Black Box Horsepower Upgrades

[Flamehara]

I am due for an engine rebuild soon, 1997 Tahoe 2dr 5.7L approaching 250,000 miles, and I want to explore the possibilities of sticking with the stock PCM. As far as I understand it, many mild modifications can be made to the engine such as a marine cam for horsepower upgrades. I am curious if someone knowledgeable would help steer me in the right direction for the best course of action of getting up to ~350-400 horsepower and whether or not that is something that the ‘black box’ can handle, and specifically, what are upgrades I can get away with while sticking to the antiquated PCM. I have looked into 0411 swaps, and I have one from a junkyard because the upgrade interested me, but this is my daily driver and I’d like to have it back on the road as soon as possible and I’d like to tackle one roadblock at a time. I appreciate any insight

 

[L31MaxExpress]

Tackle the PCM upgrade first. Very little needs to be altered in the van tune to run a stock L31. Big difference in performance just from a properly tuned 0411 or P59 swap.

 

[L31MaxExpress]

For comparison sakes this was the difference in my mostly stock L31/4L85E with a 3.42 gear before and after a good tune. Both the same 0411 which actually ran better than the Black Box stock tune for stock tune. A good tune really wakes up the 350. Mine had shorty headers, high flow cats, freer flowing muffler, the EGR diffuser removed off the throttle body and streamlined intake ducting at the time. Fueling was pretty much spot on but the timing was a bit retarded with the increased airflow from what a stock 0411 runs a L31 timing wise.

Stock L31 0411 Tune

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Tuned 0411

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[Cadillacmak]

I am due for an engine rebuild soon, 1997 Tahoe 2dr 5.7L approaching 250,000 miles, and I want to explore the possibilities of sticking with the stock PCM. As far as I understand it, many mild modifications can be made to the engine such as a marine cam for horsepower upgrades. I am curious if someone knowledgeable would help steer me in the right direction for the best course of action of getting up to ~350-400 horsepower and whether or not that is something that the ‘black box’ can handle, and specifically, what are upgrades I can get away with while sticking to the antiquated PCM. I have looked into 0411 swaps, and I have one from a junkyard because the upgrade interested me, but this is my daily driver and I’d like to have it back on the road as soon as possible and I’d like to tackle one roadblock at a time. I appreciate any insight

It only took a few hours to 411 swap my 97 K2500 Suburban, and it ran fine off of the base tune!

 

[Cadillacmak]

Mine had shorty headers

Do you get any false knock with those? I had some timing retard around the 2400 to 3600 rpm and .48g -.52g MAF, pulled a few degrees out there and it didn't change.

 

[L31MaxExpress]

Do you get any false knock with those? I had some timing retard around the 2400 to 3600 rpm and .48g -.52g MAF, pulled a few degrees out there and it didn't change.

If I did it was overshadowed by the false knock from the 4L65Es geartrain in 2nd gear. 4L65E died about 4K miles later and I did the 4L85E swap. Knock retard mostly went away with the 4L85E swap. What was left was actually one of the heat shields in the engine bay had broken loose and was touching the header. Got some new larger retainer clips for like a BMW application, resecured the heat shield and the false knock went away.

 

[L31MaxExpress]

10 is a tin metal heatshield it has actually worked loose twice. First time I put new stock retainers on it and they fell off again after the 383 was in it. It was held in place by the garbage Saab retainers GM used. Looked up the number and it was a Saab part before GM started using it. 2nd time I found the much thicker replacements (VW/Audi not BMW as I stated earlier). As soon as I re-secured the heatshield off the headers I stopped getting false knock retard both times. The shield was actually touching the header tubes because it fell and was resting on them. What I learned there is even a rattling heatshield is enough to make the knock sensor pick it up.

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OE GM garbage clip that was much thinner and smaller in diameter. Most of them had just fallen off and vanished and others were loose and missing some of the tabs.

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Whoever would have thought an Audi/VW part on a GM would be a signifigant upgrade, LOL. I replaced every one I could get my fingers on with this clip and they have held tight since.

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[L31MaxExpress]

The heatshield actually threw me off even. At higher rpm the rattle it makes contacting the headers actually sounded a bit like actual spark knock too. I had the timing down in the high teens though with the AFR in the low 12s and it was still doing it. Decided to look into what it actually was and found the heatshield resting on the header tubes. The offending shield on the van is just below the red mark I added and wraps around the back 3/4 of the engine bay. I had a factory clamped on exhaust heatshield on a Nissan product cause massive knock retard once too on a 65K mile car. Re-secured it with a large hose clamp and the car had far more power. A failing catalytic converter with a loose catalyst brick can also cause knock retard. Ran into that on a 5.3L Tahoe.

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[Cadillacmak]

The heatshield actually threw me off even. At higher rpm the rattle it makes contacting the headers actually sounded a bit like actual spark knock too. I had the timing down in the high teens though with the AFR in the low 12s and it was still doing it. Decided to look into what it actually was and found the heatshield resting on the header tubes. The offending shield on the van is just below the red mark I added and wraps around the back 3/4 of the engine bay. I had a factory clamped on exhaust heatshield on a Nissan product cause massive knock retard once too on a 65K mile car. Re-secured it with a large hose clamp and the car had far more power. A failing catalytic converter with a loose catalyst brick can also cause knock retard. Ran into that on a 5.3L Tahoe.

That is a lot of good information that I didn't think about. When I get back to that truck, I will take a close look at things.