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Carb spacer 1 or 2” on HP500 merc

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Carb spacer 1 or 2” on HP500 merc

Old 12-26-2018, 03:22 PM
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Default Carb spacer 1 or 2” on HP500 merc

I’m rebuilding my gen VI HP500 (carb) and since my original Dart single plane intake manifold had to much corrosion I had to replace it so I bought a Holley Strip Dominator intake (less than half price compared to a new dart). The Holley is about one inch lower then the dart (se pictures). I’m thinking about adding a carb spaces 1 or 2 inch and would appreciate some input on the subject. Will it make any difference at all? I know this probably is a trail and error and should be tested on the dyno but since I’m on a budget and the engine is pretty much original besides from new intake I’m not sure I’m going to dyno it. Thankful for any input. The engine should run in my 271 fastech.
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Old 12-26-2018, 03:30 PM
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I would advocate for the dyno. Not just for power numbers but you get a sense of running an engine through it’s oaces under load. Much better to find an issue on the dyno rather than in the boat. At that rate swapping a spacer is very simple to see if there’s any gain. For instance on one of mine we found a bad dist cap that allowed it to break up at over 4500 rpm. The small pin that touches top of rotor had a weak spring. Very odd. However we found it on the dyno
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Old 12-26-2018, 03:58 PM
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As mentioned dyno tell the tale or trial and error on the water. All engines react differently combo/CI depending. I'm not familiar with that particular intake as far as my own personal use however some like a 1" open blended spacer combined with a 1" super sucker. Just never know without trying. Might like nothing at all.
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Old 12-26-2018, 04:06 PM
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They will typically help the fuel distribution and atomization resulting in better efficiency and some additional hp. Others may have better advice on the subject. I played with on the dyno with 496 builds and swaping carbs, spacers, super suckers to nothing and got some increases but nothing real significant.
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Old 12-26-2018, 04:22 PM
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Thats a pretty high rpm intake.....4500-8500....what heads are on the engine ..are you doing anything else on the rebuild, Smitty on here has done some dyno testing with different spacers, maybe he will see this and chime in.
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Old 12-26-2018, 05:13 PM
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STRIP dominator. Don't see many on marine builds that I know of anyway. Merlin x, Vic jr and darts. I look forward to hearing how it works. Appearance wise they look a little similar to Vic jr but I have no clue what the port volume and cross section is on the Holley.

These XS from cp etc seem to be talked about from time to time. I have no experience with them though however price is right.


https://www.cpperformance.com/p-1354...-manifold.aspx


Last edited by getrdunn; 12-26-2018 at 05:20 PM.
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Old 12-27-2018, 05:25 AM
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I think I would be very tempted to go with a RPM Air Gap for better low and mid range. Unless you change ignition and run above the rev limiter the Air Gap may even be stronger on the upper end. If not it won't give up much.
Different animal but I tried a Vic. Jr on a 454 Mag. years ago and went back to the factory GM high rise dual plane.
Presently using Dart's though. Did not need to replace because of corrosion plus running a bit more RPM then when it was limited.
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Old 01-14-2019, 10:07 AM
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yea, it would interesting to see numbers with differnt intakes.
i was thinking of updating my intakes to dart style
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Old 01-14-2019, 11:46 AM
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and if you are not dynoing your engine, a stop watch and gps can determine what is best for as far as spacers goes. Bring along some new gaskets, your different spacers and go to town for the day on the water . Just saying
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Old 01-14-2019, 12:28 PM
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I'm running a Brodix HV2000 with a 1" 4 hole tapered phenolic spacer from JOMAR and a 1: open spacer under that. I determined my configuration through trial and error. Fortunately the differences where fairly noticeable. The 4 hole blended spacer added a little extra staring at about 3000 rpm all the way through to 5600. I added the 1" just for fun and noticed it picked up a little from 3500+ on up. Again this is only seat of the pants testing, but even my wife noticed the difference. FWIW
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