Individual cylinder timing maps

[brn12345]

As much as I have been on the dyno fiddling I never tried to zero out the timing retard that is present in the number 1 and 2 cylinders in high rpms (see picture of cylinder 1 vs 3). I also recently noticed that on some open source E85 maps those tables are all zero'd out. If high octane gas is used, can those be safely zero'd out or is there another reason for the retard in cylinders 1 and 2?

[jamesm]

I've run mine zeroed out for a while now, haven't noticed any ill effects. It supposedly makes for a smoother idle, but I haven't noticed anything in that regard either.

[brn12345]

Originally Posted by jamesm

I've run mine zeroed out for a while now, haven't noticed any ill effects. It supposedly makes for a smoother idle, but I haven't noticed anything in that regard either.

How can it make for a smoother idle if it only impacts high load / high rpm? Are you confusing these with other tables?

[Shiv@Openflash]

With high enough octane fuel (ie, race gas) zeroing them out will improve performance. On pump gas it will have the opposite effect as then you will have to make your base timing map more conservative to account for the more knock prone cylinders. It has no effect on idle quality that I'm aware of.

[jamesm]

I could've sworn I had seen where the OTS map release notes mentioned zeroing it out for a smoother idle. Maybe I'm not remembering correctly...

[mad_sb]

Originally Posted by jamesm

I could've sworn I had seen where the OTS map release notes mentioned zeroing it out for a smoother idle. Maybe I'm not remembering correctly...

There is a lot of talk on romraider about that affect as well... even though the tables don't look to be active at idle I've had mine zeroed out on E85 for a long while now. I reduced them by about 1/2 on pump gas AFTER doing my full exchaust, including header.

[mad_sb]

Originally Posted by brn12345

As much as I have been on the dyno fiddling I never tried to zero out the timing retard that is present in the number 1 and 2 cylinders in high rpms (see picture of cylinder 1 vs 3). I also recently noticed that on some open source E85 maps those tables are all zero'd out. If high octane gas is used, can those be safely zero'd out or is there another reason for the retard in cylinders 1 and 2?

BTW, the stock mapping pulls timing at lower rpm's as well as upper so that map you are showing has already been modified from the stock rom map.

[brn12345]

Ok just zeroed all individual cylinder timing trims on shivs map 1.55 stage 2 el. Will be running a test tomorrow to see potential top end gains. On another note the 1.55 map is a big step up from the 1.3x I was running before!! Very responsive in mid rpms.

[Kodename47]

Why are those cylinders more knock prone? Is there any way to adjust this on ECUtek?

[arghx7]

Originally Posted by Kodename47

Why are those cylinders more knock prone? Is there any way to adjust this on ECUtek?

Most engines have some variation between cylinders on knock limit. You can see it with combustion pressure sensors. A lot of it is due to individual differences in air and coolant temperatures or flow that are basically unavoidable.

If you're on E85 or race fuel it might make sense to change those compensations because you may never knock much at those speeds and loads. But on pump gas--do you really want to run spark harder there? You might pick up power from zeroing out the compensations, but you're probably knocking the engine harder. Knock occurs at different levels of severity, rather than a "well it's knocking or it's not knocking" kind of deal. Changing components like exhaust might help reduce knock sensitivity for those cylinders on pump gas, or it might not.

And the knock control system is unreliable at that high of speed--there's too much noise. So I wouldn't go off that. The guys who made those tables probably dialed them in in a lab somewhere.

Are you really sweating those extra couple degrees of timing?

[Sportsguy83]

Originally Posted by arghx7

Most engines have some variation between cylinders on knock limit. You can see it with combustion pressure sensors. A lot of it is due to individual differences in air and coolant temperatures or flow that are basically unavoidable.

If you're on E85 or race fuel it might make sense to change those compensations because you may never knock much at those speeds and loads. But on pump gas--do you really want to run spark harder there? You might pick up power from zeroing out the compensations, but you're probably knocking the engine harder. Knock occurs at different levels of severity, rather than a "well it's knocking or it's not knocking" kind of deal. Changing components like exhaust might help reduce knock sensitivity for those cylinders on pump gas, or it might not.

And the knock control system is unreliable at that high of speed--there's too much noise. So I wouldn't go off that. The guys who made those tables probably dialed them in in a lab somewhere.

Are you really sweating those extra couple degrees of timing?

When i saw last post arghx7 got excited knowing I was going to read and learn something new.

F*cking walking library....

[brn12345]

Originally Posted by arghx7

Are you really sweating those extra couple degrees of timing?

I agree that 2 odd degrees on just two cylinders might not make a world of a difference, but I do have a theory that I want to test out.

1. I have a hunch the stock map pulls timing in the 1/2 cylinders not because they are detonation prone.
2. When I changed to headers I measured the stock header primary's and noticed that 1/2 primaries are shorter than 3/4.
3. I installed Equal length headers.

So my theory is that the timing retard on 1/2 is there for pulse tuning purposes and since I moved to equal length that now the pulses are out of sync. I went ahead and zeroed out the tables and will be testing tonight to see the difference.

Does this make sense or am I just theorizing too much?

[u/Josh]

Originally Posted by brn12345

I agree that 2 odd degrees on just two cylinders might not make a world of a difference, but I do have a theory that I want to test out.

1. I have a hunch the stock map pulls timing in the 1/2 cylinders not because they are detonation prone.
2. When I changed to headers I measured the stock header primary's and noticed that 1/2 primaries are shorter than 3/4.
3. I installed Equal length headers.

So my theory is that the timing retard on 1/2 is there for pulse tuning purposes and since I moved to equal length that now the pulses are out of sync. I went ahead and zeroed out the tables and will be testing tonight to see the difference.

Does this make sense or am I just theorizing too much?

This is an interesting thought. At 6000 rpm the engine will rotate through 2 degrees in

6000 rotation/min * (1/60) min/sec * 360 degree/rotation = 36000 degree/sec

2 degrees / (36000 degree/sec) = 55 * 10^-6 seconds

Assuming the speed of sound is close to the speed of sound at sea level, the distance the exhaust pulse would travel in that time:

55*10^-6 seconds * 343 m/s = ~ 2 cm

I am making a lot of huge assumptions about systems that I don't fully understand so this could be way off, but my back of the envelope calculation and basic understanding say your theory is feasible. One thing to note, however, is that if their only goal with that timing table was to match up exhaust pulses then the timing retard should increase linearly with engine speed.

[arghx7]

How would retarded spark change the pulse tuning enough to matter if the exhaust valve opening events are the same?