mercwizard

Gents.....I posted earlier on an engine vibration with the 454 mag in a Cobalt 252 I bought this past winter. Boat originally had a Gen IV motor and was re-powered with a Gen V motor and the Gen IV flywheel was reused. This was the cause of the vibration. Soooo.......

While the motor is out of the boat, I got to thinking......

Money + speed addiction = a new Gen VI Bowtie CNC block sitting in my shop. Wow.....these bowtie sportsman big blocks are a work of art. I have used Dart Big-M's on a few occasions, but, the machine work on these CNC bowtie blocks looks to be a cut above. Finish hone to 4.500 and done.

Built a lot of big inch street motors, but, a newb to the marine environment. Please help me with any tips on getting this build done quickly and correctly....especially any experience using late model bow tie blocks in marine applications.

More than anything else I want RELIABILITY and not to have to f@ck around with this boat constantly. As I do with my occupation (I am a Design Engineer), I will overbuild the engine to a near ridiculous degree thereby assuring a large operating envelope and long lifespan for components. The short block is all forged....Scat 4340 crank, Scat 4340 Rods, SRP 4032 forged pistons, King bearings.....good stuff.

5500 max rpm......probably more like 5000. Likely for no more than 5 minutes at a stretch. I live in Illinois (Inland lakes) and will never be on the great lakes or big water running flat out for hours at a time.

Top end is Quickfuel 850 sitting on a Weiand Stealth dual plane (the new design). Current fuel system is newer Carter marine pump (75gph), mercruiser water/fuel separator filter....smallish looking lines.

F.A.S.T dual channel LCD display monitoring wideband o2 sensors on each manifold. I have this setup ($400) on both of my street cars. Immensely helpful with carb jetting and cheap insurance against running lean at WOT. ebay has o2 adapter sandwich plates that mount between manifold and riser. These work? Leaks?

Boat already has Tbolt IV ignition with MSD6A. Stock distributor looks new, and I have a hardened gear for use with steel roller cam.

I need help on head selection, exhaust, and rigging. Various items to consider:

Would prefer aluminum heads.......gut tells me with 540 cubes around a 320 runner is probably close. Key requirement is reliability.....no dropping valves or broken valve springs. Iconel exhaust valves required?

I want no issues with reversion.....especially with the stock y pipe. I have a Comp Cams XM284HR on hand from a truck motor. This is a marine cam and seems a good choice for a 540 with 230/236 @ .050 and .547 lift......any issues with reversion using this cam?

The boat came with a set of new GLM aluminum manifolds and 4" risers. I just had these surfaced to prevent leaks at the riser manifold joint. Use or don't use? Recommendations?

Through prop or through hull or both (Captains call)

The 454 mag currently has a remote oil filter mounted to the port side riser....I like this setup. Larger lines, or stay with stock lines?

Oil bypass valve in block? Whats the deal with this on a bow tie block.

Oil cooler size. Stock Mercruiser or larger aftermarket?

Please allow me to tap the vast pool of knowledge here.....I will repay in kind at some point. Tips and recommendations no matter how small are most welcome.

the deep

iTrader: (8)

I am also listening and waiting for wisdom .... Welcome to OSO wizard .

HTRDLNCN

I had brand new GLM/Hardin aluminum manifolds from CP Performance
(GLMs sold as Hardins)
leak internally and kill my just rebuilt 502.. They are junk..

With stock style manifolds and a y pipe I would make sure your camshaft overlap lsa is around 114 to prevent reversion

With the O2 inserted bewtween the manifold and riser it isnt gonna last long, my advice would be tune it and then remove them.

stlliberator

iTrader: (1)

Thats alot of motor to be building for a 252 cobalt..and what outdrive are you going to be running? Im not sure your going to want to run the y pipe, you might just want to stick with switchable mufflers, just for the reversion issues.

Trash

Not necessarily true. I'm utilizing the Wags Engineering O2 spacer with an Innovate wide band and gauge over the last 70 hours running time with no issues. No leaks and the wide band still works. Innovate makes a nice insert which protects the sensor from downstream water should reversion be an issue.

HTRDLNCN

Interesting, you have a link to this?
Thanks..

Philm

320cc heads should be fine. Dart/AFR/Brodix are all good choices. I know that Dart has a hard coating for the water passages that is highly recommended for open cooling.

Definitely use Inconel valves.

850cfm carb should be enough

That cam isnt very big for a 540, but you are talking low 5k rpm range so it could work.

Plug the oil bypass in teh block if it has one. My Dart Big M did not have one.

Big oil lines.

Big oil cooler, a 3" x 18" tube style should work just fine.

good luck.