Air fuel ratio talk.

[nightspeed87]

This may seem basic to some but I have never tuned, and had no reason to ever learn deeply about air fuel ratio's. I just know what rich and lean means and the conditions of both. I have an idea of what ratio youd what to be in with a turbocharged car ( from 10 something- to 12 something ) and Im guessing the higher the ratio the more lean?
I am going to eventually be getting a keydiver chip from Jeff; mainly for true injector compensation, and for correcting the 1g timing advance since im running the 2g pistons/ 6bolt combo and now have higher compression. ( 8:5.1 now )
and he said he normally makes the ppl running 93/94 pump gas a 11:1 air/fuel ratio... Sounds good to me, but how does this sound to others in conjunction with knock and timing and other factors.
How much power have some of you experienced just from leaning out your "overly" rich stock a/f ratios to something more on this scale? "And also how does having this permanent ratio embedded into the ecu affect everytime you raise boost?"
( Im sure that is why a SAFC II is needed exactly for that last statement?! )

 

[zippyshoe]

An AFR of 11:1 is what most people strive for on premium pump gas when tuning. With race gas, you can tune for leaner AFR's such as 12:1 because of its higher resistance to knock. Of course, this AFR only applies when the ECU is in open-loop operation (hard acceleration, etc.) When the ECU is in closed-loop operation (cruising), the ECU will attempt to maintain a 14.7:1 AFR (stoich) - it will utilize feedback from the O2 sensor to help achieve this.

I haven't had an opportunity yet to adjust my AFR from factory-rich stock values which can be as rich as 9.5:1 (depending on RPM's and airflow). However, I understand that leaning it out from factory will give you a significant performance gain as long as you watch closely for knock.

 

[andymoraitis]

Nicely said Zip. That's dead on and saved me a bunch of typing.

Just for reference, here's an old thread I started many moons ago when I didn't understand tuning too well. Actually I still don't but manage to muddle my way through:

http://www.dsmtuners.com/forums/showthread.php?t=180544&highlight=optimal

 

[donmagicjuan]

Actually I still don't but manage to muddle my way through.

Don't let this old timer fool you. He likes to speak softly and carry a big stick. I'm sure he could tune circles around a lot of the members here. I mean you have to pick up something along the way when you sift through countless threads each day, right?

 

[andymoraitis]

Actually, I really do suck. It just takes time for people to figure it out.

 

[donmagicjuan]

I'll go warn the others!

Thanks Andy, I needed that after a boring day.

 

[andymoraitis]

Good deal! I'm here to entertain.

 

[CanadianTSi]

11:1 is a good number, its safe and there really isn't that much more power to be made going leaner...Better safe than sorry

Also when you turn up the boost the ECU see's the extra airflow and in turn Injects more fuel, keeping the 11:1 Ratio.

 

[Auto RS T]

Good deal! I'm here to entertain.

Entertainment Wiseman... I dont think so.

I know who I am asking about tuning with A:F/FP/chip/big injector/16g powered sidemount vehicle when I'm in the posistion to discuss.

(Don) don't think your getting off the hook either. Is meth on my wishlist?...better update.

(Nightspeed87)- Basically what DSMchips says about the running the AFC. The AFC is suggested because the changes in the chip are made on the Global Fuel and MAS Compensations. Every car is different and you still may still need the fine tuning adjustment.

I think this thread and the link should have answered your questions. From reading your post I know you are familiar with DSMchips. You will be answering your own questions soon enough. I apologize for being off topic above.

 

[andymoraitis]

I apologize for being off topic above.

Yeah, you'd better apologize or you're going to get some pretty wild chip settings (just kidding).

I wouldn't put it past Don to rig your methanol to inject under vacuum though. Gotta keep an eye on that kid!

 

[donmagicjuan]

You mean that's not good? I thought all the cool people were doing it that way.

 

[nightspeed87]

matter fact from that 11.1 ratio versus the stock ratio ( supposeing on identical boost levels and everything else important were the same ) what kind of gas milage increase could you expect ?

Oh and Andy in that thread you linked it talked about how the 11.1 a/f ratio is actually still slightly rich and is more of a safe zone to initiate tuning, therefore should I ask for my chip to be a little bit leaner or would it be smarter to leave it with the 11.1 ratio. ( I want to still be able to run a good amount of timing also so maybe going leaner would hurt timing )
Therefore what is more of a sacrifice... timing/ or a leaner air fuel ratio?

 

[donmagicjuan]

People normally aren't concerned with gas mileage at WOT. During normal cruising, closed-loop operation controls AFRs at 14.7:1 for both cases, so there shouldn't be any difference there.

 

[nightspeed87]

ok yea that makes perfect sense... Just figured it even giving better WOT gas milege too because I like to punch my car alot any open chance I get to be honest and after about a week of doing this ive gone thru 20 extra dollars worth of gas . Hopeing maybe Id see better wot gas milege.

 

[donmagicjuan]

I guess I've never thought about it because mileage will be very dependent on engine speed and what gear you're in, but you might see an appreciable difference by leaning it out. You'll probably require about
10-12% less fuel to get from stock to 11:1 AFRs, so that would be a good ballpark for how much longer a tank of fuel will last you (assuming you drive everywhere at WOT .

 

[GVR4592]

When I switched from Dsmlink to AEM I went from 22 mpg to 28 mpg. I put a big lean spot(15.5:1) right in the highway cruising area of the map. WOT A/F was changed from 11:1(Dsmlink) to 11.5:1(AEM) I believe you can accomplish something similar to this with the Zeitronix wideband, when using the narrowband output. It has the ability to "trick" the ecu into thinking A/F is stoich, when it's actully not.

Just keep in mind anything leaner than 14.7:1 causes higher emissions output.

 

[droppinbottom]

anything leaner than 14.7:1 causes higher emissions output.

Them darn people from the west coast and their emissions

 

[GVR4592]

Yeah we are adopting California's emission's laws by 2012, I'm not looking forward to that. Tuning won't be a problem, but getting past the visual inspection will require a miracle.

 

[Coup D E'Tat]

FWIW, I haven't seen any significant gains (or, for that matter, losses) in going from an estimated ~10.4 to ~11.5. HP estimates and 70-90 sprints were very similar in DSMLink.

I've found much more power in timing and boost adjustments than anything. I usually get the "A/F" to a general spot in the mid-high 10's and forget about it

As always, YMMV. This is just one nut job's way of tuning.

 

[nightspeed87]

FWIW, I haven't seen any significant gains (or, for that matter, losses) in going from an estimated ~10.4 to ~11.5. HP estimates and 70-90 sprints were very similar in DSMLink.

I've found much more power in timing and boost adjustments than anything. I usually get the "A/F" to a general spot in the mid-high 10's and forget about it

As always, YMMV. This is just one nut job's way of tuning.

Thats contradictive to what some of these guys believe?
What compression ratio are you ( not that it matters too much ) But if your a 1g with upped compression like me, timing isnt as friendly.

 

[andymoraitis]

I agree that if A/F's are pretty much in a reasonable operating range that the motor will be more responsive to timing adjustments than anything else. Going from 11:1 to 11.5:1 may create 5 horsepower, but turning up the timing from 16 to 20 degrees will certainly make more.

As with anything there are limits to what you can do, especially on pump gas. Any fuel that has low resistance to knock will require a timing subtraction in light of compression ratio, intake temps and boost levels. In addition, you can only run so much peak advance before the motor starts to lose power, but in the general scheme of things these motors don't mind being a bit on the rich side, but they do like adequate timing. Strokers seem to be an entirely different breed however.

 

[donmagicjuan]

I would say it's most people's experience that leaning out beyond 11:1 on pump gas, say from 11:1 --> 13:1 does not yield any appreciable gains, but I certainly noticed an increase in power from the stock sub-10:1 AFRs to 11:1. With my then stock setup, I netted at least 10 hp if I remember correctly. But as always, individual results may vary.

 

[Kevin Jewer]

I spend a lot of time at the track. At least once a week. It's been my experience that 11:1 on pump gas is the best ratio to run, even on all of my very different setups (from mildly built 2g, to fully built 2.3 2g, to stock turbo/motor/head EVO). On race gas I like 12 even the best. I've gone as lean as 13:1 (evo motor/head is very knock resistant) and picked up no mph whatsoever. In fact I had back to back runs at 13:1 and 11.8:1 and MPH was 118.02 and 118.03, IIRC. It was one hundreth difference, whatever the actual mph was.

Timing has a large effect on power production. With the EVO on the dyno recently each degree was worth about 10 hp. You eventually reach a point of deminishing return, and after that, negative return. The EVO on pump gas does not need nearly as much timing as the 2g did for some reason. I dropped my timing map from a peak of 15 degrees to a peak of 9 degrees, and did not lose any mph last night. In fact, it went slightly faster, but within the normal variability anyway.

Boost, or more accurately airflow, increases yield the largest gains, especially when AFR and timing at least make sense. 1 lb/min is worth 10 whp in my experience, and 1 lb/min is not terribly hard to come by (as long as you are not maxed out on boost (knock) or turbo size). A 2 liter will pick up 1 lb/min for every 1 psi increase in boost, approximately. A stroker will do a little better. This is why I have been saying for years that the absolute key to pump gas power is good intercooling and increasing airflow without increasing boost (cams, intake manifold, displacement, etc).

Of course, this is a vast subject, and there are many different schools of thought that are often in disagreement. Anything I post on this subject is just the sum of my experiences and the line of thinking I have developed over the years. YMMV.

 

[zippyshoe]

I think that someone has posted this link before, but I found the following site to contain lots of information concerning the relationships between airflow and horsepower, as well as between airflow and boost pressure. It also has information to aid in interpreting compressor maps. There is also discussion about how engine displacement factors into all of this:

http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech103.html.

I thought it was interesting that horsepower is very closely linked with airflow and that a larger displacement engine will achieve a particular airflow level (horsepower goal) with a lower boost pressure vs a smaller displacement engine.

 

[andymoraitis]

I can pretty much validate Kevin's results although I was tracking my 2.0 in different conditions. With a 9.5:1 A/F and 16 degrees of timing, it wouldn't run over 100 mph no matter how much boost I tried to run on pump gas.

Correcting for an 11:1 at 16 degrees made a massive difference and it ran 12.95 at 105.20. Leaning out more did nothing and I tried maps at 11.5 and 11.7:12 with the same timing and only minimal changes in trap speed. A sizeable came from taking the timing to 23 degrees on the 11.5:1 map. That netted me my 12.57 at 107.85 and the power delivery was markedly different. I only wish I could have run it again after adding cams on the same tune.

This is why I have been saying for years that the absolute key to pump gas power is good intercooling and increasing airflow without increasing boost (cams, intake manifold, displacement, etc)

I couldn't agree more. It's all about VE and getting optimal flow for the setup. I know that my stock intake manifold and lack of a front mount holds the motor back from making even more power and that it'll be a whole new ballgame when those parts go on.