That sentence was from the department of redundancy department

 

Correct. There isnt an "upper limit" on making more power until you go really lean and then theres just a lack of fuel to combust. Most people that own FD's tend to refer to 12.5 afr's as the uppermost limit for a rotary engine because of the risk of detonation. But if you could get away with 15's, it would make more power IIRC.

 

Incorrect. An internal combustion engine makes best power on the slightly rich side of stoich. This is simply a fact. If you want an explanation why...

Combustion requires both fuel and oxygen molecules. Stoich is where you have exactly the same number of each molecule in the combustion chamber. In theory, this is the point of greatest potential power, presuming all the molecules are paired up. In reallity, it's harder to get every oxygen molecule a dancing parner without sending more fuel to the party. This only works up to a point and beyond that it is wasteful...unless you use it for additional charge cooling, as with turbocharged engines. Where people get confused is that leaner *is* more powerful, when you are starting out on the ultra-rich side of the AFR band. But, once you reach the natural "best power" AFR (slightly rich), power falls off again.

 

I have always read that around 12.5:1 to 13.0:1 AFR is your best power. This is even mentioned in a book that I have that is about 40 years old... I don't think much has changed since then AFR-wise

Since my car is a non-daily driver, I tune it for 12.8:1 everywhere in vacuum. Yeah, it sucks up a lot of gas and makes people behind me faint from the fumes, but the throttle response and driveability factor is a little bit better than at 14.5:1 in my opinion.

My "under boost" AFRs go down from low 12s to high 10s as you go from 1 psi to 17 psi of boost. Yes, I am a chicken.

Brian

 

Yes but a chicken with all 6 apex seals

 

In a catalytic equipped vehicle the stoichiometric ratio is around 14.6:1 since this is the level where the three pollutants cross at approximately their lowest possible levels. Most engines are most fuel efficient at air/fuel ratios leaner than stoichiometric at around 15.5:1 and most produce their most power at air/fuel ratios of around 12.5:1.

The exact ratio for maximum power output is different for each engine and different even for the same engine across the rpm and load bands. However, substantially all engines at all operating ranges produce their most power somewhere between 12:1 and 13:1 air/fuel ratios. This is an undeniable fact that all tuners rely on heavily.

Again volumetric efficiency at a given rpm point or range determines the exact air-fuel ratio where an engine will produce its maximum power, but in general most people would agree that performance designs produce their maximum power somewhere between 12:1 and 13:1 air-fuel. The following quotes should reinforce that idea:

Bosch state (sic) that most spark ignition engines develop their maximum power at air/fuel ratios of 12.5:1 - 14:1, maximum fuel economy at 16.2:1 - 17.6:1, and good load transitions from about 11:1 - 12.5:1. However, in practical applications, engine air/fuel ratios at maximum power are often richer than the quoted 12.5:1, especially in forced induction engines where the excess fuel is used to cool combustion and so prevent detonation.
Source: http://www.autospeed.co.nz/cms/A_1595/article.html

Typically cars make best power at about 12.5:1 air/fuel ratio
Source: http://www.sficc.net/features/feature4.html

Usually the air/fuel ratio which produces maximum power is from 12.5:1 - 13.5:1, but this varies with engine type.
Source: http://hondata.com/techlambda.html

The chemical minimum for complete fuel combustion is a 14.7:1 air-to-fuel ratio, termed the "stoichiometric" ratio. Generally, peak horsepower is achieved when an engine (any engine) is run on about 5% to 15% less air than stoichiometric.
Source: http://www.autotech.com/powermod.htm

Maximum power is found when the ratio is about 12.6:1 (Lambda 0.86)
Source: http://www.ffp-motorsport.com/tuning/o2meter.php

Maximum Power is achieved with a slightly rich mixture of approx. 12.8:1 or .9 Lambda.
Source: http://www.datsuns.com/Tech/oxygen_sensors.htm

As a general rule, maximum power is achieved at slightly rich, whereas maximum fuel economy is achieved at slightly lean. (relative to chemical stoichiometric combustion)
Source: http://www.uvi.edu/Physics/SCI3xxWeb...solineFAQ.html

for any given quantity of air inside the combustion chamber there is an ideal quantity of vaporized fuel (ideally about 12 or 13 to 1 for maximum power under acceleration).
Source: http://www.svrider.com/tips/jetting.htm

this is all from the site I linked. It would seem that for most cars, 12.5 is spot on with a possibility of a little more power pushing 13.0. None-the-less, there is an upper limit which will set ultimate power and it is no where near 14.7 to 1.

In another article I read, it stated that any fuel added beyond 12.0 to 1 was only for cooling as the combustion process can not physically consume this extra fuel. This is why we can tune for 12.5 to 1 afr using the water as coolant instead of the fuel. This is also what determines the amount of water needed.

Mike

 

Damn Mike lol. Someone should make those last few posts a sticky...

 

ANY NEWS ON THE ANTI-DET FRONT?

Jason: Any definitive results? Or did you stop evaluating when PG dropped out?

Has KDR dropped this thing?

What happened to those 60+ testers? Still gagged by NDR, I suppose?

Anybody know any details about the 'whole package'? (stock-ECU chip swap for timing and fuel-defenser kill for stock injectors / upgraded fuel pump / etc / besides just the plugs).

There's whispers but no shouts. It'd be nice to hear some shouts.

 

I have not had the time to test the device. It could be a few weeks before I can get it on the dyno.

Jason

 

[QUOTE=Michael Filippello]
Flame suit on. You can't hurt my feelings. Even Jim doesn't bother me. I just think he is funny. He is always right though, if you don't believe me, just ask Jim
QUOTE]

I love ur "sheep's blood" on the door trick.

Ooops, I might have just summoned YZF-R1.

 

Don't Vipers, vettes, 911s and most other sport cars have MAF?

Sorry for not doing the search, but why hasn't someone come up with a MAF conversion for the FD?

 

There's a thread on the subject in advanced tech.

 

I'm hoping more people read the links you posted, as well as do more of their own research on MAF (and other) fuel mapping systems to get a real understanding of how they work so that this subject doesn't get beaten to death.

 

What? Here on the rx7club forums? A subject being beaten to death???

 

No subject is ever beaten to death

 

i still don't see the light on this reason/hypothesis. the only reason that i would run "slightly rich side of stoich" is because of what's been mentioned already, cooling. i had a talk w/ one of the employees at Mazdatrix and he mentioned that although it's a little more risky playing on the slightly leaner side of stoich, you maximize each oxygen molecule per fuel.

the way i see it, it boils down to this (in the most simplest manner):
motor running on the richer side of stoich has of course, cooler combustion temperatures. but w/ cooler combustion comes lower pressure. (think of it as a whistling tea kettle where it'll only whistle when the kettle reaches that point where water is boiling, in this case, only when the motor is running on the lean side of stoich)
but when the motor is running just a smidge even on the leaner side of stoich, you're maximizing power through hotter combustion temperatures, therefore creating higher combustion pressures, therefore making them rotors spin more, therefore making more powah! weeeeee!

for example, i think if both FD's w/ exactly the same mods were tested, but with different AFR's, i believe the FD w/ a higher EGT reading would pull out a higher hp/tq.

running rich is just a way i see to prevent any detonation; a safety measure. that's all.

btw.. this is just "my" personal hypothesis, and am not trying to prove you wrong. though it would be nice to hear any other reasons so i myself could perhaps get a better understanding at this.

 

I was wondering it someone can make an ignition that can disable the trailing plugs and let an ECU like the PFC to automatically compensate for that adjustment.

 

Its kind of funny...over on the RX-8 forum, people are complaining about the MAF and talking about using a MAP sensor for forced induction mods.

jds

 

Do some serious research under the topic "thermodynamic efficiency of various combustion chamber types", and then see which category the Wankel falls into....

 

A few years ago, I talked to a couple of MK4 owners and they stated that MAF is the best, up to a point (BPU?).

However, APU and heavy mods, MAP is suppose to be the way to go.

 

ya.. it falls directly in "internal combustion engines" along w/ piston motors, 2 cycles, etc.

 

It falls directly in the bottom...

 

No wonder...

Thank you. Thus the reason why the Wankel isn't "maximizing each oxygen molecule per fuel" and "maximizing power through hotter combustion temperatures." Hotter EGTs do not necessarily equate to higher combustion pressure.

 

oki doki.. enlighten me then.. i'm open to learn. so if Hotter EGTs do not necessarily equate to higher combustion pressure, what else does it equate to?

btw, i was talking about both pressure and temperature for the wankel, not only combustion pressure in regards w/ EGT

 

It equates to much of the charge still burning inside the exhaust manifold rather than getting it done in the combustion chamber. Any burning not taking place in the combustion chamber is robbing the engine of power. The problem is the rotary's combustion chamber is shaped like a flat rectangle and the flame front likes to travel in a sperical shape. Hence a round, hemispherical combustion chamber has a much better combustion efficiency when you look at the travel of the flame front. The rotary also has a lot of surface area exposed to the flame and so the engine absorbs more heat from the combustion cycle than a piston engine; this also robs the engine of potential power. Rotaries run richer than stoic because they have too. The burn of the fuel is so inefficient you must compensate by adding extra fuel. Not burning all your fuel in the combustion chamber also isn't good for emissions.

These reasons explain why EGT and coolant/oil temps are so high in a rotary. Any heat that is leaving the engine through the exhaust or coolant is energy that is not producing power. The fact that the EGT and coolant temps are so danged high tells you right away the engine is not as efficient. Of course the gas mileage tells you that too...