What does advanceing timing do to a stock 212 motor?

[badgerinemini]

How will timing affect a predator with a rejetted carb, filter and pipe? I am confused as to what timing does on a stock motor like this.
I have read that it can increase low end torque and then other posts that it moves the torque more to the top end. Which one is it?
I am looking for low end torque probably going to mill the head down as well . Should I just leave the timing stock?

 

[LSCustoms]

imho, as there are more qualified people that can better explain this, but since you didnt get a response, i thought i would try and tackle it

it has to do with when the spark occurs in the cylinder... as the motor increases in rpm (or performance capability), ideally (i would think) you would want the point at which the spark occurs to change... i think in our cases, with most of our motors, we are setting it to occur at the best point, when the motor is higher in rpm...

if the spark occurs too soon, it will be in a sense fighting against the piston... it needs to occur when the crank/piston are on the power stroke, just passed top dead center (or i believe right before the piston starts to travel in its power stroke)... if you could imagine the piston being all the way up in the cylinder, close to the head, the the spark occurs at a precise time, igniting the fuel and compressed air, causing the explosion that forces the piston back down and crankshaft to spin...

if the timing is off, say too far advanced, the spark would occur too soon and try and force the piston back down when its on its way up... you would lose power this way. if to far retarded, then i believe the explosion would be caused after the piston was already on its way down, you would lose power this way too... if you could imagine that...

say you are pushing a kid on a swing... you pretty much want to push the kid, right as the swing reaches the point where it is stopping, but before it starts to go back down... imagine pushing the kids back, too early, while the swing is still in full momentum up toward you... and then likewise, after the swing has passed its tdc and already on its way back dowm... you lose momentum either way

 

[Prowler08]

And to add to that...
On these small primitive engines the spark starts to retard it's self past a certain rpm.
So we also advance it to counter act the retarding effect to obtain a good spark event.

 

[chazdaddy]

LSCustoms, that was an excellent explanation, thank you. :thumbsup:

and, Prowler08 you too. :thumbsup:

 

[roccosbike]

Advancing the timing in a stock motor hurts low end torque,if you put stiffer springs and a cam with more duration then you want the timing advanced to take advantage of the new mods.Milling your head is a very good way to increase low end torque and if this is what your after leave your timing alone

 

[Motra]

just passed top dead center

Actually ignition occurs just before top dead center. This is because combustion really isn't an explosion as it's commonly called, it's actually a controlled burning. As the fuel burns, the piston is forced downward by heat expansion. The burning process needs to begin just slightly before the piston reached TDC so the majority of the heat expansion occurs after the piston passes TDC. As engine RPM increases ignition needs to happen earlier in the cycle because it takes time for the fuel to burn (a very small amount of time that is, engines can have several hundred power cycles per second). So, there are other factors involved, but generally speaking, advanced timing = high RPM, retarded timing = low RPM.

 

[LSCustoms]

Actually ignition occurs just before top dead center. This is because combustion really isn't an explosion as it's commonly called, it's actually a controlled burning. As the fuel burns, the piston is forced downward by heat expansion. The burning process needs to begin just slightly before the piston reached TDC so the majority of the heat expansion occurs after the piston passes TDC. As engine RPM increases ignition needs to happen earlier in the cycle because it takes time for the fuel to burn (a very small amount of time that is, engines can have several hundred power cycles per second). So, there are other factors involved, but generally speaking, advanced timing = high RPM, retarded timing = low RPM.

you are correct the spark actually does need to occur a little before... i was typing pretty fast... :thumbsup: i said it in the parenthesis, just didnt proof read my stuff after i typed it...

 

[Newoldstock]

If you move to the 18 or 14cc head you can worry less about the need for advance because those smaller chambers burn faster.

The 22 and hemi are big and require more time for the flame front to cross as RPM increases.

There is a new Honda CDI unti that offers more stable ignition and a little retard at low RPM.

More investigation required.
Coil, Digital Ignition, GX270/390 (UT2) NON REV-LIMITED

 

[badgerinemini]

I am going to follow your advice and stick with my stock timing and mill my stock head. Very informative posts thanks guys for taking the time to clear that up for me . :drinkup:

 

[Stangrcr1]

Florida? Go to the beach, soak some sun, carve some waves, call it a day.

Repeat tomorrow, unless there is a hurricane. In that case, suck it.