06-16-2014, 03:16 PM #1
- Join Date
- Nov 2013
Fuel Consumption Differences 2006 FX v. FXHO
I have a pair of 2006 FXs, one is an HO (blue), one is not (red). Owned them for about 6-8 months. Normally, I would expect the HO to use more fuel, since it has more power. But the HO is using almost 20% less fuel, consistently (over the last four rides).
I (45 yr old, 210lb) normally ride the HO with my 140lb son. My older son (15yr, 150lb) rides the red (non-HO) one with my youngest (90lb) son. We ride together, no big separations in speed, distance or acceleration. Blue (HO) will walk away from the red at full throttle with the riders listed above, which seems about right based on the expected 20HP difference. Getting about 58mph on GPS for blue, about 56 for the red. Both spin right up to 10k (factory tach) for a top speed. I suppose there is the possibility that my son doesn't let off the throttle as much as I do when airborne, but we have discussed technique and I can see he's not abusive.
Both have new plugs and oil levels are correct (blue was overfilled when we bought it, so both of them got new Riva flame arrestors).
Blue (HO) got a new Solas impeller and wear ring about 4 months ago, red (non HO) has good clearance and prop is in good shape.
Fuel consumption is measured by filling them slowly till I see the foam coming up the neck of the filler tube, so it is possible there is a difference between the two machines, but if they are both refueled consistently, that shouldn't matter.
Ride mainly in the ocean in Miami and the Keys, ranging from fairly flat to 2ft seas.
Latest example, a +/-60 mile ride, blue used 10 gallons, red 12. So the overall consumption seems about right, just the relative numbers seem off.
Can anyone suggest why the higher HP, heavier loaded machine is using less fuel? Is something wrong with the red one? I pulled the plugs, they all look similar, so I don't think I have a leaking injector or bad coil.
Its not that I actually care about the fuel consumption (or I would have picked a different hobby!), but don't want to find a problem when I'm stuck out in the ocean somewhere with my kids...
Thanks for your thoughts!
06-17-2014, 12:26 AM #2
- Join Date
- Jun 2014
HO might have higher compression or just be more efficient.
Did you check the air filters?
06-17-2014, 01:22 AM #3
The HO was a better tuned ski
It is also lighter and has a better pump
And yes it's strange that a bigger capacity and more hp equals less fuel used
Adding the riva kit didn't seem to increase fuel use either
06-17-2014, 07:44 AM #4
- Join Date
- Nov 2013
No air filters, just the Riva flame arrestor....
I did some further checking, seems there are more differences between the machines than I originally thought.
The FXHO has a slightly larger bore - 76mm v. 74mm and the same 58mm stroke. So the engine is slightly larger at 1052cc v. 998. Compression ratio is also higher, 11.9 v. 11.4. Calculating the BMEP (Brake Mean Effective Pressure, yes, I'm an engineer) of each engine shows the HO has a BMEP of about 196.2 and the Base has about 182.2. So the compression ratio difference is approximately 5% in efficiency, and the BMEP difference is another 10% or so, well within the measurement error.
Thanks for the thoughts!
Last edited by finsfanscott; 06-17-2014 at 01:05 PM. Reason: I is an enginer
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