Tuning larger LT-5 cams

[XfireZ51]

Ron,

Running O/L forces the fueling to be based strictly on the VE tables. O2 sensors feedback to the ECM for pulsewidth mod for the Integrator and BLM calcs. There are some threads on ThirdGen.org that discuss Closed Loop tuning for larger cams. The greater overlap does cause fresh air to be detected in the exhaust by the O2. Consequently the ECM interprets that as a lean condition and adds fuel. That's why you see the BLMs drop to minimum 115 that is in the calibration. In fact, the INT goes lower than that. What most people don't realize is that a 128 BLM DOES NOT necessarily correspond to 14.7:1 AFR. When running C/L, you'll see the AFR toggling rich/lean in order to not oversaturate the cats. Probably a reason why yours may very well be shot.
The magic 128 BLM for C/L indicates where the O2 swing points are. The voltages can be manipulated based on airflow. It means you can modify the calibration to tell the ECM that what appears to be lean actually is not. And it can be done
in such a way to affect principally only the idle. Being able to use C/L with the larger cams also allows use of additional parameters such as proportional gains which make a difference in managing surging for example.
At Bowling Green, Graham said something very interesting, if I recall correctly, in that the LT-5 wants to stall. Increasing the overlap exacerbates the oscillation bringing the LT-5 into areas where it will stall. One reason why people raise the idle when going to larger cams. So being able to control idle more tightly becomes even more important when using larger cams. C/L presents finer control of the motor which is why I believe Graham suggested C/L for your emissions calibration.

[rkreigh]

Originally Posted by XfireZ51

Ron,

Running O/L forces the fueling to be based strictly on the VE tables. O2 sensors feedback to the ECM for pulsewidth mod for the Integrator and BLM calcs. There are some threads on ThirdGen.org that discuss Closed Loop tuning for larger cams. The greater overlap does cause fresh air to be detected in the exhaust by the O2. Consequently the ECM interprets that as a lean condition and adds fuel. That's why you see the BLMs drop to minimum 115 that is in the calibration. In fact, the INT goes lower than that. What most people don't realize is that a 128 BLM DOES NOT necessarily correspond to 14.7:1 AFR. When running C/L, you'll see the AFR toggling rich/lean in order to not oversaturate the cats. Probably a reason why yours may very well be shot.
The magic 128 BLM for C/L indicates where the O2 swing points are. The voltages can be manipulated based on airflow. It means you can modify the calibration to tell the ECM that what appears to be lean actually is not. And it can be done
in such a way to affect principally only the idle. Being able to use C/L with the larger cams also allows use of additional parameters such as proportional gains which make a difference in managing surging for example.
At Bowling Green, Graham said something very interesting, if I recall correctly, in that the LT-5 wants to stall. Increasing the overlap exacerbates the oscillation bringing the LT-5 into areas where it will stall. One reason why people raise the idle when going to larger cams. So being able to control idle more tightly becomes even more important when using larger cams. C/L presents finer control of the motor which is why I believe Graham suggested C/L for your emissions calibration.

this explains it very well really need someone who can tune the car with the exh gas analyzer going

I've got a wazoo guy graciously stepped up to loan me some nice cats and hopefully I can get this stroker to blow clean

I believe 48 HC is going to be a BIG challenge as even the stockers are failing at this level

it's ridiculous that VA cut the standard from 98 to 48. cars are getting any cleaner as they get older

[Kevin]

Originally Posted by rkreigh

it's ridiculous that VA cut the standard from 98 to 48.

that's ********

[XfireZ51]

Driving the car back from BG was a low point for me. The car felt like it was running like Sh*t. MPG was not very good IMO. There is a rhythm to a well tuned motor and the trip back from BG, it sounded like a out of control orchestra. Just didn't have that harmony. One of the things that has really
made this package sing is playing w the SA tables. More timing
has brought it together. Adjusting the Accelerator Enrichment also helps with giving you that sense of being directly connected to the motor. You tune it to eliminate that count to 1 before you actually feel the response from
the go pedal. At cruise now you get just a steady purr of the exhaust with no motor sound coming from the front end. Happy noise!
So now the tuning is focused on things like getting rid of the annoying surging on decel for example. Little nit picks but since I don't need to live with it, I choose not to.
With Part Throttle pretty well locked in, I'm looking forward to optimizing WOT.
The cool thing about ECMs and tuning the ZR-1 is how you can create a Jekyll and Hyde car. A motor perfectly fine idling at 775-800rpm with little to indicate that there's a motor under there producing 500+ hp and 1/4 mile speeds of 120+. As the Octane Magazine describes it, the perfect Q ship.
I love sleepers.

[XfireZ51]

Here's a bit of the "proof of the pudding". A vid of idle after my last calibration change. Very nice.

[ZZZZZR1]

Dom,

Unreal tuning!

I want a dyno and 1/4 mile run ASAP!!!!



David

[XfireZ51]

Dave,

Here's one with camera resting on plenum.

[Paul Workman]

Originally Posted by XfireZ51

So now the tuning is focused on things like getting rid of the annoying surging on decel for example.

Yeah, baby! I'm all over that one! Apparently the surging is "one of those things" to be addressed when bumping the GO peddle output to some point over 500 ponies. Adjusting the idle screw helped a little. My IAC counts are a bit erratic tho.... Marc has a cal tweak for the surging, and I'll R&R the IAC motor this week sometime.

Anywayz, Dom, I really eat this tuning stuff up. (Comes from decades of tuning rifles for competition, I guess.) Ya gotz me on the edge of my chair, buddy!

P.

[tomtom72]

Jez Dom...the camera isn't even moving



Way to tune Dude!