Yes, I know I'll need a retune for optimum performance, but will it be safe to run on the current tune. I'm assuming it will go lean because of the extra air getting in, but the computer should be able to correct right? Reason being, due to my exhaust leak at the header my gas mileage has gone to utter **** and I need to get these new heads on asap.

 

I would imagine it would atler your VE table, and your MAF table.... Also I bet you need to take a look at your timing, depending on the bowl work and compression you may get to add some timing since the combustion chamber is more effiecient or it maybe be the opposite you might have to take away some timing....

 

do you have a wideband?

 

Most definatly

 

the stage 1 ls6 heads dont have any bowl work done on them, but my compression is going up half a point

 

Assuming comparable combustion chamber design, increased compression would require a timing reduction.