06-27-2009, 07:25 PM #1
Prop testing today on Lowell 1390 Triple...
I have been down (in my opinion) on RPMs in the summer heat with my prop.
It is a 15/25 DF in the HO pump. My mod list is:
StockOem carbs with F/a's
Factory Triple pipes
Jims FF plate
SS 800 grate
Today this setup went 7550-7570 @ 82.0-82.4 on the seat in 103 degree temps.
I changed the prop to an out of the box stock 14/20 DF.
It went 7860-7880 @ 79.3-79.6.
The boat feels like it has much more top end power with the 14/20. It is very
responsive and fun to ride. It accelerates to peak speed instantly but just will not pull
the speeds that the 15/25 will.
I thought the 14/20 would run comparable speeds to the 15/25 and maybe let the pipes make a little more power. With the 15/25 it takes forever to get to peak rpms and peak speed.
Could it be that the pipes and this 1390 could be peaking in horsepower at 7550? Last summer I tested an Impros 15/23 and the results were similar. The rpms rose about 60 but I lost 1 mph in top speed.
Could a 15/25.5 or 26 gain more speed even though rpms are likely to go down.????? Just thought I would share, these pipes in conjunction with the 1390 and this GPR setup is going against everything I have previously learned about triples.....
06-27-2009, 07:32 PM #2
The motor does not have to work hard with the smaller prop. Lowell's or My porting needs a bigger prop in order to make the engine work! Look at your temps also, its very hot there so your rpm's will be way down compared to a cooler day. Just give it all the fuel it can take. I highly recommend a fuel pressure guage when testing. Plate angle,tab shimms fuel level,heat will all be big factors in speed and performance. Might try a 23 pitch.
06-27-2009, 07:37 PM #3
I have already tried a 23 it did the same thing. Gained about 60 rpms but lost a mile per hour.
I do have a fuel pressure gauge.....6 psi at WOT.....
Last edited by OutlawGPR; 06-27-2009 at 11:32 PM. Reason: w
06-27-2009, 09:44 PM #4
A stock 14/20 makes really good speed at 8100 rpms, I don't know
why your not turning it at least over 8000 rpms. You would be making
more speed than the 15/25 at that low of rpm. But you need to use
a 85mm nozzle on the 14/20.
For a 100 degree day I like a 14/22 spinning around 8K, great acceleration
and doesn't load the motor like your 15/25.
06-27-2009, 09:46 PM #5
if my boat was turning a TRUE 25 at 7500 RPMs, I would be running 85-86. Something is up with your hull maybe dragging or something.
I think you should be turning it 7800-7900 RPMs...
06-27-2009, 10:07 PM #6
What timing curves?
Have you tried an 85mm nozzle with different pitches?
What rpm in cool weather with this setup?
06-27-2009, 10:51 PM #7
Hey kip, glad to see you got a 14/20. Keep up on the updates. How are the cyls doing? Thoughts......Going to see how the pinned 1390 cyls work out. Let me know how the pv ported ones are working .......Might want to get some.
Hey kip I know it might sound stupid but what about going back with the advent and seeing if that changes anything. Were you running the lowell set before it fried out?(before the R&D)
06-27-2009, 11:08 PM #8
Are these props true? Or ya just tried them from sum bozo that said that what they were? Save some money and bring it to a repuatble ski tuner willin to bet its got 87+mph in it sumwhere......
06-27-2009, 11:23 PM #9
06-27-2009, 11:28 PM #10
I have not tried the 85 mm nozzle with the 14/20. Will do....
The advent slows the boat down on top end. It pulls much harder in the middle but
will not rev as high as the R+D unit. This is a 139 curve....
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