Tuning Afrs

[BoostedBarge]

Sorry to go back a page, but I struggle to understand how the cat makes the mixture at the muffler leaner than before the cat. The O2 sensor is just that, an Oxygen sensor, the cat is not producing oxygen. Therefore, I'm thinking that if the mixture at the muffer is leaner, it's most likely caused the fact that the O2 sensor is being affected by air mixing in the tail pipe. Just food for thought...

[Rolls]

Sorry to go back a page, but I struggle to understand how the cat makes the mixture at the muffler leaner than before the cat. The O2 sensor is just that, an Oxygen sensor, the cat is not producing oxygen. Therefore, I'm thinking that if the mixture at the muffer is leaner, it's most likely caused the fact that the O2 sensor is being affected by air mixing in the tail pipe. Just food for thought...

Nope the cat helps burn the excess fuel, hence the RATIO of fuel to air changes, the amount of physical air however does not increase.

[scotty nm35]

Correct, any unburnt fuel will ignite in the cat, using up any leftover oxygen in the process and giving a false reading on the wideband.

There is bugger all difference with a highflow cat. Worst case you will run a little richer than you thought anyway so who cares.

[Don Dada]

I checked out a mines dump pipe for a 26 that was lying around and noticed the insides were thick with black soot /carbon build up which to me seems more than usual...

This engine did come thru the importers and was stock except for a pfc and the O2 sensors disconnected

Is this proof of one of those rich ass tunes again????

[blitzkreig]

i have a friend that has a top fuel r33gtr and his a/f is in the low to mid 10's and timing is (my pov) is very aggressive.

[D_Stirls]

What do you mean by "Top Fuel", If you mean Nitromethane i think you will find that the AFR's are closer to 2.5:1.

[HYPED6]

Hey guys,

Im not expert, but I think this is a very good topic. One that is grossly miss under stood and one that is very important for engine longevity.

Now. AFR's are primarily there for thermodynamics. There are many factors in choosing the correct A/F ratio for an engine than just boost levels.

There are many guys who have done the hard yards, blown up a few engines in the process and will keep there information closely guarded.

Now. Engine type is very important. How many valves, piston type, head design all play a major part in choosing the correct AFR. All these things play a major part in removing heat from the combustion chamber. Which is exactly what we are trying to do with the fuel.

Is the engine boosted, How is it boosted? Is it supercharged, Turbo, Nos, or a combination or all of the above. Does it have forged pistons? As they can take a little more heat than there cast brother.

Fuel type is obviously important. Its funny now that E85 is commercially available there are a lot of theories being thrown around about EGT's, Lambda's and so on and so forth.

Now every engine has to be taken on a case by case basis for AFR. I have seen 140+mph 1JZ's with standard pistons rods and cams running Lambda of 0.78 because it had the correct fuels (yes fuels, we had to mix 3 fuels to get the correct blend for this application) to support it.

I have also seen 140+mph 1JZ's running 0.69 lambda (10.0:1) because for thermal dynamics it needed it.

On the other side of the coin, 600 rwhp stock piston turbo LS1's at 0.76:1 on a pump methanol blend.

An RB3025 with a 35R.... on E85 Lambda 0.90 is where it worked its best.

Now how can you know what s right for what engine? Measure the air coming out, asses what you are trying to achieve with the engine and its general usage. Use individual cylinder EGT's. That way you know exactly the tempreture of the air coming out of the cylinder. Have a pre determined heat ceiling and no matter how excited you get, don't go over it. Don't even go near it. Just like timing, use the richest or leanest possible mixture to achieve your desired results. I will move an AFR from 12.3:1 to 11.1:1 and I may loose 10 rwhp but I may also loose 100deg cylinder temp. I know what one I'd rather.

I have seen twin supercharged 1UZfe's running 13.5:1 on BP98 with EGT's in the 600c. Now for you kids playing at home for a forged piston engine, Thats low. I have also seen RB26's with -5's on 18 psi needed to be run near 10.2:1 AFR because the EGT's where soaring over 800c. Not so good for cast pistons. How ever, By measuring, this engine went on to make well over 450rwkw on NOS and is still alive today

A good rule of thumb, and this is measuring around 1 inch from the head is Cast pistons, 750c. Forged will live with 900+, how ever most of the time its not needed to go any where near this so I usually aim for around the 800-850 mark, or even lower if the engine allows.

This is from engine that I have seen. None of them melt pistons and thats why they get tuned that way. So Choosing the correct AFR for your engine is up to your engine. Choosing the right tuner that has all the information necessary is up to you.

End of write up. (rant)

Edited November 18, 2010 by HYPED6

[DVS JEZ]

Good little write up. I wouldnt call it a rant but.

[DVS JEZ]

Also i think what makes tuners tune leaner on wot is to keep the customer happy when they see the extra couple of kw.

Thats all most people want. A good number then they think theyve got a good tuner and spent theyre money right. Not many tuners measure egts. Most street cars dont see those temps and if they do they dont see em for long.

I always tune richer and have also noticed that when a cars has been tuned on a dyno for say 11.8 when i go on the road test with my wideband it shows theyre running about 12.3.

My thinking on this is all the fresh air letting the engine breath cleaner.

The car in example was tuned with sensor on the dump pipe both on dyno and on road tune.

[HYPED6]

Also i think what makes tuners tune leaner on wot is to keep the customer happy when they see the extra couple of kw.

Thats all most people want. A good number then they think theyve got a good tuner and spent theyre money right. Not many tuners measure egts. Most street cars dont see those temps and if they do they dont see em for long.

I always tune richer and have also noticed that when a cars has been tuned on a dyno for say 11.8 when i go on the road test with my wideband it shows theyre running about 12.3.

My thinking on this is all the fresh air letting the engine breath cleaner.

The car in example was tuned with sensor on the dump pipe both on dyno and on road tune.

Does the dyno Cell you are tuning in have adequate air speed to supply the engine with enough fresh air? There shouldn't need to be a difference provided it is set up correctly.

And with street cars are the ones that need the EGT's the most. They are the ones that when you are finished the tune, anything could happen and I mean anything. 4th gear standing start skids, they could tow a trailer, pull the engine out and stick it in a ski boat and hold it flat for an hour on the Murray river.

For your average 300rwhp R33, yes EGT's are probably not so viable, but knowing how rich your engine needs to be, and knowing how rich it is are 2 completely different things.

[DVS JEZ]

I totally agree. But most cars i have tuned are silvias and skylines. None have tow bars. Lol

The dyno that his old tuner used had an open area and a good fan.

Have u ever checked a car On the road directly after a run on the dyno? I suppose it could be a difference between my innovate and the dyno 02 sensor.

[HYPED6]

I totally agree. But most cars i have tuned are silvias and skylines. None have tow bars. Lol

The dyno that his old tuner used had an open area and a good fan.

Have u ever checked a car On the road directly after a run on the dyno? I suppose it could be a difference between my innovate and the dyno 02 sensor.

I surely have, In our cell I saw 0 difference. This is using the same Motec PLM on the same engine.

With open (closed) air dyno cells, tuning say an RB25 at full throttle in one power cycle will consume 2.5 liters of air.

Now if that engine is reving at 6000rpm thats 3000 power cycles so thats 7500 liters in 1 min. Thats a lot of air. And thats only NA. Imagain when you start to push 15/20/45 pound of boost through it. This is where the air you are tuning can get very hot and very contaminated very quickly.

You would be suprised with the difference between Autronic/DD 4 wire sensor and a proper 5 wire 0-5V sensor. Both read the same at and around Lambda 1 but once you get into say 0.76 and lower the 4 wire wont show small changes where the 5 wire will soldure on. Let alone the 5 wire being way faster any way.

Edited November 19, 2010 by HYPED6

[JonnoHR31]

I totally agree. But most cars i have tuned are silvias and skylines. None have tow bars. Lol

The dyno that his old tuner used had an open area and a good fan.

Have u ever checked a car On the road directly after a run on the dyno? I suppose it could be a difference between my innovate and the dyno 02 sensor.

i wouldnt trust the innovate wideband to be that accurate. sure theres probably a small different between dyno and road but i think most of the different in your case would be from different sensors

Edited November 19, 2010 by JonnoHR31

[blitzkreig]

What do you mean by "Top Fuel", If you mean Nitromethane i think you will find that the AFR's are closer to 2.5:1.

no, Top Fuel is a Japanese tuning shop. same as Signal, Top Secret etc.

[Toshi]

no, Top Fuel is a Japanese tuning shop. same as Signal, Top Secret etc.

Japanese tuner adjusting to around AFR 11 for safe.

AFR 11 map is for std fuel pump.

If your car changed to hiflow fuel pump , AFR will richer than 11.

Timing map is for 100 octane fuel (because fuel is 100 octane in Japan) so timing map bit higher than Australia 98 fuel.

[Rolls]

whats the pump got to do with AFRs? If it is flowing for the power level why would you change them?

[DVS JEZ]

i think he means if the pump is changed without retune it will affect the afrs due to pressure and flow changes

[Strik3r]

If you adjust the fuel regulator, the AFRs wont change at all...

[SS8_Gohan]

i can post this now

my R was built by Midori, and they used an Impul ECU with their tune - from what Trent can tell the timing is pretty damn aggressive but it's pretty rich by our standards, easily 11's - and something in the order of 200-220kms of normal issue driving, shifting at maybe 4K, absolutely grandma-ing it i 'think' i managed 300km once, but generally in the 200's.

we'll see if we can get some more info from the ECU, be interesting to see what the maps look like

[scotty nm35]

i can post this now

my R was built by Midori, and they used an Impul ECU with their tune - from what Trent can tell the timing is pretty damn aggressive but it's pretty rich by our standards, easily 11's - and something in the order of 200-220kms of normal issue driving, shifting at maybe 4K, absolutely grandma-ing it i 'think' i managed 300km once, but generally in the 200's.

we'll see if we can get some more info from the ECU, be interesting to see what the maps look like

Get a bit of ethanol in that sucker. You got a wideband for it yet? 20% would probably cure it.