Air/Fuel Ratio discussion thread...

[Chaotic_Warlord]

OK, so I'm thinking of upgrading my fuel system in the my S14, yes it's a KA, no it's not turbo'd but I am slowly working my way towards the KA-T route. But I would like this to be a respectable discussion, so if the only thing you have to contribute is SEARCH or to flame me just keep your mouth shut. This has the potential to be a very good subject that is not understood by a great many of people and instead of trapping in a section that not many go into or bumping a long dead thread just to get some answers seems pretty stupid to me. Again, if you can't add anything productive don't bother posting, I'll just request that your post be deleted.

I've searched all over Google trying to get an idea about Air/Fuel mixtures and while there are some fairly generic explanations out there, I can't really find anything that explains the positive and negative of running rich or lean, how to figure out what kind of power you will make by upgrading your air/fuel systems, or even anything that explains when to run rich or lean (IE... do I want to run rich to make power in the lower RPM's or Higher RPM's?)

Here is what I am thinking, I have a KA24DE, it has roughly 120K on it, I have a very free flowing exhaust (MR 4-1 Header, DP, TP, BC Spec II exhaust), emissions have been pretty much taken out of the equation (No EGR valve connection or lower o2 sensor, Upper o2 sensor only thing that is connected). I know I am running slightly rich with the stock injectors based on you can smell it, however I still pass Emmissions testing (OBD1), go figure.

Now I am thinking of installing a 255lph fuel pump, an adjustable FPR, and larger injectors and a Z32 fuel filter. I would also like to upgrade to a ram-air style intake and possibly a MAF upgrade (which would mean I would need a tuned ECU, which I don't want to get until I go to install the turbo).

My questions are:

- If I were to upgrade to an aftermarket intake, and get the fuel pump and FPR, what would be a good upgrade size for the injectors that would give me an increase in power with out running the risk of being too rich?

- Is there a such thing as running too rich, if so what are the effects and symptoms of it? I know that too lean leads to detonation and engine failure, that's about the extent of my air/fuel ratio knowledge.

- Is there a formula to calculate how much power can be made from adjusting your Air/Fuel ratio?

- If I were to get OEM SR injectors, the 255lph fuel pump and an adjustable FPR would I need to get a piggyback AFR computer (like the Apexi Neo) or would I need to get a tuned ECO in order to make power?

-What would happen if I were to upgrade to a 555 SR injector?

I'm not really concerned about fuel consumption, as long as gas doesn't start running through my exhaust I'm fine with running rich, if I wind up having the occasional fire ball if I downshift or upshift hard all the better. I'm not trying to be a ricer, I'm trying to make as much power as I can without having to get into any serious high dollar items (internals, turbo, ect...) and no I do not intend on doing a motor swap, I like the KA, and I don't have the money to do a swap. I've changed to a 5 speed, a 4 puck clutch, lightened flywheel and aluminum driveshaft, the next logical step before I upgrade internals or introduce FI, is to increase my air/fuel mixture, but I am totally lost.

Again my questions pertain to my KA powered S14, but the answers will probably speak to anyone with an engine, as Air/Fuel mixtures are as misunderstood as a car's suspension, so Mods/Admins please don't move this. I want to make as much power as I can by introducing more fuel to the engine without doing damage or hindering power output. TIA for any advice.

[Razi]

1.370cc injectors, which can be found on the SR and VH45, and other engines, is big enough for N/A.Though, you could run a larger size, but that's pointless for a N/A KA.The 370cc injectors don't top out on KA-Ts until you start scratching at 300hp, you'll never see that much on a N/A KA.

2.Yes, you can run too rich.It'll wash out your cylinder walls of oil, ruin your rings, and contaminate your oil.Engine oil + gasoline is no good, you'll run the risk of spinning a bearing with that stuff.

3. I don't know of a formula that calculates power vs air/fuel ratio, doubt there is one.

4.Yes, if you get larger injectors you will need to adjust your tune for it, or else you'll run rich as heck and never run right and kill your engine.A piggy back doodad is good enough, but if you want to make more power down the road, most of those things don't let you adjust timing which isn't good.

5.If you were to upgrade to a 555cc SR injector (You mean aftermarket right?), you'll need a tune to compensate for it obviously, but too large for any power you'll make in N/A status.SR and KA's all use sidefeed injectors, so they are all interchangeable.

I basically lived in the KA-T section for the first few months before, during, and after going KA-T.Lots of good people there, and the information is only growing.

[PoorManQ45]

Now I am thinking of installing a 255lph fuel pump, an adjustable FPR, and larger injectors and a Z32 fuel filter. I would also like to upgrade to a ram-air style intake and possibly a MAF upgrade (which would mean I would need a tuned ECU, which I don't want to get until I go to install the turbo).

Unless the stock fuel pump is running at maximum output there is no need to upgrade the fuel pump with the listed mods.

My questions are:

- If I were to upgrade to an aftermarket intake, and get the fuel pump and FPR, what would be a good upgrade size for the injectors that would give me an increase in power with out running the risk of being too rich?

Stock. You will be supplying more pressure. Adjust pulse width to regulate flow.

- Is there a such thing as running too rich, if so what are the effects and symptoms of it? I know that too lean leads to detonation and engine failure, that's about the extent of my air/fuel ratio knowledge.

Bogging, rough idle, low MPG, failing catalytic converters, backfiring. Also, your oil will be ruined in short order.

- Is there a formula to calculate how much power can be made from adjusting your Air/Fuel ratio?

I don't believe so.

- If I were to get OEM SR injectors, the 255lph fuel pump and an adjustable FPR would I need to get a piggyback AFR computer (like the Apexi Neo) or would I need to get a tuned ECO in order to make power?

Anything that can manage the fuel injection system accurately will be fine.

What would happen if I were to upgrade to a 555 SR injector?

With the mods you listed the injectors would never approach their flow limits.

I'd recommend doing your listed performance modifications and go with a Piggyback FMU of your choice. Upgrade the pump and injectors later.

[Chaotic_Warlord]

Thanks Razi, but if I get an aftermarket 255lph an adjustable FPR, and run the 370cc injectors, but stayed with the OEM air flow system (intake, intake manifold) would this make me run to rich or no, and if I upgraded my entire fuel system and switched to an aftermarket intake, what kind of power gains can I expect?

Will doing this bring me closer to the 190hp mark or no, given age and the mods I have already I'm guessing I'm close to the 175hp range, but since I have only the butt dyno as a judge I have no idea, it sure feels a lot quicker than when I first got the car.

[Razi]

Thanks Razi, but if I get an aftermarket 255lph an adjustable FPR, and run the 370cc injectors, but stayed with the OEM air flow system (intake, intake manifold) would this make me run to rich or no, and if I upgraded my entire fuel system and switched to an aftermarket intake, what kind of power gains can I expect?

Will doing this bring me closer to the 190hp mark or no, given age and the mods I have already I'm guessing I'm close to the 175hp range, but since I have only the butt dyno as a judge I have no idea, it sure feels a lot quicker than when I first got the car.

If you're tuned right, you should never run rich.If you don't get a tune for your change in injector size, your car will never run right.

I doubt you'd get to the 190hp range on a N/A KA, 200hp has been the holy grail and many moniez and time has been spent with little success.If you want more power, turbocharge it, that's what I did.

[PoorManQ45]

Thanks Razi, but if I get an aftermarket 255lph an adjustable FPR, and run the 370cc injectors, but stayed with the OEM air flow system (intake, intake manifold) would this make me run to rich or no, and if I upgraded my entire fuel system and switched to an aftermarket intake, what kind of power gains can I expect?

No, it is all in how you tune everything.

Get that thing on a Dyno with a sniffer and get it tuned properly.

[Chaotic_Warlord]

I don't have a Cat, just a test pipe so I'm not worried about my cat failing, fouled oil, bogging, and hesitation on the other hand are bad and I want to avoid that. I know that running rich can destroy spark plugs, but if you run a hotter indexed spark plug will this be an issue?

Does temperature have a drastic effect on air fuel ratio's? With it coming into the summer months, it's about to get pretty effing hot, but where I live it gets really humid too, so the air is thicker, what kind of effect will these conditions have on a modified air/fuel system?

Is an AFR meter an absolute necessity or can I just get an FPR gauge and tune with that?

I thought the Walbro 255lph was a a must get item when upgrading to an adjustable FPR and larger injectors. I still plan to get it, as it will be one less thing to get when I do finally go FI.

What are some good FMC's that I can get fairly cheap? I really like the Apexi' Neo but haven't heard anything to terribly good about them. Are the older Apexi' AFC's better?

[PEZi]

running rich or lean... both are bad in their extremes... meh

running a tad lean will generally net you more power... but at what cost??? lean engines tend to 'pop' easier

the only real problem with running a tad rich is oil contamination... which if not maintained properly causes all the issues mentioned by razi above

basically... run it lean... but be careful

*use the above statements at your own discretion**the above statements have not been evaluated by the Food and Drug Administration**This product not intended to diagnose or cure any disease*

[Chaotic_Warlord]

At what part of the power band does running rich give you the most power and where does running lean give you the most power. Ultimately I'd like to have the power higher up as the lightened flywheel and solid aluminum drive shaft allow me to reach the higher RPM's pretty quickly.

Is there an FMC available that will allow me to run the proper level of lean say in the lower RPM's and fairly rich at the upper RPM's? being that I generally shift around 4-5K I rarely reach redline, and even if I do I don't bounce off the limiter.

Are there any good sites that I can go to to understand Air/Fuel ratio's that break it down into lay mans terms, preferably as it pertains to performance and not from the maintenance stand point?

[Chaotic_Warlord]

So I found a couple similar discussions on other car forums, it would appear that this is a much debated discussion. While the perfect A/F ratio is supposed to 14.7:1 but it would appear that 12-13.5:1 is the more ideal A/F ratio which would lend to a leaner condition. But at the same time a richer mixture would seem to not only keep the engine cooler but also lend to more power at WOT.

So is there a way to run leaner at part throttle and then change over to a richer mixture higher up the powerband towards WOT?

Also if I were to get just the AFR and an FMC would I need to upgrade my air intake system as well (more than just an aftermarket intake)

[car nut]

So I found a couple similar discussions on other car forums, it would appear that this is a much debated discussion. While the perfect A/F ratio is supposed to 14.7:1 but it would appear that 12-13.5:1 is the more ideal A/F ratio which would lend to a leaner condition. But at the same time a richer mixture would seem to not only keep the engine cooler but also lend to more power at WOT.

Actually, 12-13.5:1 is richer then 14.7:1. 14.7:1 is the stoichiometric ideal (read: chemically balanced) mixture, but people generally run a tad richer to stay on the safe side. You do not want to be running lean at WOT.

So is there a way to run leaner at part throttle and then change over to a richer mixture higher up the powerband towards WOT?

I think that's actually what your stock ECU does.

[Chaotic_Warlord]

I think that's actually what your stock ECU does.

So a FMU system would allow me to tune my AFR's to how I want them to be all throughout the power band, correct? Or would i need to get a Piggyback system like the Greddy E-Manage in order to tune to that level of detail?

I'm trying to make as much power as I can on the cheap while I get the parts to go FI together without having to rip open my engine. While I can probably pick up a used AFC for relatively cheap or even a used E-manage, the cost of taking the E-manage to a tuner to not only get a base tune but also a couple of different tunes will cost me a couple hundred dollars, for that I can get parts I need to go turbo. I know I'm going to have to have it dyno-tuned at some point down the road, but I'd rather not have to do it more than once if I can help it. @ $95+ a dyno tune run that will get real expensive after a handful of runs.

[PoorManQ45]

So a FMU system would allow me to tune my AFR's to how I want them to be all throughout the power band, correct? Or would i need to get a Piggyback system like the Greddy E-Manage in order to tune to that level of detail?

The FMU will only allow you to control the the fuel system.

You also need to control the ignition system. Specifically spark advance/retard at different RPMs

[PEZi]

You also need to control the ignition system. Specifically spark advance/retard at different RPMs

^ this

this is the only reason my engine has not asssssploded on me yet

[Chaotic_Warlord]

See, the feedback I'm getting on here is the very reason I started this thread. I never realized that timing would come into play when tuning your A/F Ratio's. But it does make sense, after all the stock ECU adjusts your timing and air.fuel mixture when the sensors tell it is starting to overheat, I believe that it retards the timing and puts the air/fuel mixture to a more rich condition to aid in cooling the block and head down.

So basically what you guys are telling me is that if I upgrade my entire air/fuel system and not go turbo that it'll all just be a waste of time and money, and that an Adjustable Fuel Regulator and an Apex'i Neo (or something similar) will actually net me more power.

[Razi]

Yep, plenty of people run FMU setups with their KA-T setup (I was one of them), but when they do, you should retard your timing via your distributor by about 2 degrees to keep your engine from exploding.

[Chaotic_Warlord]

Interesting, thanks for the input.

Can someone explain what an injector duty cycle is and why you some injectors need resistor packs. Do injectors have a set amount of electrical current before they are maxed out? Is that what the resistor packs are for? If this is case what is the normal amount of flow of the stock KA injectors?

[Razi]

Duty cycle is how fast the injector can work, if you're making too much power, you'll max out the injector duty cycle and it won't be able to shoot out enough fuel even if it stays open almost all the time.This will result in your cylinders not getting enough fuel and running lean, and resulting in death of your engine.

Some injectors have different electrical resistance, ECUs are tuned to operate a certain type, so you attach resistors to lower it to what you want.

Stock KA injectors are 270cc injectors.

[krimsonviper]

SEARCH NOOB! :P

[Klits562]

Actually, 12-13.5:1 is richer then 14.7:1. 14.7:1 is the stoichiometric ideal (read: chemically balanced) mixture, but people generally run a tad richer to stay on the safe side. You do not want to be running lean at WOT.

I think that's actually what your stock ECU does.

The voltage output of the o2 sensor determines if you run lean or rich and that constantly changes.and thats about all i have to add to this convo sorry guys

[PEZi]

you should retard your timing via your distributor by about 2 degrees to keep your engine from exploding.

or get a big carb and advance it 16 degress

[raremotive]

To calculate theoretical hp:

You need to assume a few things:

A/F Ratio = 11 to 16 (for best power 12 to 13)

BSFC (Brake Specific Fuel Consumption)- .5 modern stock engine or turbo charged intercooled engine, .47 Hi-Perform engine, .42 Race Engine, .55 Supercharged/Turbo Charged non intercooled engine

VE (volume efficiency) - any where between .8 to .95

Now you can calculate the following:

Displacement (DISP) = (1/1.27)(#cylinders)(stroke)(bore)^2 (note bore and stroke are in inches)

Volume Flow Rate (VFR) = (1/3456)(DISP)(RPM)(VE)

Mass Flow Rate (MFR) = (1/(T+460))(2.703)(P)(VFR) T (Fahrenheit), P(psi) are outside temperature and atmospheric pressure. (Note this is MFR isn't accurate for boosted applications, I have another method actually...)

HP=(1/A/F)(1/BSFC)(MFR)(60)

Also a general tip.. if you are using around 12 a/f and .5 bsfc... a rough estimate of power is 9.5 to 10 HP times MFR... ( on in LB/MIN)


Modified by Rare_f8 at 2:14 PM 4/9/2010

[Razi]

or get a big carb and advance it 16 degress

[PoorManQ45]

Interesting, thanks for the input.

Can someone explain what an injector duty cycle is and why you some injectors need resistor packs. Do injectors have a set amount of electrical current before they are maxed out? Is that what the resistor packs are for? If this is case what is the normal amount of flow of the stock KA injectors?

An injector is simply a solenoid that opens for a specified duration to allow fuel to flow.

100% cycle would be the absolute maximum amount that the injector can flow.

What gets interesting is that by increasing the fuel pressure you can increase the maximum flow rate of the injectors.

The voltage output of the o2 sensor determines if you run lean or rich and that constantly changes.and thats about all i have to add to this convo sorry guys

To a certain point this is true. But usually if you go more then 1 point in either direction you're approaching the limit of what the system can compensate for.

A wideband O2 sensor would be a great thing to have as this would allow you to tune without having to go to a shop.

[Chaotic_Warlord]

To calculate theoretical hp:

You need to assume a few things:

A/F Ratio = 11 to 16 (for best power 12 to 13)

BSFC (Brake Specific Fuel Consumption)- .5 modern stock engine or turbo charged intercooled engine, .47 Hi-Perform engine, .42 Race Engine, .55 Supercharged/Turbo Charged non intercooled engine

VE (volume efficiency) - any where between .8 to .95

Now you can calculate the following:

Displacement (DISP) = (1/1.27)(#cylinders)(stroke)(bore)^2 (note bore and stroke are in inches)

Volume Flow Rate (VFR) = (1/3456)(DISP)(RPM)(VE)

Mass Flow Rate (MFR) = (1/(T+460))(2.703)(P)(VFR) T, P are outside temperature and pressure. (Note this is MFR isn't accurate for boosted applications, I have another method actually...)

HP=(1/A/F)(1/BSFC)(MFR)(60)

Also a general tip.. if you are using around 12 a/f and .5 bsfc... a rough estimate of power is 9.5 to 10 HP times MFR...



Modified by Rare_f8 at 1:10 AM 4/9/2010

That's a ton of math, I'm confused just looking at that.

As far as the Wideband o2 sensor goes, I really want to pick one of these up, but it would seem that the Innovate systems seems to be the best one out there but it's sooo freakin expensive. Can I just get a Bosch 5 wire wideband, and a AFR gauge and just use that to tune without having to get the whole Innovate system? Or are there other offerings out there that do the same job as the Innovate System for a cheaper price?

I know that if I pick up an adjustable FPR that I'm going to also pick up a fuel pressure gauge.

I don't have an aftermarket intake, so I want to get one of those, but I also want to pick up an aftermarket Intake manifold, with these 2 mods does your air/fuel ratio change since you are supposedly bringing in more airflow or is this a myth?

Also if you change to say a Q45 throttle body, can you still run on the stock ECU or does the ECU freak out and not know how to handle it?

[PoorManQ45]

As far as the Wideband o2 sensor goes, I really want to pick one of these up, but it would seem that the Innovate systems seems to be the best one out there but it's sooo freakin expensive. Can I just get a Bosch 5 wire wideband, and a AFR gauge and just use that to tune without having to get the whole Innovate system? Or are there other offerings out there that do the same job as the Innovate System for a cheaper price?

As long as you can hook everything up to the computer so you can chart everything out over the RPM range it doesnt matter what sensor you get.

Obviously you'll still need a management system to change everything though.

I don't have an aftermarket intake, so I want to get one of those, but I also want to pick up an aftermarket Intake manifold, with these 2 mods does your air/fuel ratio change since you are supposedly bringing in more airflow or is this a myth?

Those two mods should decrease restrictions in the intake.

Also if you change to say a Q45 throttle body, can you still run on the stock ECU or does the ECU freak out and not know how to handle it?

IIRC, isnt the Q45 TB a 90mm? That's overkill. LOL. But anyways, to answer your question, the ECU will have no idea what's going on as the TPS sensor voltage is much different. Now, a piggy back unit will be able to be set for a wide range of inputs. Or, better yet, a full control unit would give you infinite adjustability. You'll be able to program the unit to accept whatever input signals that you want, even add sensors and dohickeys if you would like.

[raremotive]

That's a ton of math, I'm confused just looking at that.

Not really. Just sit down and plug in the numbers...

Besides, three more steps... and you will be able to plot your theoretical engine rpm line on a compressor map of any turbo.
Modified by Rare_f8 at 6:54 AM 4/9/2010

[DevilMB3017]

tl;dr thread.

First off, if you want KA-T info, stop by the KA-T forum.

Secondly, there is an ideal AFR if your turbo. When your turbocharged, in boost especially, fuel has two purposes - one is to burn to move the piston, duh, and two is actually to cool the cylinders. Run too hot and you're more likely to knock (pre-detonate) and blow your motor.

Many tuners can and will actually tune by EGT (Exhaust Gas Temp) rather then AFR depending on what ECU setup you are using.

That being said, definitely stop by KA-T.

[numbnuts240]

tl;dr thread.

in that case, your entire post is useless for some time lol.

[AZ89two4Tsx]

I'll just leave this here.

zerothread?id=237970