Building a pair of 548 NA motors for my own boat, should touch 800 hp. Knowing they will fall off the face of the earth with "typical" performance manifolds once installed in the boat (too small of CSA/runner ID) , My choices (and budget) are limited. going to dyno with the manifolds on once motors on my dyno and everything's happy. Cant spend 20,000 $+ for new big tube headers and tails, eickerts are too small and on back order anyways, stainless marine 3's are physically too big and I'm NOT going to buy some used big tubes that been repaired. Looking hard at Imco power flow plus, 2.25 ID runners, around 28 to 33" total runner length depending on what risers you choose and the 8500 or so for 2 pairs and tailpipes is IN my budget.
Who's used them, cant find hardly any mention of it on net anywhere
prefer to use the 85 degree or 30 degree tails to keep internal length LONG
IF you have used them, which risers did you use for your Bravo boat?
https://imcomarine.com/cal_store/cat...t-kits/id/118/
Thanks for any info, Smitty

Why aren't Lightnings on your list? I have them on my boat and they are now 22 years old and still mint. Yes I have pressure tested them and do inspect them regularly with my boroscope. They are long tube with a nice long collector before the water is introduced. They look to be the best performance option for a boat out there that isn't insanely expensive.

I’m curious to see how those run. Would like to see them compared to eickerts too. I suspect eickerts are still the best for your application though.

I havent been able to get a set to test, at 1 7/8 id seem pretty small for a little bit bigger, higher reving NA motor, when I sim it, they add a little tq and kill a bunch of hp. The powerflow plus at 2.25 id vs 1.875 with runners same claimed length seems like a great candidate, cant barely find anyone that has used them with any real world answers as to how good they actually work

Are you running the standard ones or big tube? I get the impression the big tube version wont fit my twin engine boat, when I ran the standard ones in past on my own boat, i gained pretty much zero at wot,ended up going to stainless marine 3's, the last boat I tuned that customer bought the standard ones for reverted water all the way to back cylinders and killed 02 sensors left and right trying to tune it. We extended the inners quite a ways and still had terrible reversion problems with tiny cam in mid 230s, Im going to be running cams in the 250/260 range and dont want the reversion drama. I suppose IF the big tubes fit a standard spaced twin engine boat and were dry enough they could work. The next dilemma if I go that route is i would need to put engines in boat (which are no where near being ready to go in) and get exact measurements as their headers are cutome built. IF I dont see the results with them Im looking for, I now have s et of headers to sell that were built for my specific boat (vs a set of manifolds that could go on any boat) Smitty

Id guess youd need a 2 inch ID to get to your hp goal

pipemax shows 2.25. When you burn 40% more fuel, (alchohol), it takes up.more space, i ordered a set of eickerts 4 months ago, I'd dyno with both and sell.the loser but with covid, diamond cant get any manifolds to sell.

Might give Fred a call at IMCO to get additional data. They are good to work with.

I just spent most of the day changing and indexing plugs and winterizing my boat and your right, the big tubes won’t work on a side by side application. But they work really good on my single. I have a really big cam and have zero problems with reversion. My collectors are pretty long they almost reach my transom. I’ve run Dyno-Sim and Pipemax when I was rebuilding this motor and the big tube lightning where the best option for me. Next boat will be staggered. Can’t imagine changing/indexing plugs on a side by side.

What size is your motor now?