Is it too lean with Diablo?

[CWCobra]

A guy I know put a 2.80 pulley, NGK TR6 plugs, and a Diablo chip on his '03 Cobra. Then he had it dyno'd on a "Mustang" dyno, which showed consistent a/f ratios of 13.2 or so until 3900 rpm, at which point it dropped to 12.7 or so until shut down at 6000 rpms. I told him it was waaaay too lean; should be running closer to 11.0 or so. I am by no means an expert on this, and was wondering what others might think. He is planning on installing the ls1motorsport 3" stainless exhaust soon, and I think he's really risking getting even leaner still.

BTW, he had stock cat-back and silencer removed, but only turned 385 RWHP. The a/f sampling was done with sensors installed in the front O2 sensor bungs.

/puzzled/

Thanks for any advice,
CW:shrug:

 

[JB]

seems to me there was a post here awhile ago that the first run of '03 chips from *some* mfg (may have been Diablo), was running lean and they were being reburned for free.....

 

[jtfx6552]

It wasn't the Diablo that were running lean.

Not sure who is operating the Dyno, but from what I understand the amount of load can influence where the a/f ends up. The Mustang Dyno is not just an inertial load like the Dynojet. I believe the operator can add as much load as they want.

I was told the reason the Diablo chips run so rich on a Dynojet (mine runs around 11.1:1) is because the Dynojet "underloads" the car. Maybe the dyno operator in this case overloaded the car?

Also, the a/f readings seem to change right after mods, temporarily until the computer learns what is going on. That could be a factor. Also , not sure what type of wideband was installed into the bung, but they can be off as well.

And last, but not least... a loose inlet connection, or an open breather can lean the cars out as well.

Just rechecked the initial post, those numbers, while they are a little leaner than I would like to see, don't seem to be in "boom" land...

JT

 

[Got Incon?]

A dynojet severly underloads a car. If your at 13.3 on a dynojet, good luck. I see a blown headgasket in your future. Much like one of mine.

 

[CWCobra]

It was a "Mustang" dyno, not a Dynojet. Not sure what difference that makes, but I'm told that it does make a difference, hence the significantly lower power observed (385 RWHP) than would have been expected from a Dynojet (420+ RWHP?) measurement with same mods/car.
Thanks,
CW

 

[F8LBITE]

I got my chip burned today. And saw some high a/f #'s, w/ no ping in 40 degree weather on Sunoco 94oct. I've had experience doing different programs on my 01 Lightning and these cars are far more forgiving on a/f and timing curves do to the higher air flow rate I beleive.

 

[2003snake]

a 2.80 pulley ---- 385 rwhp....that seems awefully low!

 

[Silver 03 Cobra]

Mustang Dynos put a load on the rollers so the numbers are quite a bit lower. There is a different conversion factor. On a Dynojet our cars use .85. On a Mustang DYno it is well below .8

I have a buddy that has a Diablo chip and I have a JDM chip. We both dynoed back to back with basically the same mods although a few different manufacturers. He was running over 13.5 at 6000 rpm. I was running 11.4 at 6k and dropped to 11.1 at shutdown.

 

[jtfx6552]

That is very odd. At the shop I dyno at, another car with a JDM chip also dynoed. We overlayed both curves. Mine was 11:1 (Amazon Racing Diablosport) and his was over 13?:shrug:
My curves are on my website. Who did your buddies Diablo chip?
JT

 

[Got Incon?]

Originally posted by CWCobra
It was a "Mustang" dyno, not a Dynojet. Not sure what difference that makes, but I'm told that it does make a difference, hence the significantly lower power observed (385 RWHP) than would have been expected from a Dynojet (420+ RWHP?) measurement with same mods/car.
Thanks,
CW

A mustang dyno uses eddy current absorbtion to actively hold the rollers back and make them seem to your car that it was actually on a road. On a dynojet there is usually no load asorbing capabilities and from what I hear about the add-on load absorbtion unit, its not that good. So on a dynojet the tuner must tune on the safe side so that when your on the road it doesn't blow.


And being at 13 to 1 at 40 F may be okay, but wait till the ambients hit 100. Your head gaskets wont last.

 

[jtfx6552]

Originally posted by Got Incon?



And being at 13 to 1 at 40 F may be okay, but wait till the ambients hit 100. Your head gaskets wont last.

As you correctly state above, the cooler the ambient air is, the safer a given a/f ratio will be.

However, I thought the real fear was that as the ambient gets cooler, the a/f ratio will get even leaner because of the dense inlet air. For example, if you dynoe'd the car in the summer and had an a/f slightly on the lean side, when the November rolled around, you could be full into the "way lean" danger zone.

JT

 

[Got Incon?]

Originally posted by jtfx6552
As you correctly state above, the cooler the ambient air is, the safer a given a/f ratio will be.

However, I thought the real fear was that as the ambient gets cooler, the a/f ratio will get even leaner because of the dense inlet air. For example, if you dynoe'd the car in the summer and had an a/f slightly on the lean side, when the November rolled around, you could be full into the "way lean" danger zone.

JT

No, that is only the case if your running out of injector or pump (fuel supply) not if you still have fuel supply in reserve and the computer is just commanding a 13 to 1. Hence the mass air meter compensates for additional air getting into your engine in the winter, but only if you still have more fuel available to put in. I suspect that in this case there is, however the computer is just telling it not too. And yes, 13 to 1 is fine in the winter because your not likely to detonate. Summer is another story and you want at the min 12 to 1 on a blower car. I run 12.5 on my twin turbo car, but thats a different story. Of course your combo may vary. If you can hear the detonation, it prob already to late.


Personally I would not pay to have a chip in my car that is going that lean.

www.fjoinc.com
www.egortech.com

And then there is also a AFM-1.

best real world check on a/f is to test it on the road.

 

[jtfx6552]

Originally posted by Got Incon?
No, that is only the case if your running out of injector or pump (fuel supply) not if you still have fuel supply in reserve and the computer is just commanding a 13 to 1. Hence the mass air meter compensates for additional air getting into your engine in the winter, but only if you still have more fuel available to put in. I suspect that in this case there is, however the computer is just telling it not too. And yes, 13 to 1 is fine in the winter because your not likely to detonate. Summer is another story and you want at the min 12 to 1 on a blower car. I run 12.5 on my twin turbo car, but thats a different story. Of course your combo may vary. If you can hear the detonation, it prob already to late.


Personally I would not pay to have a chip in my car that is going that lean.

www.fjoinc.com
www.egortech.com

And then there is also a AFM-1.

best real world check on a/f is to test it on the road.

I understand what you are saying, and agree that is what should happen. However, I'm glad my a/f is running in the low 11's to give a nice safety factor. that way if the computer/chip allows the car to lean out a little for whatever reason, hot air, cool air, whatever it is doing, the car will be safe.

I'm not sure what all the computer is using to decide what the a/f should be, but it seems to have some sort of adaptive strategy that causes the a/f to vary from time to time. By that I mean I've done dyno pulls on different days and the a/f is not always what I would expect. When I first installed my Diablo and pulley, the a/f was on the lean side (high 12's-low 13's), this was after several hunderd miles of driving, so I thought any "learning" would have happened. When I rebaselined on the same dyno, on a different day, before adding a catback, it was at 11.2-11.3. We added the catback, which I thought might lean up the a/f with no inbetween chip tuning or even a test drive for any 'learning' (if it even does do any learning?), the new exhaust, the car fattened up just a little to 11.1 to 11.2. Came back a third day to add some other stuff, rebaselined and it was still 11.1-11.2. I still don't know why it was leaner the first dyno pulls after adding the Diablo, and I'm not sure that at some times it doesn't go back to that?

Anyway, I'm glad I have some saftey factor in there. If I am losing a few ponies, it is worth it to be safe.

I agree he should explore why the a/f is where it is and get it fattened up, if it hasn't manged to do it by itself already.

JT

 

[Lomancobra]

Originally posted by 2003snake
a 2.80 pulley ---- 385 rwhp....that seems awefully low!

ditto, something is wrong :uh oh:

try a different dyno

 

[Cobra'03]

One thing that never seems to get discussed about A/F - what is the need? For drags, it is optimum power, but for road racing, you also have to factor in engine temps and longevity. A richer mixture in a high temp track race is often desirable to ensure you finish the race. I know for a fact that at the Bondurant School in phoenix, where they use a gaggle of Stangs, one of the mods they make to the cars is to enrich the A/F way beyond stoichiometric to help offset the high AZ temps, and keep the engines in one piece longer.

I am going to get a Delta chip from Rick, with the stock tune available at a switch, in case I need to race at VIR or Summit, where I can go back to the stock tune. Also, keep in mind that over time, a car tends to lean out more as deposits form on the intake valves - I would strongly advise running a good top engine cleaner like Red Line SI-2 or SI-1 or Regane regularly for that reason.

 

[CWCobra]

Just for the record, the Diablo chip in question was from Rick at Amazon Racing.
Later,
CW