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wes I think this is right. 1 mm ='s 39 thousands....
+7 is 82 thousands.
so if all this is right and my math is right. 2mm is 78 thousands.

all this could be wrong hopefully somebody that knows will jump in.
 

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[quote name='wesw78' date='Nov 5 2008, 08:33 PM' post='15041']
going? been lol was told 1.85mm was +7 but brad thinks its different trying to get some opinions and advice.
[/quote

mm to degree conversion is dependent on stroke and rod length. I'll edit and post the formula. Remember that +7 on a plate, and stock CDI is actually +24 at 0 - ?? rpms. Not sure if the pvl advances the timing or not. I know there is a retard curve built in. I'm new to pvls and have been researching these things.


Here is the forumula:

A= Cos^-1 (P^2+R^2-L^2)/2PR

Where A = ignition advance in degrees
R =engine stroke divided by 2 in mm
L= con-rod length (usually stroke multiplied by 2) in mm
T = iGNition timing in mm
P= R + L-T
 

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Discussion Starter · #8 ·
english j madd english lol


if you can use that fancy math to figure out 7 degrees advance in mm please let me know. i dont know about the advancing of curve like stock cdi.
 

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Im absolutely dying because I cant find my folder with my ignition curve info...but I did go look on the net for you.

Here's a curve from MSD- I use it because it shows the stock curve- or at least MSD's take on the stock curve which I believe to be accurate.


Then the curve from Penton Imports
The analog set-up


So the data is there for the curves....just have to read it now....and man I really hope I can find those notes....
 

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QUOTE (Backcountry @ Nov 7 2008, 08:29 AM) index.php?act=findpost&pid=15269Im absolutely dying because I cant find my folder with my ignition curve info...but I did go look on the net for you.

Here's a curve from MSD- I use it because it shows the stock curve- or at least MSD's take on the stock curve which I believe to be accurate.


Then the curve from Penton Imports
The analog set-up


So the data is there for the curves....just have to read it now....and man I really hope I can find those notes....


THe penton curve is interesting. I'd think you would need way more than 7 degrees advance with that curve...I'm thinking it needs about 14 degrees just to put the timing where it would be with a plate on 7, and stock CDI. Am I correct??? Is a stock flywheel keyed to be at zero degrees btdc??? This would greatly help me understand where to put a pvl.

Here is a stock CDI curve:


wes..post your rod length and stroke, and I'll tell you what 7 degrees is in mm. Stock stroke is 54mm, stock rod length is 110mm.
 

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QUOTE (J-Madd @ Nov 7 2008, 11:23 AM) index.php?act=findpost&pid=15284THe penton curve is interesting. I'd think you would need way more than 7 degrees advance with that curve...I'm thinking it needs about 14 degrees just to put the timing where it would be with a plate on 7, and stock CDI. Am I correct??? Is a stock flywheel keyed to be at zero degrees btdc??? This would greatly help me understand where to put a pvl.

Here is a stock CDI curve:


wes..post your rod length and stroke, and I'll tell you what 7 degrees is in mm. Stock stroke is 54mm, stock rod length is 110mm.


he has a 421 cub with 115 rods
 

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QUOTE (wesw78 @ Nov 7 2008, 09:46 PM) index.php?act=findpost&pid=15330ya 4mm setup cub.


1.85 mm = 18.4 degrees btdc with my calculation; which with the PVL ignition curve should yield a max timing of +5 over the the stock cdi timing of 22 degrees. The max pvl (according to the curve above) will be 18.4 + 8.5 =26.9.

Does this make sense to anyone? Am I correct? I'm learning this as I go along.
 

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A couple more figures for a 421 Cub with 115 mm rods:

2 mm = 19.1 degrees btdc
3 mm = 23.5 degrees btdc

Note that you can't extrapolate a graph between 2mm and 3mm to figure out what..say 2.5 mm would be. It is not linear, but I think that should already be clear by the complex formula, lol.
 

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Discussion Starter · #15 ·
so by your calcuatulations for +7 degrees 2mm would be about right .

and does the pvl have a base timing curve to it, dont know if that was ever explained.
 

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QUOTE (wesw78 @ Nov 8 2008, 09:12 PM) index.php?act=findpost&pid=15435so by your calcuatulations for +7 degrees 2mm would be about right .

and does the pvl have a base timing curve to it, dont know if that was ever explained.


I don't know how to do the calculation backwards to convert degrees to mm; only mm to degrees..but it looks like 2mm would be real close to +7 degrees over the MAX timing of a stock CDI.

Refer back to the Penton Banshee analog curve that backcountry posted above - that is the pvl curve. You can compare that to the stock cdi curve that I posted and see that they are very different.

Please if someone knows more about this please contribute!!!

It's easy just to set it at 2mm or whatever and run it, but I want to know exactly what is going in with the timing across the entire curve, compared to stock cdi. I think I know; just want it confirmed that what I have posted is correct.
 
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