sprink58

I want to compare notes with you on the 355. I have 2: fresh ones that I haven't taken past 5600 yet but they seem to still be making power. They made 425 at 5600 on the dyno with dyno headers and 750 Double Pumpers. Cams are Comp XM 272 with Comp Roller Rockers, Vortec Heads with Spring Pockets for the big Comp Springs, Edelbrock Air Gap, Stock exhaust. I figure I lost 25+ Horsepower on the install.

The boat runs great...75 so far on a short burst with 23" Mirage Plus thru Bravo I's

What is your set up...cam, intake, etc?

sprink58

Nice...has that nice "snotty" sound but not too radical...must be a Roller Cam.

79formula

I copied the 412hp build here exactly except my cam has 3degrees less exhaust duration and my cam is just hydraulic not a roller. Except the cam though I built my motor off the article. My compression is the same, I used speed pro teflon coated pistons, flat tops with 4 reliefs. And my intake is the air gap version. Here is the article http://www.chevyhiperformance.com/te...cam_355_build/

79formula

Sprink your 355s probably will pull to 6k. My cam is the comp xtreme marine cam 262. You have 10* more cam.

sprink58

Mine wind up quick !! I'm still running thru some old gas in my boat so even though I added a can of 104 Octane boost I kept my timing at 29* total at 3000 so as not to burn a piston or valves with crap gas. Even still...everyone is amazed how good it runs. I have a heavy boat (5600# dry) and i was wondering how the twin 355's would handle it. Let me tell you...with close to 900 ft lbs of torque in the water this thing jumps!! It cruises at 50~55 about 4000 RPM which is perfect.

when I pull up to the ramps everybody that knows in gawking at at Twin Bravo's hanging out of a '79 model boat. They're thinking "Big Blocks"...but when I open the hatches to reveal "Mouse Motors". They ask why Bravo's? The answer is 425 HP per side in a 5600 # boat is why!!

Once I get about ten hours on the motors I will drop the oil and start focusing in on the timing and carburetors. I have big block 800 CFM Q-Jets on it now and have a pair of Quick Fuel 750 Mechanical Secondary carbs waiting to go on. I put 12" oil coolers on both of mine to make sure everything stays cool. I run long distances down here hour after hour and can't afford a failure half way between here and the Bahamas!!

79formula

I have 10hrs on mine and have to change oil as well. I run 31* of timing with 93 octane. It really is pretty amazing the difference the vortec heads make.

sprink58

I'm old school and go back to the days of building 327's and 350's with "186" and "041" double Hump Fulie Heads with 2.02 intake valves. We thought 1 horsepower per cubic inch was incredible and the only way we broke 400 HP was with all sorts of wizard head work and cams that idled at 1200 RPM and wouldn't work with an automatic unless you had a 3500 rpm stall converter.

Vortec Heads changed ALL of that and sort of makes it all look "cave man" in comparison., Hell... stock Vortecs out of the box are better than Darts from the '80's that were thought to be the best that ever could be.Vortec heads changed everything. As good as the Vortecs are...these new LS motors are even better..6 bolt main bearing caps and heads that have intake ports the size of a pack of cigarettes!! I have one in my Cadillac Escalade and it snatches that 6000 Lb box around like it's nothing!!

In any case..for our use...Vortec Small Blocks make 400 HP a reality as well as Fat Torque curves that are right there with most Big Blocks. Lot of bang for the buck!!

Danielsosa

I'm new to the boating world I have a 1985 formula f-18 when I took it out to the lake it started over heating what could be wrong any help would be highly appreciated?

sprink58

It's not getting cooling water. I would change the drive impeller and try it again.