Head gasket went... D'Oh!
10-17-2007, 01:37 PM
#61
Rennlist Member
if you have boost or increase displacement, like i have done many times, the ratios will be the same, as long as the fuel metering system is working.
scots for example went from 4.5 liter to 5 liter and the fuel ratios didnt change a bit. you put a blower on and increase fuel pressure or if the MAF can meter the air , then the ratios could be near the same. I agree, the distribution is the key, and STOICH is the killler so, if you do have an "average " of 14:1, i would be nervous, as some will be higher and some lower and the cylinders near 14.7 could be in danger of having heat / detonation issues. thats why aircraft engines had EGTs for all the cylinders. we should have that. It would have saved Andersons engine! the cost is not that great either.
mark
scots for example went from 4.5 liter to 5 liter and the fuel ratios didnt change a bit. you put a blower on and increase fuel pressure or if the MAF can meter the air , then the ratios could be near the same. I agree, the distribution is the key, and STOICH is the killler so, if you do have an "average " of 14:1, i would be nervous, as some will be higher and some lower and the cylinders near 14.7 could be in danger of having heat / detonation issues. thats why aircraft engines had EGTs for all the cylinders. we should have that. It would have saved Andersons engine! the cost is not that great either.
mark
For a stock street car though, it's fine.
which looks something like this at cruise:
leanest, leaner, lean, nearly-stoich, stoich, rich, richer, richest
And the air/fuel at WOT per cylinder(..purely guessing, and actually they should average 12.5:1):
14.1:1, 13.4:1, 13.8:1, 12.1:1, 12.5:1, 12.2:1, 11.9:1, 11.5:1
What happens if one increases the displacement, and/or adds a blower?
I think it's easy to see that, due to the higher airflow, the problem will be exacerbated proportional to the amount of extra power, as the range between the leanest to the richest cylinder will be greater.
So theoretically at 15 psi, an extra atmosphere of pressure, the leanest cylinder will now be much leaner than before. In the meantime though, the single wide-band O2 sensor reports 12.5:1 air/fuel at WOT, since it's measuring an average of all 8 cylinders.
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which looks something like this at cruise:
leanest, leaner, lean, nearly-stoich, stoich, rich, richer, richest
And the air/fuel at WOT per cylinder(..purely guessing, and actually they should average 12.5:1):
14.1:1, 13.4:1, 13.8:1, 12.1:1, 12.5:1, 12.2:1, 11.9:1, 11.5:1
What happens if one increases the displacement, and/or adds a blower?
I think it's easy to see that, due to the higher airflow, the problem will be exacerbated proportional to the amount of extra power, as the range between the leanest to the richest cylinder will be greater.
So theoretically at 15 psi, an extra atmosphere of pressure, the leanest cylinder will now be much leaner than before. In the meantime though, the single wide-band O2 sensor reports 12.5:1 air/fuel at WOT, since it's measuring an average of all 8 cylinders.
.
10-17-2007, 01:42 PM
#62
Captain Obvious
Super User
Super User
10-17-2007, 03:44 PM
#63
Rennlist Member
Mark, did you miss where I stated I was referring to an S4 intake manifold? If not, then you're mistaken.
