Saturday, April 29, 2006 - 09:22 am, by: Damian Ware(Frozenpod)
What is the ideal A/F ratio, does this change for turbo or N/A cars.
My understanding that in closed loop cruising the ideal is 14.7:1.
While accelerating the open loop is factory set rich, but what would the ideal tune be which wont cause engine damage or pinging. Is the ideal setting still 14.7:1.
Saturday, April 29, 2006 - 09:52 am, by: Damian Ware(Frozenpod)
Thanks
So I guess my idea of the closed loop performance was incorrect. What is the normal closed loop A/F ratio.
When dyno tunning what is the A/F ratio set for, you would have to think about all other atmospheric conditions which will occur. How much safety margin is usually allowed.
Saturday, April 29, 2006 - 11:35 am, by: Braden Murdoch(Ribfeast)
I was told 11.8:1 for the 1JZ...so you reckon I should retune to 13.2:1? Should I make it 13.2:1 across the whole curve? Or maybe leaner at less than 3000RPM?
Saturday, April 29, 2006 - 12:03 pm, by: Daniel Clarke(Dieseltrain)
Braden, I wouldnt go any higher than 12.5:1 Remember that the reason most people retune the TT motor, is the fact it runs AFR's in the range of 9.8:1 ( yes i have seen a chart this low) up to 11.0:1 The fact you can retune it up to 12.0:1 or even 12.5:1 will help make power and better economy.
But If you run too lean, then * BOOOM *. Most tuners wont run any turbo cars leaner than 12.8:1 or very rarely have i seen them at 13.0:1 As its still better to have a little more fuel than not enough.
Lets say a car has been tuned on a cool day. 22Degrees at 2pm. Air temp is nice and cool and humidity somewhere around 30%. The car is running 14psi boost and the tuner manages a nice 12.8:1 mixture. What do you think will happen on a nice HOT 38 degree Summers day with hot air temps and 70-95% humidity? My bet is its probably gonna be running lean, and may cause some damage. AFR's are mainly tuned for turbo cars anywhere from 11.0:1 up to 12.5:1 depending on the conditions of the day, whether the car in question is going to run more boost in the future( More boost needs more fuel, so if your car is running 10psi and is tuned lightly and on the lean side, running it up to 14psi or more aint gonna be pretty, especially if your boost system spikes up to 17 or 18 at that point)
Im only going off what i have been told by a few tuners and people that i know drag race and circuit race. These cars run super rich from the factory as a safe guard for any climate or conditions. Too much fuel may hurt power(in a tuners mind) but its better than hurting the pocket when something leans out too much and melts a piston or breaks the rings/ringlands.
Saturday, April 29, 2006 - 12:13 pm, by: Damian Ware(Frozenpod)
There is less oxygen in the air at hotter temps thus the car will run richer under those conditions. I would have thought on a dyno in the hot environment and the effects of heatsoak ect. This would require the tune to be rich as normally your intake temperature is never going to get that high and the oxygen is going to be much denser, hence have a leaner mixture.
Saturday, April 29, 2006 - 06:17 pm, by: Ben Socratous(Socrates)
14.7:1 is the 'isolated system' or perfect world scenario. Basically, if you want to burn standard petrol to get the most bang for your buck, then it's 14.7:1. Unfortunately, that doesn't take into account confines of a cylinder, latent heat, boost, nos, water, etc, etc, ie it will always be slightly different from car to car, even soarer to soarer!
Sunday, April 30, 2006 - 08:43 am, by: Braden Murdoch(Ribfeast)
12.8 might be the go then Tune it on a super cold day/night and then it is known to be safe. I have rigged a bypass switch for my SAFC, so I can also flip that to disable it on a cold night. It runs 11:1 without the SAFC, at the top end of the rev range. I currently have it leaned out to roughly 12.5. It seems to feel like it has less power though when I do gentle town driving with the SAFC enabled, no idea why. When I pan it it takes off hard though.
Sunday, April 30, 2006 - 10:29 pm, by: Cihan Aday(Cihan)
Manufacturers tend to run these engines extremely rich, and then advance or retard timing to compensate for temperature changes.
Basicaly, if your using a fuel piggyback ecu, your confined to the manufacturers method of tuning. You cant run 13.2:1 with a toyota factory tune, there is too much timing advance.
I have been advised by professionals, that 12.5:1 is ideal for a turbo engine under WOT with the correct heat plugs etc. Timing should then be adjusted to suit these conditions. Running above 13:1 means your not extracting the maximum cooling effect of additional fuel being present in the mixture. Its a form of detonation suppression, much like water injection. 12.5:1 is rich, but it will take into consideration fuel temperature changes, octane differences and injector condition changes for the long term, for those of us who actually drive our cars daily.
All proper tuning should be done with the wideband freshly calibrated and placed before the CAT converter. All exhaust leaks should be resolved and your TPS sensor checked for consistency before tuning commences. Tuning after the CAT falsifies the sensors reading, showing leaner than it really is. The same thing applies for exhaust leaks.
Monday, May 01, 2006 - 09:30 am, by: Mark Paddick(Sparks)
The 14.7:1 AFR is the stoichiometric ratio. This is the ratio at which there are fewest of certain pollutants produced in combustion and where the catalytic converter works best. It has NOTHING to do with how well the engine is running; rather it is pollution control related. This is determined by law not by the requirements of the engine. It is very important to understand the difference between the AFR required in closed loop operation for pollution control and the AFRs in open loop that give best power or economy.
Monday, May 01, 2006 - 11:58 pm, by: Roger Costello(Roger)
Cihan
I don't wan't to start an argument but the majority of fuel injected road going normally aspirated car engines achieve maximum power for much of the useable RPM range with AFR's between 12.5 and 12.7
Engine manufacturers may use richer mixtures at high RPM maximum throttle and leaner mixtures at lower RPM, but if you are tuning a NA engine like a 1UZFE 12.5 is a good starting point for maximum power
For turbocharged or supercharged engines, yes a richer mixture can be better for power and safety especially at higher boost.
Saying that "Fuel consumption is linear with the air fuel ratio, after all, it is a ratio." is complete bollocks, please think about what you are typing. If you think I am wrong please explain why.
Tuesday, May 02, 2006 - 09:06 pm, by: Cihan Aday(Cihan)
Although sometimes i come across as arguing, no arguments were intended.
Your correct about the fuel consumption Roger, I was incorrectly referring to percentage calculations regarding boost and AFR as its a linear relationship when you have a map sensor(this is how i base my preliminary tuning). Actual 'economy' is not linear as stated initially. I wasnt thinking straight.
Regarding max power for an NA engine, would you agree that it differs to an extent between engines? Ive personally seen many cases when 13:1 is about perfect with timing done just right (base timing on a standalone), and richning up towards redline a little. Could it me an uncalibrated wide band?
Either way, it seems as though you've had enough experience with tuning so i'll leave it at that.
Tuesday, May 02, 2006 - 11:22 pm, by: Roger Costello(Roger)
Cihan
Yes I have seen many engines especially American racing setups where leaner mixtures than 14:1 were used below 4000 Rpm and richening right up to 11:1 at redline. It seems to be more common on engines with less than ideal combustion chamber designs where in race refueling is restricted. Some Ford race engines use Air Fuel Maps that look like this:
Which is just plain bizarre, incidentally these particular engines (SRF) are known for self destruction due to pre-ignition and need cold plugs just to stay alive. They are a fairly poor design in my view.
A well designed normally aspirated Japanese road going engine tends to look more like this in terms of Air/Fuel effects:
One factor that tends to keep ECU programmers mapping on the richer side of the curve during open loop is that small variations between 12:1 and 13:1 do not hugely affect power but above 16:1 the power alters a lot with minor variations in air fuel ratio
I am sorry if I was a bit harsh in my initial posting, thank you for your thoughtful reply
Saturday, May 06, 2006 - 10:01 am, by: Justin McLernon(Zz32)
Roger, could you tell us what, in your opinion, would be a sensible AFR tune for the 1UZ-FE across the RPM range? Is 12.5-12.7 a safe AFR from idle to redline, or would one expect richer mixtures past, say, 5,000RPM?