Good question. But I still have mine tuned for mid 11's, even with methanol.

As I say, any extra power just isnt worth the risk of meltdown IMO.

If you need that extra bit of power, build it in.

That said.....if monitoring AFR's in conjunction with EGT's, you could push that little bit harder in terms of leaner AFR's as long as the EGT's were kept within sensible limits.
Until I can log EGT's though, I'll play safe with my AFR's

 

so... ignoring everything said in this thread....
i go for 13:1 to 12.5:1 on cammed LS1 cars that never see nitrous, and they're always really happy. on LS1s, its always around that area, usually with little gain by going leaner, and lots of loss if you start going too rich.

 

Mine is now 11.8 - 12.0 with alcohol (it keeps the IAT at 30°C or 86F).
17* advance at WOT, no KR.
Without alcohol it's about 12.5 and the IAT jumps up to 80°C or 176F.
The WI system is reliable (it checks itself )
The alcohol kicks in at 1 PSI: it's pretty soon but I haven't seen any disadvantage.
By the way: my system isn't intercooled...

 

^That was the most pointless post ever (Next to this one, of course)

 

https://ls1tech.com/forums/dynamometer-results-comparisons/690275-402-afr-205-results.html

there is my dyno at like 11.5 and then 12.8 ish up top look down low though the at the TQ it made more a little richer than lean

 

I see... really interesting!
Between 13 and 12.x (12.2?) there isn't a huge difference, but going lower than 12 rally made a difference.

Thanks for sharing this info!

 

yepper anything i can do to help

 

It's worth looking at that initial point of activation and the ramp speed for methanol injection, you're absolutely right. Apparently not detrimental to start early on your Vortech setup, but if I ramp up the pump too fast on my FM turbo setup it doesn't spool as quickly... has a little micro-lug condition.

 

Using a tailpipe sniffer as a means to measure AFR down in the low end of the graph is probably a naughty-naughty..

 

Sorry I dont understand what you mean.
You suggest to doublecheck my actual WB?
It's installed pretty close to the front O2 (passanger side).
The exhaust is completely stock.

 

If I can throw in my two bits folks, you've not covered the most important point of the A/F discussion...and that is combustion chamber pressure. Sure, it's easy to say that ideal combustion for complete fuel burn is 14.7:1 (if combustion were truly complete) and we can all throw out the A/F ratio numbers that we, in our own experience, have attained best hp with. But the best and most effective way to ascertain what the perfect A/F ratio is for any engine (to attain max power) is to test for brake mean effective pressure (BMEP) in the cylinder. BMEP acts on the crank and is measured on an engine dyno. Obviously, measuring BMEP is out of the question for most people (including most tuners). And yes, this figure will change depending on the fuel used due to the fuel burn rate. Combustion chamber shape (and thus efficiency), fuel type (properties of) and amount, ignition timing, etc, all contribute and factor in to the efficiency of combustion in a given engine. Flame propagation is what counts, and at what point it produces maximum cylinder pressure that acts on the crank. This is why you're all correct, you just haven't looked at the root. The root when looking for maximum power in an engine is to obtain maximum cylinder pressure (thus crankshaft torque) at any given rpm which IS directly related to ignition timing as this dictates the beginning of the combustion event and, combined with the fuel properties, will determine the peak cylinder pressure attainable. And when we speak of BMEP, we mean CONTROLLED combustion event...not detonation. If ignition timing is optimized for the fuel used, then the A/F ratio is changed to allow the most complete combustion of fuel possible given the engine design factors. How rich or lean you run the engine depends on how much power you're willing to make vs the longevity of the engine. Yes, you do lose power as you move richer from stoich, but you gain longevity and reliability. In short (too late for that, isn't it!), pick your fuel type, run a little rich to start (like 12.2:1 on n/a gas engine) then tune for best ignition timing, then dial in the A/F numbers to make more power with the understanding that the leaner the mixture is, the sooner the engine will need a rebuild. Nothing is free, least of all power. And like BlownAlky Jack said, it's a complex subject. Let's not try and be so definitive with our opinions regarding A/F ratios for the less knowledgeable. If anyone would like to be definitive, I invite them to first teach those seeking knowledge about the combustion event, then follow up with the variables we have to play with when tuning our engines as well as the tools needed to monitor our progress. Volleying numbers back and forth is not as effective as describing why we have done what we have. This will help the less knowledgeable infinitely more in their understanding of what they need to do in order to achieve the goals they have set for themselves and their cars.
Cheers to you all and happy motoring!

 

You typed the only problem I see with this post. MOST people have NO way of measuring BMEP. That is why you are probably the only person who mentioned it. Unmeasurable goals are extremely difficult to hit. This is an unfortunate example of one of those times when theory and reality are hard to correlate. I am not arguing any of your points, just relating why no one else has made them yet.

 

When I had my car on the dyno I gained 5 hp going from 13 to 12.7 AFR.

Good luck,

Al

 

While there is some truth to using different AFR's at different RPM to make the best power curve I wish people would stop relating that to Power and Torque as it really has nothing to do with them.

The answer lies mostly in the induction peroid of the fuel and sometimes it works in opposite of what people think. It is entirely dependant on the advance used.


My advice is to think of power or torque output as a function of two variables... Think about it as a 3d map with timing running N-S and fuel running E-W. There is a broad area for the car to make say within 5hp.. but at 2 edges of this area you have a hard drop off in power.

Get yourself in the middle of that map where you are making good power and away from the areas that decline in power quickly. Guys who tune on the street are often facinated with hitting some goal like fitting the most timing possible into a engine or some specific AFR. Alot of dyno tuners are interested in only maximizing output on the dyno. Both of these types suffer when they go to the track and the car doesn't perform.

 

Are you saying that it would be better to evaluate ET instead of power curves?
...why not?

 

Nope, intellegent use of dyno is best. Someone who actually goes to the track. I know quite a few tuners both dyno and road and I'm not sure some have ever been on a track.

 

No tracks over here
On the dyno (and tuning myself) it's at least $300
I can only choose a "quite" highway ant try there, hoping there aren't cops around, check for AFR and scanning for speed and time...

Or go to Germany (1 hour from here) and try some Autobahn-tuning

 

I still say, nothing but acceleration matters and you can log it
(with an external accelerometer) or you can just plot MPH vs
time in Excel for the various AFR and spark settings you choose
to exercise, and stitch together the ideal table by just looking
at the "top line" tune at any given RPM and using its values,
where they were the best. A 40-80MPH roll can show you
almost everything you need to know. Pad it a little for higher
gears / loads if you don't have the road to try it out in higher
gears.

 

Yep. Completely true. Its that "gray" area, where you're very close to optimal, and slight changes either way dont make significant changes.
Thats where you add 2 degrees of timing and it doesnt do anything. Better to reduce it 3, not loose anything, but gain a little in the comfort zone.
Same with A/F ratios. Big jump from 11.5:1 to 12.8:1, but not much at all from the 12.8 up to 13:1.
PS, with the exception of monitoring EGTs, monitoring NOX is probably the best indicator of cylinder temperatures, and therefore your safety zone.
Unfortunately, not everyone has the benefit of owning a 5 gas analyzer.

 

NOt to be pedantic, but stoich doesn't mean that harmful gases are minimized. It's a chemical terms that just means that the proportions of reactants to products are consistent with what is "predicted." Harmful gas production is only partially related, and only then with certain kids of pollutants (NOx comes to mind, as it's associated with surplus oxygen).

I'd also submit that timing and fuel ratio are interrelated such that you can end up chasing your tail. Leaner mixtures might want less timing, for example. So you have to establish if you are tuning the timing to a fuel ratio or tuning the fuel ratio to the timing. I would start with the former, as Sampson outlined (good post, btw!).

I'm of the mind that EGT is the best way to tune, but not everyone has access to that.

JMO