Offshoreonly.com - 454mag top end rebuild

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Sold my 188 casting heads and full valvetrain from stb side last night. I'm eager to see this guy on the water next year. He's pushing a 23 scarab with 454MPI and wieand 250 blower. Says he built the engine this year and 18hrs into the season ingested water and sand due to exhaust mani/riser gasket failing. That's right, still had stock merc exhaust on that set up. He brought his mech/builder with him last night and when he saw that my stock pushrods were thicker than his he recommended to take my rods as well. He ended up taking the whole setup. I sold them what they wanted and suggested upgrading the valves.

If your crankshaft just needs a polish, same size bearings go back in. Does the crank have any deep scoring at all? The machinist will need to measure all journals to assure all are same size. Not truly knowing the history of the engines completely, nothing can be assumed as you know.

Quote:

Originally Posted by Borgie (Post 4019094)

No scoring at all on stb side. Haven't taken apart the port engine yet. I agree, I want the machinist blessing on this before proceeding.

I didn notice that the prt "stock" engine had the rods and main caps stamped with their respective position number. Did merc stamp their engines or would this be an indication they were apart before?

Always the smart approach. Never know if the rods have been ground or cranks. Even when my stuff is marked ie 10/10 for crank and rods, I still double check it. I don't trust someone's previous work. It's a good feeling being confident that everything is properly set up! Great news about selling those heads. You are getting there slowly but surely!

Regarding the numbering question, I'm not sure on the mag motors. I've only been into the 330 motor and know the rods are not marked. Mild thunder should have an answer for you on that.

Quote:

Originally Posted by Borgie (Post 4011479)

Ah I see! They actually did test the Dart 308 heads and they produced less hp. I need to locate the article. Before I bought my 275 oval pro 1's I spoke to a engineer at DART at length. He said that the 308 head are awesome but that the 275 outflow them and the aluminum composition obviously allows more compression to be run. That and the 275 head makes more torque sooner. I was seriously considering iron eagle 308's until I saw the dyno pulls and spoke directly to dart. Don't get me wrong the 308's are a definite step up from the 088's, but fall short of the PRO 1's.

Some folks won't accept the fact that oval ports are better under a certain HP. But results don't lie. The 088 rect port head is ok, and I agree it should be considered for a build that's restricted budget wise, but it's proven that the AFR 265 and DART 275 flat out spank this head into the gutter HP wise. Some folks don't like the fact that their big port heads are getting trounced by high velocity small ovals. To each their own I guess.

One thing to remember regarding the above article is that this 496 tested was using a pretty mild camshaft: 224/232 DUR/ 555/565 LFT 112lsa

Add a larger cam into the mix and the full potential of these heads will be seen!

Guys its great to see you offering advice to folks on this board. My knowledge is limited to power block every Sunday and I am jealous at your knowledge. I have some questions if you don't mind. I am replacing the original 1996 454 330 hp in a 26 ft Wellcraft bow-rider. I just bought a 502 that was rebuilt by a reputable shop in my area but never installed by the owner. It was bored 30 over has stock rectangle port heads stock carb and a "mild cam" I don't have the specs yet. The price was right especially considering I am selling my 454 and I chose this over some for sale on OSO because of proximity, bulit by a good shop, and zero hours. I have to use stock style exhausts for now or ( captains choice in the future no headers). Reliability ranks above outright power for me although not by much and fuel economy would be nice. While the engine is out would you recommend any changes like roller rockers and a specific cam or just install it as it is. It wont spend a ton of time at WOT because of the family/passengers and because I don't want to break anything. Just stroke my ego once in a while. Your recommendations are appreciated [email protected] Steve

Any merc mag engine I've been into from original did not have rods marked.

Stimleck, if it has a flat tappet cam I would change it to a roller setup or become schooled on how to properly breakin a flat tappet cam.

Quote:

Originally Posted by blue thunder (Post 4019779)

I didn't think merc would stamp their rods and main caps. I'll find out more next week after shop takes a look.

Quote:

Originally Posted by ramos45 (Post 4019801)

I didn't think merc would stamp their rods and main caps. I'll find out more next week after shop takes a look.

Correct . Especially because merc didn't touch the bottom ends on those when they arrived in a crate from gm

if duration on a cam is in the 230's, is there still a necessity to keep a high LSA? Or is 112 ok to go with? How would LSA of 112 compare to 114 in power? I've done some reading but still not sure on this one.