My 454 Magnum MPI has needed a valve job for a while now. A compression test by my mechanic showed two weak cylinders (#2@30 & #5@70) and although the engine has performed flawlessly (except for a rough idle and less-than-max RPMs) during the last 40 hours, I think it’s time to move forward and get the work done along with a tuneup.

Other than performance restoration, my objective is to stay somewhat “stock” yet obtain a solid 385-400hp with cost and reliability being a key factor. Since there is some corrosion on one of the manifolds, I am considering replacing the stock manifolds and risers with Revolution Marine’s polished aluminum product, primarily because of the appearance. Although I boat exclusively in saltwater, the engine is flushed completely after each use with SaltAway included every third flush. With this increased exhaust capability, I was thinking about replacing the stock flame arrester with a K&N version to hopefully allow an increased airflow through the MPI. I am assuming this simple exhaust modification, along with restoring all of the cylinders, should bring the engine to the 385-400hp level.

Do you think my assumption is correct ..... and
is the use of an aluminum manifold on a saltwater boat a mistake?

I went w/ Stainless Marine Gen2 manifolds.
Come w/ a 5yr warranty. Great Quality, just not the prettiest.
Salt water use only for me.

Thanks Stormrider
Did you notice an increase in performance with the Stainless Marine manifolds?

Well, i did a full performance rebuild to a 461ci and 560hp & 550lb/ft.
So i'd have to say yes.
My engine was also very tired prior to rebuild.