AFR's why tune so rich??

[Ben Wilson]

Not sure where I got this, but it seems relevant:

Air Fuel Ratios
Rich run limit - 6.0:1
Low power, black smoke - 9.0:1
Rich best torque @ WOT - 11.5:1
Safe best power @ WOT - 12.5:1
Lean best torque @ WOT - 13.2:1
Chemically ideal - 14.7:1
Light load, part throttle - 15.5:1
Best economy, part throttle - 16.2:1
Lean run limit - 18-22:1

[chris davey]

Another reason is that you can make more gains running a richer AFR but with more advance timing e.g. 12:1 with 18deg timing at 15psi boost or 12.5:1 with 15deg timing at 15psi boost.

Both may be a safe no knock tune but from all the reading I have done on the microtech forums and from the tuning I have done, I have found that leaving it rich and utilising a bit more ignition advance has helped.

I did read about some stuff where they were tuning for best fuel economy in race conditions though. I think it was a 24hr race and they had the engine tuned very close to stoich at WOT. Similar to what Linden said, these guys had a goal in mind and they obviously knew how to achieve it. Don't try and run your 1j at 14.7:1 at WOT please. (unless you want to strap a video camera in the engine bay to record all the kabooms )

[Ben Wilson]

Rinning rich can use excess fuel to cool the combustion chamber which is particularly useful with forced induction engines. One of the big advantages of water injection is that you can use the water for the cooling and run leaner mixtures to get more power..

[DigitalPho3nix]

I feel only reason people run richer you get a more complete and even burn during combustion. You want to burn all the oxygen before you run out of fuel, so you get maximum torque from each combustion (but not so much that you flood the cylinder obviously).

Running slightly richer than normal in race conditions can also be beneficial. You may show a small decrease in overall power, but the engine is much more drivable and compliant resulting in faster lap times (given everything else is constant of course).

[jezza323]

also running slightly richer in race conditions (along with timing retarded 1-2 degrees from absolute peak torque timing) will allow the engine to run much cooler,and therefore last longer

[VeeP]

as has been said, running stoich is ideal for making max power, but results in EGT that are way too hot - plus stoich is asking for detonation/pre-ignition as the cylinder walls and head heat up.

Running rich cools the cylinder and carries alot heat out of the exhaust as the extra fuel leaves the cylinder.

mind u at part throttle the cylinder heads and walls can dissipate enough heat to keep EGT safe

[DigitalPho3nix]

also running slightly richer in race conditions (along with timing retarded 1-2 degrees from absolute peak torque timing) will allow the engine to run much cooler,and therefore last longer

You'll find that many racecars have a 'magic' engine temp. At this temp the car is fastest on a given track. Only extensive testing, solid data, good car management, and a good driver can help you get to this stage though.

[cambelt]

Put a 7mgte or a 1jzgte on the dyno , stock they do 10 AFR,s
Dave

[o_man_ra23]

Be warned though, too rich and you produce excessive NO output (thats nitrogen oxide, not nitrous oxide... dont get the 2 mixed up) which in turn heats the shit out of your system and can be just as dangerous as running lean. If you have a good EFI system, then the knock control circuit can be used to retard the timing in case of pinging which can account for bad fuel batches. Of course, if this happens regularly, you should re-tune so it doesnt get to the knock sensor retardation stage.

Looks like I will need to do plenty of research on ideal AFRs before I go tuning.

[brett_celicacoupe]

Put a 7mgte or a 1jzgte on the dyno , stock they do 10 AFR,s
Dave

or a 1GGTE

mine went so rich it couldnt read any lower

[Kyosho]

Be warned though, too rich and you produce excessive NO output (thats nitrogen oxide, not nitrous oxide... dont get the 2 mixed up) which in turn heats the shit out of your system and can be just as dangerous as running lean. If you have a good EFI system, then the knock control circuit can be used to retard the timing in case of pinging which can account for bad fuel batches. Of course, if this happens regularly, you should re-tune so it doesnt get to the knock sensor retardation stage.

Looks like I will need to do plenty of research on ideal AFRs before I go tuning.

From what I've seen.

Too rich = high counts of CO and CO2.
Too lean = High counts of NOx

Nitrous Oxide can only come about from excessive temps, high pressures, and a huge excess of oxygen. Hence, when you're lean.

[Esteban]

...You want to burn all the oxygen before you run out of fuel...

Are you on drugs?

[Ben Wilson]

Thinking about it, combustion chamber design probably makes a difference.

A well designed head will probably be able to run a much leaner mixture than a poorly designed one (more homogeneous mixture).

[worldwalker]

Sorry to dredge up an old thread but I've got a simple question that doesn't need a new thread.

What are the most accurate means of measuring real time AFR? Is it a case of cross referencing MAP/MAF/AFM with fuel flow; or exhaust chemical measuring; or EGT measurements; or a combination? I can only see the first working if you have exact measurements and is still not representative of the actual combusted values (manifold efficiency etc, if this should be considered). Chemical measuring could be seen as slightly slow and not representative of what goes in, only what comes out. And EGT needs a baseline peak figure for the current conditions to know where stoich is. I'm probably way off, but I'd love to know how AFR is measured, both on in car gauges and for dynoing.

Thanks

[oldeskewltoy]

just got my little monster checked because I had failed recent emissions check**... I found out that my wideband had "lost" its perspective (hahahahahaha) and I was running AFRs as high as 16, with ignition timing up as high as 35 degrees - normally a recipe for BIG BOOM . I'm guessing its a good thing I haven't actually abused her.

With her on the dyno, the tuner was able to remove 9 degrees of timing before there was any power fall off!!! Now she is running about 26 degrees of total timing, the AFRs are down in the 12s on WOT.


By the way... can someone confirm/deny the following (something said by my tuner), "Less ignition timing is required (to make = hp) when a head is ported correctly"