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We had dyno'd two bone stock jones z125's.
First one 8.3 second 8.5.

1St one we installed the exhaust only then dyno. We lost power bring it down from 8.5 to 8.

2nd one we installed the steady garage intake, yosh exhaust and a pcv. Dyno'd this machine it only yielded a .5 gain bringing it to 8.8.:frown2:

I must admit this is a little depressing as my buddies grom with intake, yosh exhaust, and pcv brought in 10.8 hp.

Hoping a cam will bring some life to the z125.

Good thing is it still wheelies.
 

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How many miles on the Z's compared to the modified Grom? I do wonder how things might change after 500-1000 miles. I'm hoping the engine is just tight when new and will respond better to tuning when run in.
 

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I had performed a dyno brake on the day of purchase. This typical helps to bring a little extra hp on every other bike we have tested.

I work at a shop and have excess to a dyno for texting purposes.
 

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Yeah, the engine definitely needs to be broken-in for at least 500 miles before it makes it's full potential. Mine went from a max observed MPH of 57 on the meter to about 60 MPH after about 500-600 miles. Then change the oil & filter with a high quality oil and you should see it is a bit quicker revving with a higher top speed before you hit 1000 miles. Mines running great now and it will be getting some mods as soon as EFI controllers are available. I can't wait to start beating Groms!
 

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Well I just got the timing side of the pcv working. Going to be dyno testing a little it later today. Hopefully the timing is the big restriction. I will keep everyone posted.

Fortunately for everyone here i'm not ok with 8.8 hp's when my grom buddies are at 11hp. I will find the issue for all of us. lol
 

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Yup......continue to march. Timing is crucial as is afr's....do you have any good baseline numbers established?
 

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I'm starting to get the vibe you may have been right...
I hate it say it but i've been wanting to do the same thing since the start but wanted something different. Just goes to show you can't ever go wrong with something that has been out and has a bit of history to back it up. The Z125... not so much.
 

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Calm down and back away from the ledges people. Do you know how many talented tuners, manufacturers and owners are hard at work on the Z125? Yes, we all would like for it to put out similar (or more!) power stock than the Honda, but if that was your biggest reason to buy one or the other then maybe you should have waited and let the rest of us have fun riding ours. Go put some miles on the Z, enjoy it for what is is today and see the many options to personalize them flood the markets in the next year. If you didn't have dyno sheet envy, would it still be fun to ride?
 

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We had dyno'd two bone stock jones z125's.
First one 8.3 second 8.5.

1St one we installed the exhaust only then dyno. We lost power bring it down from 8.5 to 8.

2nd one we installed the steady garage intake, yosh exhaust and a pcv. Dyno'd this machine it only yielded a .5 gain bringing it to 8.8.:frown2:

I must admit this is a little depressing as my buddies grom with intake, yosh exhaust, and pcv brought in 10.8 hp.

Hoping a cam will bring some life to the z125.

Good thing is it still wheelies.
.


Are you doing this testing in Vegas at Dyno Jet ?


.
 

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No matter what the dyno says, I would still buy a z125 over the grom. The first time
I have seen the grom was 3 years ago and i was never attracted to it.
The way it looks and if I like it, is for me the most important consideration.
I don't bring my z125 to the highway anyway. Its all city and small road
driving and i feel very uncomfortable running above 55mph.
 

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...........
I don't bring my z125 to the highway anyway. Its all city and small road
driving and i feel very uncomfortable running above 55mph.
.

When we switched to taller/wider tires, it greatly improved the bikes stability.

The stock ones are way too twichy.

.
 
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Any idea how the Grom and Z engines are different, fundamentally? Displacement being equal, what about their construction and parts would lead to such different results from tuning?

It's not just a matter of AFR/timing, since those are equally adjustable on both bikes. Is it the cams? The compression?
 

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I spoke with a friend at Kawasaki who mentioned the Z125 having a shorter stroke than the Grom, which makes it revvier. The longer stroke on the Grom should help with torque.
 

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I spoke with a friend at Kawasaki who mentioned the Z125 having a shorter stroke than the Grom, which makes it revvier. The longer stroke on the Grom should help with torque.
As above:

Z125 is oversquare ( bore is larger than stroke )

Z125 Bore = 56.0mm Stroke = 50.6mm

Grom is undersquare ( bore is smaller than stroke)

Grom Bore = 52.04mm Stroke = 57.9mm

Standard accepted knowledge on larger vs smaller bore is as follows:

Comparing two engines with the same displacement, a long-stroke/small-bore combination is simply less efficient than a short-stroke/big-bore combination on several counts.

"Big bores promote better breathing. If you compare cylinder head airflow on a small-bore test fixture and on a large-bore fixture, the bigger bore will almost invariably improve airflow due to less valve shrouding. If the goal is maximum performance, the larger bore diameter allows the installation of larger valves, which further improve power.

A short crankshaft stroke reduces parasitic losses. Ring drag is the major source of internal friction. With a shorter stroke, the pistons don’t travel as far with every revolution. The crankshaft assembly also rotates in a smaller arc so the windage is reduced. In a wet-sump engine, a shorter stroke also cuts down on oil pressure problems caused by windage and oil aeration."
 

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Great info. What is surprising is that the early dyno reports have the Grom with more Hp and torque, despite the indication that the Z125 shorter stroke should have a hp advantage. This means the other factors like valve size, cam timing, parasitic losses, intake and exhaust restriction etc have room to improve on the Z.
 
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