engine swap questions

[04sierra25hundy]

i have an 04 sierra 2500hd with a gas 6.0l LQ4. i have to replace the motor becuase the block has a small crack by one of the head bolts. so i need to swing a new motor in it. i have a few questions about my options. where is the best place to order a long block. i was thinking about upgrading to the LQ9. having a few more hp would be nice for towing. my question with tha,t is will my ecm work with an LQ9 engine or would i have to buy an LQ9 ecm or have my custome tuned. any help would be great. thanks

[Chris]

I went from a LR4 to LQ9 and everything stays the same, just custom tune. The difference in the 2 is just the pistons and rods. They use the same heads

[04sierra25hundy]

did you just send out your ecm to black bear and they tuned it. if so do you just plug it in and your good to go or do the keys need to be reprogrammed?

[Chris]

The shop did custom Dyno Tuning. I had Black bear change it with the Autocal handheld

[Badass69]

Truck will run fine with the LQ9 and the stock tune. That said it may ping more at wide open throttle with the LQ4 power enrichment delay and the LQ9s higher compression ratio. LQ4's will even knock on 87 occasionally because of this, not because of excessively advanced timing as the LQ4 is in a severe deficit that way over an LQ9 stock for stock.

 

The only difference that matters in the 2004 model year is the compression ratio between the two engines. Everything else is identical. For those wondering, if your 04 is a later build with the 13 mm valley cover bolts it will have the full floating pin rods of the LQ9. At that point the only difference between the two engines is the dished pistons in the LQ4 versus flat tops in the LQ9. That's it...... Otherwise they have the same cam, heads intake, injectors and all. Get a good custom tune on an LQ4 and an LQ9 and I doubt anyone could tell a difference. 0.6:1 compression doesn't account for much...

 

The horrendous stock LQ4 tune is the big difference with its power enrichment delay and 17 degrees of advance wide open. Yes I own both engines lol. Older LQ4's from earlier in 2004 and downward have weaker press fit pin connecting rods....... not that it will matter unless you are really throwing boost to the engine to the point they break, lol.