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Stock 502 carb questions

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Old 05-08-2013, 09:46 PM
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Default Stock 502 carb questions

Have stock 502 carbed motors. Both have about 580 hrs or so. We aren't sure the history on these motors but as far as we know they are stock and haven't been rebuilt or modified.

We put Imco power flow exhaust two years back and are looking to do something to the intake and or carbs this yr. what are some suggestions for switching out the carbs and or intake? We would like something that will be suitable for the current set up but also something that when we have the motors rebuilt down the road and upgraded power, they will compliment the internal upgrades.


Suggestions?


Thanks in advance


Ricky
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Old 05-08-2013, 09:53 PM
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what carb&intake does it have now?
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Old 05-09-2013, 12:23 AM
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If more power is what your looking for, you may want to get a nice set of heads, and a new cam as well. Those motors need to breathe to make any noticable difference, and it seems like you are alreadt set on the exhaust side. I would look at a nice set of AFR heads, good cam, single plane manifold and bigger carb. Not to mention, everything can be used down the road when you want to build up the motors
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Old 05-09-2013, 07:08 AM
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Not sure on the specifics - it is bone stock. Factory merc intake and what appears to be something similar to a quadrajet on a Chevy set up.

Gun slinger- what intake and larger carb do you recommend?
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Old 05-09-2013, 10:48 AM
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If it were me you could make some replica hp500 motors out of them fairly cheap, If you're not looking to spend the money on cams heads intake and carbs right now I'd say go with some Holley 850s like the 500s had and the Merlin intake to match. Something you could when rebuilding put some decent heads, cams, use the Intake and carbs and get 500-550 hp all day, not breaking drives and run the heck out of it. Just my 2 cents...

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Old 05-09-2013, 11:03 AM
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Originally Posted by mickeymcclgn View Post
If it were me you could make some replica hp500 motors out of them fairly cheap, If you're not looking to spend the money on cams heads intake and carbs right now I'd say go with some Holley 850s like the 500s had and the Merlin intake to match. Something you could when rebuilding put some decent heads, cams, use the Intake and carbs and get 500-550 hp all day, not breaking drives and run the heck out of it. Just my 2 cents...

More time boating less time wrenching...
The HP500's had a holley 800, with Dart single plane intakes. And in my opinion, somewhat of a poor camshaft choice.

But to get back on topic. What you have there Ricky, is GM aluminum dual plane intakes, with a quadrajet carb, flat tappet cam. They are nice engines, and were rated at 390HP stock in 1993.

With 600 hours on them, I'd say your getting close to a freshen up. The valve springs are probably getting weak, guides a bit worn, etc.

IMO, bolting on a different carb and intake wont net much. The cam is very mild for a 502. I'd say run them as is another season, and save up some money. When your ready, go thru them, convert to a hyd roller setup, new carbs, intakes, roller rockers, etc. 550-575HP is doable with the heads you have and proper cam, intake, etc, without getting radical.
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Old 05-09-2013, 04:05 PM
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MT pretty much nailed it. Run them as is and enjoy trouble-free boating for a couple more seasons. Simply changing carbs and intakes will not do much for you with the small (222/222 @ .050, 115 LSA, .483 / .483 lift) cam that Merc was running in those engines. Friend of mine dropped a stock 502 mag in his boat with the dual plane and an 850 Holley, and was getting about 65 MPH. He didn't want to get into the internals of the engine until his warranty was up, so he put an HP 500 Dart single plane and 800 Holley on it, and added Lightning headers - so he basically had the HP 500 setup minus the cam. Net result was about 4 MPH more on the top end. He didn't see any real gains until he got much more aggressive on the cam. Merc set these motors up very conservatively, particularly on the camshaft lift, for longevity.
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Old 05-11-2013, 11:59 PM
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Hey thanks for the feedback. Looks like we will be going with either the 800 or 850 Holley carbs. What are y'all's thoughts on dual plane vs single plane intakes? Brand experiences or recommendations? If I have researched right, dual plane for better mid range and single for top end. Is there a significant difference with the proposed set up?


And yes at the end of summer, I'll be asking for thoughts on heads and cams to go with the carbs and intake y'all all have helped with!




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