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Anyone?

Nobody has used them or tried with big power?

Sorry I was gone for a while-

Yes they have been used with very big power- boostpowers 900- 975 & superlight 1000 use them.

Those are IMCO Powerflow PLUS manifolds. Water is introduced into the exhaust stream alot further down than in the plain IMCO Powerflow manifolds that I think Cold Sweat is talking about.

If any one has a set and needs a spare manifold or two spare SS risers, let me know. I recently pulled a set off my 540. The "bad" manifold has one of the screw holes stripped. It could probably be tapped or helicoiled, but is currently pretty useless to me.

I know this is old, but I tried to send you a pm about the risers (your pm box is full). If you see this, let me know if you still have em.

I've still got them. Just to make sure that you know which ones they are... they are not the PLUS ones. They're like these:
http://imcomarine.com/ca_store/image...it-02-8312.jpg

but they have the round holes instead of the triangle looking water passage...

What kind of power gains are usually seen with these thrown on a stock 502 efi?

Essentially.......none. You will not see any appreciable gains with just the exhaust. Most guys change them because they either want the look of aftermarket exhaust, the cast iron stockers are leaking, or they intend on future upgrades so they will need to be changed at some point anyway.
Eddie

Any exhaust out there where I would find some HP gains that would be noticable? I'd be happy just bumping my motors up to putting out around 500hp at the prop, but from what I've read there's not many if any options without new cams, heads & intakes, which currently will not fit n my budget.... Eddie I ever hit the lottery or accidently fall into some nice cash you'll be getting a call

Not really without tweaking the EFI.

My experience on a carb setup is that you will gain a modest amount of power. I used the imco powerflows (not the plus's I showed in the other post)

Your exhaust is the foundation by which all other engine mods stand on.