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Have You Had An Ecu Remap ?


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#181 Oldgit59

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Posted 16 January 2020 - 12:58 pm

I notice the most jerkiness at very light throttle just off the stops. Applying more throttle clears it immediately but of course I am then accelerating sometimes more than I want meaning I am forced to slip the clutch.

#182 Bjørge

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Posted 16 January 2020 - 03:51 pm

My '03 runs smoother with oem exhaust than the Scorpion cans...
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#183 Oldgit59

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Posted 16 January 2020 - 06:48 pm

Bjørge, do you know why? Is it about back pressure rather than free flow?

#184 Bjørge

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Posted 17 January 2020 - 05:17 am

Yes, I believe it has to do with less resistance. But I'm no expert 😐
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#185 fixitsan

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Posted 17 January 2020 - 07:44 pm

I'll throw in my tuppence. I've read a great deal about this, but absorbed very little, but I think it's because it's a pretty complicated subject and it isn't enough to try to make something which is the best exhaust, because there are so many compromises to be made depending on the operating mode of the engine -cruising, accelerating, high load, low load, high rpm, low rpm,  etc....but here goes...

 

If you imagine an open exhaust, or the cylinder head exhausting straight to the air around the cylinder head, when the piston reaches TDC , or at around that time depending on the cam,  the inlet valve opens a little bit before the exhaust valve shuts, and often (depending on the cam profile) the piston starts to move down again before the exhaust valve closes. Under this situation some of the air around the head is drawn in back through the exhaust port, and mixes with the exhaust gas which was left in the cylinder (there's always a bit of exhaust left in the head), but because the inlet valve is opening quickly most of the cylinder is filled with fuel/air mixture. Not ideal but it will run pretty well all the same.

 

Now imagine an exhaust pipe or header pipe which has a diameter that matches the diameter of the exhaust port. When the piston is pushing out the exhaust gas into that pipe some of the piston's energy is used in that pushing action, but it means that the gas traveling down the pipe has been accelerated to a fairly high speed. It has quite a lot of kinetic energy and is quite dense.

 

Now at the top of the piston's stroke the exhaust port is connected to a pipe which has a 'slug' of exhaust gas moving through it and away from the engine, creating an underpressure (partial vacuum) at the exhaust port now, and that helps to scavenge the exhaust gas out from the head chamber as well as help to draw in the new inlet charge.

 

Backpressure, is proportional to the amount of energy the piston/crank/flywheel gives up to force the exhaust gas down the restrictive exhaust pipe, and that in turn is (usually) proportional to the velocity of the exhaust gas going through it. In theory a narrower pipe means a higher gas velocity, which is useful, but then the smaller pipe has a smaller volume so the mass of the moving exhaust gas is lower than before....so it isn't as simple as just giving more and more backpressure to get better cylinder scavenging, because you need enough volume in the pipe too.

 

When you change the end can for a more open one, if the original exhaust was designed to consider the volume of the silencer to be in with the total volume of gas slug needed to help scavenge the cylinder, then you lose some of the cylinder clearing, especially at lower rpm, and essentially that reduces the torque, but it does mean the reduction in backpressure allows for greater maximum potential power at high rpm.

 

Now I want to go into the idea of the reflected power pulse which travels back up the exhaust to the head, but I barely understand that at all. Step forward the experts.

 

What I know is just the basic idea though, that you use the energy of the escaping exhaust gas to create underpressure at the head to help clear the head and bring in the fresh charge. The concept of having both the inlet and exhaust valves open at the same time forms the camshaft design parameter known as 'overlap'.

 

The opposite is usually try for turbo induction , where the best situation is a clear run to the turbine so that the turbine takes as much energy from the exhaust gas as possible, with an open exhaust after the turbo to reduce the drag on the compressor vanes

 

 

That's how I've rationalised it all anyway...there are a few missing ideas from this description I'm not going to go near !


Edited by fixitsan, 17 January 2020 - 07:47 pm.

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#186 PICARD

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Posted 18 January 2020 - 10:25 am

Well put fixit! I think for us (me) laymen, it's just important to know that the exhaust system is way more than just a pipe to get rid of smoke!
A techy guy who writes in m/c sport and leisure goes into great detail on this and it's really interesting, especially when getting into 2 strokes and expansion chambers, pulses etc.
Main message is beware of what you try without remapping, theres a real potential for running and even mechanical problems. I'll leave it to the big boys..
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#187 dandywarhol

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Posted 18 January 2020 - 10:49 am

Pretty much sums it up fixitolbhoy. The overlap also sends some fresh mixture down the exhaust pipe which can cause more hydrocarbons to exit with carbs but can be better controlled with injection. The volume of "slug" should also be proportional to total exhaust system volume which cheapo manufacturers don't always factor in. If the slug volume/system volume are divisible by a whole number then the slug leaving the tailpipe/can will also help create a vacuum behind it to draw out the next slug.

 

Reflected power pulse - that's more 2 stroke science imo - doesn't really matter about how torturous the route is, it's the shape that determines performance. Every year the GP teams came out with different exhaust system designs in the quest for more power - I don't know if even the best fully understand it.........................

 

My lightly tooned 900 came with CCC silencers and I got a pair of Akrapovics, took it back to the same dyno shop for a remap on the Power Commander and instantly picked up 10 bhp at 5000 rpm whilst maintaining the same peak power. I put it down entirely to Akras design


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#188 fixitsan

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Posted 18 January 2020 - 09:57 pm

Pretty much sums it up fixitolbhoy. The overlap also sends some fresh mixture down the exhaust pipe which can cause more hydrocarbons to exit with carbs but can be better controlled with injection. The volume of "slug" should also be proportional to total exhaust system volume which cheapo manufacturers don't always factor in. If the slug volume/system volume are divisible by a whole number then the slug leaving the tailpipe/can will also help create a vacuum behind it to draw out the next slug.

 

Reflected power pulse - that's more 2 stroke science imo - doesn't really matter about how torturous the route is, it's the shape that determines performance. Every year the GP teams came out with different exhaust system designs in the quest for more power - I don't know if even the best fully understand it.........................

 

My lightly tooned 900 came with CCC silencers and I got a pair of Akrapovics, took it back to the same dyno shop for a remap on the Power Commander and instantly picked up 10 bhp at 5000 rpm whilst maintaining the same peak power. I put it down entirely to Akras design

 

Yep it's a fine art indeed, and funny you should mention Akra. One of the teams I've followed recently in the Race 2 Dakar (not to be confused with the 'Dakar' race in Saudi Arabia....which Honda just won to break KTM's 18yr reign !)    Is run by Lyndon Poskett, who produced this vid about his factory visit to Akra !

 

I bet there aren't many Chinese companies with this sort of investment inside !

 


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