Any dyno tests with Imco Powerflow exhaust system for the 496HO? Had them on my 454mpi in my old boat and I loved the look and the sound. Considering upgrading my exhaust manifolds--DANA, CMI E tops, IMCO. Can't decide!!

The stock Merc exhaust is pretty decent on the 496's. I've not tested any other brands of exhaust but I'd be surprised if there was much improvement over the stock exhaust with turbulators removed. I've got a couple of 496 builds going on this winter if anybody wants me to test some other manifolds, I'd be glad to try them.

Different engine packages can use different header units
 

Imco's Powerflow manifold and riser combination with the seperate exhaust ports in the riser are a very good manifold design and should be similar in power to the Dana and CMI sporttubes in power levels. The problem with the Imco units is these 4 tube risers are quite a bit taller than the Dana, CMI or even Merc stock risers and may be a hatch clearance issue on a lot of boats, not to mention they are not yet set up for a kit that remounts the brackets, sensors, remote oil filter, ecm and such an an install would be a lot of custom fabrication and cost on a Merc 496 engine. Keep these issues in mind when converting the exhaust on a Merc or Volvo 496 in any boat.

Best Regards,
Ray @ Raylar

I believe Ray is refering to the IMCO powerflow plus exhaust. These and the Stainless marine Gen III manifolds seem to make excellent power from what I've seen. But like Ray said, they don't have a turn key kit to fit the 496. I was thinking along the lines of the regular powerflow, thumper, eddie mairne and stainless marine systems not being much of an improvementover the stock Merc 496 manifolds.

Sorry dont mean to hijack the thread , do you guys know if the intake and timing cover gaskets are reusable on the 496s ,and can the timing cover be removed with out dropping the oil pan?merc and gm manuals dont mention oil pan removall,
thanks and sorry about the questions,
seems you guys have knowledge on the 496s

I do know that the intake gasket is reusable but,I do not know if the timing cover is i would guess not.

Yes all those gaskets are reusable if you are careful during disasembly and yes the timing cover can be removed w/o dropping the oil pan.

Just read this whole thread and it was very interesting. Especially the part about the turbulators. My thoughts on this are I wonder if instead of removing them entirely, trim them down so that there is roughly 1/8"-1/4" of the "lip" left on them to capture any condensation that might form and still letting the exhaust flow better.

Seems reasonable, maybe I'll test it out. I'll be dynoing an engine next month with stock exhaust. Of course it's just a guess as to how much material you'd have to leave to be effective?? I've never had a problem with them removed, so you really wouldn't know if they were doing any good. I'm tearing down an engine that has about 400 hrs running without turbulators. I'll give it a close inspection for water damage.

Obviously the aftermarket headers don't have turbulators so what is used for protection or is it a non issue with anything else other than factory merc manifolds?