MT - good running boat your buddy has in that video. I miss that skyline. I grew up in NW Indiana just 55mi from downtown CHI. Live in Vegas now but with I could enjoy Lake michigan in my boat.

Borgie - thanks for that article. Yea, I've been looking everywhere for info on this. If the change happens it WILL be the Brodix Race Rites. I'm trying to find some comparative data on the rect/oval port race rites. They both flow about the same but different shape so........what's the deal here? I'm almost positive I wouldn't even feel the difference between the two but I figured if I'm buying new might as well try to find the best combo I can afford. Also, switching over to oval would require me to switch intakes now also instead of later. A necessary evil ($$) I suppose if I want the best combo. Already picked up some blue holley 800's so I'll need an adapter for the time being if I keep the stock intake.

BT - Thanks for the input. That is still a possibility. I was already set on new valves and definitely replacing worn parts, i.e. springs, rods....I figured if I can get my heads back to a stock quality standard and upgrade the valve train components I would be happy. I don't pull any skiers/tubes and I don't race anyone and don't gun it out of the whole but I do like to open it up while cruising. She comes on plane pretty easy as is. I already spoke to RM Builder about some quality solid cams and about the added expense but less headache roller conversion. I put new heads out of the equation until I came across these bare Brodix heads and for what they can be had for. I like the idea of bumping up my compression and still running 87 gas. Plus new tech and lighter ass end. Dumping the stock exhaust for some 496 aluminum mani's and al heads would yield around 375lbs savings.

I've spent all weekend prepping the boat for motor removal and building my gynormous gantry. Just finished it up tonight so motors should be coming out next weekend. 11W x 13' 4" high at it's lowest point. That gives me room for the chain hoist and clearance out of the bilge. I already listed my current heads on local CL so if any takers want them then I'll get new heads. If not I'll reassess once I remove them and check them out.


Thank you all for your comments.

If its an aluminum magnum intake, you don't need an adapter for the Holley's. They have holes tapped for square bore and spreadbore carbs.

Griff - yes, it is the stock aluminum and I see the extra holes. Won't I need some sort of adapter for a square carb to spread intake?

I'm not debating you on those heads working nicely. I just always try to figure in cost vs gain. Without a doubt, the GM rect ports suck. For starters, the huge intake runner is vastly oversized, for a 454 especially. What they lack in intake port velocity, they definitely do not make up for it on the exhaust side. The exhaust ports flow is like a small block chevy head. Its what mercury had to work with though at the time. I definitely recommend someone wanting to upgrade, to go to a newer aftermarket head. For the cost, its hard to beat a Dart 308 Iron Eagle as a replacement, as they will out perform the GM's by far, still retain the durability of Cast iron as far as marine, and can be had ready to bolt on for under 2k a pair.

Which brings up the cost again. 500 bucks each for the race rite bare castings is a good price. However, keep in mind what you will have in these heads, by the time they are fully dressed and ready to bolt on. Stainless intake valves, extreme duty Inconel ex valves, springs, retainers, machine work, etc. It adds up quickly.

Another nice option for a 454 Mag Upgrade on a budget, is the edelbrock 290cc ovals. With the 110CC chamber, it will yield around 9.3:1 using the stock 454 mag bottom end. Usually you can find them for around 900 each, ready to go just add your springs. Now your getting into a price point that doesn't hugely exceed rebuilding the stock GM heads.

At the end of the day, its all about the budget for most. A pair of stock 454 mags, are gonna need pretty much the following parts, not just heads, for a nice upgrade

Exhaust manifolds. Stock irons have to go.

Intake manifold

Carb

Roller rocker arms

Cam and lifters.

Gaskets, etc

A lot really depends on how much power you want to make, and how fast you want to go. Hands down the biggest improvement on those engines, is a cam swap and exhaust. My buddy's scarab in the above video, gained a bunch just by ditching the stock exhaust, larger cams, roller rockers.

I redid my 454's two years ago. I am running Dart 308 Race series aluminum heads with some port work, a 236/245 114 LSA hyd roller .630 lift, B&M 420 blowers making 6psi, no chillers. They made 804HP at 6000RPM and been running great for 2 seasons. My boat with stock 454 Mags, would run about 65mph. It runs upper 80's now and still need to play with props.

Engine masters did a build up related to what we are talking about. They took a 454HO crate engine, and did a top end upgrade. In stock form, the crate engine is similar to a 454 mag as far as bottom ends. Forged components with mini dome pistons. This engine was actually going in a Jet boat.

Baseline engine.
Stock GM Iron rect port heads.
Edelbrock Performer Dual plane
Holley 850 carb
211/234 HR Cam .510/.540
8.75:1

New setup
Dart pro 1 310 Rectangle ports
Dart Single Plane intake
Holley 850
236/242 .521/.540 HR cam
8.55:1

By adding the darts, they lost a little compression due to the larger chambers.

Baseline engine made 434HP at 5200RPM, 486FT lbs at 3800. Peak numbers.

Modified Version made 524HP at 5600RPM, and 518FT lbs at 5000RPM.

You might say, well, yes, but what about the low speed numbers????

At 3200RPM stock, 464 FTlbs. Modified 472 FT lbs. At 5200 where the stock engine peaked at 434HP, the modified version was making 509HP.

A 8.5:1 Aluminum headed engine should be able to run on 87 octane all day long. 500+ft lbs of torque, and 525HP is nothing to sneeze at considering the compression ratio, 454CI, and RPM band.

The other engine article posted was comparing a 496CI 10:5:1 setup using good flowing oval port heads. Of course that's a stump puller combo. The oval Brodix on that 10.5:1 were making 597HP at 5600. 73HP more than the above engine with almost 2 full points less compression, and 42 less cubic inches. No magic there.

A 10.5:1 marine engine in a heavy old scarab, using a somewhat small camshaft in quest for peak torque down low, is a recipe for detonation on pump gas. Its unrealistic. And, the camshaft part # in that article is for a ford small block, so who knows what it really had for a cam.

Oval port heads can work well, especially in a street engine, where low rpm stump pulling power is needed. They definitely have their place. Nice thing about the 310 Darts talked about here, is that if the 454 mag owner bought them, ran them, and decided a couple years from now to build some 502/540 Short blocks, he can reuse those heads. I know of several marine 540CI builds making 700+ with them. Not gonna happen with some 265 ovals.

For the record the DART 275 ovals made 595hp with 9.8:1 compression, not 10.5:1. 9.8:1 is actually a perfect range for a aluminum headed marine performance engine. I think we are losing sight of what the original poster is looking for power wise. The smaller oval heads are better for a 600hp and below engine in a boat. That's just impossible to argue. From your above post it sounds to me like you are saying low end torque is irrelevant in a performance marine application. I would much rather have a 496 which makes more low end torque sooner than a 496 that makes it later both being 600hp engines.

Truth be told I think the ovals from 265-290 are perfect for what the OP wants. He never stated he wanted 700hp or did I miss that? I guess I'm just perplexed by some of you that think the oval headed engine will be somehow much slower than a compatible rectangle port aftermarket head. But I guess AFR 265's are fancy peanut ports and a 600hp marine engine featuring them is only good for pulling skiers........

Dude chill out. Nobody's picking on your oval port heads.

You have a raging boner over a 496 that made 600hp with 10:1 and aftermarket heads in some magazine article with a unknown camshaft.

I've had buddy's bolt box stock edelbrock marine rect ports on a 502 with same compression and a Hyd roller make the same numbers.

There's a lot more to putting a solid marine engine together than flow numbers or intake port shape/size. I'm not saying the rectangles are superior to the ovals. But there's more to a package than that. Cam size, bore size, valve sizes, piston design, chamber design etc. plus a engine on billy bobs dyno vs a good dyno can tell a different story

I am not defending "my heads" and im far from being pissed off on a boat forum by some guy i really could give two s**ts about. I would venture to say that the small oval has proven itself beyond the flow numbers and different magic dynos and I'm speaking in marine applications not your cousins 70 Chevelle. I realize it's the combo and the sum of the parts, but it all is made or broken power wise in the heads. If he wanted to make above 600hp sure I agree rect is the way.

And I'm sure your buddy's make this power all day long blaaaah. All talk

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Whoa guys, getting a little heated in here. This should calm everyone down a bit, an actual dyno sheet from my previous build a few years back.

MKIV block 498 stroker
Ultradyne 230 intake 238 exhaust, 601 lift with 112 lobe sep
Heads were gm performance aluminum with Baker stamped on them. My machine guy said they looked like ovals that were hogged to be rect. there was a steep ramp at the bottom of each runner. Cam and heads were bought used from a gentleman who said they came out of his marine 502. I used flat top pistons and heads were milled to achieve 9.8 static comp. It was dynoed on 87 gas. Almost forgot, RPM airgap and BG Demon 850 marine carb.

Never quite got it tuned in on the water before selling the whole thing due to getting my scarab. This motor was in a 89 Maxum 23 open bow that originally had stock 454 with B1. It ran great but I just couldn't leave well enough alone and built the new motor and cannabalized the stocker for accessories. Ended selling the stocker for $400 just to get it out of the garage.

I agree with you that the ovals you mentioned would work great on a 454 mag. But , I wouldn't discount a small rectangular port either. I'm not suggesting bolting on a pair of 360 darts on a 454. Something in the 300-310cc would work just fine also, and can be had at a reasonable price.

You were raving about how those aftermarket ovals will stomp a GM rect port head on a build like this, and they would. But it's not the port shape size , as much as its the crappy flowing GM port designs