What's a "normal" A/F ratio for S/C car?
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14.7 is not "perfect" for making power. It's impossible to make best power at 14.7. For NA, best power is around 13:1. Best power for SC is usually 11.5-12.5...
10.0:1 on NA is way too rich. Can run upper 10's with FI, but not needed. Low 10's are simply too rich. Upper 10s is just using more gas than what's needed. For most SC applications, you should be looking for 11s and 12s...
10.0:1 on NA is way too rich. Can run upper 10's with FI, but not needed. Low 10's are simply too rich. Upper 10s is just using more gas than what's needed. For most SC applications, you should be looking for 11s and 12s...
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I'm starting a philosophical discussion now; If you need to be that rich (12:1) then my guess would be that the combustion chamber is a very poor design in this engine... What other reasons would the mixture not mix? The other potential design problem would be ignition...the spark plug is not in an ideal spot... again poor combustion chamber design. Anybody else have any thoughts or ideas?
Phil, is there a piston that is better for mixture that you have noticed?
Phil, is there a piston that is better for mixture that you have noticed?
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The air filter has nothing to do with the air/fuel ratio...just the quantity of air going through the intake tract.
I just installed a REV300TVS kit (with Kold-Fire Tune) and put a wideband O2 + boost gauge to make sure everything looked good after the install since I did it myself.
Idle A/F bounces around 14.7 as it should. Vacuum is around 17 when it first starts, 20 once it warms up.
At WOT at low RPMs it will go a little rich, around 10.5 - 11. I can definitely feel a difference when it goes rich as there is a slight bogging feeling at the 10.5 ratio (just doesn't feel right), although no sane person would really hit WOT at 2.5k rpms in 3rd gear. I was just doing it for a test to see how the A/F looked. Boost at low RPMs starts around 5psi and jumps to 9psi pretty quick.
At WOT at high RPMs the A/F is solidly between 12.0 - 12.5, doesn't move much from that. When rolling on the throttle at high RPMs boost starts round 7 psi and peaks out at 9psi.
Idle A/F bounces around 14.7 as it should. Vacuum is around 17 when it first starts, 20 once it warms up.
At WOT at low RPMs it will go a little rich, around 10.5 - 11. I can definitely feel a difference when it goes rich as there is a slight bogging feeling at the 10.5 ratio (just doesn't feel right), although no sane person would really hit WOT at 2.5k rpms in 3rd gear. I was just doing it for a test to see how the A/F looked. Boost at low RPMs starts around 5psi and jumps to 9psi pretty quick.
At WOT at high RPMs the A/F is solidly between 12.0 - 12.5, doesn't move much from that. When rolling on the throttle at high RPMs boost starts round 7 psi and peaks out at 9psi.
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It doesn't work that way. Stoich is not where best power is made. It never has been in any combustion chamber. All sorts of good books have been written on this and they dedicate chapters to explaining why this is the case. It's not just a single sentence to explain.
So you'll have to take my word for it or read the books on engine design. 13:1 for NA and richer than that for FI are typical. How much richer depends on several factors. There is not a magic AFR though. So we should use ranges and generalities when talking about AFR, fwiw. Spark is more of a precise science though.
As for 2zz pistons, the more efficient designs will be generally quite flat as to not interrupt the flame front-- get a more complete burn, etc. 2zz pistons are generally that way--flat'ish. When you get into high compression motors the pistons have large domes, and there's no way to avoid some flame front interruption. Obviously the greater compression offsets that deficiency though.
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Philosophically... is it related to mixing?
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Essentially, 14.7:1 is the mixture under ideal conditions. Pure fuel, pure air, complete combustion products. None of these things happen. Neither the fuel nor air are pure, the fuel does not completely evaporate into the air before combustion, the combustion does not have time to complete, not all the fuel burns, and temperature issues cause chemical formation that isn't considered in the 14.7:1 formula. So you have to run rich to make the most of a real world situation. The rich mixture maximizes the air that's combusted and helps to keep the engine cooler.
University of Wisconsin - Small Engine Research Center '00
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Yes, partially.
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OK...so what can the University of Wisconsin do to improve on the efficiency of the 2ZZ-GE engine? I'd contribute to that cause...Essentially, 14.7:1 is the mixture under ideal conditions. Pure fuel, pure air, complete combustion products. None of these things happen. Neither the fuel nor air are pure, the fuel does not completely evaporate into the air before combustion, the combustion does not have time to complete, not all the fuel burns, and temperature issues cause chemical formation that isn't considered in the 14.7:1 formula. So you have to run rich to make the most of a real world situation. The rich mixture maximizes the air that's combusted and helps to keep the engine cooler.
University of Wisconsin - Small Engine Research Center '00
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the 2zz is already quite efficient as far as production motors go. It makes 100hp/L or better. Not many production motors do that even today. How does one complain about that?
Of course better intake, exhaust and head porting will make it more efficient. You're welcome to implement those features as many of us do. The head is quite good right out of the box, as evidence by greater than 100hp/L. All that said, making the motor a more efficient pump, it will still take about 13:1 in NA form and about 12:1 in FI form to make best power on pump gas (again, there are ranges here)...
Phil
Of course better intake, exhaust and head porting will make it more efficient. You're welcome to implement those features as many of us do. The head is quite good right out of the box, as evidence by greater than 100hp/L. All that said, making the motor a more efficient pump, it will still take about 13:1 in NA form and about 12:1 in FI form to make best power on pump gas (again, there are ranges here)...
Phil
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A lean mixture also helps keep the engine cooler.Essentially, 14.7:1 is the mixture under ideal conditions. Pure fuel, pure air, complete combustion products. None of these things happen. Neither the fuel nor air are pure, the fuel does not completely evaporate into the air before combustion, the combustion does not have time to complete, not all the fuel burns, and temperature issues cause chemical formation that isn't considered in the 14.7:1 formula. So you have to run rich to make the most of a real world situation. The rich mixture maximizes the air that's combusted and helps to keep the engine cooler.
University of Wisconsin - Small Engine Research Center '00
Either direction from peek EGT helps it run cooler.
Max power is usually at peak EGT.
So the rich mixture is not more efficient, it is using more fuel and making less power. It is just easier on the engine.
This all depends on your definition of efficient.
14.7:1 is usually where a lot of engines run that need to be efficient and have low emissions.
If your measure of efficiency is BSFC then one usually goes lean, rather than rich.
Any definition that requires lots of boost and lowering the compression is usually not more efficient, but it is more powerful.
To anyone that would like an introductory article on the basics of air-fuel mixtures, google "Pelican's Perch Mixture Magic". It's a well written, easy-to-read classic.
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But the OP dd not want theory, only the number.
And the pelican man says that he only deals in understanding how the engines work, and not OWTs...??
Do you have the stock tune? As others have noted, 10 is awfully rich. Which A/F meter are you using. Many, such as the NGK, need to be calibrated when first installed. So the values you are seeing may not be accurate if it was not calibrated.
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