this year. Or thats an after market unit.


« Last Edit: February 04, 2010, 05:05:47 AM by chinoy »

RGT

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Re: Questions for Ace / Bob and other gear heads.
« Reply #9 on: February 03, 2010, 10:11:25 AM »
my '94 350 pipe has the same C bend, though it extended a little further back as it has a short silencer. the ID is about 1 3/8" or 34mm and change, I have the OD at 37mm..

baird4444

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Re: Questions for Ace / Bob and other gear heads.
« Reply #10 on: February 03, 2010, 11:53:36 AM »
my 2003  500 has the bend you are looking for.
The 350 pipe is 1.5" od and the 500 pipe is 1.75" od
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ace.cafe

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Re: Questions for Ace / Bob and other gear heads.
« Reply #11 on: February 03, 2010, 02:57:18 PM »
Most of the US model Iron Barrel Bullets have the gentle curved "C-bend" on the exhaust pipe.