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Fuel consumption - merc. 502?

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Old 08-08-2002, 10:48 AM
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Mark, I have an '96 272 w/502 EFI and cruise around 3400-3800 and my consumption falls into where others are at 15-18 GPH. I don't believe the fuel you are burning is the boat/weight issue. Something isn't right with your set up. Prop/tune of motor. You are burning to much fuel.
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Old 08-08-2002, 10:48 AM
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1995 MPI 502. Boat weighs about 4500 lbs (guessing)

Half throttle - not very much
Full throttle - A LOT!!!
 
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Old 08-08-2002, 11:12 AM
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Thank you, fellow powerboaters for your input on the fuel-issue... I think 15 gph sounds reasonable at 3500 on a 502... next time I'll have to fill'er up a little more... In sweden (where I live) the fuel costs about one dollar/litre... on the other hand it's worth every penny to start up and go for a ride in the archipilago (did I spell that right???) outside Gothenburg... Do I love those waves from the passengerferrys...? YES!
 
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Old 08-08-2002, 12:51 PM
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Yeah, you guys burning 10/15 GPH in your 4000 lb deep V's also get 25 MPG with your tow vehicles too...
Isn't the furmula something like: 100 lbs fuel/hour per 100 HP ?
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Old 08-08-2002, 01:14 PM
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Yes, my 3500lb deep V does in fact burn approximately 10 GPH at 3500 RPMs. This is provided my hour meter and the meter on the gas pumps are working correctly. Do you think we are making these figures up? Unfortunately my tow vehicle only gets about 14 MPG.
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Old 08-08-2002, 01:50 PM
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Default How are you guys figuring this out?

I have no idea how you could figure this and be accurate. Close maybe, but not accurate. You would have to fill up, drive your boat at a certain rpm for a designated time and then go fill up again to be on the money. Using your fuel guage would not be very reliable.

By the way, my truck gets about 13 mpg. That could have something to do with how I drive it though!
 
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Old 08-08-2002, 01:50 PM
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Uh...correction... I get 25.5 MPG towing my boat w/an SUV
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Old 08-08-2002, 02:05 PM
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I gotta get home and look at some gas bills. Im thinking I would be pretty happy to get 15-17. I have a 502MAG hooked to a 60 gallon tank and I can burn that up much faster than one would think.
My buddy has a 29 Outlaw w/ 454's and he doesnt burn much more than me. ???.. go figure.
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Old 08-08-2002, 02:09 PM
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Quote:
Yeah, you guys burning 10/15 GPH in your 4000 lb deep V's also get 25 MPG with your tow vehicles too...
1st of all GPH and milage are not the same thing a 502efi makeing 200hp at 3500rpm will use the same gph whether in a 15,000 lb cruiser or 2000lb flat bottom rocket. If the engine is proped heavy ( lugging) it will use a little more but if proped the same, i.e. both boats = 5000 rpm wot then gph will be close to the same.

Now mileage is another thing, the cruiser buring 16gph is going 16 mph, = 1 mpg. The rocket is going 48 mph = 3 mpg

as for pounds of fuel actually it takes about .5 lb of fuel per hp per hour so:

17 gph * 6lb/gal = 204hp at cruise
_____________
0.5lb/hp/hr

and

34 gph * 6lb/gal = 408hp at wot
_____________
0.5lb/hp/hr

go look at boattest.com at the gph numbers of a dozen dif boats, cruisers, sport, and high perf offshore, the 502 efi's will all be about 15-17 gph @ 3500 rpm and 30-34 gph at wot, 17.3 gph in a 15000 lb cruiser in the link above for e.g.

Driving habit can make a big difference to, going on plane takes a lot of fuel, if you are up and down a lot it makes a big dif versus if you get up and cruise for an hour then stop

Last edited by ursus; 08-08-2002 at 02:26 PM.
 
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Old 08-08-2002, 02:29 PM
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I guess my calculations are not that scientific. Although the above formula and my findings work out pretty close. I simply divided my gallons used when I fill up by the amount of hours I ran since last fill up. Sure some of that time is at idle and some is at WOT, but most is at approx 3500 rpms. Knock on wood, I have never ran out of gas. Also when I am at the gas station I will usually know within 3-5 gallons how much it will take to fill. I rarely even look at my gas gauge. I record the numbers everytime I fill up and this average holds up over hundreds of hours.

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