550 hp seems a stretch for a Wieand 142 on a 350. They advertise a boost of about 100 hp. I think 400, or maybe even 450 is realistic, but 550 sounds suspicious.
Did you actually put it on a dyno? Or is that an estimate?
Please be careful with manufacturer's claims for hp gains. For example, spark plug companies that claim a 25 hp gain are usually lucky to see an improvement of 1 or 2 hp. K&N claims 10% gains, but you might actually only see about a 5 hp improvement. Headers gain a lot, but it's usually in the 25 hp range, not nearly what they advertise. And when you add everything together, they are almost never exclusive, meaning, its more of a package improvement. Instead of seeing a 120 hp improvement by adding all the manufacturer's claims individually, you might only see a total of a 25 to 35 hp improvement from the combined effect of all of them.
Another good indicator of true horsepower is the trap speed at the end of a quarter mile. Not so much the elapsed time. That has too many variables, such as traction, reaction time, tire size and gear ratio. But the trap speed rarely lies. There are programs you can enter your trap speed and the vehicle's weight with you in it, and it will tell you how much hp it took to acheive that.
A friend of mine has a 350 with a 142 blower on his truck, and it feels real good. So I have no doubt you've got a sweet motor there...
