I agree. From what I remember the price difference is very little. If you are going to swap pistons, you might as well do rods... since you are doing rod bolts as well. If you are going that far than you may as well get a forged bottom end with good bearings, rings, etc.
Im sure you could make killer power on the stock LQ4 bottom end as long as you are intercooled and are running a good tune. I would invest the money in a good tuning setup before I went crazy with the motor. Are you planning on running an onboard WB?
I would think an LQ4 with 12# of boost, tune, intercooler, cam, maybe a little port work on the heads could get you over 500 pretty easily. From there its up to you as to how far you want to go.

 

Same problem here. Power adder in the sig. on a stock 5.3

 

11 psi, stock 4.8.

so far on my 6.0 project, stock crank and rods from a LQ 9, dish pistons from a LQ 4, with the stock 6.0 heads I will see a comp 9.48:1, the cam I have is from comp cams
.525 / .532 on a 114 lsa, not going any bigger I have to drive it every day, after it is all done with a tune I hope I will see at least 550 at the rear wheels

 

STS 8 lbs on stock 6.0. I just need to get traction under control. Last time i went to NPR i did some weight reduction ( pulled 5th wheel hicth out, tail gate and tools out of tool box) and all i did was spin tires.

 

I've been hearing this a lot. Is there any downfall to running the D1? This will be a daily driver with occassional towing.

 

Thanks for all your input.
Greentahoe-Thanks. I will probably be running a 3 core intercooler and very good tuning from Allen Futral. What is an onboard WB?

Pappydan-Why didn't you just use the whole LQ4 bottom end?

I've found a 2003 LQ9 with 22,000 miles for $1500. Sounds like a good deal?

 

10 psi, 6.0, twin turbos

 

That sounds like a great deal, but you will have to deal with the higher CR unless you change the pistons.
WB is wideband. Most just use them to get the tune initailly. Im still looking for one that will be on every time the truck is on so that I can always take a look at it to reassure myself that everything is good.

 

7 psi on stock 5.3. Soon to be 13 psi on forged 5.7 c.r. 8.8-1.

 

No downfall that I know of. The impeller blades have a curve in them and move more air with less RPM. Some people say that the P1 gets more boost sooner than the D1, but every dyno sheet that I've seen comparing the two says otherwise.