Best AFR for stock motor

[IndyPete]

I know everyone says that there is no such thing as best timing/AFR for the LS2 motor but I'm asking anyways. I'm crazy like that.

Whats be the best AFR / Timing in your experience on a stock TBSS? Surely they cant be that different from vehicle to vehicle that there wouldn't be a ballpark happy number?

[murphinator]

normally aspirated will typically make good power and be safe somewhere around 12.8-13.0 at WOT

[bartender_77]

normally aspirated will typically make good power and be safe somewhere around 12.8-13.0 at WOT

Just remember that he asking about a trailblazer SS that its quite heavy and that truck has an LS2 and in my experience those trucks in stock form or with with mild mods like an A/F of 12.4-12.5, any higher and you start getting knock on third gear and sometimes on 2nd gear too, and dont go higher than 22-23 on timing either or you will get knock at any A/F, but if you have a lot of mods like headers, cam. exhaust then you can run a little more timing in the 23-25 range, i always use a wideband and play with the A/f to see what the engine likes, so.... just my 2 cents

[BBA]

Just remember that he asking about a trailblazer SS that its quite heavy and that truck has an LS2 and in my experience those trucks in stock form or with with mild mods like an A/F of 12.4-12.5, any higher and you start getting knock on third gear and sometimes on 2nd gear too, and dont go higher than 22-23 on timing either or you will get knock at any A/F, but if you have a lot of mods like headers, cam. exhaust then you can run a little more timing in the 23-25 range, i always use a wideband and play with the A/f to see what the engine likes, so.... just my 2 cents

I'm with bartender (especially since I have a TBSS). They like 12.3-12.5 the best.


Murphinator: AFR numbers are irrelevant since 12.3 on 10% ethanol is probably more like 13:1 on PURE gas, which you can't get anymore...

[DSteck]

I usually end up with a PE ratio somewhere in the 1.17-1.18 vicinity on any Gen IV engine. They seem to ward off knock better, make more power, and run more consistent.

[bluegoat06]

I usually end up with a PE ratio somewhere in the 1.17-1.18 vicinity on any Gen IV engine. They seem to ward off knock better, make more power, and run more consistent.

+1, I've always got better results at .84 -.85 lambda

[S2H]

+1, I've always got better results at .84 -.85 lambda

thats more of the right answer...
you should think in terms of lambda...not AFR
AFR will be skewed easily...especially when there are uncontrolled amounts of ethanol being added to pump gas..."contains up to 10% ethanol" around here may mean it has 10% or it has 2%....

in general most fuels make the best torque around .85 lambda and the best power at higher romps when slightly leaner... some fuels continue to make power well below .85 lambda...but it becomes a factor of diminishing returns...
e85 makes power way below .85 lambda, but the gains are not that significant compared to what you get up to that .85

[BBA]

I usually end up with a PE ratio somewhere in the 1.17-1.18 vicinity on any Gen IV engine. They seem to ward off knock better, make more power, and run more consistent.

Heh...something we agree on. Imagine that.

[johnh]

Interesting, I thought LS motors made best power 12.5 - 13.1? (Forget the lambda for a moment easier for me to think in AFR where lambda is 14.68). My G8 is set around 12.7 and I don't see any knock [Disclaimer: I haven't put the WB on it yet that's the commanded value--WB testing will be this weekend]

Also, so are you guys fans of a flat fuel curve? Or would you recommend leaning it out a bit in the lower rpms and higher rpms (past the torque peak)?

[DSteck]

Interesting, I thought LS motors made best power 12.5 - 13.1? (Forget the lambda for a moment easier for me to think in AFR where lambda is 14.68). My G8 is set around 12.7 and I don't see any knock [Disclaimer: I haven't put the WB on it yet that's the commanded value--WB testing will be this weekend]

Also, so are you guys fans of a flat fuel curve? Or would you recommend leaning it out a bit in the lower rpms and higher rpms (past the torque peak)?

People that end up with leaner numbers for best power are possibly reading at the tailpipe.

I set the PE table to a flat value for tuning... it's easier to hit a non-moving target. Once it's all done, if you've got access to a dyno you can tweak it. I've played around, and moving away from 12.5 (roughly 0.85 lambda) is almost inconsequential. When I say inconsequential, I'm talking less than 10hp. If I really get a hair up my ass about it, I'll play around and richen up around peak torque.

[S2H]

most motors tend to make best torque around(not exact) .85 lambda and best power in the top end slightly leaner...around(not exact) .86~.87 ish...

its like saying 12.5 for torque and 12.8 for top end power.


and yes.. I'll agree.. the power gains from anything slightly richer or leaner are so small its usually not worth the fight....especially since its going to be slightly different day to day anyways

[S2H]

and just because theres no knock, doesnt man you are making best power and torque... it just means you arent knocking...

and without a wideband to verify..commanded doesnt man jack shit...
it just means that you have commanded that ratio.. if the VE tables or MAF tables are off.. then so is your fueling...
if you command 12.7 and your MAF is 15% high.. then its going to add 15% more fuel making it way rich...

and with more fuel you can usually push a little further in the timing before it knocks.., but that doesnt mean that you are making the best power at that spark timing...
I've seen tunes with 32* at WOT and no knock...but on a dyno..where we could actually see power gains... they made best power and torque around to 26~28...

[DSteck]

and just because theres no knock, doesnt man you are making best power and torque... it just means you arent knocking...

and without a wideband to verify..commanded doesnt man jack shit...
it just means that you have commanded that ratio.. if the VE tables or MAF tables are off.. then so is your fueling...
if you command 12.7 and your MAF is 15% high.. then its going to add 15% more fuel making it way rich...

and with more fuel you can usually push a little further in the timing before it knocks.., but that doesnt mean that you are making the best power at that spark timing...
I've seen tunes with 32* at WOT and no knock...but on a dyno..where we could actually see power gains... they made best power and torque around to 26~28...

Yep. I hate when people do the whole "tune until it knocks and then back off 2 degrees" crap. More timing is not always better. From experience, I've picked up how much timing tends to do best, and on similar setups, if I don't have dyno access, I just go off of past experience.

[KLUG'S SS]

Yep. I hate when people do the whole "tune until it knocks and then back off 2 degrees" crap.

Yeah that statement is so far off base it's not even funny.

[DSteck]

Yeah that statement is so far off base it's not even funny.

I don't know... it kind of is funny.

[KLUG'S SS]

Funny to me for the guys not gaining any more power or maybe even losing power all while pushing the knock threshold even closer.

[DSteck]

Funny to me for the guys not gaining any more power or maybe even losing power all while pushing the knock threshold even closer.

Just deaden the knock sensors to feel better about it. 32º and no timing retard!

[KLUG'S SS]

Just deaden the knock sensors to feel better about it. 32º and no timing retard!

All joking aside I redid a tune for a guy that had his original tune done by a so called "pro" and that is seriously what the tuner had done was had the guy's timing run up to 30*-32* and had the tune setup to where it had no authority to pull any timing if knock was detected.

[johnh]

and just because theres no knock, doesnt man you are making best power and torque... it just means you arent knocking...

and without a wideband to verify..commanded doesnt man jack shit...
it just means that you have commanded that ratio.. if the VE tables or MAF tables are off.. then so is your fueling..

Agreed.

If my MAF Tables are on, and VE is on..then my fueling will be pretty darn close. Seen it verified by a WB in several cases.

I was looking for a good target and I think I've got that...now dialing it in will take more effort.

[rynez06]

Just deaden the knock sensors to feel better about it. 32º and no timing retard!

lol i hear you there, i had a c6 z06 come in to me that was tuned by another shop, the customer stated that he could hear alot of audible knock, well the car had about 27* peak timing from 5200+rpm @ .8+ g/cyl of airflow but no knock retard on the dyno, i go look at the base retard table and the value is set to .5 lol wow, audible knock city, and the af was 12.8 af .... sounds like a great tune for a ls7