502 water reversion
06-19-2014, 01:01 PM
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502 water reversion
I have seen a ton of posts on this but have not found one describing my problem so ill start a new one I guess, I have a gen VI 502 with comp cam xtreme marine roller 11-461-8, 360 cc square port heads and 1150 dominator, mercruiser exhaust manifolds with through hull exhaust below water level, angle tips, I am getting enough water reversion to drop cylinders and run rough anytime boat is not moving, no matter if rpm increases over 2000 rpm, I noticed last night there are no flapper valves in the tips, a straight vertical bar is located inside the tips but no flapper, but I do not see how that is my problem, even with a flapper they will leak and have some water in the exhaust pipe, especially if you were anchored for a while, is this camshaft to large for this setup? cam is .575 lift 112 degree lobe center that I did degree, 254 and 260 @.050, Thanks for your help!
06-19-2014, 01:22 PM
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I hope you are not using factory iron manifolds, that's just asking for trouble.
06-19-2014, 01:29 PM
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Heads, cam, carb are way too big for a 502. The torque curve is going to be terrible and it won't have any low or midrange power.
Stock Merc exhaust is choking everything. You can't use stock Merc cast iron exhaust with any performance cam or it will revert water.
Stock Merc exhaust is choking everything. You can't use stock Merc cast iron exhaust with any performance cam or it will revert water.
06-19-2014, 03:05 PM
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Don't take this the wrong way, especially since you where smart enough to ask, but you almost couldn't have a worse combination for a 502 powered I/O with wet exhaust...factory at that.
06-19-2014, 03:39 PM
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Lol! I will certainly not take it the wrong way! I have Drag raced for many years and this boat thing is a whole another ball game, I had this engine in the corner, a spare for my super gas car, and I thought I could detune it enough to make it go, sounds like even if I put a stock camshaft in it, I will still have the problem? I know the heads and intake and carb will not make any low end power, changing the exhaust around will take some fab time, it is june and I would at least like to go chase some bikinis, I do appreciate the responses.
06-19-2014, 07:48 PM
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OMG.
Yes, I agree. A 360CC runner head is way big for a 502, ESPECIALLY a naturally aspirated one. Even blown 360 would be way big.
That cam you have, is also too much duration, and not enough lift.
With stock exhaust, and that camshaft, the only way I see reversion not being an issue, is more than likely with an aftermarket exhaust, and full dry tails. Even so, its still gonna be way to much duration for a marine 502 turning 6000RPM or less, in my opinion.
It sounds like you just want a useable boat right now. The only way I see that happening anytime soon, is ditching that cam. While the heads are too big, and the carb, at least you'd be able to run the boat. While it still wouldn't be ideal, Right now its useless unless you find a dry exhaust system. The stock merc iron exhaust is worthless above about 400HP. Best bet to get going, would be find a better exhaust, and downsize the cam a bunch.
To answer your last question, I think changing the cam out for something with a lot less duration than you currently have, and a wider LSA, would help fight reversion, and help crutch the monster port size in the heads. I'd like to tell you to call Bob Madera at Marine kinetics to grind a custom cam for you, but not sure he would want to until you're ready to put a solid package together. Like, the proper size head, carb/intake/exhaust, etc. You might consider something like a stock 500EFI cam or something like that for time being. That cam is 230/236 .598/610 114lsa. Even that might be borderline with iron exhaust. Merc used performance exhaust on the 500EFI. Only thing they used iron manifolds on 502 wise, was the 502/415HP mag engine. Which was like 224/224 115lsa I believe.
Yes, I agree. A 360CC runner head is way big for a 502, ESPECIALLY a naturally aspirated one. Even blown 360 would be way big.
That cam you have, is also too much duration, and not enough lift.
With stock exhaust, and that camshaft, the only way I see reversion not being an issue, is more than likely with an aftermarket exhaust, and full dry tails. Even so, its still gonna be way to much duration for a marine 502 turning 6000RPM or less, in my opinion.
It sounds like you just want a useable boat right now. The only way I see that happening anytime soon, is ditching that cam. While the heads are too big, and the carb, at least you'd be able to run the boat. While it still wouldn't be ideal, Right now its useless unless you find a dry exhaust system. The stock merc iron exhaust is worthless above about 400HP. Best bet to get going, would be find a better exhaust, and downsize the cam a bunch.
To answer your last question, I think changing the cam out for something with a lot less duration than you currently have, and a wider LSA, would help fight reversion, and help crutch the monster port size in the heads. I'd like to tell you to call Bob Madera at Marine kinetics to grind a custom cam for you, but not sure he would want to until you're ready to put a solid package together. Like, the proper size head, carb/intake/exhaust, etc. You might consider something like a stock 500EFI cam or something like that for time being. That cam is 230/236 .598/610 114lsa. Even that might be borderline with iron exhaust. Merc used performance exhaust on the 500EFI. Only thing they used iron manifolds on 502 wise, was the 502/415HP mag engine. Which was like 224/224 115lsa I believe.
06-19-2014, 08:12 PM
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OMG.
Yes, I agree. A 360CC runner head is way big for a 502, ESPECIALLY a naturally aspirated one. Even blown 360 would be way big.
That cam you have, is also too much duration, and not enough lift.
With stock exhaust, and that camshaft, the only way I see reversion not being an issue, is more than likely with an aftermarket exhaust, and full dry tails. Even so, its still gonna be way to much duration for a marine 502 turning 6000RPM or less, in my opinion.
It sounds like you just want a useable boat right now. The only way I see that happening anytime soon, is ditching that cam. While the heads are too big, and the carb, at least you'd be able to run the boat. While it still wouldn't be ideal, Right now its useless unless you find a dry exhaust system. The stock merc iron exhaust is worthless above about 400HP. Best bet to get going, would be find a better exhaust, and downsize the cam a bunch.
To answer your last question, I think changing the cam out for something with a lot less duration than you currently have, and a wider LSA, would help fight reversion, and help crutch the monster port size in the heads. I'd like to tell you to call Bob Madera at Marine kinetics to grind a custom cam for you, but not sure he would want to until you're ready to put a solid package together. Like, the proper size head, carb/intake/exhaust, etc. You might consider something like a stock 500EFI cam or something like that for time being. That cam is 230/236 .598/610 114lsa. Even that might be borderline with iron exhaust. Merc used performance exhaust on the 500EFI. Only thing they used iron manifolds on 502 wise, was the 502/415HP mag engine. Which was like 224/224 115lsa I believe.
Yes, I agree. A 360CC runner head is way big for a 502, ESPECIALLY a naturally aspirated one. Even blown 360 would be way big.
That cam you have, is also too much duration, and not enough lift.
With stock exhaust, and that camshaft, the only way I see reversion not being an issue, is more than likely with an aftermarket exhaust, and full dry tails. Even so, its still gonna be way to much duration for a marine 502 turning 6000RPM or less, in my opinion.
It sounds like you just want a useable boat right now. The only way I see that happening anytime soon, is ditching that cam. While the heads are too big, and the carb, at least you'd be able to run the boat. While it still wouldn't be ideal, Right now its useless unless you find a dry exhaust system. The stock merc iron exhaust is worthless above about 400HP. Best bet to get going, would be find a better exhaust, and downsize the cam a bunch.
To answer your last question, I think changing the cam out for something with a lot less duration than you currently have, and a wider LSA, would help fight reversion, and help crutch the monster port size in the heads. I'd like to tell you to call Bob Madera at Marine kinetics to grind a custom cam for you, but not sure he would want to until you're ready to put a solid package together. Like, the proper size head, carb/intake/exhaust, etc. You might consider something like a stock 500EFI cam or something like that for time being. That cam is 230/236 .598/610 114lsa. Even that might be borderline with iron exhaust. Merc used performance exhaust on the 500EFI. Only thing they used iron manifolds on 502 wise, was the 502/415HP mag engine. Which was like 224/224 115lsa I believe.
06-19-2014, 09:28 PM
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I don't agree.
I don't agree with the word crutch.
The person who invented the word crutch was a disaster in the offshore forums.
That's how well 'crutching' worked.
Don't tease this guy. Many parts need changing.
I don't agree with the word crutch.
The person who invented the word crutch was a disaster in the offshore forums.
That's how well 'crutching' worked.
Don't tease this guy. Many parts need changing.
