06-21-2007, 02:52 PM #1
More of Red Devil's GTX/EMS results
Hit the lake today and here's what we've got:
Fuel type: 50% racing (C12) and 50% 93
Blade: Tweaked Sloas 4 blade 15/20R
Of the multiple runs once warmed up: Top: 76.4 -- Lowest 75.7
RPM's: barely getting to 8550 and only bumped 8600 one time.
13.2 lbs of boost
Absolutely NO blow by, not even a drop.. (Thanks to Nils' rebuild)
A/F at WOT: 12.0 - 12.2 (Thanks to Jerry on the mapping )
6 injector set up (Thanks to Dan at Jet Draft)
And Thanks to Mark Underwood from Race Tech for supplying all of the Rotax Racing parts and putting me in the poor house...
Still need at least 200 more RPM's to run close to 8800 and hopefully the Skat 15/19 3 blade can get me there, which is where those 2 more mph are hiding.
Jerry says to take 1 more mm out of the 15/20 if I want to try the 15/20 again but I have never done a blade before.....
But, if I am looking for 200 RPM's, do I bend it 2 mm's? Never done this before which is why I always send the prop to Jer.
When the prop is in the vice (nose cone pointing downward), and the crescent is on the blade, do I lift up or push the crescent downward to take a mm out? And where EXACTLY do I place the crescent? Thanks..
06-21-2007, 03:20 PM #2
With the impeller sitting on the adapter in the vise, nose cone down, hub facing up, put a straight edge across the hub, and use a micrometer to measure the distance from the (side) end tip of each blade to the straight edge. Record each one (write it on the blade, or). Then ADD 1 mm from the average (not all the blades will likely measure exactly the same), pick a new number for all the blades, and bend.
To take pitch away or add rpms, with the prop sitting as stated, you need to bend it down, towards the front of the impeller, adding at least 1 mm to the number(s) you recorded from the baseline measurement. Take a peek at the impeller bending tip thread to help feel more comfortable too. Oh, put the crecent wrench 1 inch up from the end of each blade and lean in on it and bend away. I used some cardboard in the crescent wrench jaws, then tightened them up, to protect the blades.
It took me some time to get results the first time; the first time you do it, you don't know how much force is required, so I pushed gently on each blade numerous times to get them where I wanted. Just my .02
Last edited by Vern; 06-21-2007 at 03:21 PM. Reason: updated
06-21-2007, 03:38 PM #3
Wow, thanks Vern. With those detailed instructions I think I'll go for it!
06-21-2007, 03:49 PM #4
06-21-2007, 03:53 PM #5
I just re-read your note again ... if you want 200+ rpms, then I think you would want to add a solid 2mm to your baseline measurement. For example, my blade ends measured roughly 6mm to the straight edge sitting on the hub; I too wanted 200 rpms, so I bent them until all the blades measured 8mm, blade tip to straight edge. To gain rpms, you are basically pulling the blade ends AWAY from the impeller vanes if that helps visualize it.
One more reason why you want to pull back the blades at least 2 mm ... some skis gain even more top speed with an 80mm ring vs an 81mm. Just a thought if your rpms come up higher than you like after the re-bend, try the 80mm nozzle possibly.
06-21-2007, 04:53 PM #6
- Join Date
- Dec 2005
jay bring it by the shop i will do it for you!
06-21-2007, 05:18 PM #7
good info Vern! I find your directions easier to follow than the other prop threads
06-22-2007, 07:19 AM #8
06-22-2007, 07:38 AM #9
06-22-2007, 04:33 PM #10
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