Thread: Found some speed for stock GPs
06-17-2007, 11:48 AM #1
Found some speed for stock GPs
Had a great ride Saturday with some friends, even with all the rain we still had fun. My 99 GP was running and handling great. But with the bad weather the speed was down, so just as a test I adjusted the nozzle up some more and was surprised to see 3 tenths, I raised it 1/2 an inch on the rod and it picked up 8 tenths. The Riva ride plate has .110’’ thick washers under the back bolts,( It’s my wife’s ride and she likes it to ride smooth)
I know that the safest and most efficient way to set the thrust angle is in line with the boats LCG, but it worked for this stock GP and ran in the rain at 63.7 all day.
Can’t wait to finish My Raider, so I can start working on the GPs speed…..
06-17-2007, 08:22 PM #2
Thanks for the info, gonna try this on something else
06-17-2007, 08:35 PM #3
Worked for me as well.
Found that out on the triple piper.
I had planned to ride a little and wrench the rest of the day but it was to much fun riding.
Took both GPs out today.
06-18-2007, 06:59 AM #4
I have a 97 that I bought last fall. Over the winter I put on the following;
R&D Ride Plate (Group K)
removed Choke (added Primer)
homebrew pump blueprinting (casting flash removal)
The engine is stock.
This weekend I finially got to run with a GPS and I got to 60.7 MPH. I have not done final tuning on the high speeds yet , they are out 1 1/4 with stock jetting. Is my 60.7 decent with these minor mods or should I see more ?
Also...what is the max for un untouched motor ?
Any input would be great.
Last edited by slaw; 06-18-2007 at 07:04 AM.
06-18-2007, 09:51 AM #5
Slaw, I have the same mods plus a trued hull. But this boat is 2 MPH faster than it should be(stock porting and 118# compression), thats why I bought it. This will be a good triple pipe ski.
06-19-2007, 03:57 PM #6
Slaw these are real speeds from back in the day from Group k
97 54-58 mph 98 59-61 mph 99 would be the same as late 98.
My 97 is running 60-61 mph my 99 is running 60+ mph but will run 62-64.5 mph when its dialed in both motors have 120 psi.
99 has group k cut plate and grate stock prop and compression.
5 deg noz and 84mm Wiseco pistons
97 has stock plate grate prop and compression it has sponsons trim tabs and some mild case porting.
0 deg noz and 84.5 mm Pro x pistons.
Its not always the case but I think the average 97 is 2 mph slower than the 99 all thing being equall.
Last year my 99 was a 62.5 mph ski ran 64+ only once or twice so if you take away 2 mph thats 60.5 mph same as you.
Mods are the same except the prop.
What rpm are you spinning that xo prop at 60.7mph ?
Do you have aftermarket sponsons ?
06-20-2007, 06:11 AM #7
The ski had the RIVA aftermarket sponsons on it when I bought it. I have them all the way up right now, the ski doesn't seem to porpose much. I have a 5 degree nozzle sitting on my desk, I need to put the bilge hose back in it and then I am going to try it.
I have a brand new industrial tiny tach but it doesn't seem to do anything when I fire the ski up. I have tried wrapping the wire at each end of one of the plug wires with no success. Once I get that working I will post the RPM numbers.
When I put the rebuilt carbs back on (stock jetting) I had the highs out 1 1/2 turns as a starting point. The ski maxed out at 58 MPH on the dream meter. I turned them in 1/4 turn and the dream meter went to 63 MPH. I have not tweaked them any further at this point because I am trying to do the tuning with the tach. I would imagine there is a little more there, hard to beleive I would have hit it right on the head.
In a high speed run the last 1/8th (1/6th ...I don't know) of the throttle doesn't seem to do anything. I can go all the way and let off some and the speed (or sound) doesn't change at all. It doesn't go faster when I let off (which was an indication of lean when I was running a Ford 2300 in my Hydroplanes). Is this a clue ?
Thanks for anyones input.
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