Volvo duo prop cruise RPM?

Discussion in 'Inboards' started by FAST FRED, Aug 9, 2012.

  1. FAST FRED
    Joined: Oct 2002
    Posts: 4,519
    Likes: 110, Points: 63, Legacy Rep: 1009
    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    Went on a 75 mile cruise for a couple of days and found that at 3300- she does 21K .

    Opening up to 4000 only gives 27K , so the more modest cruise of 3300-3400 seems fine.

    Best I can figure (lots of no wake zones for first miles) , 80 miles is just under 40 gal.

    So 2 mpg seems like the cruising bill. I will replace the old ignition system with new cap, wires, points and rotor , and see if it improves. REGAL 223

    FF
     
  2. 7228sedan
    Joined: Nov 2009
    Posts: 333
    Likes: 11, Points: 18, Legacy Rep: 60
    Location: New Jersey USA

    7228sedan Senior Member

    I had a 23 foot Monterey (236 Montura). Purchased new in 1997 with a Mercruiser 5.7LX & Alpha 1 drive. The motor was a 4bbl 350 250HP. We'd cruiser her at 2800-3000 RPM getting 28-30 mph. WOT speed was right around 51-52 MPH. Cruise consumption was 8gph. Out of curiosity what rpm's are you getting at WOT? They're GREAT motors, just don't over rev them or over prop them. I'm not too sure what Frosty is complaining about with their durability however.
     
  3. FAST FRED
    Joined: Oct 2002
    Posts: 4,519
    Likes: 110, Points: 63, Legacy Rep: 1009
    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    I show 4000 at WOT , but the tach has not been calibrated , I plan on doing that next.

    Da Volvo book for my 305ci claims 400-4400 RPM at WOT is proper.

    The speed of 21-22K at cruise is fine for me , the boat feels good at 3300rpm.

    Will try new ignition wires as I get engine RFI in the AM radio , so perhaps there shot.
     
  4. whitepointer23

    whitepointer23 Previous Member

    more likely you need a new radio suppressor on the alternator. petrol tacho's are factory calibrated, i have never had to get 1 recalibrated.
     
  5. 805gregg
    Joined: Apr 2010
    Posts: 57
    Likes: 1, Points: 0, Legacy Rep: 20
    Location: Ojai, Ca

    805gregg Junior Member

    My very heavy Skipjack 262 with a 383 small block, gets better mileage at 3500 rpm than it does at 3200 rpm. Get a fuel flow meter (like Flowscan) it will tell you where your best rpm is. You may have too large a prop, you should be able to hit at least 4400 RPM.
     

  6. Submarine Tom

    Submarine Tom Previous Member

    We ran these at 3200 for years before pulling them out and replacing with two Merc 250Hp O/B's.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.