fasteddie14
Member
Is it because it needs the higher engine temperature or performance?
Why higher timing on clone engine
- Thread starter fasteddie14
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alvin l nunley
Site Supporter
A fuel starts detonating (a real horsepower killer) with excessive heat and/or pressure. Advancing the timing, starts the burning process sooner, causing higher pressures in the cylinder when the piston reaches Top Dead Center. Higher pressures is how we make higher horsepower. There are limits of course, so be careful. With the clones lower compression ratio, you can start the burn process sooner and not get detonation.
Big Chris
Member
Not this ^^^
The coil on the clone retards timing with rpm. It's just the nature of the beast this this particular piece of equipment. It's been observed, documented, and written about here.
Therefore to get the timing you want at higher rpm, you overly advance the base timing or timing at idle, so when it retards as rpm increases, it lands where you want it.
If Alvin ever owned a clone, or actually dyno'ed one, or did any work on them whatsoever, he'd know this. There are just some things you can't figure out with a spreadsheet.
Here's a video of it in action.
https://www.youtube.com/watch?v=AOciGx-ofnI
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I do not disagree with the fact that ignition timing is slightly retarded at higher RPM, that is no fault of any manufacturer, you can blame science not a nationality, it is simply the effect of magnetic induction. More elaborate systems have electronics or mechanism to advance the ignition timing with RPM. I would have to say the video was questionable the sheet metal indicator was flexing further than the ignition changes in the very narrow RPM range the engine was reved to.
Jody / ARC Racing
Site Supporter
Actually most OEM coils will retard no matter what flywheel you are using. Flathead, Honda, Clone, Predator, Kohler or Wisconsin. They were all intended to turn 3600 RPMs on a generator or water pump, not 7000-8000 on a track. The only exception to this is the blue Briggs PVL coil. It will stay at the same timing from 2000 to 12000. It does retard a little below 1500 to help the engine start but after that it remains the same. Chris explained very well why we run such high timing on these type of engines.
PVL coils are not as simply designed as the regular lawn mower coil sorry but they are controlled by electronics. They are designed and manufactured to specifications stated by the user (Briggs Racing) you do not find PVL coils on Briggs equipped tillers, snowblowers. Harbor freight does not call china and demand $100 aftermarket coils on there $75 engines to satisfy 10% engine sales base. Now Honda does equip some of it's high end GXi engines with high end electronics but they are not for Harbor Freight rotor tillers.
Big Chris
Member
Thanks Jody
standup guy
New member
So... Then do people run less initial timing with the PVL as they're not trying to overcome the high RPM roll-off? I would think that we'd still want 32 to 36 degrees even with the more accurate PVL. Any comments on that from the folks actually familiar with the PVL?
Big Chris
Member
If you're talking about the entire PVL coil/flywheel system on the Briggs animal, then yes, it doesnt change timing like the clone. Jimbo had a graph demonstrating that on his website at one point. And for many reasons, the animal simply doesn't respond to timing like the clone. 30ish degrees seams to work best on that engine with a resitrictor plate on the dyno.
If you talking about the clone, the PVL is not more "accurate" than the ARC, if that's what you've thought was the take away here, you've misinterpreted this thread.
I'm almost certain that Zack (Kart 43) was referring to the briggs animal in his comment.
The PVL is positioned in the clone market as the economy racing flywheel. And that's all it is. The PVL and ARC use different type magnets, and without giving too much away, that adds up to a different characteristic between the two. I find the ARC6619 to work better (when setup correctly) than the PVL, at least on the plate engines. Plain and simple, and I've tested them back to back repeatedly. It's all I use. And I am in no way a sales rep for ARC.
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standup guy
New member
I know what the PVL is, I have one, and I understand that the PVL holds it's time across the entire RPM band, I was responding to your earlier comment:
"to get the timing you want at higher rpm, you overly advance the base timing or timing at idle, so when it retards as rpm increases, it lands where you want it."
If folks are setting base timing higher on the stock coil to account for the retard at higher RPM, the obvious question then is do you folks run less initial with the PVL since you dont need to overcome this problem.
"to get the timing you want at higher rpm, you overly advance the base timing or timing at idle, so when it retards as rpm increases, it lands where you want it."
If folks are setting base timing higher on the stock coil to account for the retard at higher RPM, the obvious question then is do you folks run less initial with the PVL since you dont need to overcome this problem.
alvin l nunley
Site Supporter
Advancing the low-speed timing, it seems to me, is counterproductive if you're just trying to get more high-speed timing. Every mechanical distributor I've ever seen did just exactly the opposite. I'm pretty sure the new electronic ignitions do the same thing.
Seems to me, because you spend so much more time at the lower RPM than you do at peak RPM, you wouldn't want to do that, i.e. advance the timing of the low-end too much.
I would try to find a balance, one which gave the most power under the curve, and see how that worked out.
Seems to me, because you spend so much more time at the lower RPM than you do at peak RPM, you wouldn't want to do that, i.e. advance the timing of the low-end too much.
I would try to find a balance, one which gave the most power under the curve, and see how that worked out.
Big Chris
Member
I don't know.
Jody / ARC Racing
Site Supporter
Yes you would run less static timing when using a Briggs PVL coil. Typically 4-6 degrees less.
Freezeman
Site Supporter
Just my 2 cents. I don't think anyone has mentioned the need for more ignition advance for proper use of methanol rather than gas.
The other thing to keep in mind, we talk about ignition timing in terms of degrees before TDC.
Say when a motor is set @ 32 degrees BTDC. The TIME before TDC is twice the amount of TIME when it is running @ 3,000 RPM's as it is when it is running at 6,000 rpm's. That means that if the ideal TIME to spark the combustion chamber is .XXX seconds BTDC at a certain RPM then when the RPM is at any other RPM it is not firing the combustion chamber at the proper TIME.
Our industrial type ignition systems are far from being ideal for proper firing of the fuel at the right time to make the most power over a range of RPM's used.
The other thing to keep in mind, we talk about ignition timing in terms of degrees before TDC.
Say when a motor is set @ 32 degrees BTDC. The TIME before TDC is twice the amount of TIME when it is running @ 3,000 RPM's as it is when it is running at 6,000 rpm's. That means that if the ideal TIME to spark the combustion chamber is .XXX seconds BTDC at a certain RPM then when the RPM is at any other RPM it is not firing the combustion chamber at the proper TIME.
Our industrial type ignition systems are far from being ideal for proper firing of the fuel at the right time to make the most power over a range of RPM's used.
alvin l nunley
Site Supporter
Good point! But don't you also have to consider that the fuel mixture has half the time to burn?
I've always understood that is why old point ignitions have mechanical advance mechanisms. I'm assuming the electronic ignitions have the same thing.
Big Chris
Member
That's exactly why we're tuning them for the RPM range we'll see at race-pace, and being "less than ideal" everywhere else...........