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Jay159866
Well-Known Member
Seeing -5 negative and +1 .. 55 on spark advance, not the total like you guys said we should use. I have seen up to +4 knock before on this car through tuning.
Chummel
Well-Known Member
How much timing is too much timing on e85 on the stock block? I'm on e70 and working with Lund on getting it tuned. On e70, Lund is saying 19-20 degrees of timing and 21-22 on e85 but my log had 20 degrees spark advance and was adding negative knock all the way up until it was capped at -4 knock with e70.
It looks to me like my car was liking the fuel, so I don't think fuel quality is an issue. Is the 19-20 cap on timing just to not overpower my block?
It looks to me like my car was liking the fuel, so I don't think fuel quality is an issue. Is the 19-20 cap on timing just to not overpower my block?
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arghx7
Well-Known Member
Guys,
The biggest concern with E85 is that even if you don't have severe knock, you will hit the cylinder pressure limit of the block from advancing the timing. Here are a few things to consider.
First,
The cylinder pressure increases as the combustion advances, even if it doesn't knock. You can see this with high octane fuel or just by moving the spark around at a lower engine load where it is not knock prone. The image shows the cylinder pressure trace according to the phasing of the combustion (location of peak pressure):
So the cylinder pressure increases with both speed and load. The image below is a chart of engine speed and brake mean effective pressure (flywheel torque basically), showing engine averaged peak cylinder pressure in bar. It is on a stock tune for a modern engine that comes with a turbo from the factory (not a Ford engine). You can see that for example at 2000rpm and 5000rpm the torque is the same, but the cylinder pressure increases.
On the previous generation 3.5 Ecoboost engines, Ford limited the spark timing at high engine speed on pump gas[/B ] in the factory tune so that the cylinder pressure would not exceed their limit for long term durability (remember those Ecoboost torture tests in the media?). You can see in the image below a comparison of cylinder pressure and cylinder pressure rise rate between the Ecoboost 3.5 and the naturally aspirated Duratec.
Finally, here is a chart showing the impact of advancing spark on E85. This is on a naturally aspirated flex fuel V6 (flex fuel from the factory, but not a Ford engine). Red line is spark for 87 octane on the stock tune (basically, very conservative spark). Green line is with the spark maxed out for moderate knocking (based on audible knocking sound and cylinder pressure). So that's 4 extra degrees at peak power (6000rpm).
Notice that peak cylinder pressure increased by 20% from adding 4 degrees on a naturally aspirated engine. Notice also that some areas such as 5200rpm could not take much more spark without knocking - this is because the knock is amplified by residual gas in the cylinder, exhaust manifold design, etc.
TL;DR; Advancing spark still stresses your engine even if it doesn't knock; don't let E85 give you a false sense of security
The biggest concern with E85 is that even if you don't have severe knock, you will hit the cylinder pressure limit of the block from advancing the timing. Here are a few things to consider.
First,
The cylinder pressure increases as the combustion advances, even if it doesn't knock. You can see this with high octane fuel or just by moving the spark around at a lower engine load where it is not knock prone. The image shows the cylinder pressure trace according to the phasing of the combustion (location of peak pressure):
So the cylinder pressure increases with both speed and load. The image below is a chart of engine speed and brake mean effective pressure (flywheel torque basically), showing engine averaged peak cylinder pressure in bar. It is on a stock tune for a modern engine that comes with a turbo from the factory (not a Ford engine). You can see that for example at 2000rpm and 5000rpm the torque is the same, but the cylinder pressure increases.
On the previous generation 3.5 Ecoboost engines, Ford limited the spark timing at high engine speed on pump gas[/B ] in the factory tune so that the cylinder pressure would not exceed their limit for long term durability (remember those Ecoboost torture tests in the media?). You can see in the image below a comparison of cylinder pressure and cylinder pressure rise rate between the Ecoboost 3.5 and the naturally aspirated Duratec.
Finally, here is a chart showing the impact of advancing spark on E85. This is on a naturally aspirated flex fuel V6 (flex fuel from the factory, but not a Ford engine). Red line is spark for 87 octane on the stock tune (basically, very conservative spark). Green line is with the spark maxed out for moderate knocking (based on audible knocking sound and cylinder pressure). So that's 4 extra degrees at peak power (6000rpm).
Notice that peak cylinder pressure increased by 20% from adding 4 degrees on a naturally aspirated engine. Notice also that some areas such as 5200rpm could not take much more spark without knocking - this is because the knock is amplified by residual gas in the cylinder, exhaust manifold design, etc.
TL;DR; Advancing spark still stresses your engine even if it doesn't knock; don't let E85 give you a false sense of security
Chummel
Well-Known Member
After Lund was finished tuning, I ended up with safe 20 degrees. They hooked me up with a "race" tune where the knock sensors can add an additional degree. By the looks of the logs that's about all the E70 has in it.
I'm happy with the results.
I'm happy with the results.
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