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Newb here, looking to turn a 502 into a 540, have questions

Old 03-15-2021, 03:46 PM
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Default Newb here, looking to turn a 502 into a 540, have questions

first time poster, short time lurker.

looking to build up a 502 in a 92 formula 27' this is a freshwater boat only for the great lakes.

engine is out of the boat and getting ready to tear down this week, its a 390hp version with a 2pc rear main block, flat tappet cam, 8.5:1 compression, qjet intake and carb hooked to a bravo 1 with a captains choice exhaust. ran about 4800rpms max

no real power goals here but to wake it up, i picked out some parts but from research it seems there is varying opinons,

the stroker kit i plan on using is from skip white, ive used his 496 kit in the past and am happy with it, scat 9000 crank, scat 6.385 rods, wiseco hypereutectic pistons.

do you absolutely have to use a forged crank? millions of chevys were built with cast cranks, this isnt an all out race engine.

heads- debating between a 290 oval port or a 320 rec port, probably gonna go with promaxx, open to suggestions. this is a fresh water boat only.
is there anything wrong with running aluminum heads in freshwater, do I absolutely have to use iron heads for some reason? are inconel exhaust valves an absolute must?

cam- what is the rules of selecting a cam? I seen its recommended to keep the lsa at 112 or wider, whats the recommended duration range, and duration split? stock cam specs are 224/224 .510/.510 115.5 lsa flat tappet
i have an edelbrock 7162 cam on the shelf, 240/246 .560/.573 lift on a 112 lsa, in a 454 car that would be considered healthy but not overkill, at 540 it would be much tamer but what about in a boat?

intake- this isnt a high rpm screamer, do i go with an rpm dual plane style or single plane with that many cubic inches? does the coolant passages have to be brass or anodized coated? will those pipe thead anode rods work for cheap insurance?

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Old 03-15-2021, 04:35 PM
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Cast rotating assembly parts really have no place in a performance marine engine. They're fine with something that isn't going to spin more than 4k rpm or so. Asking for trouble otherwise.

If you do not have a specific power goal in mind, I wouldn't go the stroker route unless you needed to replace major parts. If the block is low hour and unblemished, you may even be able to get away with a hone of the cylinders. Polish the crank and replace the rods with a set of Eagle H-beams. JE/SRP makes a replacement forged piston that allows you to run standard rings. This would be a good foundation.

I like AFR heads but they come at a premium compared to others. Being you're in fresh water, aluminum is a good choice, but there are also good iron choices too. Budget will dictate. There is a whole bunch of information here on OSO regarding head selection. Grab some beverages of your liking and start reading. A 305/315 CNC AFR would make great power with the right cam.

Lots of reading to do on cams that will work with your choice of heads too.

I'm sure others will chime in. There is a ton of information to be found here.
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Old 03-25-2021, 07:37 PM
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Whether or not a forged crank is needed or not may be debatable, but I wouldn't want to find out for myself.
For heads go 320, you won't miss any lost low end in a 27.
For cams, overlap matters, and lsa is just one component of overlap, duration is also important.
For intake, go single plane, not much to be gained down low with a dual plain in a boat.

As Tomz said, you may not need to go 540 if you're looking for just a bit more power. A 502 can make good power with a head/cam/intake swap with a slight bump in compression.
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Old 03-27-2021, 01:20 AM
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All I know is how I made the decision to use a good crank on my build. I had enough into the build I wanted a $500 insurance policy. Odds are I wouldn't destroy a cast crank but I didn'twant to take the chance so I went for the forged crank option. It also leaves the option open to add more hp with a power adder or more RPM .As far as the stroker option, I knew i wanted good power with good idle quality to make docking easy . More cubes makes good power without having to spin the motor past my target rpm (5500), the rpm target will determine the camshaft size.
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Old 03-27-2021, 01:36 PM
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Just an opinion, go with the 540, boats like cubic inch. Scat, Lunati, Compstar, forged crank kit, 320 or so cc heads, 8 degree split on the cam, 112 lsa, air gap dual plane will make more torque and just as much HP as the single plane but in the RPM where you will use it.
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Old 03-28-2021, 07:12 AM
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Just had 502’s built that made 622hp and 630 torque. Dart 308 heads, crane 741 cam, crower solid lifters, scat rods H beam rod , comp rockers, Srp dome pistons, 9.5 comp, edelbrock single plane intake, dui distributor and 850 AED carburetors. Very pleased with the outcome.

Last edited by cig28; 03-28-2021 at 07:51 AM.
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Old 03-28-2021, 10:11 AM
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Is this going in front of a Bravo drive? At some point torque becomes an enemy in a 27 boat.
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Old 03-28-2021, 12:48 PM
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Originally Posted by cig28 View Post
Just had 502s built that made 622hp and 630 torque. Dart 308 heads, crane 741 cam, crower solid lifters, scat rods H beam rod , comp rockers, Srp dome pistons, 9.5 comp, edelbrock single plane intake, dui distributor and 850 AED carburetors. Very pleased with the outcome.
Similar build to mine. Easy to build.
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Old 03-29-2021, 07:29 AM
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Simple reliable build with new gm blocks . I didn’t want to bore brand new blocks to get more cubic inches. 622hp in my 30ft twin step boat will plenty fast. We calculated somewhere in the 90’s.
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Old 03-29-2021, 10:38 AM
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This one post wonder is really involved in this discussion.. hasn`t been back since he made the post .
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