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Re: Ignition timing questions
Posted: Thu Oct 15, 2020 6:50 am
by GRTfast
Camaromeo wrote: ↑Thu Oct 15, 2020 6:28 am
What is your altitude? The higher, the more timing is needed.
Is your WOT-AFR maybe a little lean? Dont go leaner than 12.5. Could also contribute to timing hunger of the engine...
What pump gas exactly? 93? Burns slower so more timing can be necessary.
remember: measured from the perfect amount of timing degree, 3° less timing produce still 99% of the max power with way less detonation likelyness.
Sea level, are at wide open is 12.5 ish, maybe a touch richer.
Re: Ignition timing questions
Posted: Thu Oct 15, 2020 1:37 pm
by BobbyB
GRTfast wrote: ↑Thu Oct 15, 2020 6:50 am
BobbyB wrote: ↑Thu Oct 15, 2020 5:52 am
GTR, What intake, carb & spacer are you using?
How does it run now compared to when you posted a year or so ago that it was surging at cruise before the new cam?
RPM air gap
QFT 1050
1 inch 4 hole phenolic spacer Runs best it ever has. Bucking/surging all but eliminated. Very happy with it.
The engine had always liked this much timing, I just never ran as much initial because it was hard on the starter. This programmable setup allows for start retard.
Did you try a 1 hole spacer? If so, how differently did it act?
At one point I think you were considering sealing up the "window" on the manifold divider, it that open or is it sealed?
Re: Ignition timing questions
Posted: Thu Oct 15, 2020 2:25 pm
by GRTfast
BobbyB wrote: ↑Thu Oct 15, 2020 1:37 pm
GRTfast wrote: ↑Thu Oct 15, 2020 6:50 am
BobbyB wrote: ↑Thu Oct 15, 2020 5:52 am
GTR, What intake, carb & spacer are you using?
How does it run now compared to when you posted a year or so ago that it was surging at cruise before the new cam?
RPM air gap
QFT 1050
1 inch 4 hole phenolic spacer Runs best it ever has. Bucking/surging all but eliminated. Very happy with it.
The engine had always liked this much timing, I just never ran as much initial because it was hard on the starter. This programmable setup allows for start retard.
Did you try a 1 hole spacer? If so, how differently did it act?
At one point I think you were considering sealing up the "window" on the manifold divider, it that open or is it sealed?
The divider window is closed, the plenums are 100% separate. That along with the 4 hole spacer far and away produces the best all around mannerisms.
with open spacer, the idle was choppier and the low rpm behavior was erratic.
Re: Ignition timing questions
Posted: Fri Oct 16, 2020 9:36 am
by Belgian1979
FC-Pilot wrote: ↑Wed Oct 14, 2020 1:06 pm
Performance engines are spoiled brats. When you give them what you want they are pains in the neck. Give them what THEY want and they are great ( just like my kid). Compression, cam event timing, chamber shape, spark plugs used, measured squish, fuel and afr, intake design and many other variables all play into it.
Nothing wrong with your engine, just find it’s sweet spot and let it do its thing.
Paul
How do you know what the sweet spot is? I follow some of the comments here saying that the mixture is what determines it to a large extent.
What I find is that with too much time it seems to want to hunt/surge.
Re: Ignition timing questions
Posted: Fri Oct 16, 2020 3:35 pm
by FC-Pilot
Great question! Poorly atomized fuel and bad wet flow characteristics have a big impact. But last time I tried to stick my head in the combustion chamber which the engine running ended poorly, so I have to imagine what is going on based off of experience (of my own as well as others). Testing timing for cruise and idle is different than full throttle. I am lucky enough to have a dyno to use, but anything that can provide repeatable results for testing can work. That is the beauty of a drag strip as it prints out the results for you. A dyno can lead you astray as well, but when you learn to read between the lines you can find a sweet spot. I don’t care if you have an open road and use a stop watch between two markers, if you can be consistent and repeatable then you can tune from there.
I realize many only have a “Butt dyno” to use. We use what we have available to us.
I like starting with the timing on the safe side and getting the fuel dialed in. Then I get the timing optimized. (Depending on the situation) I will go back and double check the fuel. That is just me though.
Paul
Re: Ignition timing questions
Posted: Sat Oct 17, 2020 2:09 pm
by Belgian1979
No wonder some people are detonating their engines to pieces...
Re: Ignition timing questions
Posted: Sat Oct 17, 2020 3:13 pm
by FC-Pilot
Belgian1979 wrote: ↑Sat Oct 17, 2020 2:09 pm
No wonder some people are detonating their engines to pieces...
Very true. A friend of mine brought back an engine we built him because his uncle “set the timing by ear”. Whole new set of pistons, rings and bearings later we put it back to where it needed to be and told him to never let anyone touch his engine again.
I don’t know how many times I have heard at the track “you need at least -blank- amount of degrees in that thing to make it run”. Sadly the guy saying that has no idea what is in it. I always like to keep things on the safe side when it co es to fuel and timing.
Paul
Re: Ignition timing questions
Posted: Sat Oct 17, 2020 7:49 pm
by GRTfast
FC-Pilot wrote: ↑Fri Oct 16, 2020 3:35 pm
Great question! Poorly atomized fuel and bad wet flow characteristics have a big impact. But last time I tried to stick my head in the combustion chamber which the engine running ended poorly, so I have to imagine what is going on based off of experience (of my own as well as others). Testing timing for cruise and idle is different than full throttle. I am lucky enough to have a dyno to use, but anything that can provide repeatable results for testing can work. That is the beauty of a drag strip as it prints out the results for you. A dyno can lead you astray as well, but when you learn to read between the lines you can find a sweet spot. I don’t care if you have an open road and use a stop watch between two markers, if you can be consistent and repeatable then you can tune from there.
I realize many only have a “Butt dyno” to use. We use what we have available to us.
I like starting with the timing on the safe side and getting the fuel dialed in. Then I get the timing optimized. (Depending on the situation) I will go back and double check the fuel. That is just me though.
Paul
I have been being somewhat scientific in my approach. I have a few test areas with landmarks, and some acceleration timing capabilities. I’m also looking at the plugs, using a borescope to check the chambers, and listening closely. I am a tad on the rich side under any serious loads as well. Nice little safety margin.
I don’t know how many times I have heard at the track “you need at least -blank- amount of degrees in that thing to make it run”. Sadly the guy saying that has no idea what is in it. I always like to keep things on the safe side when it co es to fuel and timing.