I was wondering what should my A/F ratio be on a N/A car??? I have a Maf translator, a LS6 intake manifold, 85mm Maf, Direct flo airlid, Corsa cat back exhaust, and a HPP3. I am getting QTP headers soon, with the cutouts. So just wondering what should the a/f ratio be?? I am going to get it on a wideband dyno soon so we can play with the maft and get the max hp out of it without damaging the engine with detonation and KR. Help please..... <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

 

12.8:1 seems to be pretty popular.

No richer than 12.5:1 and no leaner than 13:1.

 

Well it depends a bit on several things. I am running at 13.1 AFR on the dyno to pull 400RWHP with no KR. However, some tuners like 12.8 AFR, its a little more rich than where I am, so its safer.

I used to use a MAFT, it worked very good for me, but I took it off and tuned my car with LS1Edit.

What you want to do is to get your part throotle LTFTs below 0% by using the base switch on the MAFT. You will have to drive the car around about 15 minutes for the PCM to relearn the LTFTs after each change you make on the base switch.
Then when you get to the dyno, work only with the WOT switch in the MAFT. A change to the WOT switch will have an immediate effect on your dyno numbers. A change to the base switch while you are on the dyno will screw you up good, dont do it.

 

[
What you want to do is to get your part throotle LTFTs below 0%[/QB][/QUOTE]
Dumb question but what does LTFT meen????

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Colonel:
<strong> 12.8:1 seems to be pretty popular.

No richer than 12.5:1 and no richer than 13:1. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I assume that is 12.5:1 at idle and 13:1 at WOT???

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by sconnor:
<strong> </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Colonel:
<strong> 12.8:1 seems to be pretty popular.

No richer than 12.5:1 and no richer than 13:1. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I assume that is 12.5:1 at idle and 13:1 at WOT??? </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Both A/F ratios are at WOT <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
And I believe the Colonel meant to type "no leaner than 13:1" <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
At cruising speeds (anything less than WOT), your car's PCM always attempts to maintain a 14.7:1 A/F.
BTW: no question is dumb. Dumb is not seeking answers <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

LTFT is an acronym for Long Term Fuel Trim.

A diagnostic scan tool eg. AutoTap, LS1 Scanmaster, etc. would show you these, and many other parameters that your car's PCM monitors.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by The Dragon:
<strong> </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by sconnor:
<strong> </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Colonel:
<strong> 12.8:1 seems to be pretty popular.

No richer than 12.5:1 and no richer than 13:1. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I assume that is 12.5:1 at idle and 13:1 at WOT??? </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Both A/F ratios are at WOT <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
And I believe the Colonel meant to type "no leaner than 13:1" <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
At cruising speeds (anything less than WOT), your car's PCM always attempts to maintain a 14.7:1 A/F.
BTW: no question is dumb. Dumb is not seeking answers <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

LTFT is an acronym for Long Term Fuel Trim.

A diagnostic scan tool eg. AutoTap, LS1 Scanmaster, etc. would show you these, and many other parameters that your car's PCM monitors. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I'm new using A-tap and the MAFT what should I have the MAFT set on at base idle?? As far as LTFT does A-tap show this?? TIA....Scott

 

Thanks for the help everyone, but also what exactly do your LTFT's do. I know that they are long term fuel trims. And I don't have any kind of LS1 edit or ATap or anything like that I have to take it to a speed shop to get this tuning work done (even though I am doing the install myself). So how should I go about this tuning?? I want to get max hp, but I am willing to sacrifice a few rwhp to stay on the safe side and protect my engine and to keep it from pinging.

 

LTFT making fueling adjustments to the car. Your car is always trying to maintain an a/f ratio of 14.8:1 during normal driving conditions. This a/f ratio provides the best fuel economy/power/emmissions combo.

The oxygen sensors in your car measure the oxygen content of the exhaust gasses coming out of your combustion chamber. From this oxygen content they can determine roughly what a/f ratio your engine is burning at. If the oxygen sensors see that your engine is not burning at the proper a/f ratio, 14.8, then the PCM will make a fueling adjustments to bring the a/f ratio back to 14.8. This adjustment is called an LTFT (Long Term Fuel Trim).


As far as your tuning goes. Shoot for something around 13:1 for your a/f ratio on the dyno. Make sure that the tuner "feels" around a bit to get a good idea of where YOUR car likes to make its peak power. It should make it's peak power somewhere close to 13:1. Most set it a couple points lower (intead of 13:1, 12.8:1) because your motor will run *slightly* leaner on the street.
To ensure that your aren't pinging, make sure that they have a scantool hooked up during the tuning to monitor KR, and that timing is adjusted AFTER your fuel.

Good Luck,
Kevin

 

Thanks a ton Kevin. That helps out big time.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Brew02 WS6:
<strong> could you elaborate a bit about how to acheive the desired 12.8-13.1 AFR?
</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Achieving the proper a/f ratio at WOT is done on a dyno with a wideband oxygen sensor, for most of us.
The wideband oxygen sensor can accurately determine a/f ratio between 9:1 to 18:1 (our stock O2's are only good for ~14:1 to 16:1).
Once you have a reading from the wideband what your actual a/f ratio is, then adjustments can be made to the PCM. Adjustments to the WOT a/f ratio typically should be done to the P.E. Table, or power enrichment table.
The power enrichment table is a set of values applied to the fueling of your car to richen the mixture from 14.8:1 to an a/f mixture that is more condusive for power and less on emmissions.
Using the P.E. tables, adjustments are made in steps until the desired a/f ratio is reached.

Moving the P.E. table value up will richen the mixture and move the a/f down (ie from 14:1 to 13.5:1).
Moving the P.E. table values down will lean the mixture and move the a/f up (ie from 12.5:1 to 13.0:1)
A 2% adjustment to the P.E. table usually equates to about 1 a/f point. Some motors are stubborn though and will require up to a 4% change for every a/f point.

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Brew02 WS6:
<strong> I was under the notion the PCM uses a multiplier number to adjust LT's to maintain 14.8 anytime under WOT. Thanks. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">You have it just a little backwards. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> The PCM uses LTerms and STerms to adjust fueling during normal driving to maintain a 14.8:1 a/f ratio.
At WOT, the PCM uses the Power Enrichment multipier to actually drop the a/f ratio to around 11.7:1 on a stock car.
We use this same power enrichment to target the WOT a/f ratio around 13:1 for a Naturally Aspirated car.

The oxygen sensors, and hence the LT's are ignored when you go WOT, because the LT's are used to maintain a 14.8:1 a/f ratio which is cognizant of emmissions. At WOT, your car is not concerned with emmissions (well mostly) but rather performance, so the LT's are ignored until you drop out of performance mode.

 

My car made the most power at 13.3:1 on a wideband <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

 

STrims are ignored during PE mode... LTrims are not. The LTrims are not updateable (due to the STrims being ignored) during PE mode but they certainly will effect the amount of fuel delivered if they are greater than 0.

Tim

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Tim Sloper:
<strong> STrims are ignored during PE mode... LTrims are not. The LTrims are not updateable (due to the STrims being ignored) during PE mode but they certainly will effect the amount of fuel delivered if they are greater than 0.

Tim </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I'm just trying to keep it simple.

You are right. LTerms are locked and not updated.

 

Hey NOGO, I'm a newbie to this so could you elaborate a bit about how to acheive the desired 12.8-13.1 AFR? I was under the notion the PCM uses a multiplier number to adjust LT's to maintain 14.8 anytime under WOT. Thanks.

 

As long as the engine is not running in performance mode, your car will adjust fueling using the Sterms and Lterms to keep a 14.8 a/f ratio.

You can use the IFR tables to move the WOT a/f ratio around, but be aware that you will also be moving your Lterms around.

For what you are implying, achieving a more powerful a/f at less throttle, there is a table in LS1 Edit to adjust the point at which your car switches to performance mode.

Under the Fuel Tab in the lower right there are two tables WOT Hot, and WOT cold. Here you can adjust what TPS and RPM combo will take your car to performance mode and adjust your a/f according to your P.E. table. You can set it so it only takes 50% throttle for your car to jump to performance mode if you like.

Good Luck,
Kevin

 

I see, The PCM uses the P.E. table to vary from 14.8 to 11.7 at WOT.

Suppose we adjust the IFR to try to acheive the desired 12.8-13.1 AFR at say 1/2 to 3/4 throttle. Will the PCM adjust the LT's no matter what to maintain 14.8 AFR?

Thanks for keeping it simple, NoGo!! <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

 

This is amazing info!! <img border="0" alt="[worship]" title="" src="graemlins/gr_hail.gif" />
What TPS and RPM settings have you had good results with on a N/A engine? I would guess
somewhere near the torque peak rpm with COT turned off?

 

My 02 LS1 is constantly at 14.6:1 AFR while cruising. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> Just had to throw that in.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Brew02 WS6:
<strong> This is amazing info!! <img border="0" alt="[worship]" title="" src="graemlins/gr_hail.gif" />
What TPS and RPM settings have you had good results with on a N/A engine? I would guess
somewhere near the torque peak rpm with COT turned off? </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I actually don't mess with this on a near stock car.

IMHO, time is better spent getting the a/f accurate for WOT through the entire RPM range.

Your car is an air pump, and it is going to make the most power with the throttle blade wide open. It is our job tuning to make the most out of this air.
Setting your car to go to WOT mode at 50% throttle kind of defeats the purpose of dropping the a/f to 13:0 for power because you are only letting 50% of the air into the motor.

Just my .02