mercruiser 165 2bbl to 4bbl

Discussion in 'Sterndrives' started by rcig, Jun 8, 2009.

  1. rcig
    Joined: Jun 2009
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    rcig Junior Member

    I am looking to increase top end on 24 cigarette with twin 165's. would changing to 4bbl's work and increase top end. is it too much fuel for those engines? suggestions please.
     
  2. Paul aka watertaxi
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    Paul aka watertaxi Junior Member

    Is this an inline 4? I've heard you can get 10 to 20 hp more from going to a 4 barrel on those but no direct experience doing this on those.

    On an unrelated note, how about posting a few pictures of your boat -- those 24s were beauties!
     
  3. Jango
    Joined: Aug 2005
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    Jango Senior Enthusiast

    I believe the 165's could be had with a 4 Barrel - 180HP. This results in about a 10% increase in Power.
    Since power change to speed is expondential, you would probably gain a little less than 5% increase in speed. In order to get any kind of increase, you would need to do a little more. I believe your engines are basically half of the 429 cu in Ford V8. If you could find some 429 CJ Heads ( Higher compression and Larger Valves and Ports) you could see up to a 25 - 30% increase in speed.
     
  4. rcig
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    rcig Junior Member

    the mercruiser 165 is a GM 250 cubic inch inline 6 cylinder. I'll get some pictures up. not a well known model (1972). what size (cfm) should I use???
     
  5. Jango
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    Jango Senior Enthusiast

    Your Engines are most likely the 250 cu in Chevy Truck adapted for marine use.

    If you're satisfied with only a 2 or 3 mph increase (less then 5%), 450 - 500 cfm carbs would probably work. Also increasing the compression ratio (milling the Head) would accomplish about the same. Just make sure of adequate piston to valve clearence.

    Probably get a little more, 10 - 15% HP increase by going to an Alum, High Compression, Big Valve Head.

    Bottom line with "Full Hop -up", cam etc. probably max speed increase of about 25% and still have reasonable low speed operation.
     
  6. Jango
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    Jango Senior Enthusiast

    By the way, I was thinking your 165 was the 4 cyl marine motor (470) Built by Mercury in the late 70,s early 80.s. This was an aluminum block motor exclusive for marine use and not from the automotive transplants. Utilized a Ford Big Block Head and had real power. Pushed my friends 18', 2000# fiberglass boat to near 50mph. Sorry for the confusion
     
  7. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    Merc had an inline 6 with a quadrajet it was called a 200 model, came with an early II drive.
    As you can see there is an adapter under the carb to go from the old 4bbl to the 2 you have on the 165 so easy job

    plenty of inline 6 stuff around... i.e.
    http://www.cliffordperformance.net/
    http://www.sissellsautomotive.com/
    some things to make a 165 last in a boat when you want to go WOT all day;

    larger sump with splash screen- install oil temp gauges - keep the oil away from the crank
    balance the engine
    screw in rocker studs
    roller rockers or just tips
    floating wrist pins
    5000 rpm no problem...
     

  8. rcig
    Joined: Jun 2009
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    rcig Junior Member

    thank you for that info. too bad you are not local, you seem to know GM 6 cyl engines.
     
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