Megabyte
Pro
Posts: 1047
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posted April 18, 2003 09:13 AM
Timing Theory
I've been reading some interesting articles that take a counter intuitive position wrt engine timing. One article claimed that advancing ignition timing @ the higher RPM range actually hurts performance because firing further and further before top dead center @ high RPMs actually creates resistance to upward piston travel. While I understand how too much of an advance could do this, to me, it makes sense to fire sooner because the piston is traveling faster. I've read posts from board members who claim as much as 9 hp gains by doing just the opposite i.e. advancing ignition timing @ the upper rpms. Alot of the older cars use to have a vacuum advance that automatically advanced ignition timing. It seems like there should be a mathematical formula for figuring this out. You know,
d/ds (timing advance) = d/di (rpm * octane) etc,
or something like that. A former professor use to say it all comes down to F=MA. Maybe there's a simple formula for ignition timing too  I've read some fairly technical posts on this board, and have to believe there are board members who could make some sense out of this ?
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We First make our habits and then our habits make us.
  
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02blkgold12
Parking Attendant
Posts: 19
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posted May 11, 2003 03:16 PM
the rule of thumb I always go by is advance for torque and retard for top end, has always worked for me especially with cam timing
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MORE HORSEPOWER EQUALS MORE FUN
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Megabyte
Pro
Posts: 1047
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posted May 11, 2003 05:49 PM
This is what I had read, but I'm wondering why retard for top end ? Back in the muscle car days, when timing was vacuum advanced, timing advanced as vacuum increased and was more or less porpotional to RPM and gas, I think ? Why would it be different with our bikes?
quote:
the rule of thumb I always go by is advance for torque and retard for top end, has always worked for me especially with cam timing
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We First make our habits and then our habits make us.
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flite leader
Zone Head
Posts: 651
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posted May 11, 2003 06:31 PM
 Edited By: flite leader on 11 May 2003 19:39
megabyte
some of what you say is true
back in the day we used to run As much as 50degrees of advance in the ol Z1's
they had a pent roof combustion chamber.....a lot less efficient
adding some only helps top end
if you're running racing fuel..... not a big problem
2 degrees less than detonation WILL make more HP
the important thing is to have best combustion
the big bang usually 3-5 degress ATDC
however much lead you need to accomplish that
thats the sweet spot
since then gasoline has lost at less 10 points
several other dynamics make it highly unnecessary
while it not a futile discussion
if someone would make a "knock sensor"
as used on BMW'S .... corvettes..... even my TOYOTA rav4
that could be hooked up to discover the threshold of detonation
would be good engineering
good money spent
& a few more good HP picked up
good luck
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bend your mind.....
or break your ass...!!
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Megabyte
Pro
Posts: 1047
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posted May 11, 2003 07:47 PM
Took awhile but...
Well, it took awhile but I finally got some intelligent feedback on my original post, posted weeks ago. Thanks!
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We First make our habits and then our habits make us.
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flite leader
Zone Head
Posts: 651
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posted May 11, 2003 08:08 PM
no biggie megabyte
yoshimura has been selling ignition advancers for a decade
most bikes could take 3-5 degress at no detriment
maybe no clear advantage either
spark advance much past 33-36 degrees also
exacerbates the emissions on most engines........ another valid reason
politcally correct(some making only 1/2 assed attempts) maufacturers
dialed out from a hot rod point of view
toooooooo much spark advance
(also witness cat cons on bikes)
you also see way tooooooo muchdialed out
in the areas of IDLE..... 25mph.... & 48mph(three EPA benchmarks !!!!)
which corresponds with some of the complaints many are having
no less some (v hill) has added ignition way down low
some have added fuel.....a Worse solution
i think i remember there is only 19 degrees...could use easily more
does not result in a performance increase
just a drivabilty issue
it works
it helps
you do have to tune for it.......& avoid detonation
good luck
____________
bend your mind.....
or break your ass...!!
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TedG
Moderator
Posts: 8222
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posted May 12, 2003 09:12 AM
Rule of thumb: If the timing is too far advanced and starts to cause resistance, baby you will hear and feel it ping. The main reason for advancing the timing is it takes a certain amount of time to burn, so the faster the engine is spinning the earlier in the rotation cycle it needs to begin the burn so it can complete the burn cycle after TDC. This is the short version. There are many factors involved and heat is a major player in this equation.
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Ted
2000 Green ZX12 sold
The fast color!!
Green 2005 ZX10R
2009 Concours Black ABS
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n da zone
Expert Class
Posts: 215
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posted May 12, 2003 10:18 AM
I was thinking of doing Fish_Antlers cheap (free) Timing Advance modification, where you spin the pickup coil CCW to give some spark advance.
I am guessing/hoping that this mod is in the 3-to-5 degree range. I'm sure some have done that before. When you do his mod of filing the dowel pins on the back of the plate, is the amount of CCW spin still limited correctly?
Am I planning to turn the coil about 1/2" or 1" or 5". .... or will it just 'stop' in the right spot?
The instructions weren't specific on how far to turn, so I am guessing you just turn it until it stops?
Thanks!
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kcadby
Pro
Posts: 1733
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posted May 13, 2003 05:33 PM
You don't just file the titties off...
You ALSO have to elongate the screw holes to be able to move the pick-up (I did John's years ago)...
You file the hole that moves the screw CLOSER TO THE PICK-UP until the screw head almost touches the pickup...then do the other one the same amount (away from pickup...of coarse)...that should be about 5* ...
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