Wondering how much power is to be gained by using unleaded race gas, & leaning out the A/F mix w/ a MAFT. This would seem to be an obvious trick, but I can't find anyone who's tried it.

<small>[ March 05, 2003, 01:49 PM: Message edited by: HITMANSS ]</small>

 

leaded gas is going to kill your o2 sensors. at 50 bucks each, i would probably stick to unleaded gas. you can get the VP gas from jacksons in hanover. they have some that is 104 motor octane and unleaded. thats what i have seen some other people run at the track.

 

Oops, my bad --- meant to say unleaded. I can buy VP at the track.

My question is whether you can take advantage of the higher octane level by leaning out the A/F mix. If so, how lean can you go, and how much power can be gained?

 

NEVER lean your A.F.R. out(you will burn up the motor the same as low octane), the AFR still needs to be the same as low octane gas.
the benefit will be in your timing, you will be able to run more spark advance

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by spanktu:
<strong> NEVER lean your A.F.R. out(you will burn up the motor the same as low octane), the AFR still needs to be the same as low octane gas.
the benefit will be in your timing, you will be able to run more spark advance </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Um, about 99% of LS1Edit and Predator users lean out their cars as well as advance the timing. No one is saying it should be to the point of stoichiometric. But going from 11 or 12 up to a 12.8-13.0 (Optimal for most of our cars/mods) is certainly not going to "burn up the motor".

As for the original question, you would really need to perform this on a dyno. But in theory, you are correct. The closer we get to stoich, the better. Unfortunately, stoich also brings tremendous heat and would melt our engine internals. But you could probably take it up a few tenths and experiment with some timing advance. Just do it in small doses to be safe. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

 

You should be able to run 93 or 94 octane and achieve 12.8:1 AFR at WOT without any KR. Thats the sweet spot I am told for max power. Higher octane that 93/94 would allow you to increase your total advance timing at WOT and maybe make more power. But optimum power might be achieved at 28* as opposed to 31* (for example). It depends on how efficient the heads are in filling the cylinders (I think).

More is not always better.

 

Bullseye:
Maybe I should have said it like this
Leaning out your motor is a risk you should not take
If you lean out 87-1xx octane gas, it will all have the same effect,the person who is asking does not know that much about tuning fuel that is why I was trying to impress upon him about lean
WILL burn up a motor.
I fattened up my tables on edit.
I have been tuning for a while 12.8-13.0 is not a optimal # 11.5-12.0 is optimal(under WOT)(14.7:1no/light load)....reason being
there is a saftey margin that should be observed with narrowband o2s..
even if you tune on a dyno with a wideband, it will not be the same under race/driving conditions. you produce more Load on the pavement
LEAN is MEAN BUT........FUEL IS POWER!!!!!
this saying has been around for a long time for a reason you should always stay on the rich side
you may loose a few HP but that motor will live longer and perform more consistently

<small>[ March 05, 2003, 06:37 PM: Message edited by: spanktu ]</small>

 

and still the benefit of higher octane is not leaning your AFR

 

My last dyno pulls, I was right at 13:1, w/ 28 degrees of timing. More timing did not help. Leaning out the A/F mix above 5500 RPMs did not work either, as it just got the cats too hot, and the PCM added fuel back in to cool them off.

That same day, 5-6 other LS1's were dynoed, & every one of them picked up 10-12 HP from LS1 Edit, mostly by leaning out the A/F mix to 13:1.

In a few weeks I will be installing twin cutouts, in front of the cats. I will then re-dyno, and see if I can improve power by leaning out the engine a few tenths more. My guess is that the cutouts alone will lean out the engine at higher RPMs, so I might be OK w/o tweaking the A/F mix. We'll see....

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by HITMANSS:
<strong>
In a few weeks I will be installing twin cutouts, in front of the cats. I will then re-dyno, and see if I can improve power by leaning out the engine a few tenths more. My guess is that the cutouts alone will lean out the engine at higher RPMs, so I might be OK w/o tweaking the A/F mix. We'll see.... </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Wouldn't opening cutouts in front of the cats cause the PCM to throw a SES? <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />

 

Probably will have to install 02 simms w/2 cutouts in front of cats to prevent pcm going crazy.... <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> You cutting them into a stock Y-pipe? (cutouts) WJ.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by spanktu:
<strong> Bullseye:
Maybe I should have said it like this
Leaning out your motor is a risk you should not take
If you lean out 87-1xx octane gas, it will all have the same effect,the person who is asking does not know that much about tuning fuel that is why I was trying to impress upon him about lean
WILL burn up a motor.
I fattened up my tables on edit.
I have been tuning for a while 12.8-13.0 is not a optimal # 11.5-12.0 is optimal(under WOT)(14.7:1no/light load)....reason being
there is a saftey margin that should be observed with narrowband o2s..
even if you tune on a dyno with a wideband, it will not be the same under race/driving conditions. you produce more Load on the pavement
LEAN is MEAN BUT........FUEL IS POWER!!!!!
this saying has been around for a long time for a reason you should always stay on the rich side
you may loose a few HP but that motor will live longer and perform more consistently </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">LS1's are of a minority in the auto industry in that most of them come from the factory on the rich side. Most manufacturers base their A/F ratio on the thermodynamic properties of the engine and it's internals. Our engines come with hypereutectic pistons which are easily capable of handling 12.8-13.0:1. GM has decided to play it safe and there's nothing wrong with that. They have to warranty hundreds of thousands of LS1 based vehicles. Setting it on the rich side makes sense for them. But the real margin of safety in the programming comes from the A/F tendency. You'll notice that on a wideband 02 the A/F of an LS1 will always dip a few tenths as it nears redline. This has been programmed in and should always be maintained when tuning. Because the closer you get to redline, the harder it is for the engine to maintain a specific A/F.

Octane is defined as a fuels ability to resist detonation. Spark, A/F, and heat are all a factor in predetonation. When any of these factors become out of range, you get predetonation. The higher the overall octane points, the better the resistance to predetonation, the more you can push each factor. The absolute optimal A/F ratio for gasoline (and any other fuel for that matter) is stoichiometric (14.7:1 for gasoline). We run stoich in closed loop for a reason, it is the most efficient. We get by with this because the combustion is still small. When you go into open loop, the combustion is much greater and the engines thermal surfaces simply cannot handle the heat. More fuel is not necessarily more power (read: supercharger). And keep in mind that anything under 14.7:1 is, in reality, rich. Yes, lean WILL burn up a motor, if it's too lean for the engine's thermal surfaces. Small engine's have been built using ultra high temp materials that could withstand the heat of stoich. The mileage is unbelievable and the HP/TQ is through the roof. But our engines are definitely not of that variety. The cost would immensely prohibitive.

And since street surfaces vary tremendously, it's impossible to say how much more load, if any, the street will produce. But let's assume we're talking about asphault only. The dyno provides a serrated rolling surface that gives a constant load on the tires, driveline, etc. The rollers might spin a little easier than your accelleration on the street, but you are still at WOT under a load. So the difference would have to be negligable at best. And certainly not anything that will generate a substantial difference in your A/F.
<img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

 

Good points
you need to check your assumptions on dyno's
It is a fact that they do not simulate a load
like street conditions therefore the tuning aspect tends to be on the lean side

And on the wideband dipping coming to redline
that is normal on any engine, fuel will be at its richest at peak torque(highest load)and taper down
as the horsepower peaks

good discussion!

 

FWIW, on a normally modded LS1 motor (read: H/C Exhaust, all the bolt-ons), I have yet to see a measureable gain using race gas. Fuel octane, simply isn't the limiting HP factor.

Race gas really only comes into play on forced induction setups, high compression setups, and nitrous setups. It is on these setups where octane is the limiting factor in power, and a substantial HP gain on race-gas can be made.

Good Luck,
Kevin

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by spanktu:
<strong>good discussion! </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Definitely. <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" /> No getting <img border="0" title="" alt="[Mad]" src="gr_images/icons/mad.gif" /> , just good discussion. Again, <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" /> .