How much will my new heads/cam and engine throw off my old tune?
 

Just about to start up my new forged 347ci engine with PRC CNC Ported LS6 heads, MS3 camshaft.

Before I did all this I had a stock shortblock with stock heads and a FM14 camshaft and had it tuned by ESP.

Anyways I know I will need to retune ASAP but just wondering how badly all my new goodies will throw off my old tune?

MAF or SD?

If you were tuned via SD, theres no way the computer will see the extra airflow since it was calibrated to the smaller setup. This could potentially cause you to go lean. If you used the MAF, the MAF will read the extra airflow and therefore add the appropriate fuel for the extra airflow.

pshh I have no idea how it was tuned. It was tuned with LS1edit on a dyno, that's all I know. I guess I'll just have to wait and see how it runs with the old tune for now.

if you still have the maf sensor it was maf tuned,if not it is sd.

Not necessarily. I set my maf fail freq to 0 when I want to do some SD tuning for my VE table. I dont have to take it out.

Although, freaky, youre in NY, so youve got OBD-II testing, so they probably would have left the MAF active for that reason.