What speed rpm and sound gains are common for adding s.s. headers to a 502 mag mpi

I've had the same thoughts- the feedback I've seen is mixed. 20-30 hp seems to be the range on the black efi motors. This is hard to see on the GPS but you may get a couple digits out of it.

Unless you've got "tweakitis" or "Need eye candy" fever it is hard to justify the cost. On the other hand, if you are planning to keep the boat and a new big inch NA motor is in your future then you will be getting them down the road anyway so why not enjoy them now. It makes less sense for mild blower motors as their is less need for scavenging.

Now if you factor in corrosion of the stock manifolds depending on age and salt or fresh water environment the manifolds need to be replaced at some point anyway as part of maintenance.

Good luck

I gained about 300 rpm. This was with lightning headers, Precision Marine recalibrated ECU and a bigger flame arrestor from CP Peformance. I can not verify the accelration gains but it seemed to accererate and come up on plane faster.

Ijust pulled my stock exhust off, and installed stainless marine headers on my 502. I would have to say the stock exhust weights more than 22 pounds heavier. Also am very glad I did because I found signs of either a bad gasket or reversion on the port side. Ialso installed a new flame arrestor and new arizona speed ecu. Seems to have picked up 3-5 mph but has made the motor MORE responsive. I am still in the testing stages(trying to find the right fuel pressure) because it seems to load up on the low end. I only had 20 minutes to run last sat and could not make any adjs to the fuel pressure. I will probley buy a msd unit to help out on the lower end. That way I can adjust the fuel pressure higher and pick up some more on the top end and not worry about the low end. As in one of my earlier threads I will post my results. [/QUOTE]