Blown motor a blessing in disguise, 496 mag questions.
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Blown motor a blessing in disguise, 496 mag questions.

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    BUN
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    Default Blown motor a blessing in disguise, 496 mag questions.

    So i was motoring down the lake and lost 10 mph and 600 rpm. Mechanic said I lost all compression in cylinder number 4. Now I need a motor rebuild and am looking at building a good motor with some power, not just going back in with a rebuilt 496. Trying to keep cost below 15k but have found a forged kit that requires a .30 over bore. Can you bore a 496 mag ho motor .30 over and have no worries? Looking to be around 600 hp on motor alone.

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    gn7
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    Quote Originally Posted by BUN View Post
    So i was motoring down the lake and lost 10 mph and 600 rpm. Mechanic said I lost all compression in cylinder number 4. Now I need a motor rebuild and am looking at building a good motor with some power, not just going back in with a rebuilt 496. Trying to keep cost below 15k but have found a forged kit that requires a .30 over bore. Can you bore a 496 mag ho motor .30 over and have no worries? Looking to be around 600 hp on motor alone.
    You can bore a 8.1 .030 over no problem. If you aren't expecting any more power, and just looking for reliability, then a forged rotator will fill that bill. If you are looking to make 600HP, your are going to get into some cash, and not sure 15,000 is going to get your there. You be surprised how fast that 15,000 vanishes before you hit 600HP.

    Dollar for dollar, bore it if it needs boring, put in a decent after market forged pistons, and put it back together.
    The pistons in the 8.1 are the weak link in the chain as you discovered. Fix that and be done with it.

    Option 2, sell the engine as it sits for whatever you can, and use the money to build something else.
    Option 3, fix the engine, build something else while you drive around with the 8.1, and sell the running 8.1 later to recover some of the money you used to build another engine.



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    Last edited by gn7; 09-03-2013 at 11:30 PM.

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    BUN
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    Default Rebuild

    I am new to building marine motors, so forgive my ignorance! What are my big dollar items going to be besides forged crank, pistons, and connecting rods? This particular motor has a Raylar kit on the top end with Raylar Big power aluminum heads, cool gap air intake, big power 203 camshaft, and 1.7 ss roller rockers. This brings the Dyno numbers to 540HP and 601 ft/lbs of torque. From Raylar I can buy a forged kit that is a striker kit for 3500 dollars, but for the forged fly cut pistons to work the motor needs to be bored .30 over. They claim an increase to 607 HP and 638 ft/lbs of torque. Just wondering what my other big ticket items, besides machine work, will be.

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    gn7
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    Quote Originally Posted by BUN View Post
    I am new to building marine motors, so forgive my ignorance! What are my big dollar items going to be besides forged crank, pistons, and connecting rods? This particular motor has a Raylar kit on the top end with Raylar Big power aluminum heads, cool gap air intake, big power 203 camshaft, and 1.7 ss roller rockers. This brings the Dyno numbers to 540HP and 601 ft/lbs of torque. From Raylar I can buy a forged kit that is a striker kit for 3500 dollars, but for the forged fly cut pistons to work the motor needs to be bored .30 over. They claim an increase to 607 HP and 638 ft/lbs of torque. Just wondering what my other big ticket items, besides machine work, will be.
    Well you didn't explain that you already spent 3/4 of the money it would take to get to 600 HP on a Raylar top end, only to find out the pistons aren't up to the task of 500+ HP.
    I think the best thing you can probably do is to buy the remaining parts you need to complete their 600HP kit The pistons and rods being part of that kit and you already buying a forged rotator, I have my doubts that that the stock Merc exhaust is up to the task, but they seem to think so. Maybe you will have enough left over to buy some better manifolds. Regardless if the stockers will support 600HP, at that level at set of CMI tubes or Dana manifolds will definitely increase the power over just the Raylar kit.
    What you don't have after buying the rotator, is a larger throttle body to flow enough air for 600HP and a camshaft that can support 600HP, both of which are part of Rayar's 600HP kit.



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    Quote Originally Posted by gn7 View Post
    You can bore a 8.1 .030 over no problem. If you aren't expecting any more power, and just looking for reliability, then a forged rotator will fill that bill. If you are looking to make 600HP, your are going to get into some cash, and not sure 15,000 is going to get your there. You be surprised how fast that 15,000 vanishes before you hit 600HP.

    Dollar for dollar, bore it if it needs boring, put in a decent after market forged pistons, and put it back together.
    The pistons in the 8.1 are the weak link in the chain as you discovered. Fix that and be done with it.
    So for someone looking to get around 600 hp on a stock bore 496 you feel the stock crank and rods are strong enough? I've been told by some/most the whole bottom end is too weak for anything more than OE power. I also get the feeling they're trying to get me to buy stuff I don't really need.

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    BUN
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    I've looked through a bunch of forum posts on a lot of sites and everyone I talk to says that the 496 weakest part are the pistons/ piston rings. My motor pushed 525HP for about 200 hours before this problem, but I can definitely see why people said that. It would have been smart to start the build with a forged assembly and then add aluminum heads, intake, cam, headers, things of that sort. I will be purchasing the Raylar kit for the bottom end and let everyone know how that all goes. Motor is getting pulled end of this month and the tear down begins! I didn't build this motor, but I will be now and it'll be done right!

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    Quote Originally Posted by BUN View Post
    I've looked through a bunch of forum posts on a lot of sites and everyone I talk to says that the 496 weakest part are the pistons/ piston rings. My motor pushed 525HP for about 200 hours before this problem, but I can definitely see why people said that. It would have been smart to start the build with a forged assembly and then add aluminum heads, intake, cam, headers, things of that sort. I will be purchasing the Raylar kit for the bottom end and let everyone know how that all goes. Motor is getting pulled end of this month and the tear down begins! I didn't build this motor, but I will be now and it'll be done right!
    I was wondering how the build went and if you put any hours on it this season ?? I have read so many pros and cons on this kit so I would love to hear your experience with it. Thanks!

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    What ever you do fix what killed the last engine before the next one does the same thing. I see this all the time.

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