Dyno Tuning Article Part IV

Dos and Don’ts for Motorcycle Power Commander Systems

Last week was all about finding and rectifying problems. This week is the fun part where we will to tune a stock bike as the manufacturer designed it to be but can’t quite do it due to compliance issues.

Before we do though, let’s deal with a few common misconceptions…

1. My bike must be running lean since I fitted a slip-on muffler because it backfires a lot when I close the throttle.

FALSE

Think about it, the throttle is closed, there isn’t any load on the engine and it’s slowing down. How does that relate to any part of the fuel mapped other than 0% throttle. The fact is the bike was always backfiring when the throttle was closed because it’s designed that way to burn off any fuel before it enters the atmosphere. You just can’t hear it with the stock pipe on. Manufacturers encourage this by injecting air into the exhaust system to create what’s known as a lean burn environment when the throttle is closed. So no that’s not true.

2. My bike has oxygen sensors so the bike will self-tune if I change the exhaust and or air filter etc.

FALSE

Modern bikes run closed loop systems to maintain 14.7:1 air/fuel ratio for light load and low percentage throttle openings. The system operates from 2% – 20% throttle on most bikes, up to about 50% of maximum revs. When in this closed loop area the ECU is more bias toward the oxygen sensor (02) readings than anything else to determine the mixtures as set by manufactures at about 14.7:1. They use narrow band sensors which are accurate between about 14:1 and 14.8:1, outside this area they do not cope so well. If you modify your exhaust and add an air filter it may correct back to 14.7:1 and only in that low speed small throttle area. Chances are it may not even manage that. See the image below, the highlighted area is where the closed loop system operates.

3. I bought a Power commander and just downloaded a map off the internet to suit, so you don’t need to get a dyno tune it’s a waste of money, just do it yourself.

FALSE

Don’t you just love the DIY experts, out there saving everybody money and so knowledgeable. The problem is few people have sufficient knowledge of the subject and inevitably run into a sh*tload of trouble. For example, how do you calibrate the throttle position sensor on a Power commander to read the same as your bike’s ECU without a dyno?

Here’s what you have to do: strap a laptop to your petrol tank, plug it into the Power Commander which is now fitted to your bike. Go for a ride and with both hands reset the throttle position on the laptop while holding the throttle wide open. Try not to do this in traffic. Get the picture?

4. Power Commanders are no good, I bought one for my bike and now it runs really rich. The bike only does about 120km to a tank of fuel and it’s lost power.

FALSE

The problem is not with the Power Commander. It’s a tool to adjust the mixtures for your bike and your modifications. By all means download a map but don’t expect the bike to run perfectly as it will still need tuning on a dyno. Our fuel is very different to other countries and in most case’s your bike will run very rich with a map downloaded from the internet. These products can work without a dyno tune, but to get the best out of them the bike needs a professional dyno tune.

Dyno Tuning for aftermarket slip-on mufflers

The bike we are going to dyno tune is fitted with after-market slipon mufflers and suffers from hesitation whilst cruising and a lack of response when the rider opens the throttle. All bikes these days are fitted with AIS valves (air injection system), which operate under light load conditions. This system needs to be disabled so as not to corrupt the air/fuel readouts we will be taking from the exhaust. The simple way is to block off the AIS pipe with a hose clamp, or for something more permanent plug the hose. If it has oxygen sensors they need to be disabled – the fittings for this will have been supplied with the Power Commander if purchased locally in Australia.

An important note here: if you buy from overseas it most likely will not have oxygen sensor optimizers as many countries do not require them (USA for example) or they may be different to the ones we have on our bikes here in Australia. Same goes with AIS valve – in other markets that may not apply.

After installing the Power Commander and plugging it into the PC we can then open the program in the Dynojet software which will not only communicate with the PCV but also control the dyno, read the mixtures and calculate what numbers to apply to each of those boxes to produce the air/fuel ratio the tuner has already preset into the software. And it will all happen live as the bike is being run on the dyno.

It’s worth noting that I don’t personally know of any other system currently available in the automotive industry which has this kind of software available for public use. It is really cool stuff and makes the whole tuning process faster, easier, and more affordable. If the job was to be done manually it would be double the price.

If you look at the PCV display you can see a host of boxes with numbers in them. The left hand side is RPM in 250 increments and across the top is TP from 0% up to 100%. Each box represents a fuel number either adding fuel or if it has a minus in front of it, then it’s delivering less fuel. In each of those boxes up to red line and across all the throttle percentages a reading is taken, a calculated adjustment is made and that number sent to the PCV to deliver the correct amount of fuel for that RPM vs TP.

Once a map has been made we then go back to the Dynojet manual screen (see photo) and check everything, making some adjustments to the map where required perhaps add the fuel pump utility to aid throttle response and check that we have not only improved performance but also have good economy as well. You see it’s not just about power you can have both if the tuner knows what he is doing. If your tuner is asking you if you want a map for the road or a map for the track then tread carefully. If tuned correctly you only need one map.

Most of this is fairly obvious except for the bar running across the screen going from blue to red. This is our air/fuel meter. The further into the blue is goes the richer the mixtures are. The further into the red the leaner they are. Ideally we like to see it in the darker green area.

So now that the bike has been tuned to suit the exhaust take a look at the graph and see how much better it runs!