Highway Lean Cruise worth it?

[PlayingWithTBI]

I have an '88 C1500 5.7L Silverado with 7747 ECM and 27FS512 chip in a ZIF socket and Moates Burn2, using TunerPro RT. I've been building it for a while and am in the process of tuning with the help of Dave w (thanks so much Dave). I'm thinking my next step would be Highway Lean Cruise for better mileage (currently getting ~14MPG), I live out in BFE, AZ where the closest Lowe's or auto parts store is 18 miles and I-10 speed limit is 75MPH (normally do ~80).

My questions are;
What kind of benefits has anyone gotten with this patch in MPH gained and/or, any issues (like meltdowns etc.)?
When I'm cruising @ 80MPH my MAP is ~51kPa where max for HLC is 37.29 in the Scalars table, Has anyone tried raising the max or am I gonna have to take the back roads (closer to 47kPa @ 60MPH)?

[Fast355]

I have an '88 C1500 5.7L Silverado with 7747 ECM and 27FS512 chip in a ZIF socket and Moates Burn2, using TunerPro RT. I've been building it for a while and am in the process of tuning with the help of Dave w (thanks so much Dave). I'm thinking my next step would be Highway Lean Cruise for better mileage (currently getting ~14MPG), I live out in BFE, AZ where the closest Lowe's or auto parts store is 18 miles and I-10 speed limit is 75MPH (normally do ~80).

My questions are;
What kind of benefits has anyone gotten with this patch in MPH gained and/or, any issues (like meltdowns etc.)?
When I'm cruising @ 80MPH my MAP is ~51kPa where max for HLC is 37.29 in the Scalars table, Has anyone tried raising the max or am I gonna have to take the back roads (closer to 47kPa @ 60MPH)?

My Express van has lean cruise enabled in the LS PCM that runs it. 16.5:1 @ 50 kpa, 16:1 @ 55 kpa, 15.5:1 @ 60 kpa and 15:1@ 65 kpa. With the 3.73s I cruised at 70-85 mph in the 50-60 kpa range on flat road turning 2,200-2,500 rpm. Running 5.13s and a taller tire with a bigger cam and 210cc heads I now turn 2,850 @ 70 and 3,500 @ 85 at 40-45ish KPA and have had no issue at 16.5:1 for thousands of miles. At that RPM and load 2,800-3,500 rpm I run 44-52* of timing. With the taller gears at 2,200-2,500 it was 38-42* It does not misfire but I also have the 24x coil per cylinder setup and Delco D585 coils. I am also port fuel injected with flow matched injectors.

[PlayingWithTBI]

Thanks Fast355, do you know what kind of gain in MPG you realized with the HLC enabled?

[Fast355]

I saw an honest 10-15% increase in MPG after. You will use more throttle to maintain speed and your KPA will increase for a given speed. Less vacuum means less pumping loss in addition to the leaner mixture. Before the cam, head, gear swap I was getting a fairly consistent 18-19 mpg running 70-80 mph. After the cam, head and gear swap with the full 1-ton running gear I see 17-18. My city fuel economy stayed about the same despite gaining 500 lbs.

[PlayingWithTBI]

Nice, what kPa limit do you have in your .bin Scalars?

[Fast355]

Nice, what kPa limit do you have in your .bin Scalars?

On the LS PCM it is a bit different. There is a whole table of air/fuel ratio vs RPM vs engine airflow per cylinder aka load. On the TBIs I typiccaly cutout lean cruise around 60-65 kpa. The engine will tell you when it does not like it. You will misfire long before you hurt the engine.

[PlayingWithTBI]

On the TBIs I typiccaly cutout lean cruise around 60-65 kpa. The engine will tell you when it does not like it. You will misfire long before you hurt the engine.

Here's a screen shot after I turned on the HLC patch, don't pay any attention to the MPH It still thinks I have 3.42s instead of 4.10s (or .8341 multiplier) I'm really doing about 81mph. the kPa limit setting went to 74.92 when I applied the patch. How does it look, O2, spark, kPa? It seemed to run OK...

HLC Dashboard.jpg