A little back story, built this “boat” (http://www.offshoreonly.com/forums/r...oon-build.html) a few yrs ago and thought I would be happy with the 4cyl (140hp) coming from a tune with 25hp. Well I I’m happy but I would like to have a cruise speed of 30mph not a WOT speed of 30mph.
I started looking around a bought a complete boat that was rotten out with a running 350 sbc in, but after doing some more thinking I like to be different I thought why not do a LS instead of a SBC. I picked up a 5.3 out of truck with less then 80k on it. Everything from flywheel to accy including wiring a computer.

I’m sticking with EFI as that will be really nice when just cruising along at Idle have a few adult drinks.

It seems LS marine manifolds are hard to come by and are not cheap, Looks like I will be making my own water cooled heaters along with risers.

Computer still a little unsure off but should be able to get 02 Sensors in the headers someplace.

What else I’m I missing?
Anything I should be aware of with these motors?

The crusader manifolds are not too bad and they are made similar to an ls7 manifold. unless you are trying to eek out the last 10-15hp don't bother with making your own headers. But if that were the case you probably would have started with a 6.0l, maybe make you own risers like the guy with 5.3l's in 24 skater.

Where can one find the crusader manifolds did some searching and didnt come up with much besides they are out there. My other reason for making them is cost, I can fab up s.s headers for alot cheaper then I can buy cast one for.

try to find manifolds, and yes you will need ones you can get a 02 in search the LS on here more info already on here...

http://www.skidim.com/prodinfo.asp?number=R028023

http://www.skidim.com/prodinfo.asp?number=R029016

http://imcomarine.com/cal_store/exha...-polished.html

http://www.marinepartssource.com/new...&mfgno=R028023

http://www.cpperformance.com/p-14931...manifolds.aspx

http://www.keperf.com/p-15856-gm-ls-...st-system.aspx

If you dont want to worry about the o2 sensors you can have the ECM given a custom open loop tune so its not looking for a signal from o2 sensors, a MAF, etc.

Thats exactly what I was planning on doing, not the "best" for HP but I'm pushing 3 giant logs thru the water.

Any one want to guess what kind of MPH I will see out of this boat with 300hp?

Right now with a worn out mid 70's 3.0l(140hp) with a 4 blade 16 pitch prop I see 28mph with me and the wife in it.

Yep, for what you are doing with it that's exactly what I would want. to do.

here is how to get a pontoon up on plane. wonder how much faster it would be without the living room furniture. https://www.youtube.com/watch?v=DLRwkrBZzsA

im gonna guess 60 mph.. here is one to vopy off of.. http://www.youtube.com/watch?v=8RhwmnWq6ZY