AFR's...the never ending debate...

[KATwo40]

Ok, let's make a thread for this so we can beat this horse (dead or alive) without jacking other people's threads.

I maintain that 12:1-12.5:1 is the best to run for optimal power/efficiency under boost. Now, I ALSO maintain that you can run this ratio on 93 pump gas and use timing retard to suppress knock. I'm also willing to bet that power will be made here, more efficiently than running advanced timing and drowning the cylinders with fuel.

For the sake of consistency, please, leave outside devices such as N2O, water injection and alcohol injection out of this discussion. We're talkin' air and fuel alone.

Now, before the "outside ambient air temp" argument comes into play, let's remember that the MAF is great because it takes temp. into account when measuring density.

Ok, I'll begin with personal experience. Here's the setup. I ran it for about 6mos. this way:

Stock S13 KA24DE (145k miles at time of turbo installation)TD04H-13C (less efficient and smaller than a T25) @ 6-7psiStock exhaust, with custom downpipe (2.5")Stock MAFStock ECUSAFC (old crusty knob-style)370cc injectorsStock fuel pumpNon-Intercooled20* BTDC base timing

Dyno -190whp/200wtq AFR -up to 13:1

After running this setup for a few months and experiencing some knock issues (combined from poor timing, no intercooler, restricted exhaust and some oil getting into the cylinders now and then), I made some upgrades.

Upgrades:

FMICWalbro 255 pumpSAFC215* BTDC timing10psi boost2.5" exhaust (custom)

I never went back to the dyno, but I turned the SAFC hi-throttle to 26% across the board. I HIGHLY doubt that the ratio ever went below 12:1, since the stock ECU runs incredibly lean through the mid-range and it's tough to correct with the SAFC2 when using 370's. I also used plug-reading to judge AFR's (can be very useful if you don't know how to read plugs).

I ran this setup for another 6mos, no more knock, no other issues.

Current setup (installation in-progress):T3/T04E .50 trim, .63 a/r exhaust, stage 3 turbine (T31, .76 trim)External wastegate (38mm)3" downpipe to 2.5" exhaustLM-1 wideband

Now, after completing the installation (tomorrow) I'm going to tune this setup to 12:1 (as close as I can get it) hi-throttle across the board. I'll post my results afterword (in terms of timing, knock readings, performance, etc., but no dyno time). I plan on running only 6psi for now, perhaps up to 7-8psi (depends on how the system reacts).

Ok, someone step in here and hash up some data with me. I'm not being antagonistic here. I want some good debate conversation, with supportive data. In the mean time, I'll also be researching literature and such that I can offer as supportive data for my end of the topic discussion.

Cheers!

[nissanfanatic]

As I stated before, I think its good to run 11-11.5 midrange due to high cylinder pressures and then lean out to 12-ish past 5500 or so...

As for what is actually good/bad, look under "Fuel flow," on this page:

http://stealth316.com/2-air-fuel-flow.htm

[KATwo40]

As I stated before, I think its good to run 11-11.5 midrange due to high cylinder pressures and then lean out to 12-ish past 5500 or so...

As for what is actually good/bad, look under "Fuel flow," on this page:

http://stealth316.com/2-air-fuel-flow.htm

Dangit. I can't work the calculator because I'm usin' a Mac laptop right now. I'll check it tomorrow on a PC.

As for the high cylinder pressures, wouldn't you be able to offset the pressures by pulling a bit more timing, to take advantage of the fuel efficiency of 12:1? Again, reverting back to the fact that peak power/efficiency is found at 12.5:1. So, either make the power by wasting the fuel and having advanced timing, or conserving the fuel with retarded timing...

I guess I'm just going to find out that this is more an issue of personal preference, rather than science. Maybe I'm looking too far into this.

[Florida240sx]

I was runnign high 12's then as boost crept on I'd have it drop to low 12's. Shooted mostly for 12.5 so took what I got and stayed with it.

[KATwo40]

I was runnign high 12's then as boost crept on I'd have it drop to low 12's. Shooted mostly for 12.5 so took what I got and stayed with it.

What boost and what power did you make?

Thanks.

[Florida240sx]

Was onyl at 5psi.Wastegate was suppose to be 7psi. I had more than 190rwhp because raced an sr and won from both a stop and a roll. Ran this setup for 1100miles. After that I installed a 10psi spring and larger injectors which leaked and got gas in my oil and spun a rod bearing. Currently have ne wmotor in garage. By end of Feb motor will be in and will have dyno #'s @10psi, possibly 14

[hnugen]

After that I installed a 10psi spring and larger injectors which leaked and got gas in my oil and spun a rod bearing.

out of curiosity, how did the gas mix with the oil?

[S14tat]

when you have a leaky injector, or a locked up injector, it would practically flood your cylinders. and to a lesser extent when your running super rich like 10:1 or less the excess fuel would wash out the oil on your rings. we all know that gasoline acts as a solvent for grease so yeah.

[hnugen]

^ thanks man, didnt even think about washed rings.

[Florida240sx]

My #1 & #3 cylinders were full of gas. My AFR was in the 9's. Thought it was because of the 555's. So went for a 5 miles cruise trying to subtract. Could only get it into the 11's. So therfore 2 of my cylinders were lean as h3ll. Live and Learn.....excuse to build the block.....

[nissanfanatic]

Dangit. I can't work the calculator because I'm usin' a Mac laptop right now. I'll check it tomorrow on a PC.

You don't need to. I just linked that for the chart to the right hand side of the screen.

As for the high cylinder pressures, wouldn't you be able to offset the pressures by pulling a bit more timing, to take advantage of the fuel efficiency of 12:1? Again, reverting back to the fact that peak power/efficiency is found at 12.5:1. So, either make the power by wasting the fuel and having advanced timing, or conserving the fuel with retarded timing...

Uhh...yea...you could... but since this is KA land, isn't torque what we are going for?? The theory is, 12.5:1 AFR+good timing=best power results.

HP=(TorquexRPM)/5252

So the objective is to make the best torque throughout the entire RPM range. This means running the most efficient fuel AND timing curves.

[KATwo40]

Yes, I know this. I was referring to the area in which you run 11:1. Seems like bumping that up to 12:1 and retarding timing to suppress knock would be the objective.

I think you and I are saying the same thing, only using different languages. hehe

[nissanfanatic]

Not really...

Retarding timing won't lower the heat caused by boost+compression. Extra fuel will...

NTM I don't have the equipment to retard timing in certian areas while advancing in others. After buying all that, I will have taken the long way around a short block.

[KATwo40]

Not really...

Retarding timing won't lower the heat caused by boost+compression. Extra fuel will...

NTM I don't have the equipment to retard timing in certian areas while advancing in others. After buying all that, I will have taken the long way around a short block.

Suppressing detonation is a direct indication of lower cylinder temps.

Also, a BikiRom is $250, fully tunable and the best way around the block. Same price as SAFC2 new. (By the way, I'm sportin' the SAFC2 right now, too...but will be swapping to BikiRom SOON.)

Oh well. We may not agree on this subject, but in the end, we're a couple car guys that dig 240's. That, I suppose, is the best part.

[Edub1]

Extra fuel does not work by cooling, it works by slowing the burn rate through kinetic interfearance. Here is an article I posted a while back explaining that pulling timing is in fact all that needs to be done. Note the author (not me).

zerothread?id=147482

[KATwo40]

Extra fuel does not work by cooling, it works by slowing the burn rate through kinetic interfearance. Here is an article I posted a while back explaining that pulling timing is in fact all that needs to be done. Note the author (not me).

zerothread?id=147482

Thank you.

[nissanfanatic]

So it has half the cooling ability of water.. That is still some cooling ability. And I tend to like that little bit at 18psi on pump gas.

I'm not selling my Enthalpy ECU for a Bikirom because I like the fact that my car will start right now and take whatever I throw at it as it did tonight. I have no worries about if "my" tune is right. I didn't have to spend endless hours tuning it. All I did was plug and go. IMO, it was worth the extra $300 or whatever.

So, run what you want. As always, I post what I run/if it works.