96 challenger 787 throttle question

[gasman_1_2]

Hi i've ask some questions here and they were very helpful because i am new to boating and with jet boats. On my boat when i move the throttle up the rpms go up of course but it only goes well wot if i get on plane and then take the throttle down half way it slows down to where i have to keep it at about 6600 rpms to keep plane and it runs wot at 7200 to 7300 rpms i would appreciate any ideas or help anyone could give

 

[Chester]

Your jet pump is cavitating/ventilating. You have a damaged wear ring and/or impeller. Your max RPM's should only be around 6750 - 6850. When you have the pump apart, I recommend replacing the impeller with a Skat-Trak Swirl impeller. You will be amazed at how quick the boat gets up on plane.

Chester

 

[vilord]

Your jet pump is cavitating/ventilating. You have a damaged wear ring and/or impeller. Your max RPM's should only be around 6750 - 6850. When you have the pump apart, I recommend replacing the impeller with a Skat-Trak Swirl impeller. You will be amazed at how quick the boat gets up on plane.

Chester

I agree that the boat is cavitating, but it might just need to be re-sealed. My '96 challenger runs like a champ now that I re-sealed the pump. No new wear ring, no new impeller, just a $7 gasket from the dealer, and a tube of ultra-black silicone sealant and about an hour to pull, seal and reinstall the pump. Let it sit overnight and you're good to go.

As for top RPM's, 7250-7300 should be max on our 787's from that year iirc... my boat's been in the garage for months now, can't wait for a few more ticks on the thermometer

 

[Chester]

...As for top RPM's, 7250-7300 should be max on our 787's from that year ...

Yes, the rev limiter is set at 7250 + or - 50. The stock engine with a stock impeller will top out at 6800 + or - 50 on the water. This can be verified with a digital tach.

Chester

 

[vilord]

Yes, the rev limiter is set at 7250 + or - 50. The stock engine with a stock impeller will top out at 6800 + or - 50 on the water. This can be verified with a digital tach.

Chester

This sounds familiar now... my engine goes to 7000-7050 on the analog tach, never tried a digital one.

 

[gasman_1_2]

Your jet pump is cavitating/ventilating. You have a damaged wear ring and/or impeller. Your max RPM's should only be around 6750 - 6850. When you have the pump apart, I recommend replacing the impeller with a Skat-Trak Swirl impeller. You will be amazed at how quick the boat gets up on plane.

Chester

I have a skat trak impeller on it and i was wondering what the difference would be with the stock. I posted a thread about pulling a tube with it and it wouldn't so i though maybe i needed to put the original one back on but it seems the boat ran fine and seemed to get on plane fairly good how long should it take to go from idle to wot to get on plane

 

[Gunsrunner]

4-5 seconds then it should be on plain. I agree, it sounds like it is cavitating.
Chester don,t know about the rev quote, mine stock motors with stock impeller 7150rpm on digital tach's on both motors. I have read that if they don't get close to the rev limit, then the impellers should be repitched to make it so, this will give the maximum thrust.

 

[vilord]

I have a skat trak impeller on it and i was wondering what the difference would be with the stock. I posted a thread about pulling a tube with it and it wouldn't so i though maybe i needed to put the original one back on but it seems the boat ran fine and seemed to get on plane fairly good how long should it take to go from idle to wot to get on plane

With the skat trak impeller on there and no pump leaks, if you ram it from idle to WOT, it should rev up to the limit almost immediately (half a second or so), then after another second it should "engage" the water (it will always cavitate for a second or so even without leaks) and take about 3 more seconds before you are on plane.
It should throw you back in your seats when it grabs the water.

With my stock impeller i've got about a 2 second delay before it "hits", and iirc scooper77515 was the one who bought the skat impeller last summer and said it cut the time to get on plane in half.

The skat impeller should be better for getting on plane, better "hook up", better torque, better acceleration, but about 2 or 3 mph slower at the top end. Most of us don't race the boats so the top end is less important than is getting there.

 

[scooper77515]

It cut the plane time to more like 1/3, but part of my gain was replacing the wear ring that had a couple of gauges in it, even though the gap was still at .040. So there was probably some cavitation going on there.

Another thing, when I had 4 adults in the boat at around 1000 lbs inc. cargo, fuel, beer, and ice, I couldn't get it to plane in less than 20 seconds, and lost most momentum on turns. (I know, boat is not rated for anywhere NEAR this weight).

With the Skat swirl impeller, it will plane with all of us in there in maybe an extra second over the 3-4 it takes with just the 2 of us. And it doesn't bog on the turns.

It does push you back into the seat, and the dog will come sliding back from the front pretty hard if we don't catch her or pull her back before we take off.

By the way, pic is just for your enjoyment and will benefit this thread in no way...I just wanted to share with the world a pic of my two girls being happy.

 

[NORCAL68]

Skat trak for 96 challenger

hello can someone tell me which skat trak swirl impeller i need for my 96 challenger??

 

[Chester]

hello can someone tell me which skat trak swirl impeller i need for my 96 challenger??

Look it up here: http://www.skat-trak.com/

Chester

 

[scooper77515]

I looked on the website and couldn't find the pitch. Just ask Dave when you call Impros, he knows right off the top of his head.

I "think" it was 16/22?

 

[scooper77515]

Found It

http://www.skat-trak.com/seadoo_app2.html

Even though it isn't listed for my boat, I still think I ended up with 16/22.