Just had my base timing advanced 2 degrees

brnjugfx45 said:

.Where they go under WOT may vary between companies,but not as low as 12.5(they really do not want you to have all the power in the motor...which is why the aftermarket can flourish)more is there!!!
I think octane below 89 is marginal with a vehicle with 10+ compression,and not a regular diet of 89

Click to expand...

I'm a bit confused about your statement regarding manufacturers not using a A/F of 12.5 or lower for "power reasons".

My 2002 IS300 ran an A/F of 11:1 under WOT, stock. (richer actually, because the wideband was reading post cat-con)

My 2003 Evo runs 10.5:1 under WOT, stock. (but in fairness, it is forced induction)

There are plenty of cars out there running rediculously rich under WOT because of cat-con placement. With emmisions running so tight, more manufacturers are placing the cat-con closer and closer to the exhaust ports. The problem with having them so close to the exhaust ports is that they run too hot and start to melt their cores. So to compensate, manufacturers richen up the WOT ratios to keep exhaust temps down.

I remember reading an article about Ford racing engines. They found that for maximum power, they ran an A/F of about 12.7 at peak torque rpm range, and leaned out to 13.5 in the peak HP range. Anything leaner resulted in detonation. Keep in mind this was in a racing application, so ours has to be worse.

Let's throw some more variables into the mix. :razz:

AFAIK, advancing the base timing will make the engine run "leaner" thus the A/F ratio will increase, correct? This is done by decreasing the "F" component, right?

If you add an aftermarket CAI, the resultant A/F ratio would even be higher because of the increased airflow, right? If the timing has already been advanced, at what point would we be losing power? Or will the ECU automatically compensate for the increased airflow from the CAI (and bump up the "F" in the equation)? In this scenario, wouldn't fuel economy be affected (as "F" needs to be raised to accommodate the increased "A")? Also since the base timing change is pretty much a "static" change, all this does is raise the baseline A/F (by decreasing the "F" component) and any the ECU will compensate for any other mods that affect the A/F (except for the timing change).

So is advancing the timing plus adding other mods (intake, plenum, etc) good or bad for the engine? Anybody??

Or is there something else I'm missing here? :?

Wow, it looks like I opened up a whole can of worms. Sorry about that.

I'll try to answer as best I can:

Wot is rarely were it should be on factory settings,but always in a safe(not too lean)area.A/F should not be measured accurately off the oxygen sensor,but off a very hi tech sensor added for tuning!

Click to expand...

Sure it can. It's called a wide-band oxygen sensor. Most dynos will have them with the appropriate software to plot the A/F as you go through the rpm range.

What I have a problem with is its implementation by the dyno operators. Most are too lazy to put them in the proper location, so instead they stick the probe into the tail pipe. This is fine if you're not running any cats, but is not as accurate if you are. But still, it's better than nothing.

A wide-band is a MUST if you're tuning for A/F.

Ok, I'm confused now. So lower numbers ARE richer?

Click to expand...

Yes, the lower the ratio number, the richer the fuel mixture. Example: 12.5:1
The first number, 12.5, refers to the amount of oxygen in the mixture. The second number, 1, refers to the amount of fuel.

So this means, for this mixture, there are 12.5 parts of oxygen for every 1 part of fuel.

I thought you gained more power as you leaned it out?

Click to expand...

That really depends on what A/F mixture you're running.

I'll use my Evo as an example. Stock A/F is 10.5:1. Most people who use engine management will lean it out anywhere from 11:1 to 12:1. All things being equal, you'll gain anywhere from 10-20 HP just by leaning the mixture out.

But there is a point where you cannot lean out the mixture any more before losing HP. I'll address that in a bit.

If the stock settings of around 14.7 are conservatively rich and a setting of 12.5 is optimal, would that not indicate that the lower number is leaner?

Click to expand...

No

AFAIK, advancing the base timing will make the engine run "leaner" thus the A/F ratio will increase, correct? This is done by decreasing the "F" component, right?

Click to expand...

Wrong. Advancing the timing doesn't change how much fuel will be entering the combustion chamber. The ECU determines how much fuel to spray depending upon the amount of air being metered by the MAF.

The timing advancement or retardation is used for sparking the fuel mixture. If "0" is the baseline, advancing the timing fires off the spark plug a little bit sooner, and retarding the timing fires off the plug a little bit later.

The amount of fuel and air still stays the same. By igniting the fuel mixture a bit sooner, you're trying to maximize the amount of power from that fuel mixture. In theory, you want the ignition to set off the spark so that you have complete combustion right when the piston is at the top of its travel, thereby using all of the combustion to push down on the piston for the longest possible path for its downward travel. If you advance the spark to the point where it fires while the piston is still traveling up, you're gonna lose power because the pressure is now trying to keep the piston from completing its upward motion.

Conversely, when you retard the timing, you're firing the fuel when the piston is already on its way down. So you're not getting the full effects of combustion since the piston is already traveling downwards.

If you add an aftermarket CAI, the resultant A/F ratio would even be higher because of the increased airflow, right?

Click to expand...

Not for our engines. Since we use a mass-airflow-sensor (MAF), the engine knows exactly how much air is going into it (provided you're using the stock MAF). Its job is to meter the amount of air.

Or will the ECU automatically compensate for the increased airflow from the CAI (and bump up the "F" in the equation)?

Click to expand...

Yes it will. The same way it compensates for altitude. At higher altitude, there is less oxygen. So the ECU dumps in less fuel. That's why you get better MPG at altitude.

In this scenario, wouldn't fuel economy be affected (as "F" needs to be raised to accommodate the increased "A")?

Click to expand...

Not necessarily. Since most of us don't drive at WOT continuously, the ECU runs in closed loop. Under closed loop, it tries to maintain a stoich mixture of 14.7:1.

The engine is only ingesting as much air as it needs to maintain whatever speed you're driving at. Let's say you're tooling along at 60 mph. The engine only has to produce 20 HP (I'm guessing) to keep you running at 60mph. It doesn't matter if you've got headers, CAI, cat-back, whatever. You only need to make 20 HP to maintain your speed. So the ECU will only burn enough fuel to make 20 HP.

To make more HP, you need more fuel and air. But just because you mod your car to be able to make 50 more HP, doesn't mean you're making 50HP while you're driving in closed loop (ie. everyday driving). You have the potential to make 50HP more IF you need it under WOT.

So is advancing the timing plus adding other mods (intake, plenum, etc) good or bad for the engine?

Click to expand...

Here lies the big money question. Adding timing and leaning out the A/F is a careful balancing act. In actuality, it takes many hours on a dyno to figure out which will provide better results for YOUR particular engine.

You can lean out the mixture and gain HP, but if you go too far, you'll get detonation.

Or you can advance the timing and keep the A/F the same and also get more HP, but if you go too far, you put too much added stress on the engine, lose HP, or worse case, also get detonation.

Or you can do both.

I'll use my Evo for example. I've got a custom-tuned ECU flash for it. The stock A/F is about 10.5 to under 10:1, depending upon conditions. Mine has been changed to run a LOT more timing, while using the same A/F ratios as stock. So I pick up about 20HP just from timing. I then added a piggyback computer for extra adjustability (so I can make adjustments as my mod content goes up). On the dyno, we leaned it out to 10.5- 11:1. I picked up another 25 HP. We tried running 11.5:1, but it started to detonate because of all the timing I was running.

Other Evo owners only adjusted their A/F ratios. With the stock timing, they could run up to 12:1, and they gained HP, but don't make as much as my car because they didn't change the timing. So my car runs richer, but makes more HP.

Every engine is different. Some like timing, some like the A/F changed. More than likely, you'll need to adjust both. But like I said, it takes a dyno, a wideband, and several hours to find out which works best.

Doesn't work that way; the ECU can only adjust so much within it's (fairly limited) fuel maps, plus the stock injectors have limits.

Click to expand...

Actually, an MAF equipped Ecu can compensate for a LOT. If it couldn't, you'd have to have special programming for cars sold at altitude. Unless our engines are injector limited, I wouldn't worry about bolt-on mods.

If anyone has the injector specs, I could easily calculate how much HP these injectors are good for.

Sorry for the long post.

Thanks mhgsx - very informative! 8)

Some questions:

You can lean out the mixture and gain HP, but if you go too far, you'll get detonation.

OK, I guess the A/F ratio for our FX35 engines pretty much fixed unless we re-flash the ECU with different maps, right?

Click to expand...

Or you can advance the timing and keep the A/F the same and also get more HP, but if you go too far, you put too much added stress on the engine, lose HP, or worse case, also get detonation.

Click to expand...

Done this. The timing was advanced 2 degrees in the VQ as stated above and it's been documented that 0-60 times are faster by MGFR.

I'm assuming that this is well within the operating limits of the engine for both 2003 and 2004 models, right? Either way, the anti-knock sensors will retard the timing if necessary to avoid detonation when using lower-octane fuel, especially when using lower octane fuel and WOT, thus hp will be lost.

Or you can do both.

Unless our engines are injector limited, I wouldn't worry about bolt-on mods.

Click to expand...

Question bout this statement. Breathing mods (plenum, CAI, etc) are stated above to "lean" out the A/F mixtures, i.e., raise the number. If the A/F ratio is currently fixed (no flash available yet) and the timing advanced, are you saying that the addition of bolt-on breathing mods are safe? Or are you saying that they won't do anything?

I still don't understand the whole 14.7 stock setting thing. wouldn't this be pretty darn lean then? So the optimum setting (for the VQ) that everyone is talking about is actually a richer setting than stock? Something about that just doesn't make sense to me. Confused

Click to expand...

I'm assuming that Nissan is being very conservative with their A/F mapping intentionally for fuel versatility. Doing this will allow us to use lower octane fuel in the VQ engines safely, right? That or they're just paranoid about their engines blowing apart if some modders decide to go crazy with the A/F mapping. :lol:

Thanks guys. I'm learning a lot.

I still don't understand the whole 14.7 stock setting thing.

Click to expand...

Stoich is short for Stoichiometric. This represents the proper air to fuel (doesn't matter what the fuel is, our example is gasoline) ratio needed for a COMPLETE burn. For gasoline, this ratio happens to be 14.7:1.

If we burn gas at 12:1, we are not getting a complete burn, thus lowering efficiency of the fuel. Ever notice that black carbon on piston rings, spark plugs, etc? That's because you're not getting a complete burn. If you burn at Stoich, the by-products you'll get is water vapor and carbon dioxide. If we burn at richer ratios, we then get the addition of carbon build up.

Most cars will try to burn fuel at 14.7:1 while under closed-loop.

So the optimum setting (for the VQ) that everyone is talking about is actually a richer setting than stock?

Click to expand...

The optimum is ALWAYS stoich. But our engines (nor any engine) is not 100% efficient, so you can't run stoich ratio at WOT. They have to add more fuel to keep detonation from occuring. (adding more fuel cools down the exhaust temps and keeps the gas from self igniting)

Something about that just doesn't make sense to me.

Click to expand...

Nothing in life is perfect. But we all try to reach perfection, knowing that we can't. It's the same thing with engines. To reach perfect efficiency, the engine has to run at WOT and at a stoich fuel ratio. But since that impossible, we try to run as lean as possible before you get detonation. For some engines it's 12.5:1, for others it's 13:1; it all depends on how well engineered the engine is.

Car manufacturers usually won't set A/F ratio, nor the timing, at the limit of detonation because they don't know the quality of gas that will be used. So they tune the car convservatively. Let's say our engine can run a 13.5:1 ratio at WOT. Any leaner, it would detonate. But because of the varying qualities of gas, the maintainence of the vehicle, the temp in which you're driving, etc, the manufacturer might only set WOT to 12.5:1. It's this difference that we can use to our benefit. But be aware that you're also that much closer to catastrophe.

Basically, if you want to play, be prepared to pay.

I'm assuming that this is well within the operating limits of the engine for both 2003 and 2004 models, right? Either way, the anti-knock sensors will retard the timing if necessary to avoid detonation when using lower-octane fuel, especially when using lower octane fuel and WOT, thus hp will be lost.

Click to expand...

I don't know the specifics between the 2003 and 2004 ecu's. You would think it would be the same, but when it comes to car manufacturers, something is always changing. I do know that the '03 and '04 ecu of the Evo is different, although Mitsu never claimed any changes. It wouldn't be hard to imagine Nissan does the same. ECU's can change mid model year.

And yes, anti-knock sensors are your friend. They protect you in case you use poor quality gas. If the ecu detects knock, it will pull timing. And you will notice the loss in HP. When it decides to try adding timing again is anyone's guess. Each manufacturer's programming is different. The only true way of reverting back to the baseline timing is to reset the ecu.

Ok. If the A/F ratio is currently fixed (no flash available yet) and the timing advanced, are you saying that the addition of bolt-on mods are safe? Or are you saying that they won't do anything?

Click to expand...

The addition of bolt-on mods is safe for most cars, since most manufacturers are not willing to tune the engine to its maximum potential. Once you start modding, it's extremely important to make sure you use top quality gas for added insurance.

Mods work by increasing the efficiency of the engine. It's easier to draw air in through a big conical filter vs. a panel filter (surface area, type of filter media) Synthetic oil is slipperier than conventional oil. So you end up gaining some HP by reducing pumping losses. (the internal combustion engine is basically a big pump)

Some mods, by increasing the efficiency of the engine, can also allow the engine to pump more air. Since the A/F ratio is pre-determined by the ECU, more air means more fuel will be used. And that means more HP.

Every manufacturer is afraid their engine is gonna blow up. That's why they tune so conservatively. But then there are people like us, who want the very best out of everything we have, whether it be in car modding, computer overclocking, etc. We will always tinker with our toys to make it better.

The vast majority of car owners look at their vehicle as just another appliance.

Because we're in this forum, we look at our cars a bit 'differently'. :lol: Some are into looks, some into the electronic toys, and others, physical performance. This may come as a shock to many people here, but I like to tinker with the performance aspect.

GeoFX said:

Again thanks for your replies.

That's interesting. That's what my Infiniti tech told me when I first inquired about aftermarket intakes. If more air = more fuel to maintain the proper A/F ratio, doesn't that mean gas mileage would suffer? Several people here have claimed that after adding an aftermarket CAI (bolt-on intake) that their gas mileage increased.

Is the ECU is doing something funky in these cases?

Click to expand...

Gas mileage won't suffer because you're NOT driving at WOT all the time. Like I said in my 60 mph example, the engine only needs to make a certain amount of power. To make power, you need fuel. To make a certain amount of power, you need a specific amount of fuel. That doesn't change.

Just because you have an aftermarket intake, it doesn't mean the engine is going to utilize the intakes capabilities all the time.

The only time you'll burn more gas, is when you drive at WOT. Since more air can be ingested, more fuel will be sprayed, thus more power.

The intake doesn't force air into the engine, it only allows the engine to take in more air, with less effort. The engine will only use as much air as it needs.

As for increasing your gas mileage with an intake, that's certainly possible, but again, only as long as you're not driving at WOT.

A good example is breathing through a straw. You could certainly do it and live, but you would need to exert more effort to breath through it, right?

Now take another straw whose diameter is twice that of the original straw. A lot easier to breathe, right? You don't have to work as hard to get the air in.

The amount of air you need doesn't really change, but because you can now breathe more freely, you don't have to exert as much. If you don't need to exert as much, then you don't need as much air as before to breathe.

That's the same way with intakes. Yes, it allows the _possibility_ for more air to ingested, but only until you need it (WOT). But because it's also easier to breathe through, the engine doesn't have to work as hard to get its air, so you free up a bit of HP that would otherwise been used for breathing. Since this means an increase in efficiency, less power is needed. If less power is needed, then less gas is needed.