That's a difficult question to answer. We have never tried just a head swap on an engine. All the tests we have done have been in conjunction with performance cam and intake as well to optimize the performance capabilities of these heads. I'm positive that you will see an increase in numbers with just the head swap but I cant say how much. The flow numbers on these are fairly close to those of the AFR 165, and Trick flow twisted wedges that are currently on the market so gains will be comparable to those offerings.