I have a set of heads from previous build that included stock lq4 heads milled .40, ported and polished, and 3 angle valve job. I want to use these heads on my 2006 Denali with LQ9 but I'm unsure of compression ratio. Will I be safe on pump fuel still with the increased compression from lq4 to lq9?

 

I'm pretty sure that aluminum 317's milled 40 will yield somewhere in the neighborhood of almost 11:1 compression (maybe 10.9?), I've read a few threads in reference to this over the past few months, but I'm not 100% sure. What you really need to figure out is your dynamic compression ratio, which will vary depending on cam selection. Either way, I'd think that even with the stock cam you'd be OK as long as you ran 93 octane. I'm no internal engine guru by any means though, so hopefully one of our experts will chime in.

 

I will be using Comp cam XR275HR.

 

My semi-educated guess is that you'll be fine, but as I said before, I'd wait for the guru's to chime in.

 

HELP Experts!!

 

That will put you a lil more then 11.1 comp with the 40k bore on a lq9. Stock comp on them is 10.1 Should be ok, but run good gas, a goood tune

 

definatly need a good tune on 93! Iwas told with a good tune you can run up to 12:1 but that's with a big cam I'm going to be running 11.65.1 with a smallish cam when I put my heads on (there sitting on the floor picking up dust) and my tuner told me he won't have a problem tuning for 93