timing for a 5.5:1 head
- Thread starter 29kc
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bruceincam
Senior Member
Why is it any different than stock timing? I can't se any reason for it to be.
nkaminar
Well-known member
Manual or automatic advance?
I have the same head on my car. Bottom line is it depends. If it is too advanced you may ruin the rod bearings by pounding. There is a knee in the advance curve that is pretty close to the correct timing. When ascending a grade, start with the timing lever in about the center of the range. Then advance it one notch at a time. The engine will run better with each notch (pull stronger). You will reach a point where another notch will not improve the engine performance. Go back one notch. That is the knee in the curve. I will be a little conservative and go back two notches. When you get home, count the number of notches to full advanced so that you can go back to the knee setting. You can put a clamp of some kind at the knee setting as a stop. I do that on my car.
Some owners will advance the timing beyond the knee if they are cruising down the highway with medium throttle at about 45 or 50 mph, but I think that is unnecessary for the higher compression heads and dangerous as, in my case, I will forget to put the timing back to the knee.
Each notch is about 4 degrees advance. So you can figure out how many degrees of advance the knee is by counting the notches from the fully retarded position, assuming fully retarded is at zero advance.
The knee may move to another position depending on if you are lugging the car at low rpm. In which case it is best to be conservative and retard the spark a little. When backing up the hill to back into my garage I will retard the spark as it makes the car a little more controllable at the lower rpm.
If your hearing is good enough, mine isn't, you can hear knocking when the timing is too advanced. This is a dangerous condition for the engine and can ruin the rod bearings in short order.
I have the same head on my car. Bottom line is it depends. If it is too advanced you may ruin the rod bearings by pounding. There is a knee in the advance curve that is pretty close to the correct timing. When ascending a grade, start with the timing lever in about the center of the range. Then advance it one notch at a time. The engine will run better with each notch (pull stronger). You will reach a point where another notch will not improve the engine performance. Go back one notch. That is the knee in the curve. I will be a little conservative and go back two notches. When you get home, count the number of notches to full advanced so that you can go back to the knee setting. You can put a clamp of some kind at the knee setting as a stop. I do that on my car.
Some owners will advance the timing beyond the knee if they are cruising down the highway with medium throttle at about 45 or 50 mph, but I think that is unnecessary for the higher compression heads and dangerous as, in my case, I will forget to put the timing back to the knee.
Each notch is about 4 degrees advance. So you can figure out how many degrees of advance the knee is by counting the notches from the fully retarded position, assuming fully retarded is at zero advance.
The knee may move to another position depending on if you are lugging the car at low rpm. In which case it is best to be conservative and retard the spark a little. When backing up the hill to back into my garage I will retard the spark as it makes the car a little more controllable at the lower rpm.
If your hearing is good enough, mine isn't, you can hear knocking when the timing is too advanced. This is a dangerous condition for the engine and can ruin the rod bearings in short order.
Last edited:
nkaminar
Well-known member
The timing will change with different heads. The timing is advanced because it takes some finite amount of time for the fuel/air to burn. As the compression is increased and as the turbulence is increased the time it takes for the fuel/air to burn is shortened, so less advance is needed. The time for the fuel/air to burn is also changed depending on the fuel/air ratio. Plus, as the engine speed increases the turbulence is increased so less time is needed for the fuel/air to burn, but since the engine is running faster about the same timing advance can be used.
Big hammer
Well-known member
When you set initial timing you could pull the hand lever down 2-3 clicks, that will retard the timing from stock TDC, with your HC head just don't pull the hand lever all the way down or your engine will complain ( spark knock,pre ignition, very bad ) Purdy simple ignition system, if it doesn't like what your doing it will tell you, just adjust it and your engine will be happy! Go for a drive and enjoy!
Bruce of MN
Well-known member
Chuck Sea/Tac
Well-known member
I run 22° on my 5.5 head but only at 50 plus. Play with your advance/ retard and you can feel where the engine is happy.
old ugly
Well-known member
do you know why we advance or retard the timing?
we advance the timing so that detonation in the cylinder is at the most optimal piston location to produce the most efficient power.
the slower the piston comes to the top of its compression stroke the more time the explosion has to happen in the combustion chamber before the piston gets there, so we can set the ignition timing to a more retarded position.
the faster the piston comes to the top of the compression stroke the less time the maximum explosion has to happen before the piston gets there, so we have to advance the timing to make that explosion happen at the correct time.
but/so
there are lots of things that can change the speed of that explosion. air fuel mixtures, types of gas and gas additives, flow of gasses into the cylinder, the flooding of the cylinder with the air/fuel mixture and who knows wat-all else.
so i would say yes you may have to adjust your spark differently for a different type of cylinder head but i think that is something you are going to have to experiment with and finds what works best on your engine.
ou
we advance the timing so that detonation in the cylinder is at the most optimal piston location to produce the most efficient power.
the slower the piston comes to the top of its compression stroke the more time the explosion has to happen in the combustion chamber before the piston gets there, so we can set the ignition timing to a more retarded position.
the faster the piston comes to the top of the compression stroke the less time the maximum explosion has to happen before the piston gets there, so we have to advance the timing to make that explosion happen at the correct time.
but/so
there are lots of things that can change the speed of that explosion. air fuel mixtures, types of gas and gas additives, flow of gasses into the cylinder, the flooding of the cylinder with the air/fuel mixture and who knows wat-all else.
so i would say yes you may have to adjust your spark differently for a different type of cylinder head but i think that is something you are going to have to experiment with and finds what works best on your engine.
ou