502 heads
 

Found two sets of 502 heads om the cheap. thinking about bolting them on my healthy 454s with matched intake. would it work or would I need lots of other teaks to make 500hp

Without knowing what heads are on it now or what you are starting with, no one can tell you.

You saying healthy 454 as already had some work done or in good health?

in health ....good compression and no oil burn
might have room to change cams in front of engines in place .... how much room do I need to swap a cam?

454 mags already have the same heads as 502 mags.

As mentioned we need more info.

REALLY, maybe you should let it be

I am not going to say that you CAN'T change a cam with the engine in the boat, but it would be ill advised. The oil pan needs to come off in order to get the timing cover off to do it properly. It would be nearly impossible to get it sealed back up otherwise.

Gotcha. Thanks

also, the different gen's won't interchange on some, can't put gen VI on mark IV

Thanks guys. Pretty sure I have Gen IV non Mags. I will keep looking for affordable aluminum heads

My friend did both cams in his supercharged 454s in a 42 fountain. No issues. Most boats don't have enough in front of the motors to slide cams in and out.

swampliz. you need to pull a valve cover and get casting number of your existing heads. you either have ovals or peanuts depending on year. if peanut 236 heads, just about any head is an upgrade. what year, type, size boat? what do you want it to do that it doesn't do now? closed cooling or raw water? fresh or salt water? affordable alum heads is an oxymoron.

Thanks Derek, Unlike many on here I have a big cruiser and am not really looking to build a poker-run boat. Don't need 6000 rpms - vessel and top speed is irrelevant with this TANK - will spend most of it's time in meat of torque curve ... be it 3500 or 3800rpms - whatever the engines like.

Vessel is 42'x10' and weighs about 16,000 without gas or water in it. It is a deep Vee - non stepped hull (looks like a tall cigarette hull with 6'3" of height in the cabin) with Arneson ASD8 drives. A few of my peers have CAT3120 diesels and cruise at 35knots and others have 454 carbed torque monsters or 502s with EFI.....some top out out over 50knots which is great for a big girl. With 330HP motors it barley gets on plane right now .... takes forever and the motors are working way too hard and oil temps too high.....goal is a reasonable cruise speed and easier jump onto plane.

I had a set of remanned 502s that were built by an unscrupulous guy in FL - they broke repeatedly so I sold them and put in a cheap pair of recent take out closed cooling 330HP Merc 454s w carbs, Gil exhausts, nothing fancy to get back on the water. Tuition s, weddings, job issues, etc have me limping along with these lumps but looking to do refresh while temps are bearable in S. FL this winter.

It is all about torque for this boat but I can't seem to find affordable 502s around here so ... thinking 496 long blocks with decent aluminum heads and upped compression 9.5:1 (I can get marine 91 octane all day long around here and will have to add octane if I go to bahamas. 93 is tough to find). Looking at pair of FiTech or similar 600HP EFIs and getting bungs put into my Gils. Maybe Victor Jr intakes and of course a reasonable CAM that wont revert water. Torque numbers near 550-600 ft/lbs would be ideal and lower the rpms the better.

BTW: Only have about 12-inches of head room above the current stock intakes so blowers or radical intakes wont fit.....engine room is below the cockpit floor.

Is this an engineering unicorn?

Adding oil bypass's and 24-inch oil coolers. Keeping the closed cooling setup I have as it is relatively new.

BTW - amazing how many web guys say to keep peanut ports for torque :bong:

For boats like yours and tow vehicles you can't beat them. Id keep my eyes peeled for a pair of 502/465 hp's or 496's like you mentioned. I can't think of any worthy mods you could do to existing engines without exceeding cost of some low hour used take outs etc mentioned above. Take out your kitchen and living room down below and see if that helps. Lol. Just kidding but seriously stay current on swap and you'll find what you need. Tearing into what you have is gonna bring you nightmares. Leave those to us go fast guys. Trust me there's times we envy you tooling across the water at 18 knots when our feet and half our legs are dangling out of the bilge.

Agreed - was not planning on re-using the existing 454s ... something as heavy as my boat needs to at least have stronger internals.

Quick side question. Could I take a pair of stock 502s, get the existing heads shaved down a bit for higher compression ... closer to 9.6 or 9.8:1, change CAMs and get to my goal on torque? Any idea how much head shaving would be needed and if the clearances would be ok? I would upgrade springs to whatever the newer CAM needs of course. Find a CAM that is torque-focused with a red line closer to 5000rpm?

I think 9.8:1 is too much for 91 octane especially for a heavy cruiser.
A stock 415 horse 502 mag is probably well over 500 ft lbs. Sounds like good running takeouts and selling yours to offset is a good start.
Also, a lot of timestuff cruisers get weighed down with a lot of unnecessary luggage. Hoe it out, might suprise you.

I have 2 sets of Merlin 043c Grumpy Jenkins heads for sale, came off great running 502's with less than 70 hours on them.

Agree. Those engines work extremely hard at ALL times. I would keep comp under 9:1 for sure.

Pm sent

What's wrong with the 454s? You're not gonna be turning a lot of rpm. A nice set of heads and decent cam they will make plenty of power. Joe on here is mild thunder. 468s making 800+. 96 mph in a straight bottom 38 fountain. I know you aren't looking for those numbers but for what you want the 454 base will be fine.

If u can get take out 502 at a great price go for it ,,if not I would turn those 454 in 496 ,,,and cam it rite

thanks Guys - good stuff. Compression-wise I guess I need to do more homework. thought the aluminum heads would let me run a couple more points of compression but that assumption may have been 93 octane based and I can't count on anything higher than 91 at the docks where I buy gas. 9:1 with big loads is safer then so be it.

What gen are the blocks? Sure, you can put gen 6 heads on a mk4, but... anyway, with your rpm range you might wanna consider L29 heads. Small chambers get 9:1 with flat pistons. The heart shaped chambers and swirl ramp in the intake ports add effeciency but are limited to about 5k rpm. 454 to 502 is 10% diff in displacement. I doubt you will feel 40 hp diff. Cast crank is no weaker than forged...at 5k or under. 6500? You gotta have steel crank. You do want forged pistons in the long run. The stock L29 heads apparently come with inconel or equivalent exhaust valves. And they are cheap and easy to find. The L19 is the same motor with steel crank and forged pistons, heavier rods.

interesting. existing ones are GenIV but not really planning to reuse them ... prefer to start fresh and swap em out over a weekend on the dry.