Filling Crossover

[surferdude345]

When you guys talk about filling in the crossover are you refering to the stock manifold- that center part see pic? I just took my intake track apart and i think relized what you were talking about... Is this something worthwhile doing, what benefit have you seen?
Can I use JB weld to fill it? Do you fill the whole thing or just a part?

 

[waxhead]

the whole thing
and yes its worthwhile doing

 

[#ZERO]

Filling the crossover passage on the intake manifold greatly improves the pulse signal clarity to the fuel pumps and makes the carbs more tunable. The passage is originally intended to offer smoother low-speed response for the stock engines.

Devcon Aluminum Putty is what I used to fill in my 760 intake manifold. Then I used 120 grit sand paper on a glass table to sand it down smooth and finished it with 600 grit wet sanding.

 

[Crab]

Filling the crossover passage on the intake manifold greatly improves the pulse signal clarity to the fuel pumps and makes the carbs more tunable. The passage is originally intended to offer smoother low-speed response for the stock engines.

Devcon Aluminum Putty is what I used to fill in my 760 intake manifold. Then I used 120 grit sand paper on a glass table to sand it down smooth and finished it with 600 grit wet sanding.

You just about talked me into doing my 750 Kawi.:hail:

 

[duckman1]

Is any rejetting needed with this mod?

 

[ROTATION]

You will need to jet down and maybe raise popoff

 

[Crab]

You will need to jet down and maybe raise popoff

So the same would apply to the SXR carbs? I wonder if the mod is really going to make a huge difference, or should I try it with the crossover first.

 

[SUPERJET-113]

That looks awesome #0. Very nice job!
Here is a quote from Harry Klemm earlier this year:

The crossovers weakens signal at "all" throttle setttings.... however the signal problem is most acute during extended full throttle use. All metering circuits in the carb are affected equally, hence jetting adjustments in all areas are required after the crossover is blocked.

Stock boats need to have the ability to run for extended periods at "no wake speeds" cleany, and then immedietly react to quick throttle application. The crossovers help greatly in this area. Since most OEM boats have very restrictive flame arrestors, the carbs get a big boost in signal from those arrestors. In addition, most OEM boats have relitively low compression and low peak operating rpms ... so high rpm signal loss is no risk.

However when owners install aftermarket arrestors (that admit more air, but greatly weaken signal).... and they additionally increase compression and peak rpms.... the combination of weakened signal and increased rpms will create a technical set of circumstanses that no stock machine will ever experience. The OEMs don't need to worry about the problem because it does not exist in the boats as they sell them.
Respectfully, Harry Klemm

 

[michael950]

Can you post a link for the original post by Klemm?

 

[SUPERJET-113]

Can you post a link for the original post by Klemm?

Sure, its: http://www.pwctoday.com/showthread.php?t=73679

 

[ROTATION]

Crab
75 LS jet
150 HS jet
38 psi
Reduce screens to one and remove snorkels from airbox

 

[Crab]

Crab
75 LS jet
150 HS jet
38 psi
Reduce screens to one and remove snorkels from airbox

With or without crossover?

 

[ROTATION]

Filled cross-over

 

[Crab]

Its interesting that with the improved carb signal you can be a bit smaller with the jetting than with a weaker signal and have the crossover. Is that because the fuel pulls harder through the carb?

 

[dirtnut99]

How did this work for you Crab? If you see this post.... Let me know.. I am getting ready to put my motor back together.. SP 750 ssxi motor- .50mm pro-x, Proks, dual Keihin cdk II, Coffman Lightning Pipe, either going Westcoast head with 30cc domes or back with my stock green head.. oh, and porting cleanup with slightly widened exh ports, cleaned up transfers, and intake tract area into case transitioned better..

Talk about raising the dead... haha

 

[CARBONX2]

Its interesting that with the improved carb signal you can be a bit smaller with the jetting than with a weaker signal and have the crossover. Is that because the fuel pulls harder through the carb?

Yes, the cylinder is sucking on one carb so higher air velocity through the carb draws in more fuel

 

[Schmidty721]

Devcon Aluminum Putty is what I used to fill in my 760 intake manifold. Then I used 120 grit sand paper on a glass table to sand it down smooth and finished it with 600 grit wet sanding.

Zero- do you recall how much putty this took? That stuff is spendy!

Any other options people have used with good success?

 

[x2skier]

Zero- do you recall how much putty this took? That stuff is spendy!

Any other options people have used with good success?

Just fill both ends. You don't need to fill the entire passage.

 

[BruceSki]

I have a 62T intake thats already filled if anyone needs one. 30 shipped.

Fits 38's.....off of a 2003 superjet

 

[Freakrider]

John at JSS holds the opinion that filling in the crossover reduces bottom end hit. He states he has done testing on the same ski by switching manifolds,one filled crossover and the other stock. He has found that the crossover helps low speed carb signal greatly and bottom end hit...This is contrary to opinion held by many threads on here, anyone believe this ?