Last night I got my car dyno tuned. My tuner is Jeff Creech of Carolina Auto Masters. When I did my baseline pull my car was very lean. around 15.1 or so. With some adjustments he got my car around 13.0. The problem is that the car lost 10 rwhp making it rich. Jeff said that there isn't ANY signs of detonation. So he inched the A/F ratio toward the lean side. The car still didn't detonate at all. Knock sensors all seemed to be in line. He adjusted the timing and it finally detonated ONE time. He adjusted the timing back to where it was on the previous run and it ran like a champ. It made the most power and torque at a 14.1 A/F ratio. Everyone is freaking me out about the ratio being too lean. Jeff thought it was too lean too. But he said the car seemed happiest at that ratio. He thinks that the Granatelli MAF might be the reason it is reading lean. My question is if the car isn't knocking AT ALL or detonating AT ALL, will running it that lean hurt the car. He did 8 dyno pulls and he tried different timing and A/F ratios and the one that I have now seemed to make the most power with out any signs detonation. What are you guys thoughts on my situation? Please give me some input.

 

im thinking no good in the long term. find a stock maf and re-tune and see how that plays out.

 

Reading lean by what instrument? A good
bung-substituted wideband or a tailpipe unit or
???

If you make the car richer, you slow the burn and
need to add timing advance to find peak power.
When they got to 13.0:1, did they then jack the
timing forward to find the knock limit? Or only at
the leaner (14:1) point later?

 

It was with a tail pipe unit.
Yes he advanced the timing with the fuel in the correct range.
I am not sure about the last question.

 

Hey, Jeff here... Agreed with the comment that the BEST approach would be to get a stock MAF and re-tune it. And agreed that it appears mighty lean, more lean that I like an LS1 to appear.

Setup: I have a Dynojet 248 (high inertia), dynojet wideband, LS1edit, efilive, and perform backup checks for AFR accuracy with a techedge unit as well as a backup sensor in the dynojet. These checks were performed Friday, and again this morning with no discrepencies found.

I tune a lot of LS1's and usually if they start lean, say 14.5:1 I can fatten them up to 13.5 and GAIN power, then lose slightly dropping from 13.5 to 13.1 or 13.0. This car made max power at 14.0/13.9, and behaved as if it was being over-richened as AFR was dropped to 13.0. At no point did the graph show signs of detonation until AFR was 14.0 and timing was 29*. Max power was made at 26* and 14.0. I usually see max power at 13.3-13.4!

Let's look at my race car experience: I see motors that like to run fat and make max power at 12.2:1 NA. And motors that want to run lean and are happy at 14.2 or 14.4:1, as long they are not detonating, no damage is being done, as long the motor is "happy".

Agreed, this is a weird one. I won't say I lost sleep over it, but it is weird. Everything about the behavior says set it at 14.0, except conventional wisdom. The car I tuned today (also an LS1) made max power at 13.2:1.

As I've told Brandon, the options are:
- monitor things, check the plugs, listen for detonation, stay the course.
- bring it by and I'll fatten that sucker up with the MAF that's in it.
- change MAF to stock, bring it back, re-tune it.

I think they are all decent options. I know he's scared and I'd be scared too if the car showed me any signs of not wanting to be set where it's set.

This is an odd one. Agreed... Anyone seen a computer controlled car that made max power at so lean an AFR??

Weird stuff....
-jeff

 

Thanks Jeff. I wasn't sure how to answer any questions. Like Jeff said my car is lean but it hasn't shown ANY signs of running bad. I even raced a riced out Honda on the way back from the tune and it did fine "under load". If the car detonates at all Jeff said I could bring it back and he would adjust the A/F for free. Or if I just want to feel better he will adjust it for free. I am going to trust Jeff in this situation. I am going to keep a close check on my plugs for a while. If there is anything wrong I will get the A/F adjusted. I just want to say that I am very happy with the Job that Jeff did on my car. He straightned out a lot of problems that I had before the tune. I will recommend him to anyone that asks me.

 

Leak?? I know it sounds too simple but it would make sense. especially if it was in the exhaust before the bung. ....just a thought.
joel

 

Yeah, I definately thought about that. This was taken from the tailpipe, and there's leaks everywhere. With the loud pedal down the force is all out, no air leaks make a difference. (I've used that setup with open headers, no good reading part throttle, but perfect at WOT.)

Other option I considered and dismissed was completely unburt fuel shows lean on narrowband and wideband sensors. But it would have had to be 2 cylinders down though, because the narrowband O2's were closely matched.

Twilight zone maybe, maybe not...
-jeff

 

If you are talking about an exhaust leak I do have one. My drivers side collector and my y-pipe leak. It is the wonderful Pacesetter Y-pipe

 

One more option - go back to the stock MAF sensor. My car also ran VERY lean with a GMAF. It fattened up a little when I changed to a Cold Air GMAF. And then it came almost back to normal when I replaced the sensor with the stock electronics, but left the GMAF ends on. And I lost no time at the track with that setup either. Note - the GMAF dropped .25 sec off my ET so I was reluctant to go back the the complete stock MAF because it loses SO much power. Now that I have headers it is FAT again....

 

I pulled some plugs yesterday and they looked almost like brand new. Judging by that I should be ok don't you think. I have run my car hard a few times since the tune and everything still looked good.

 

And my car (TR224, stock heads too... though with CATS) likes to run real rich- low 12s. Wish I could explain it. Wonder which was spark plug gap would push it.. i.e. is it harder to light off a rich or lean mixture .. and thus does it tell you if you're going to far with gap in either direction..

 

Grantelli's do make the car run lean. That's one of the "tricks" they play to get a few more hp. I had one, went to dyno, then swapped stock one in, re-dynoed. Result = +10hp. I had LT headers and ported TB though. Every car is different. I'm not knocking the Granatelli, but have read numerous posts that the stock MAF performed better inmaking better hp. My advice is the same as above, put a stock MAF back in and re-tune. I'll bet you will see better numbers and at a more optimum A/F ratio. Just my $.02

 

when you're tuning the car to make it lean or richen the mixture...what tables are you using and what do you do to the values to make it rich or lean?

 

TIMMEH, not sure who you are speaking to, but I (and most) are adjusting the one PE vs. RPM table.

 

And higher #s in the table richen and vice-versa. It works something like this stoich AF 14.7 / 1.2 (PE "multiplier") = 12.25 target WOT AF

 

Oh...I get it now. Thanks! I'll check it out and see where it's at. All I know right now is I'm going through gas like it's going out of style. Already been through 3/4ths of a tank and only got 160 miles out of it. I need help tuning this damn thing.

 

But the PE vs. RPM is only for WOT. If you aren't on the card hard a lot, you shouldn't be killing the gas mileage, as you should be then in closed loop and the computer/O2s normally do a great job of running at 14.7 AF.

 

that 160 miles is from simple daily driving...

 

I got 200 miles out of a full tank. WTF?