So I have the option of going between lq4 and lq9. From what I recall the LQ9 has a different piston than the LQ4 giving it a different compression ratio = more punch(?)

I planned on boring the engine out and buying new pistons, rods, etc. so would the LQ9 really have any advantage over the LQ4 if I am going to just bore it out and swap new stuff into it?

I am relative new to this still so if I have some information incorrect please feel free to correct me. I just thought that the only reason the LQ9 had more hp and trq than the LQ4 was because of the pistons and if I was to bore it then I would need new pistons and rods anyways? Meaning that the $600 extra for the LQ9 would be moot correct?

 

Correct!!!

Don't waste the money up front if your going to bore it.

The LQ9 is a flat top piston with about a 10:1 compression.
The LQ4 is a dished piston with about 9.5:1 compression

 

Thank you, could not find any info on this and I planned on getting the engine bored still in the planning phase though

 

Yeah the only differences between the two are the pistons and the LQ9 has a slightly more aggressive camshaft to take advantage of the higher compression ratio. All LQ9 rods are stronger than the LQ4's and come with full floating wrist pins. The later LQ4's started coming with the better rods around 2004. That said there is no advantage with buying expensive aftermarket rods until you're making big power around 900+ wheel hp. In most cases the factory LQ4 rod will be strong enough. My LQ9 has the factory rods and I drive pretty hard with no issues.

 

So I’d probably just be buying pistons correct?

 

Yes no need to replace the rods unless you've spun some rod bearings or are looking to make BIG horsepower. Just have your machinist that's doing the block check the factory rods for any issues.

 

There is no difference between the lq9 camshaft vs. the lq4 camshaft, they are the same. I also believe the connecting rod change was across all engines starting sometime around 2004 and that first gen lq9's weren't "stronger" than the lq4 counterpart.

 

Building a 6.0 soon and I'm torn between using lq4 dished pistons with 243 (smaller chamber) cylinder heads OR flat top lq9 pistons with the 317 (larger chamber) cylinder heads. I don't want crazy high CR that will require Premium 91 fuel, which is why my two choices are one or the other, but NOT flat top pistons with 243 heads. I have both sets of heads already so I can go either way.

Are both options equivalent in a daily driver application or is one advantageous over the other?

It seems like the 243 head is higher regarded for it's flow characteristics vs. the std. 317 "truck head." True?

Thank you.

 

it depends on the year. Earlier LQ4s have smaller cams than later ones

 

The 243's and the 317's flow about the same and since you're not building a high performance engine... I'd save the 243's for a future build or sell to fund the current build.

Correct on the camshaft specs. All LQ9's were equipped with the better rods with the dimple and floating pins even with the 99-00 iron head LQ9. The LQ4's had the better rods 2004+

I pulled and cleaned the 120,000 mile varnish from the pins & pin bore during my build. I trust these rods more than the standard GEN III rods... enough so I just upped the rev limiter to 7000 today after banging off the 6500 limiter earlier today