why?
10-20-2007, 07:09 AM
#3
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I've wondered that myself. To start with the mixture you find best power at isn't as simple as saying this is where best power will be found with gasoline. It's very engine dependent. What works for one probably doesn't work for another. A good 4v pentroof head will be able to make best power leaner than a large bore, 2v dinosaur breathing through a carburetor. It all has to do with how the fuel and air molecules mix and how much of the available oxygen is combined with the fuel. Could be that the rotary produces a good swirl or tumble effect and better mixes the fuel with the air allowing all available fuel to be burnt with less air. That's really the reason you need to run fatter than stoich in most combinations in order to achieve best power. Running just enough fuel to be able to combine with all available oxygen atoms. When you run at stoich in most any engine you are leaving oxygen molecules that have not found fuel molecules to attach themselves to....you could of burned more fuel and made more power. If the charge is fairly static and there is not good mixing of the fuel and air you'll need to run fat in order to achieve that complete burn using all available oxygen. If there is good mixing then less fuel is needed to attach to all available oxygen.
10-20-2007, 07:28 AM
#4
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In my limited experience and knowledge, I've always felt that power would increase as the AFR got closer to stoich, with the downside being an increased possibility of detonation. The critical detail in tuning any engine would be to find the best compromise between safety and maximum power.
10-20-2007, 10:06 AM
#5
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Originally Posted by 1988RedT2' post='885900' date='Oct 20 2007, 08:28 AM
In my limited experience and knowledge, I've always felt that power would increase as the AFR got closer to stoich, with the downside being an increased possibility of detonation. The critical detail in tuning any engine would be to find the best compromise between safety and maximum power.
Believe JD is talking specifically about an NA engine that would not be knock limited.
10-20-2007, 12:26 PM
#6
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Originally Posted by C. Ludwig' post='885898' date='Oct 20 2007, 05:09 AM
I've wondered that myself. To start with the mixture you find best power at isn't as simple as saying this is where best power will be found with gasoline. It's very engine dependent. What works for one probably doesn't work for another. A good 4v pentroof head will be able to make best power leaner than a large bore, 2v dinosaur breathing through a carburetor. It all has to do with how the fuel and air molecules mix and how much of the available oxygen is combined with the fuel. Could be that the rotary produces a good swirl or tumble effect and better mixes the fuel with the air allowing all available fuel to be burnt with less air. That's really the reason you need to run fatter than stoich in most combinations in order to achieve best power. Running just enough fuel to be able to combine with all available oxygen atoms. When you run at stoich in most any engine you are leaving oxygen molecules that have not found fuel molecules to attach themselves to....you could of burned more fuel and made more power. If the charge is fairly static and there is not good mixing of the fuel and air you'll need to run fat in order to achieve that complete burn using all available oxygen. If there is good mixing then less fuel is needed to attach to all available oxygen.
yep it has to be something like that. i think my tr3 would make more power by richening it up
10-23-2007, 08:13 PM
#7
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Originally Posted by rotarychainsaw' post='885892' date='Oct 19 2007, 10:09 PM
I coulda swore that 14.7 was the best for power and emmisions. Don't remember where I heard that though.
14.7 is the point of stoichiometry, or in fewer ten dollar words, it's the point where there's exactly enough fuel for the amount of oxygen and vice-versa.
For best power, you want to run a bit richer than that for various reasons. It runs a little cooler, and since you can never perfectly atomize fuel, it ensures that every oxygen molecule can find fuel to combine with. Adding more fuel is easy, adding more air is not!
11-10-2007, 01:44 PM
#8
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I have been messing around with a inovate motorsports LC-1 wide band A/F system ( or Lamda) Of couse they say that 14.7 is stoich and is the best ratio for gasoline and air, But they also say that most engines can make a little more power running slighty rich....
On a turbocharged car it should be tuned rich for saftey, because the extra fuel cools the combustion chambers... I've heard of high boost rotarys running somthing like 10/1 A/F ratios.. does that sound right???
On a turbocharged car it should be tuned rich for saftey, because the extra fuel cools the combustion chambers... I've heard of high boost rotarys running somthing like 10/1 A/F ratios.. does that sound right???
11-11-2007, 01:33 PM
#9
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Originally Posted by RE_TurboFB' post='887594' date='Nov 10 2007, 11:44 AM
I have been messing around with a inovate motorsports LC-1 wide band A/F system ( or Lamda) Of couse they say that 14.7 is stoich and is the best ratio for gasoline and air, But they also say that most engines can make a little more power running slighty rich....
On a turbocharged car it should be tuned rich for saftey, because the extra fuel cools the combustion chambers... I've heard of high boost rotarys running somthing like 10/1 A/F ratios.. does that sound right???
On a turbocharged car it should be tuned rich for saftey, because the extra fuel cools the combustion chambers... I've heard of high boost rotarys running somthing like 10/1 A/F ratios.. does that sound right???
yep. my STOCK 91 non turbo @wot was 10:1 by 7000rpms.
11-16-2007, 09:30 PM
#10
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Originally Posted by j9fd3s' post='885887' date='Oct 19 2007, 09:07 PM
ok, another stupid question.
if best power on gasoline is 12.5:1 afr how come everyone with an NA motor makes best power leaner than 13:1?
shouldnt that be too lean?
if best power on gasoline is 12.5:1 afr how come everyone with an NA motor makes best power leaner than 13:1?
shouldnt that be too lean?
going by my atomization theory, rotaries have high enough turbulence that it helps the combustion.
also, 12.5:1 is just a rule of thumb. lots of piston engines make best power in the 13-13.5:1 range as well. I've heard of some funky technology ports and chambers that make best power in the 16:1-18:1 range.