How expensive would gas have to get for this to pay off?
Let's say your car currently gets 18 mpg, and that it would cost $1000 (on the low side) for the head replacement, and removing 50-75 pounds of weight would improve gas mileage by 3 percent (I think that's generous).
With gas at $8.00 a gallon, you would have to drive 80,000 miles to get your thousand bucks back. And you wouldn't want to swap out heads until your existing engine was out of warranty, right? So better be prepared to put 120,000 plus on her.
How expensive would gas have to be to make this deal pay off in a more reasonable 50,000 miles. Between $13 and $14 a gallon. And at that point we'll all be driving Fiat 500s anyway.
I love to run the numbers for people.......