Super Jet Speedwerx Dry pipe on 62T 760?

[kevbo]

Are your carbs tuned rich of peak rpm? Are you sure there is no air getting into the fuel line? I always have to add a second pump and air/fuel separator to keep pistons from melting in a race boat.

 

[Flash-FX]

I had a almost identical setup in my FX. X-scream SS900, power factor, 48 Full specs, "pump gas domes", 144 Mag 1" setback, ect. The MAJOR PROPLEM I had was the result of a unstable Epic Ignition CDI (airtime products). They, (I had 3) would program nice and behave normally when just putting around. When you would run WOT (7800rpm) the timing became erratic and lift the head, (detonation) chewing o-rings and eating pistons. I imagine you don't have one of those CDI"s in you ski (thank goodness), but It sounds like you are running in the neighborhood of maximum output. Total load is determined by your impeller. Are you slightly overpropped? When running on the ragged edge, just 1* less in pitch can make a difference, and not loose your top end.

 

[Half flip95]

I can't imagine being over propped and turning 7650, It gets there in a hurry. But I have always questioned the accuracy of the zeel 760 set-up.
Kev, I use the PETX-2000 DXR to tune for max rpm. It will hold stable rpm on long pull. I gave it a 1/4 extra and air temps have gone up by about 20* since then. But I will revisit this and error on the rich side after any changes.

 

[Flash-FX]

I can't imagine being over propped and turning 7650, It gets there in a hurry. But I have always questioned the accuracy of the zeel 760 set-up.
Kev, I use the PETX-2000 DXR to tune for max rpm. It will hold stable rpm on long pull. I gave it a 1/4 extra and air temps have gone up by about 20* since then. But I will revisit this and verify after any changes.

How sure are you about what pitch impeller is actually in your ski? Did you ever check it against a pitch ring like the thing Watcon sells? I went through my impellers and found that what's etched in the hub doesn't always match what it is. Ex: I have (advertised on the box and etched inside the hub) a 15/19 that turned out to be a 16/20. That would mess with you if you're trying to fine tune the pump. A buddy of mine bought the 155 rings and discovered his impellers also had #'s that didn't match. Check your stuff. Don't go by "My 900 should easily spin that". Not saying that this is your piston melting solution, but it's part of the puzzle that can contribute to it.

 

[Storbeck]

I got confused reading this because the title of the thread says 760 and speedwerx pipe, but you have a pfp pipe and an xscream 900 (right?). The people offering up advice might be thinking you have the 760/speedwerx combo (especially @waxhead with the stinger size comment).

WAAAAY outside of anything I'm familiar with so making no claims to know what's up....but my first thought is a typical xscream motor/pfp pipe combo is going to be intended for short bursts of power freestyle riding, so you probably need much less compression than a freestyle ski could get away with (or much higher octane) and possibly a bigger stinger, I believe the pfp comes with a pretty small pipe exit doesn't it?

Also cooling maybe an issue?

Apologies if you are already well aware and way ahead of me on all of that, just throwing out the stuff that comes to mind.

 

[waxhead]

Increasing the squish made it more likely to deto but i dont think its a deto is

I got confused reading this because the title of the thread says 760 and speedwerx pipe, but you have a pfp pipe and an xscream 900 (right?). The people offering up advice might be thinking you have the 760/speedwerx combo (especially @waxhead with the stinger size comment).

WAAAAY outside of anything I'm familiar with so making no claims to know what's up....but my first thought is a typical xscream motor/pfp pipe combo is going to be intended for short bursts of power freestyle riding, so you probably need much less compression than a freestyle ski could get away with (or much higher octane) and possibly a bigger stinger, I believe the pfp comes with a pretty small pipe exit doesn't it?

Also cooling maybe an issue?

Apologies if you are already well aware and way ahead of me on all of that, just throwing out the stuff that comes to mind.

Oh i thought we were talking about a speed werx pipe here to be honest, The 760 zeel timing is the best one out there as its works on a pulse as it goes past a lump. the rising rate/voltage ones would not be as accurate. that being said i doubt either of them are moving that much if any.

 

[kevbo]

Those are large diameter pistons , you will have to find a way to reduce temps. I suspect lower compression and later ignition timing may be required for sustained WOT.

 

[Half flip95]

Increasing the squish made it more likely to deto but i dont think its a deto is

Oh i thought we were talking about a speed werx pipe here to be honest, The 760 zeel timing is the best one out there as its works on a pulse as it goes past a lump. the rising rate/voltage ones would not be as accurate. that being said i doubt either of them are moving that much if any.

The stinger on this pipe is tiny, i don't think it is flowing enough exhaust, i've heard of people going bigger, but how big?