gMAG

iTrader: (1)

I have a mailorder tune, which runs rich.
What happens to the ECM controlled A/F ratio, after I port my heads.
Does the A/F remain the same (keeping the mixture rich), or, does an increase in the amount of airflow, lean out the mixture?

MWatson17

I'm not an expert tuner, nor do I have experience tuning with ported heads, but I expect that if you have a MAF tune, it will account for the extra airflow and the AF ratio should stay the same. If you have a Speed Density tune however, I expect that the porting would slightly lean out the mixture given the same tune.

redtan

iTrader: (5)

No it won't, not even the MAF. That's because the MAF measures airflow in the intake tract, not in the combustion chamber. So the MAF has no idea that all of a sudden more air enters the combustion chamber due to the ported heads. All the MAF sees is air in front of the throttle, which remains the same regardless of what happens internally.

Now the o2 sensors will in fact see a leaner mixture due to the increase in air volume, but then again the narrowband o2 sensors won't be able to do squat about that.

So you need to get it tuned with a wideband and should be adding fuel to compensate for the increase in air entering the chambers.

MWatson17

Did not know that, thanks!

gMAG

iTrader: (1)

So, to sum up, I can drive around town/on the highway, but no WOT?
(until a tune is done)

gMAG

iTrader: (1)

I understand the part about the O2s.
While the MAF & the heads are two separate portions of the same air tract, ...if more air goes through the heads, doesn't more air have to pass through the MAF?

redtan

iTrader: (5)

Not necessarily, the engine pulls in all the air it can muster through the intake tract and stores it in the intake manifold. From there the air enters through the head runners into the combustion chamber as much as it can....so if you have better heads then more of the air from the manifold enters the chambers. But that doesn't mean that more air gets pulled through the intake/MAF unless you improve that portion itself.

You can have the most badass heads in the world, but if you have a shitty intake then it won't make the most power. Badass heads don't magically pull in more air through the same intake tract as the stock heads. They just use more of the air from the manifold, but the manifold gets fed by the intake tract with the same volume of air.

For the MAF to see more air, you need to improve the portion before the MAF.

gMAG

iTrader: (1)

Good tech info.
Thanks for the education.
I see how there could be a lag in airflow, depending upon the complement (or lack of it) of the various components.

ZL1Killa

iTrader: (17)

please tell me how you know it is running rich? I hope you are using a wideband and seeing this.

gMAG

iTrader: (1)

At idle & normal cruising. ..Sooty tail pipes, black/rich smelling exhaust, so-so mileage.
I don't know what it's doing at WOT.

ZL1Killa

iTrader: (17)

all of this is irrelevant, other things can cause this. no cats can cause rich smell, even with cats it can smell. black soot can also occur.

whats the mileage? over 100k? I suggest replacing oxygen sensors, but it would be a good idea to get a log of their activity at idle and part throttle. If they are still responsive and oscillating they are fine.

can you post the tune, can you post a log file? has your tuner or can a tuner you trust look at it? can someone you know look at it with a standalone wideband and see the AFR at part throttle and WOT?

gMAG

iTrader: (1)

35k mileage. Compression/leakdown is even among all cylinders. O2's switch normally, at idle, cruising. I have a new pair of Bosch O2s...didn't make any difference (and I didn't expect that they would).
LTFTs look good. All verified with AutoTap.
There are no vacuum leaks-verified.
I have no way of verifying the tune at this time....don't know anyone with a tuning device or a wideband. In the spring, after some head porting, I'll have Slowhawk do a dyno.
A spare MAF was swapped, with no change.
Thanks.

Old Geezer

iTrader: (3)

gMAG

iTrader: (1)

Chuck, it's called Fudd's law of opposition.

ZL1Killa

iTrader: (17)

biggest thing to do is grab a wideband and stick it on there and see what its actually doing.

gMAG

iTrader: (1)

Well, eventually I'll spring for these tools.
I was reading about the wideband, and didn't see a model with two O2 sensors.
Can a wideband with one sensor be used on a true dual exhaust?

MWatson17

You can use them with dual exhaust, both banks should be relatively close, but if you're nervous of it you can tune it with one bank and then plug into the other just to verify.

I'd also like to know if there's a single wideband module with two sensors for this kind of application.

joecar

Innovate LM-2 with dual sensors.

joecar

Glenn,

The MAF will register any increased airflow, but ultimately the O2's will be used to trim to stoichiometry, so in CL the AFR will be stoichmetric...

if trimming produces positive trims, these will be applied when PE is commanded, but you should avoid relying on these to keep the motor safe.

gMAG

iTrader: (1)

Thank you, Joe.