Flow Control Valve tuning question

[King Kang]

So, I recently went to put a FCV (brand new Jetworks red kind: 3/8" that you tune with washers) on my 6m6 SJ with a Coffman Sizzler wet pipe. I installed the FCV according to the pic below, below, and sat the ski into the water with the hood off and braced the ski so that it couldn't go anywhere. I disconnected the water line going into the stinger, and hung the FCV over the side. After I started the ski, I let the cooling system fill up with water and revved all the way up to the rev limiter, but the FCV did not open.

Before I start to cut the spring, I want to see I made a mistake when attempting to tune. When revving the motor, I didn't cap off the cooling line that went into the stinger. Could this exhaust leak have been enough to prevent the water lines from reaching full pressure?

 

[Christian_83]

No, maybe you should try and put a T or Y in the inlet water, from the pump. And have the one part going directly to the FCV. I think you might have to little cooling pressure at your FCV.

 

[Tyler Zane]

No, maybe you should try and put a T or Y in the inlet water, from the pump. And have the one part going directly to the FCV. I think you might have to little cooling pressure at your FCV.

It should actually have a T before the fcv so that its not stopping all water flow.

 

[King Kang]

I've considered running the cooling lines like this, but I think the water pressure would be the same, no?

 

[tntsuperjet]

Your second diagram would be better.
Never t your inlet line like one suggested if you only have one cooling line.
Stock cooling is not enough for a engine even slightly built.
Just a pipe adds almost 20hp to stock engine. Horse power builds heat.

 

[King Kang]

Your second diagram would be better.
Never t your inlet line like one suggested if you only have one cooling line.
Stock cooling is not enough for a engine even slightly built.
Just a pipe adds almost 20hp to stock engine. Horse power builds heat.

Yep, I'm not planning to splice a pisser off my inlet line. I hate to ask, but can you explain why the second diagram would offer better performance? You obviously know a lot more about pipes that I ever will.

 

[Tyler Zane]

I like the second diagram better as well. I'm just not certain the Coffman works that way.. It works for a b pipe but I don't know the enginering behind a Coffman to say it will work that way.

The second diagram will build more pressure and doesn't cut flow off completely either. It let's the flow control valve do its thing and dumps all the unneeded water overboard. That's how most run a b pipe. If you have to snip the fcv spring that's fine. Just do so little at a time.

 

[Raddog]

Tyler
That second diagram is how you did in your old SJ that I have
Cheers Ray

 

[Tyler Zane]

Tyler
That second diagram is how you did in your old SJ that I have
Cheers Ray

Indeed and it worked well. I spent many hours with a tachometer and temp gun getting everything even. There where restrictors on all outlets to keep temps level and even per cylinder. I did have dual cooling on that ski though. One line was dedicated engine and the other was dedicated exhaust. That way I could restrict the poop out of the exhaust so the pressures where high which made the head pipe respond better to adjustments. I always did a pre install check on the water hose to insure the bottom and middle screw didn't leak.

Sorry if I'm getting off topic OP.

 

[Quinc]

Your second diagram would be better.
Never t your inlet line like one suggested if you only have one cooling line.
Stock cooling is not enough for a engine even slightly built.
Just a pipe adds almost 20hp to stock engine. Horse power builds heat.

I thought HP numbers didn't matter on pwc. According to coffman the pipe is good for around 8HP on a 650.

When I had my sizzler i ran it like your second diagram.

 

[rowsto]

I've considered running the cooling lines like this, but I think the water pressure would be the same, no?

View attachment 312377

Someone correct me if I'm wrong (it's been a while) but shouldn't the line from the head go to the bottom of the head pipe and the line out the top of the head pipe go to the stinger? That way the head pipe cooling jacket is always full of water

 

[Tyler Zane]

Someone correct me if I'm wrong (it's been a while) but shouldn't the line from the head go to the bottom of the head pipe and the line out the top of the head pipe go to the stinger? That way the head pipe cooling jacket is always full of water

It sounds good, and if it makes you feel better than by all means. Ive thought about this too but have seen many many skis plumbed either way. In theory, as long as there is resistance on the outgoing line the head pipe will fill either way.

 

[King Kang]

It sounds good, and if it makes you feel better than by all means. Ive thought about this too but have seen many many skis plumbed either way. In theory, as long as there is resistance on the outgoing line the head pipe will fill either way.

This is what I was trying to get clarification on from @tntsuperjet. I don't doubt his advice that this is a better way to plum the head pipe, but I'm the type of person who likes to understand the science behind things. I'm going to try rerunning my water lines this weekend.

 

[Tyler Zane]

I know what you mean man, I overthink everything. But i do work on my skis a lot less at the beach than my friends, they always have their hoods off...

 

[rowsto]

It sounds good, and if it makes you feel better than by all means. Ive thought about this too but have seen many many skis plumbed either way. In theory, as long as there is resistance on the outgoing line the head pipe will fill either way.

You've got less resistance going out then going in, so it won't be full of water all the time. I guess none of this actually matters if you've got your ski tuned for the warmer head pipe. But anyway, both will work, I just like my way better

 

[Quinc]

To really understand what the pipe is doing run it on the trailer with a pressure gauge in the water line. Then take the pipe out of your ski and hook it up to a hose and run it at the same pressure. See how much water is being sprayed into the head pipe etc with different routing.

 

[Tyler Zane]

You've got less resistance going out then going in, so it won't be full of water all the time. I guess none of this actually matters if you've got your ski tuned for the warmer head pipe. But anyway, both will work, I just like my way better

I don't agree at all. It isn't less resistance going out, if anything its equal (inlet and outlet fittings are the same size) and that's if its not restricted at the pisser and stinger. Its not just trickling into the head pipe. There is quite a bit of pressure in the cooling lines, especially under heavy loads. Water cant free flow out of a 3/8 hole faster than it can be pumped in under pressure.

 

[tntsuperjet]

Going in the bottom of the head pipe and out the top works good if you don't have the top screw open.
My testing has shown that if your setup likes bottom screw open all others closed you get best results bringing the water in the bottom. If your setup likes too open. Seems to work slightly better bringing water in the top of headpipe.
The theory. The colder the water you inject the less water you need to accomplish the same pipe temp the cleaner crisper the boat responds.
If you bring second cooling line into the bottom head pipe at lake temp water you will gain low end and sacrifice top. No matter what your pipe chamber temp. The head pipe stays colder so your pipe still reacts to that temp as well as chamber temp.
Back in the day I welded solid plug into the bottom of headpipe drilled tapped it with spray bar ran water into bottom of headpipe with a 45 jet and had a 60 jet on average in the spray bar. This let headpipe get really hot and I gained more rpm then with the FFP mod chamber without the loss of power that the mod chamber has

 

[King Kang]

The Coffman pipe that I'm running doesn't have tuning screws like a B pipe does, but I'm still willing to try reversing the flow of the water through the head pipe to see if it makes any difference.

 

[tntsuperjet]

King, sorry I rambled two things together.
We welded a solid insert into head pipe and installed spray bar on both the Coffman and factory pipe.