How much will headers make a difference ????
 

I have a 496HO with a Whipple in a 28 Nordic heat and a XR drive with stock exhaust running 5 pounds of boost. I just order some lighting headers to help the motor breath a little better. How much do you think it will add hp and rpm??? I dont know if I'm going to have to get my prop tweeked or not or how much it will really make a big difference. I could use maybe 100 or 200 rpm but I'm close to the rev limitor now. It all depends on how much I trim up. I would think that If I trim up a little less and gain maybe 200 rpm that the boat might get 2mph??? I know that the stock 496 exhaust is not the worst stock exhaust out there for stock but its not a good as headers. I really dont know what to think about it, but I hope is sound way BETTER. And frees up a little hp! What do you guys think. "Lets try to be real about this" no stretching it . Real world answers.

O yea I run a 26p p5x right out of the box 5300 to 5400. Rev it set a 5450.

I doubt they will add enough to make much of an HP/rpm difference on an SC's engine. On an SC'd engine, the SC just makes more boost pressure and forces exhaust out. You may see the same or 50rpms more and maybe .5 less #'s of boost.

problem with most boat headers especially if they use the stock
piping is they are not really headers, just fancy looking tube manifolds. Most people get them for the bling factor more than anything.
True equal length long runner headers are very expensive and a royal pain to use in most boats that are not race boats. KE's are probably the best real header compromise in a pleasure boat but most dont like them because they dont look "cool" .

Dusten at Whipple told me that I would loose 1 pound of boost from freeing up back pressure. So I also got a new pully that is 1/4 inch smaller to keep the boost at the same level.

So does that mean that I will gain 1 pound of boost worth of power?? Or not because I'm still at 5 pounds??? Thanks for all the info.

You should gain some power from the pulley switch. Maybe 20hp or so, I would guess. You will be pushing more air/fuel through the engine, just with less resistance.

If you are moving more air and fuel through, you are making more power.