Ok Deciding on new exhaust.

Boat 33, 10 meter fountain. Engines are 34in spacing.

509s, 580hp fully assembled on dyno @ 5800rpm,with dry short headers at time.

Boat is running imco powerflow manifolds which need changing & run the long stainless risers, The exhaust manifolds actually cover part of the exhaust ports (afr 305 heads) as heads have round ports and manifolds square ports.

Thinking of imco powerflow plus (bigger ports) with the long risers, cmi etops or even better keith eickerts.

Would like to gain a little top end if possible with the change.

Any thoughts. Any body done a similar change to eickerts and gained a few mph ? Boat runs 5500rpm with a little trim would be nice to get a few hundred rpm at same trim !!!

cheers for the info.

If you've got the height for the Kieth Eikerts cast header manifolds, for best power and torque I would consider those or the Dana Flo-Torques with #5 long riser. Just my two cents. In any event if you boat in salt you've got to flush any of them after every use.

Best Regards,
Ray @ Raylar

KE's are nice....I got a set with tails if your interested. Save some cash since you need two pair. Let me know.

I doubt you'll see any difference between the your existing exhaust and the powerflow plus. If you decide to change them I would go to something with individual runners like the dana's, CMI's or lightenings. I have Gils and CMI etops. TheCMI's have the 1 7/8 tubes and just barely clear 33" center. I originally planned to use my Gils until Dean Gelner told me the difference in power on the dyno with my application. Simular CI and HP as yours.
There are a pair of CMI's on the Swap shop that look pretty decent with tails for sale. Once again Raylars opinion on the Dana's would be a great improvement also. He has done a great deal of testing. It's all down to how much you can or want to spend. Individual runners will always make more power. On the gils and powerflows the inner two exhaust ports are married. As far as I know that still remains with the plus's. I had the lightenings on my 28 Challenger with twin BBC's years ago when they first came out and they were awesome. Made good power and sounded kick Ass.

Thanks for the input

Havn't measured the boat for the KE's yet, but will also look at the Dana and the lightning's. I cant find info on width on Dana's web site of there manifolds bolted up??. There #5 risers look a great product design.