11-14-2007, 08:39 PM #1
Hey old school dudes...
Has anyone tried enlarging the exit nozzle on there old school machines..??
I see from the workshop manual that my GP1200 has an 86mm exit..
would the same principles apply to these as the GPR's
So would going to say 87mm help in any way...???
Not that the GP's really need much more holeshot..!!!
My thinking with mine is, It'll mostly be used for wave jumping..
Any thoughts on this Guys..???
11-14-2007, 08:50 PM #2
It can't hurt going to a bigger nozzle (especially 1mm) for holeshot, IMO.
11-14-2007, 09:17 PM #3
Hmmmmmm Thats promising so far..
Has anyone actually tried this yet..??
I know Ross(nemo) has been posting some real interesting findings with his GPr..
Basically it win-win with what he's done with the 85mm version..???
Thats really what got me thinking about this..
11-14-2007, 10:10 PM #4
It's a trade off. Bigger nozzle moves more water down low, but you loose velocity up top, so your speeds come down. Worst case, you will be bouncing off the rev limiter.
If you go with a bored nozzle, it will also probably mean that you will have to start over on prop pitch selection.
11-14-2007, 10:10 PM #5
I know my Skat 148mm pump had a 84mm ring in the nozzle, it was one of those interchangable rings...
11-14-2007, 10:40 PM #6
I have a Riva Rev-b box going in with the rest off the mods..
Which are trued/welded crank,. Group-k ported cylinders (first size over)
Pro-x pistons,. Group-k modded head,. Group-k modded(jetted) carbs,. R & D plenum f/a,.
Premix,. (I'm thinking use the oiltank for 100+ octane premixed on the reserve fuel setting for some zoom-zoom)
Now do i want to port the top case half..(is this something i could do myself..??)
what should i set the riva box at..?? i'm thinking around 7200rpm..??
What about reeds.. one set of petals on mine were chewed a little...
So i ordered a set from boats.net, thinking i'd get six petals to overhaul em all..??
I got two petals and eight little screws/bolts..??
According to boats.net they sell a reed set..!! amount required = 1..??
Did i get shafted..???
All opinions/feedback welcome
11-14-2007, 11:41 PM #7
First step is to get with group k, tell him your motor setup and see what rpm's his porting is designed for. get the reeds and everything else sorted out, then try props. Adjust your pitch to get your target rpm's. if you do that, I doubt you will want to play with your nozzle
my ported 65u was spinning 72-7300 rpm's this summer with a riva box on mod 1, 93 octane on a stock solas XO. the holeshot was stupid. The ski would just leap out of the water, but then again, it was ported for surf riding.
11-14-2007, 11:41 PM #8
Boring the nozzle will increase the low end and midrange. But before you do anything to the pump, you should get the engine dialed in with the stock pump. I would imagine if your are using the stock prop with those engine mods, you will be right on the edge of blowing the pump, and boring the nozzle might put you over.
as far as a prop, a 14/19 swirl would be my best guess. Once you put the prop on and redial the engine for the prop, then you can bore the nozzle and get more low end and midrange, but you might lose a little off the top when you do that. If you put an Adjust-A-Thrust on it after you bore the nozzle, then you can get back your lost top end withut losing any of the lo end and midrange.
11-15-2007, 09:59 AM #9
Thanks for the feedback/info so far..
Bruce(wolf) this might be something i'll look into when i get this motor broke in...
Need to get some data from the thing to work with first..!!!
Mike(addict) i'm about to email Harry at Group-k, I'll send him some pics to see what he recommends..??
I think this could be an interesting idea....
Any more input Gentlemen, Post it up..!!
11-15-2007, 05:19 PM #10
If you are going to mess with nozzles maybe this would be a good time to test one of those props that change pump cones like......help me out guys. It was just a thought. They said it would give you the hook up plus better top end.
Last edited by krispaintballz; 11-16-2007 at 08:16 AM.
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