Other Epic Timing Question

[QJS]

This brings us to the cut off point for maximum advance and this is a difficult one as the engine will come on pipe at different rpm depending on where the water adjusters are set on the B pipe but its usually around 4-4500rpm I would consider starting to pull the timing at 5000rpm very safe. The torque peak is again not set in concrete but around 6000rpm is common and this is where the timing should be down to around 18*. The final advance should be at about 7000rpm and a good number here seems to be 14-15*.
Hope this is not confusing, one other thing I would like to say is if you are using an engine builder and he does a curve for your particular engine then use it. If you still feel the urge to play use the B curve and fit a switch.
Chris.

 

[QJS]

This is a good curve.:smile:

 

[QJS]

Would these guidelines work with a SS BB set-up?

I am putting an 865 BB on the dyno next week so I will have more info then, you don't say what cylinder you are using but if its an XScream you need to be talking to Chuck, I think he has his own particular curves.
Chris.

 

[steve-uk]

Not sure what motor you are running but they can/will load two curves. One more aggressive than the other. Install a waterproof toggle or one of the rotary switches and you are in like flynn

XMetals 771 with all the bolt ons

Would these guidelines work with a SS BB set-up?

arent you running the 771?

 

[steve-uk]

Also I spent a day last week with an EPIC on a dyno on an engine that was also run with a stock ignition, it is fascinating stuff and I have a lot of facts and figures that are really interesting. All the runs are on video but I am having a problem getting them off and onto the computer at the moment but as soon as I do I will post it all up.
Chris.

for ease of finding
http://www.x-h2o.com/threads/89034-EPIC-Dyno-Testing&p=1067884#post1067884

 

[munki63]

arent you running the 771?

Yes, Stock stroke Big bore

 

[augustaf]

What do you do if you are a Tard? My epic is installed and I have no idea where to begin, my motor is a Jetmaniac 710, I run 93 octane and amsoil dominator at 40/1 per Jetmaniac. I was told the epic curves that come preinstalled are good, and I've heard that they are too conservative. My ski is in a million pieces waiting for the new hull to get here so I cant really experiment at this time.

Anyone have a curve that will hit noticably better than the stock cdi I had in before. Also I hooked it up per the diagram in the literature, but I have extra parts, I have another splitter and the red from the start stop switch is still not connected. I do some more research online and I'm sure I can find the answer unless someone wants to save me some of the legwork and help a brother out. Ultimately I'd like one curve I can ride aggressively, but I still need the ability to go wide open we run down alot of boats, and one that I can use in the surf. I ride flat water sometimes too. So should I rock 3 curves. I pretty much don't know where to begin if you can't tell

don't worry too much about how many different curves to use. One will do just fine! Just go with ATP's latest dyno curve, or if more adventurous waxhead's

 

[Schmidty721]

This brings us to the cut off point for maximum advance and this is a difficult one as the engine will come on pipe at different rpm depending on where the water adjusters are set on the B pipe but its usually around 4-4500rpm I would consider starting to pull the timing at 5000rpm very safe. The torque peak is again not set in concrete but around 6000rpm is common and this is where the timing should be down to around 18*. The final advance should be at about 7000rpm and a good number here seems to be 14-15*.
Hope this is not confusing, one other thing I would like to say is if you are using an engine builder and he does a curve for your particular engine then use it. If you still feel the urge to play use the B curve and fit a switch.
Chris.

One question I have is why you continue to pull timing out all the way to max RPM. If you say max torque is at ~6000 rpm why isn't this the lowest timing setting for the curve? Does cylinder pressure continue to increase as you approach rev limit? From my experience tuning V-twin motorcycle's after peak torque is surpassed you can start adding timing back into the curve.

 

[waxhead]

The reason is you do it is to increase the heat in the exhaust pipe.
The increased heat makes the pipe pull on further into the power band by way of the heat increase making the pressure wave travel faster.
When the pipe is finished making power you can put some timing back in and increase the rpm more ( this is more done on race boats)

If you have a look at the logo for my bussiness you will the timing curve I am talking about from the days when I used to sell my own jetski iginitions

 

[QJS]

On the dyno test we just did, it was the final timing at 7000 rpm that surprised me most. At one point we were running 14* , the engine revved out perfectly but a drop of just 2* to 12 completely ruined the high end performance.
Chris.

 

[easyrhino]

One question I have is why you continue to pull timing out all the way to max RPM. If you say max torque is at ~6000 rpm why isn't this the lowest timing setting for the curve? Does cylinder pressure continue to increase as you approach rev limit? From my experience tuning V-twin motorcycle's after peak torque is surpassed you can start adding timing back into the curve.

Very cool...
I was thinking that timing was use as a rev limiter while the prop is under load. RPM rev limiter is for no or partly load.