Yamaha SR250 Power and Temperature Testing

Jadus dyno session 2.0

I'll start by saying this, the day was a mix bag of feelings - sometimes stoked, sometimes gutted. If you were looking at numbers alone, things are not that impressive - gutted, but, as with what most dyno sessions show and tuners say, it is a relative thing, i.e.. what did you start with, and what did you end up with? In this case, the graphs and the gains were strong and I was pretty stoked.

Right off the bat things didn't go to plan. The rear tyre was out of round and bounced on the dyno drum and the stock suspension on these sr’s is shit so the thing was bouncing pretty bad and giving pretty bad readings. This makes the power curve bounce a bit at the top and affect clear readings on how the carb should be adjusted.

Once we got things somewhat sorted - tightened straps, established which gear to do our pulls in (in contrast to last time where we just did 5th gear pulls all day) and then did some roll ons from 30kph-105kph in 3rd. Plus some gear ups - throttling hard all through the gears.

I had made a spreadsheet with columns to fill in for jetting settings and a full days test plan - with exactly which tests I would do and how. It went like this:

Test 1: Completely stock - 2 pulls to confirm

Test 2: Add Jadus header and silencer - stock everything else, tune to strong AFR’s, get reading

Test 3: Add K&N filter to carb - remove airbox, tune to strong AFR’s, get reading

Test 4: Remove K&N filter and add Jadus intake bellmouth and foam filter, tune to strong AFR’s, get reading

Test 5: Add Jadus ignition advance brackets and tune to strong AFR’s, get reading

At this point, it is possible that this could be the final Jadus kit, so best power could/should be achieved at this stage.

Test 6: Swap carb (with same jetting) to one with the butterfly shaft mod, tune to strong AFR’s, get reading

Test 7: Swap out cam sprocket and install with 4 degrees advance, tune to strong AFR’s

Test 8: Adjust cam sprocket so it has 8 degrees advance, tune to strong AFR’s, get reading

Test 9: Add Jadus harmonic intake, tune to strong AFR’s

YEAH, NAH. That didn't happen and became apparent within the first half hour that this is not how things work. It is just such a time consuming process to do the tuning and swapping of parts that this plan went right out the window!
 

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It turns out there are huge differences in dynos, not only in the way they measure but in the accuracy and the results too. It also turns out lamda is only good up until a certain point - to get you in the near zone. Then it is a bit of an experience/feeling thing to dial things in according to what just that motor/engine needs. 0.8-0.9 (AF 11.5-13ish) for example seems to be a sweet spot for the SR and this was the same with the last testing too.

Anyway, after doing these tests we established a baseline of 12.55kw at the engine, 10.4kw at the wheel with 16.5Nm at the engine. Which is almost exactly what all of the period tests found - if you go back through the thread you will see the different dyno charts. Even the power curve and torque curve graphs looked like the period ones. Great, on track, but meant we had a long way to go.

The next step was to swap headers. We did that and did some pulls, good increase, not amazing - got up to 17Nm and 14kw at the engine - around 10%, to be expected I guess. Then we tried the k&n filter, no change to power or Lambda (believe it or not), then the Jadus intake bell mouth, also no change to power or Lambda , then even the carb with the shaft mod and nothing made a difference, we were stuck on these numbers. This somewhat lines up with what I was finding back in Autumn last year when I was testing all these different settings with the O2 sensor and A/F ratio gauge installed - nothing on the intake side seemed to make a difference to power or A/F ratio. Really weird. The conclusion? Something I already suspected/knew/is obvious...

An engine is just an air pump and can't suck in any more air than it needs. The best thing you can do then is to make that flow in and out as easy and as smooth as possible and remove any restrictions in the system - in the SR's case, the header is the restriction, not the air box. But in saying that, if you like the look of a pod filter and want to ditch some extra weight, getting rid of the air box is not going to affect your max power or torque or even it's delivery in anyway, not even the A/F readings!

Right around this time, the clutch started slipping - as it did last time. So it was out with the old springs, in with the new!
 

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And onto the results... Here is the before and after curves comparing stock to the set up with the Jadus header and repacked silencer, plus a foam filter (although as mentioned, any changes to the intake side did diddly squat).

What you can see is an increase in both torque and power, plus a longer power curve - extended by around 1500rpm. You can also see the flat spot in the stock SR's torque curve completely cured.
 

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Then we swapped out the foam filter and stubby bellmouth (which did nothing) for the harmonic intake tube, and did some pulls. Results were immediately promising - even with the same jetting. We decided to throw on the advance brackets too, before adjusting the carb and there was a slight pick up in torque low down without any adverse affects up top. This actually gives the engine a bit more time to burn its fuel if you are running rich in the midrange but think the engine has more to give - rather than leaning out the mixture. We fluffed around with jets for a loooong time and realised that the power really falls off after 7000rpm - we checked this when shifting too - the dips etc. What became clear was that if you shift quickly between 7000 and 7500, you get a good torque curve through all gears, if you leave it too late, the engine doesn't recover well and come back on the power as hard. So best power was from 5000-6500 and best torque was 2500 to 4500. Anyway, the jetting settings we ended up with were almost exactly the same as the previous bike on the previous dyno sessions. This harmonic intake must really do something special because the carb settings end up way different to what one would expect. For example, the main jet ends up being a 115 - much smaller than the stock 122.5 and way smaller than the 135 that we used when tuning with the foam filter and stubby bell mouth. I think this makes the engine run much more economical and get a much cleaner burn and more complete combustion.

The graphs speak for themselves - dotted lines stock, next lines Jadus header and silencer, final (top) lines, Jadus full kit (so to speak).

So why did the harmonic intake do so much? I still think the harmonic tuning has something to do with it, the engine benefits from both a 3rd and 4th harmonic at different points in the rpm range with this particular length and this shows. However, after working with water flow in my day job for the last few months, I am now also convinced that the longer intake tube smooths out the flow A LOT and gives incoming air a chance to get some laminar flow before it goes through the carb and picks up fuel droplets - meaning a really nice mixture. Neither a pod filter nor the stock air box can provide this nice smooth straight shot to the carb - the air is still very turbulent and non-laminar. At work, through simulations and testing, we have found some crazy stuff that water does as it navigates though a plumbing system and pump, but of you give it a long enough straight section after a bend, it evens out again.
 

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One thing that really bothered me through the latter part of the testing was the results from the previous testing - where the hell was this 22hp at the wheel business? No where to be seen! I asked the tuner about that and he reckons the other guys were either wrong, pulling my leg, or I misunderstood and it must have been power at the engine. Even still, this bike didn't make nearly that even at the engine! He then also explained to me the variations in quality and measuring accuracy of different dyno machines and the different costs for different set ups - the more expensive, the more accurate. Anyway, this left me convinced that I needed to return the the other mob and speak to them and also get a run down in standard trim with the other bike - to be able to have a comparison figure. I would just bolt that damn stock header on anyway I could - even if it meant re-using that bloody wood screw!!! Ha. Since this days test I have been back to get the figures in stock trim (just last weekend actually) - more on that in another post.

Comparisons… We will take at the engine first. Stock vs Full kit. Check the graphs too - red vs red is stock rwp (kW) vs Jadus kit rwp, blue lines are power and green lines are torque - both at the engine, before and after pretty obvious.

From 12.5kW to 15.2kW at the engine is a 21% increase

From 10.4kW to 12.6kW at the wheel is also a 21% increase

Torque went from 16.4Nm to 19.6Nm at the engine for an increase of 20%, but look at the area under the curve, it is chunky!

Then if you want hp instead of kW, here are the conversions:

Hp at engine went from 16.7 to 20.4 - a 21% increase. I guess you could say, wow, the engine now actually makes what Yamaha claimed it did from the factory haha.

Conclusions...

The thing is, as mentioned earlier, carb settings make things vary quite a lot if the actual modification has done something to the engine. To test every detail as much as I wanted to would have taken daaaays. We were at it from 1pm to 9:30pm straight - no food or smoko breaks either, just head down get on with it. That's over 8 hours straight of testing and fluffing around.

I will close in the same way I opened these posts, looking at the numbers, not so impressive, right? Looking at the graphs and the percentage gains? Pretty damn good. I thought anyway. And do you think a 20% increase in both power and torque is felt in the seat? You bet ya. I rode the bike home with the mods in place and the thing rips. It certainly feels 20% faster. But it doesn't end there, the throttle response and crispness is really nice, the power comes on sooner with that chunk of torque and pulls right up to 6500rpm before the power really starts to fall off.

These mods and these power gains are what could be considered 'the low hanging fruits'. With just bolt on parts, modifications to the intake, ignition and exhaust, we have gained 20% power. If I/you wanted more from this engine, it would entail head work - valves, porting, springs, etc and a big bore kit. I think there is potential there, but I will save that can of worms for another development project when funds are available again and if any interest arrises.

Oh yeah, I didn't get time to test the cam advance mod. I'll have to do that on my own sometime and test by the seat of the pants or some timed runs somewhere :D
 

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Very cool man.
20% increase across the board is huge.

Different dynos read different numbers. Even two of the same brand will read a bit differently. They are really better for exactly what you're doing, comparison on the same dyno on the same day.

When I was playing with cars I've seen 10-15% higher numbers on one dyno to another. In my experience it has to do with the who the audience is for the shop. The tuner car shops tended to read higher than the true performance shops, because the tuner boys are just looking for high numbers and not actually doing comparison runs. Mustang and dynojet brands even have conversions so you can truly compare one to the other.
 
SONIC. said:
Very cool man.
20% increase across the board is huge.

Different dynos read different numbers. Even two of the same brand will read a bit differently. They are really better for exactly what you're doing, comparison on the same dyno on the same day.

When I was playing with cars I've seen 10-15% higher numbers on one dyno to another. In my experience it has to do with the who the audience is for the shop. The tuner car shops tended to read higher than the true performance shops, because the tuner boys are just looking for high numbers and not actually doing comparison runs. Mustang and dynojet brands even have conversions so you can truly compare one to the other.

Thanks Sonic. That's some good advice and a good point about which audience the dyno shop is looking to cater to. I can't imagine guys building competition cars - rally, road race and the like give a damn about bragging about high numbers. They'd just want to be continually improving on what they have got right.
 
So as I mentioned in a previous post, I decided it was critical to get the stock header back on the first test mule and get in to the first dyno shop I went to - to be able to put down a stock comparison run. Last weekend I managed to drive in an M6 tap just a couple mm deeper than it was previously, then used gasket cement on the exhaust gasket as well - in case there would be any leaks or the screw let go a little. It held up ok and didn't leak at all to my pleasant surprise. Will still take this off the road and do another build out of it - and get the thread repaired properly.

Anyway, as I somewhat anticipated (and also, somewhat dissapointed), the stock figure for this bike was higher than the other bike - just like the modified figures were - meaning the percentage gain was not as high as I had hoped (was looking for 25%). The guys there were adamant that the power was at the back wheel and that the dyno was accurate, and even suggested that this bike must be more powerful than the other test mule. I find that hard to believe! Although this engine did rev higher? Oh well, the interesting thing here is the before and after of coarse, rather than the numbers.

We got things all set up and did a couple runs to make sure we were getting the same results. Then we logged one of the runs to make the comparison - take a look at the print out I got from them. I asked them if I could get one more test overlaid onto the graph too - the one we did with the extra long intake - the one in the picture - the one made for the 2nd wave harmonic. This actually showed really good potential but proved very difficult to jet correctly and in the end we abandoned it for the slightly shorter, 3rd wave harmonic version. You can see that torque and power were up all the way to 5500rpm, then it falls off pretty bad and the mixture went super rich. I remember we couldn't get the top leaned out enough while still maintaining a rich enough midrange. This also backs up a lot of what I have read about 2nd wave harmonic intakes - that they are hard to tune and often very 'peaky'.

So what you see is both stock power and torque in red, then the Jadus kit (ignition brackets, exhaust system, intake system) in blue - with the 3rd wave harmonic intake, then finally the Jadus kit, in green, with the 2nd wave harmonic intake, the one we abandoned.

All in all, pretty happy and glad I went back to get this baseline. It has calmed some of my ponderings and given a more concrete picture of how these parts affect the SR250 engine. I'll be honest, I was hoping it was going to under perform and post a low number - so the comparison number would be higher! But it is what it is and at least I can really claim these numbers now. Oh yeah, numbers, this before and after works out at roughly a 22% gain (if you ignore the last spike in the Jadus kit curve - which the guys suggested I do) - these are the blue lines. Another interesting point here, as with the other bikes results, is the area under the torque curve, it's pretty fat in this case too - from 2500rpm to 7000rpm it's pretty steady ;D

I'll be looking at putting a kit together, pricing it out in production and seeing if there is enough interest in it. I hope there will be, but not holding my breath!

I might be speaking too soon, but with that blue SR250 test mule, when I rebuild it, I am hoping to get 30hp (at the crank) with a special piston, beehive valve springs, titanium retainers, SS valves, port job, lightened rockers etc. Time and money, time and money.
 

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Oh yeah, the pen over the print out, decided not to share the lengths of the different harmonic intakes, in case anyone wants to rip off all this hard work, time and cost I have put into the project. Sorry if anyone thinks thats shitty! You can see the jetting settings in Swedish still though ;D
 
It's been a while since posting here, but I have been riding the bike for most of the summer and loving it. For some reason it feels quicker than the black SR and I have a feeling this is just because of the wheel set up - because the engines make the same power. So lighter wheels/tyres will be in order for the next project.

Anyway, no more to report on in the engine department, other than I bought another O2 sensor in order to be able to do some more jetting testing for my customers.

I would however like to share my nightmare of an experience replacing the fork seals. I will add photos only here - very detailed, and all the text/write up is available on the blog here: https://www.jadusmotorcycleparts.com/single-post/2017/08/17/SR250-Classic-Fork-RebuildSeal-Replacement

Check this method out... :eek: ;D
 

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More process photos. Not the whole shabang, but the interesting ones anyway.
 

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Hello from across the pond! I was given an sr250 a few weeks ago so I've been studying your research and many posts on this site like crazy. Love it all so far. I thought I might mention some of my experience with innovate afr gauges. I noticed you were using an innovate gauge versus their competitor AEM. We constantly have problems with innovate gauges reading as much as two afr points off here in the U.S. Most people I know including myself use the AEM gauge and many people with much more experience have recommended it. I only mention this because your research is so science based that id hate for you to waste too much time and money only to find your gauge is faulty. Please keep up the good work! Im watching your work like a hawk while I tinker with my new bike.

Thanks
-Joie C
 
Hey man, cool you got yourself an SR! Hope you have fun with the project.

Thanks for the tip on the AEM gauge. All the findings I have made on the road have then been backed up on the dyno as well, so the jetting settings are still optimal. I use the gauge more to skip the guess work of listening and feeling and to get in the ball park. But the thing is, every engine likes different AF ratios anyway. So even if I was shooting for 13s for best power, there might be more power at a certain rpm range in the 12s or the 14s!!! That you don't know out on the road. That needs to be qualified with a dyno run/pull ;)

Cheers,
Jake
 
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