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New 290DC Over-Propped

Posted: Tue Oct 21, 2008 9:35 pm
by Trent
My new 290 DC with twin DF250's is not performing up to the standards shown on your site. With 180 gallons of fuel, 80% water tank but NOTHING else on boat (except me) I am maxing at 45MPH, 5400 RPM WOT and at best 1.5MPG, 4000 RPM at 29 to 33 MPH in a flat calm or light chop. I've trimmed the outboards for maximum RPM without cavitation. My boats performance is considerably different than the specs shown at http://www.worldcat.com/boats/dual_cons ... e_prop.php

I noticed you delivered my boat with 3x16x21.5's. Your tests show 3x16x20. Is it possible this was an oversight? Thanks for your consideration.

Re: New 290DC Over-Propped

Posted: Fri Oct 24, 2008 11:11 am
by conehead39
AskHarry.
5400 is about 500 rpm low. Ideal is 5900-6000, but your cruise mpg may not change if you go to 3x16x20.

There are lots of factors that enter the best cruise mpg. Just read the various OB mfgs test.Try some other rpms like 3800and 4200.
Reread WCC test data NOTES about no electronics, no gear, ie like outriggers, fishing rods in rod holders,anchor ,anchor chain.
1. Did you bottom paint it? Harry and Us have gotten very good results with Micron 66 with very low mpg reductions and application life. We know for a fact that another cheaper Micron gave less gas mileage, We only left it on 4-6 months.
2. Were you going into a head current, ( go both directions)
3. Was it a hot + humid day = less HP for a given rpm.Yam and Honda prop tests were Jan. Feb
4. 180 fuel x 6.3 lb/gal= 1134 lbs
5. 35 g fresh water + 15 gal waste =50g x 80% x 8 lb/gal= 400 lbs.
6. How much additional equipment have you added .If you did you probably put it up front making it more nose heavy.

Re: New 290DC Over-Propped

Posted: Fri Oct 24, 2008 11:46 am
by Harry Brosofsky
I don't believe any of the test reports...they use the stock gagues, and generally have not calibrated them over several hundred gallons. My Navman 3100 Fuel is very well calibrated (showed 325.8 gallons on the last trip and the boat took 323.7). Bottom line is don't use the gauge...fill the boat completely (til it is just about to spray out the vents), run the boat on a two way trip at a fixed speed (your cruising speed), then fill again and do the calcuation...fuel used divided by roundtrip miles to determine your real economy. Also, your mileage will go up about 10% once the motors are broken in. Finally, use Merc synthetic in the lower unit and Mobil 1 synthetic in the engine for another 5% increase.

Harry

Re: New 290DC Over-Propped

Posted: Fri Oct 24, 2008 12:16 pm
by conehead39
I knew Harry could add something worthwhile.
I know when I worked for the airlines flying 4 engine jets.
All the engines burned different rates and the Fuel flow gages were suppose to be within 1%.
However, we also checked the burn rate by using the same method Harry talked about on fill ups.
If one engine burned more than 5% vs others then they went a looking ,WHY?
Most of the time it was the compressor blades = nicks in an OB prop.

Our Yamaha Command link is also very accurate within 2 gal burning 250 gal vs fuel truck meters.
We use it and the GPS . We also buck Yam CL gages, gph vs 2 Garmin GPS's.
Recently 29 mph / 20 gph =1.45 after breaking in engines 100 hours;
End of the day, 1/3 fuel, 6 people, 3 live wells,etc.
1.35 mpg full fuel,300 gal plus 6 people,3 live wells.
see CONTAGIOUS with new F250s.
yamaha command link fuel gage readings portion can be calibrated up to 7%.
We have never had to calibrate them.They are a network gage system. It measures individual fuel injector pulses or pulse width,similar to new cars.

Re: New 290DC Over-Propped

Posted: Fri Oct 24, 2008 2:06 pm
by Harry Brosofsky
Ken,

My Ford F-450 "lie-o-meter" tells me I'm burning 12.9 MPG, but fuel up to fuel up I average about 11.5...That's over 10% 0ff. My Harley is a lot better, though it is overly optimistic until the last 1/4 tank, at which point the remaining range falls a lot faster than the miles tick off. I average 43 on the bike (which is why I ride to work most days). In the UH-1N, the fuel flow is just about useless, so we do burn computations for the first 10 minutes on the aux tanks (which we burn first), and then the first 10 minutes on the main tanks after the aux is dry.

Harry

Re: New 290DC Over-Propped

Posted: Fri Oct 24, 2008 4:55 pm
by conehead39
The brand new Silverado Duramax I delivered would only get 14-15 mpg the first 200-300 miles @60. Then it improved considerably at 1,000.Noticeable drop above 70 mph.

My 07 Camry max mpg is 32 @ 65-70. or bucking it against the miles vs gal to fill,it comes out the same.
96 Corvette seems to have your lie o meter in instaneous mpg but trip mpg is close to the fill/vs miles, but still less.

One thing I do note on the vette is the oil temp does not get to 215 F until you have driven over 10 miles; then the instaneous mpg goes up by about 2-3 mpg. Even Hot Mobil 1 oil thins down thus better mileage.

Either type system , ECM pulse width counter, or your calibrated paddle wheel Navman 3100 you need some way to calibrate them.

The UH-1N sounds like the old F4 Phantom . It covertered JP fuel into noise and leaked like a sieve the first 20 minutes of flight.

Re: New 290DC Over-Propped

Posted: Mon Oct 27, 2008 5:54 am
by Greg Manning
Harry Brosofsky wrote:Ken,

My Ford F-450 "lie-o-meter" tells me I'm burning 12.9 MPG, but fuel up to fuel up I average about 11.5...That's over 10% 0ff. My Harley is a lot better, though it is overly optimistic until the last 1/4 tank, at which point the remaining range falls a lot faster than the miles tick off. I average 43 on the bike (which is why I ride to work most days). In the UH-1N, the fuel flow is just about useless, so we do burn computations for the first 10 minutes on the aux tanks (which we burn first), and then the first 10 minutes on the main tanks after the aux is dry.

Harry


Harry is that mileage on the F-450 towing or not towing?

Re: New 290DC Over-Propped

Posted: Mon Oct 27, 2008 6:55 am
by Harry Brosofsky
Towing my boat and weiging in at over 23,500, I get 7 MPG.

Harry

Re: New 290DC Over-Propped

Posted: Mon Oct 27, 2008 10:09 am
by Greg Manning
Harry I thought you said earlier in another thread you were getting something like 17mpg with that rig. Could be mistaken....I was interested in comparing fuel mileage of the new 6.4. Originally a big 7.3 fan the new motor scared me off.
I get really varying reports from friends with the new motor.

Not trying to question you or start a mileage war...seriously interested in just comparing.

Re: New 290DC Over-Propped

Posted: Mon Oct 27, 2008 3:46 pm
by Harry Brosofsky
01 Excursion 7.3 - 16 city, 21 highway, 17+ average
04 F-250 CC SRW 6.0 - 15 city, 18 highway, 16 average
06 F-350 CC DRW 6.0 - 13 city, 16 highway, 15 average
08 F-450 CC DRW 6.4 - 11 city, 13 highway, 11.5 average

Great motor, lousy economy. Of course I also have 4.30 gears and it's a 450, which weighs more than 500 more than a 350.

Harry