LQ4 Down On Power After Mods + Tune

[TurboSportTSi]

I recently bought a 2006 2500HD with 190k, LQ4/4L80E, 4.10s, and 32" tires that felt much slower than I expected, so I jumped into some basic mods right away. While it does feel a bit faster now, I don't think it's right. Judging by the Delivered Engine Torque PID, I'm barely making factory power (340ish at most). Compression is even, with about 8% total variance.

The truck came with a Spectre CAI and a non-aggressive aftermarket muffler, then I added a TBSS intake manifold w/ 36 lb injectors (retained the factory throttle body), and a TN/Low Buck Truck cam with LS6 style springs. The tune is pretty dialed, from what I can tell. I just changed to the LQ9 high octane spark table today (with more added at idle due to the cam) to see if I was just missing a bit of timing, and it seemed to make a slight positive difference in around town responsiveness, the truck still feels pretty slow and doesn't make any more max power. I have not been to a dyno, just street tuning myself. I do have a WB O2 in Bank 1.

PE has been changed, per usual. Injectors aren't anywhere near maxxed out, even with it going fairly rich up top. I have not verified the fuel pressure (have a new pump on the way, just to rule it out...because 190k...), but it is not going lean at all. Hardly ever sees KR, though it has some at low RPM/medium load knock with the LQ9 spark table that is never present with the LQ4 table. Running 87 octane.

Is this truck just that slow? Should I be making more power? I have a feeling that a converter and 4.56s are in my future, which I'm OK with...but I do want to make sure that the truck is in good working order first. A second set of eyes and some experience would be greatly appreciated.


Drive_20250706.hpl

WOT_20250706.hpl

20250706_LQ9 HiOct-LQ4 LoOct.hpt

[RDF1]

These things are no speed demons thats for sure. Mine prolly runs 18s in the 1/4 haha.

But really surprised as to not see any KR at 3400rpms and 29* timing at WOT.
But your timing is falling off to 22* at higher rpms.

The only way to have a decent heavy truck is boost. It fixes everything.

What is your elevation? I see WOT MAP KPA is 85 and falls off to 83 at 5500rpms

[Alvin]

You could be leaner in PE. There is too much timing in it IMHO especially for 87. Your altitude does come into play here a bit on this though.

[TurboSportTSi]

Good eye, gents. I live around 4,000' elevation. Not super high, but maybe enough to make a difference.

I will split the difference between the LQ4 and LQ9 spark table and see where that leaves me, unless you'd suggest just sticking with the stock LQ4 tables.

I'll lean out PE a bit, too. I wanted to err on the rich side early on, but it's fairly dialed now, so I'm not as worried.

Boost may be in the future, but I wanted to keep it simple, mechanically, as it's my daily and tow rig, not my hot rod. Not that I can leave anything alone!

[RDF1]

Good eye, gents. I live around 4,000' elevation. Not super high, but maybe enough to make a difference.

I will split the difference between the LQ4 and LQ9 spark table and see where that leaves me, unless you'd suggest just sticking with the stock LQ4 tables.

I'll lean out PE a bit, too. I wanted to err on the rich side early on, but it's fairly dialed now, so I'm not as worried.

Boost may be in the future, but I wanted to keep it simple, mechanically, as it's my daily and tow rig, not my hot rod. Not that I can leave anything alone!

Towing with turbo = mo better.

[TurboSportTSi]

Quick update: I halved the timing advance increase from the LQ9 table, leaned out PE a tad, and went on a long drive to run an errand. It got about 2-3 MPG better economy, according to the truck, but it had a bit of knock in spots. I just flashed 25% of the difference instead of half (unscientific, I know), which resulted in 1-2* increase in advance across most of the powerband.

Either way, it still shows about 330-340 peak torque. From what I've read that tends to be fairly accurate. I'm wondering if I'm seeing a few things compounded...if stock is roughly 360 lb-ft, and the mods add (for the sake of argument) 60 lb-ft, I should be around 420ish peak at the flywheel. If ~10% of the horses escaped from the engine due to age & wear, I'd be back around 380. If I lose another ~10% from elevation, I'd be right around 340 brake torque. Maybe I'm right where I should be, and the truck is just that slow!

If nothing in the tune stood out to you guys, perhaps this is a non-issue.

[Alvin]

You can't go on calculated torque. That assumes the rest of the tune is 100% dialed in.. and even then it's just a guess.