ph4824 wrote:
I've booked my bike in for a rolling road test locally next week. This should clarify what I need to do! My only worry is that the tuner will not know what to do with a Buell but that shouldn't be the case should it?
Sounds good in principle, but what will it tell you?
They will put an O2 sensor in the tailpipe, do some high powered runs and, assuming they get an ignition pickup, give you:
* Power v's RPM
* Torque v's RPM
* AFR v's RPM
And what will you do with that information?
Let's look at what the problem is...
Your bike has a flat spot, the first question is, when do you find this flat spot?
I don't know, but I am pretty sure it is at part throttle, and here is the crunch... you will be testing at wide open throttle on the dyno.
The next question is, what is causing that flat spot?
We need to go back to the basics of the fuel control on your bike...
Your ECM contains two base fuel maps. These are defined as an injector pulse wirth (fuel flow) as a function of engine speed and throttle angle. The assumption here is that the throttle angle, in conjunction with the engine speed, tells the ECM how much air is going into the engine. Of course, we know that the air flow is a function of a little more than the throttle plate angle; namely temperature and pressure. The important thing to note is that these have been derived with the stock exhaust and the stock intake. The ECM is able to cope with changes to the engine/intake/exhaust, but only to a degree, with the use of the AFV. A K&N filter is no problem, a muffler change has little effect, basically cos they affect both cylinders by the sme amount, however things start to go wrong when the header lengths change, and I'll explain why.
The position of the collector, or junction, affects the interaction of the reflected blowdown pulse (a wave which propogates from the cylinder as the exhaust valve opens) on the other cylinder. The trick is to allow the maximum cylinder filling by having the exhaust valve still open, just a smidgen, when the inlet valve starts to open, which allows the inlet charge to wash out the remainder of the combustion products, then you time the reflected blowdown pulse to return as a positive pressure wave which reduces the effective area of the exhaust valve and makes it appear more closed than it is. The inertia of the air coming in, in conjunction with the reflection of the pulse emitted as the inlet valve opens results in increased pressures at the inlet valve, allowing more air to be squeezed in.
Now, if you look at your fuel maps, you will see two peaks. One of those peaks is the result of the length of the exhaust from exhaust valve to the tip and back, the other is the result of the length of the exhaust from the exhaust valve of the OTHER CYLINDER to the tip and back to the exhaust valve of the cylinder the map belongs to.
Your Free Spirits exhaust has different header lengths to the system which was used to determine your maps.
How does that affect you?
Well, you may have noted that, on your bike, there is one O2 sensor. This is mounted on the rear cylinder. The ECM can compensate on the rear cylinder, but the AFR is as free as a hippy (with a flower in her hair) in the front cylinder. So the peaks in the front cylinder map will bear little resemblence to the amount of air coming in. At some speeds, the front will be running lean, at some, it will be running rich.
But there is more... Even though the rear may have an O2 sensor to correct the AFR in closed loop, correction is more efficient as the target fuel flow gets closer to the basic fuel map (with corrections for temperature applied). The further away you are from the base map, the more you are likely to overshoot the target (dominance of the P in a PID controller). The thing is, if you measured the AFR at the tip of the exhaust from a single cylinder, you would see some instability, but the average AFR will be stoichiometric, which is what the ECM is controlling to.
Now, lets get back to your O2 sensor at the dyno. It will be measuring a mixture of residual oxygen in the front and rear cylinder exhaust gases. This gives you very little information to work with for generating maps.
And since we think that the flat spot is caused by a difference in front fuelling relative to rear fuelling, how will a bolt on fueller help you if it doesn't allow you to change fuelling on front and rear independantly?
In my experience, if you seek the Holy Grail, you need to weld two lambda sensor bosses on your headers. Maybe Trojan or Free Spirits would be interested in sponsoring the activity in exchange for a free map, or maybe you could persuade Albert666 to make you some slave header pipes for test purposes.
You then need to follow the process I used, on the old forum and in the tuning guide.
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That leaves EBR but they don't do a map for my exhaust so I would have to buy their ECM + tuning software and then find someone with knowledge to do it = back to dyno people again. There is always yourself you has offered to help, and I am grateful but I need hands on rather than try this, try that over a forum like you are doing with "philgood"!
