This sounds interesting. Look forward to reading the results.

 

After having been postponed a few times since the beginning of March, I finally got to the dyno with my bike yesterday.

The good news is that North American bikes, with the reduced timing advance compared to AUS ones, are not deprived of any horsepower. Running a 250cc bore with 35deg. advance vs 25deg. does not result in performance gain.

Not a single tenth of hp gain
Not a single % torque increase

That was hard to believe, we spent a few hours checking that everything was allright and validating the experimental procedure, but this is it. You must understand that we were hoping for performance gain. I've believed from the start that NA bikes get delivered with a detuned timing curve to help meet emissions requirements (more agressive timing tends to produce more NOx pollutants), but that is not necessarily the case. Why would Kawasaki do more advance for Australia then? I have a few ideas on that but I'll leave others the possibility to chime in first.

That result (or miss of results, depending on one's viewpoint) is expeceted to be different with a big bore. It is known for sure that the bigger the cylinder, the more advance at a given rpm for best torque/hp. I will go 300cc soon and report again by then.

For now, let's look at what we got. Here is the dyno curve with 25deg. advance:



Forget about the two dotted curves below the solid ones: they were taken last year, and I have improved things a little since then. Actually, the biggest contributor to this difference is probably that this year's session was without an airbox lid. Yet I run with the lid on usually as it's too noisy to my taste with no lid. Anyway, what is most important is that all the runs we did were with the same configuration, the same day, spaced only a few minutes apart. So, just take care of the solid lines in that picture.

Another note about this figure: you see a quite pronounced dip in torque at 7300rpm, this could be tuned out, but it does not matter for the purpose of this report. Actually that dip is not so serious, it's only 4% in amplitude, but appears more because of the expanded torque scale.

We did runs with these advances:
- 15deg
- 25deg (stock NA timing curve)
- 30deg
- 35deg (stock AUS timing curve)
- 40deg.

In all cases, the timing curve consists of a linear increase from 8deg @ 1500rpm to whatever advance mentioned above at 5000rpm. From that point on, the advance goes flat up to ignition cutoff. These curves mimic what the stock cdi's do but with variable height of the plateau between 5000 and 11000 rpm.

It turns out that the three middle values of advance (25, 30, 35) all produce the same torque/hp curves, within 0.2 lb-ft for torque and 0.3hp for power. So does the stock OEM cdi. At first, the dyno operator did not believe I changed anything at all between those runs! 40deg. results in slightly less power/torque, about 4% loss. 15deg. is significantly less also, about 10% if I recall right.

Thus, the programmable cdi we offer has a value only for hard core modders who want the most out of their big bore kit or want to push the cutoff beyond 10500rpm. Or those with a stock bike who need a replacement cdi. Prove me wrong if you can, this would be welcome!

 

My guess would be that it allows the Aust bike to have a bigger main jet (118 v 132) with less chance of pinging or detonation.

One observation I had was that the CDI units for the US & Aust bikes are quite different with the Aust CDI (ignitier) unit having more wiring.

 

Very interesting. It is great when someone comes along and can prove that what he is saying is fact. Thanks for posting this RayCour It would be interesting to see how fuel mileage is affected by timing changes

 

Thanks for all the interesting info RayCour! Good stuff there. Since I'm no expert on these things, could you fill me in on what sort of engine mod scenario would benefit from a tuneable CDI. (FYI: I have an '07 250S on the stock bore that's got an FMF exhaust, twinair filter and JD jet kit, and would like to do more performance mods in the future.)

 

Hmm, this does not fit with what I know about it. But, good trial... Anybody else has ideas?

This is true for 09 and later models, if I am not mistaken. I think 06-07 ones had the same wiring, only the cdi is programmed with different timing curves.

 

I'm no engine expert too, I'm in electronics. But working on engine electronics for the past ten years, I'm exposed more and more to engine side of things.

I expect with a big bore like 351, there would be performance gains. Most of them with a 351 bore seem to have all the power they want, but those that are after every bit of hp will want to play with ignition timing.

Other than that, with aftermarket cams it is possible to benefit from a tuneable cdi, if only for the ability to get a higher ignition cutoff. One could conceivably come up with cams making a peak hp at 11 krpm, which is not possible to reach with the stock cdi.

In short, those engine mods you do if you want to race your bike.

 

Very interesting.
I wouldn't consider myself an expert here, but to my knowledge, ignition advance has an increasingly larger impact the larger the bore of the cylinder is. It enables the engine to use the most energy it can from the fuel/air charge in the cylinder by igniting it earlier, so that the majority of the explosion is happening when the piston is at the optimal position in the cylinder. Since it takes time for the fuel to ignite and spread, the faster the engine is running, the earlier the advance needs to be to time it correctly - but only to a certain degree. Add to that, the higher the compression, the more easily the explosion travels.

If we're talking about 249cc, there isn't much of an expanse of bore for the ignited fuel to travel across - in fact, it's downright tiny. The KLX also has a relatively high compression ratio in comparison to your average auto or non-racing motorcycle. These things seem to have conspired to make the increased advance not much of a factor here.

But, it sounds like in these comparisons, you simply changed the max advance and left everything else constant. That's a great way to test, but it may not be the entire story. In addition, while more power is always welcome, ignition advance can also increase fuel efficiency, particularly with a TPS.

Personally, I'm not as interested in increasing power at 8,000 RPM as I am at 4,000 RPM, and since that is below the stock advance of all the tested curves, there may be something to be gained. The small bore and high compression may again cause no change, but it sounds like that part hasn't been tested. It may also make a difference on the big bore kits, since the displacement increase is achieved 100% by increasing the bore (hence the name of course). And after all else, if power is unchanged no matter what, there still may be hope that creating some custom mappings to use the TPS (on '06 - '07 models), the MPG could be increased (there may be potential on '09+ also, but you'd have to balance advance and predetonation more carefully at lower RPM). If power between AUS and US models was not impacted by the advance, maybe Kawasaki did it for a different reason, such as achieving MPG based on likely available fuel quality? There's obviously no dyno for that, so it's much harder to quantify. If the only thing this mod did for me was to get me an extra 20 miles of range from a tank (Acerbis) of gas, I'd be more than happy.

 

I think you got it covered perfectly. Higher rpm calls for more advance, bigger bore too.

Again, well said. Though the compression ratio is not exactly high in the KLX, typical off road small bore go higher there, like 12.5:1.

You're right, but consider that the ramp is also steeper when using more advance, as all the timing curves start to ramp up at 2000 rpm and reach their max at 5000 rpm. For example, at 3000 rpm, the 25deg. curve gets 15 deg. while the 35deg. curve gets 19.6.


True again. But the second gen bikes (09 and later) don't have a TPS, thus...

It's true that we did not test at length the effect at mid rpm, in fact not test at all at part throttle, and there might be something to be gained. After all, the KLX300 is reported to do 40deg at 3000rpm in OEM form, there must be a reason for it. We might know more within a few weeks.

Could be, but I feel the timing given to AUS bikes is based on tradition, while north american bikes get it based on "maximum chances of getting EPA certifications".

Please chime in if you have other ideas!

 

Another current thread on this is running, but I thought I'd post this here since this is the nuts-and-bolts of the timing issue anyway. I understand the application that might be more beneficial in the big bore scenario, but I wonder about cam timing...either in the form of the cam gear mod covered in a sticky or the installation of performance cams like the Webcam setups.