Tommy, here are the Dyno Runs and build specs on my 355s:

SuperFlow
Dynomometers and Flow Benches
SF-902S

355 MARINE CHEVROLET Result Summary Date 12-20-2012 1:46 PM Temp 80 Deg F. RH 74%

RPM TQ* HP*
2600 399 198
2800 408 218
3000 421 240
3200 430 262
3400 436 282
3600 440 302
3800 444 321
4000 448 341
4200 451 361
4400 450 377
4600 443 388
4800 438 401
5000 431 410
5200 421 416
5400 409 421
5600 396 422
5800 373 411
Max 452 422
Avg 426 339

* Test Exhaust 1.5" Diameter Dyno Tester Supplied Headers.

355-cid VORTEC SPECS

Bore / Stroke / CID: 4.030 / 3.48 / 355 cid
Compression: 9.4:1
Block: GM factory four-bolt 350 L-31 VORTEC
Crank: SCAT forged-steel PN 1101-11133
Pistons: Probe forged (PN 130212334-030)
Rods: Probe (PN 1201-10062) 5.7"
Rings: Total Seal Moly
Bearings: Clevite
Gaskets: Mr. Gasket and GMPP
Cam: COMP Cams (XM264HR) 212/218 at .050, .488/.495 lift, 110 LS
Lifters: COMP (PN 875-16)
Chain: COMP (PN 2100)
Pushrods: COMP (PN 7372-16)
Rockers: COMP 1.5:1 (PN 1417-16)
Heads: GMPP Vortec (Scoggin-Dickey PN SD8060A)
Manifold: Edelbrock Performer RPM Air Gap (PN 7516)
Carb: Demon (PN 1402010VE)
Distributor: Davis Unified Ignition DUI-7000
Spark Plugs: Autolite AR103
Oil System: Milodon HV (pan PN 31505)

I bought the motors complete less water pumps, ignition, carbs and fuel pumps for $4500 !! A Hi Po shop in Pompano had built them for the owner of a 27 Ft. Pachanga. His charge was $10K for the pair. He put $5K down and never came back. I had to basically finish all the externals including starters so I guess I spent another $3500 total including oil coolers and exhaust. From scratch it would cost between $10K~$12K to reproduce what I have motor wise.

I thought about raising the motors to get a shorter "X" Dimension but the boat runs so good I never did it. It will run 75 GPS at about 5200 RPM without a whole lot of fooling around with trim...I've scared myself a few times approaching 80 and backed out of it....this old hull was never intended for those speeds. It feels very much like my 272 did up until about 65. Beyond that it feels heavier...probably because there is a lot of hull in the water...very deep freeboard on these 255's. I'm running twin counter rotating 23" Mirage set up by Jimmy's in Ft. Lauderdale.

This old heavy boat with that power will cruise 35 at 2200 RPM !!...50 at 3000. So I can run around all day at 50~55 on the primaries....stab the throttles and it jumps to 65.

Honestly...it's a bit over powered. Lots of times I've been out and wished I had 6' more of boat under me !!! LOL

What kind of money you have into the long blocks ? You buy them pre assembled or have them built?

What kind of speed you end up with?

I edited the post with that info...

I agree. My old SBC setup's used to raise some hell!

https://youtu.be/fyKTqEhzfCc

How does the boat go with that power? Any issue with taking that much weight off the stern?, I found they can get unbalanced/bow heavy. What did it run before, a friend has that boat with a 502 and runs 63 or so.

With the 454 the boat ran upper 50's and saw low 60's on one or two occasions with just me in the boat, 40 degree air and running on fumes, lol. I haven't had the boat wide open with the new set up yet. I spent a lot of the summer fighting my reversion issue. Once I got that all worked out, I babied the boat for awhile just making sure everything was working right and the engine was properly broke in. I designed the cooling system myself, so I wanted to make sure everything was ok with it, which it was, and I also was trying something a little different for my power steering, so I wanted to make sure it was working properly. Once I was ready to really start hammering on it, I developed a water temp issue. The temp issue ended up being a blown starboard head gasket. I originally thought it might have had to do with the reversion, but we have since found out that it was most likely due to a faulty MAP sensor that didn't let the ignition retard the timing at low rpms. My guess is that it was detonating while I was getting on plane, but between the dry exhaust and the hatch, I couldn't hear it. This is why I will be re-dynoing it this spring. I'm going to try a different style MAP sensor. I have also picked up a set of Drew Marine Shotgun Mufflers that I am going to run. I have identical twin 3 year old girls, and while they love loud boats, with the dry exhaust, its a little too loud with them in the boat.

As far as handling goes, I haven't had it up to speed yet, so we will see. However, just cruising around, the boat feels great!! Brett from BBlades doesn't think the weight loss out of the stern will be an issue at all once we get the prop figured out. He's thinking a worked Bravo will make the boat handle just fine and should push it into the upper 70's, maybe knocking on 80 in perfect conditions. I will say that you can definitely tell I have cut a lot of weight out of the stern when the boat is setting idle. This past summer at the Annual Checkmate Owners Rally at Lake Cumberland I tied up with a buddy of mine who has the exact same boat, even the same year, that is running a hp500, and the back of my boat sat about 2-3 inches higher out of the water than his.

Cool, good luck with it and have fun

Just saw on finnegans garage his LT4 weighs 461lbs. With some decent exhaust and cooler air coming in that's easily a 700-750hp boat motor. The only reason we aren't seeing the LS in new boats is that the performance market is dead.

My 33 Apache has twin 350s in it top speed 65 in rough water. Have 2 M&W turbo kits all the parts except bonnets for the carbs. Thinking of selling the boat and parts though from time to time.
Economy beat out my 7.4 in my Sunsation Agressor while apache was travling at a higher average speed

The LS's being used in Seven Marine outboards and I think Volvo just bought that company,