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ssozonoff
07-30-2013, 11:19 AM
Hi All,

Can anyone recommend out of experience what the optimal speed / rpm would be on a Classic 22 with a standard 496 HO for optimum fuel consumption ?

I realise the is a bit of dead question but I am just looking for a ballpark figure.

Thanks,
Serge

Sidney073
07-30-2013, 10:11 PM
My personal experience has been that Carbureted engines have the best fuel consumption in an application/environment like we use them in the 2,500 to 2,750 RPM range depending on Camshaft, Intake, and Carb selection. I have also found this with Fuel Injected engines as well, the characteristics of internal combustion engines are pretty consistent with where they "like" to run. I would say a "milder" engine would be at 2,500, while a "hotter" engine would be higher in the RPM range. Milder being mild cam with a little thump, Performer style intake, and 650 - 750 CFM Carb.
Another thing I've found with boats is that playing with the trim to optimize your speed and keep from "lugging" the engine helps with fuel econony. I've seen this and proven it with my tow vehicle, it's a 2003 F-150 Supercrew 5.4, 3.55 gears. I have towed a 21' enclosed trailer on an 800 mile each way trip with a good load in it. Goin out to the event I was running alone, I had the trans in OD, used cruise, drove 72 - 75 MPH, on the return trip I was running with a group, I had the OD off, used cruise, and drove 82 - 85 MPH. I kept detail records of mileage and fuel this entire trip, and used exactly the same amount of fuel each way! I figure I was Lugging the engine below the sweet spot on the trip out, and winding the engine above the sweet spot on the trip back. I have spoken with a tech at a ring and pinion distributor, and he confirmed that this engine transmission combination actually gets better fuel mileage with and without a trailer with lower ratio (higher numerical) rear axle gear ratio's, and he agreed with the 2,500 - 2,750 RPM range.
Hope this helps,
Sid

Ghost
07-31-2013, 12:35 AM
I'd expect it to be in the 27-37 mph range. With a prop that really grabs at low speed, or a bravo3, maybe down nearer the bottom of the range. With a 3 blade, more likely higher. I'll take a stab at 33 as not being far from peak efficiency, regardless. (Meaning, even if peak actually occurred way up at 45, it still wouldn't yield much higher MPG than you'd see at 33.) As for RPM, I'm guessing it'd be between 2350 and 2900.

osur866
07-31-2013, 07:24 AM
My engine builder wanted me to prop my boat to cruise at 2700-2900 rpm he told me that if I cruised at that rpm it would yield the best fuel economy and if I cruised at anything above 3,000 I'd use twice the fuel as cruising at 2,800 I thought he was full of it until I got the Diacom software and was a me to track gals per hr at every rpm level and ill be damned if be wasn't right, now to disclose I'm NOT running a stock 496 however I have tested other stock engines again not the 496 and this seems to be the norm. So if ya wanna not see the gas gauge move like your trim gauge run below 3,000 if it doesn't matter don't look. Fwiw my set up will yield 2.85 mpg at a 2,900 rpm cruise that gets me about 38 mph'ish

Greg Guimond
07-31-2013, 08:00 PM
I am surprised that the carb and efi carry about the same fuel burn in the mid range. Does the EFI do better as the rpm's climb above say 3000?

biggiefl
08-02-2013, 02:54 PM
I have done a lot of fuel comparos in my time with carbed 454's. I have found anything below 3500 is decent as above that the secondaries kick in and you can watch the needle move. I read MANY write-ups in mags with comparable setups and find it to be true as well. EFI I can't speak for. Most carbed 454's will get close to the same MPG at 2500 as they will at 3500 due to the fact you are cruising 28mph vs 48. Most write-ups show 3000 or just below as the best economy and that is where I run. My 454 burns roughly 10-11gph at that speed and I run 36-38mph so I am roughly getting better than 3.5mpg. Powerboat mag was the best for comparing this as they would run 15 boats an issue so you just dialed in the weight, engine, prop and compared it to your setup. If you run 38 at 3k with a 23 mirage on a B1 and so does a 23 Warlock, numbers will be close enough to use from a magazine.

biggiefl
08-02-2013, 03:00 PM
"I am surprised that the carb and efi carry about the same fuel burn in the mid range. Does the EFI do better as the rpm's climb above say 3000?"

No...the higher the rpms the closer they get. In a car this is not true, in a boat it is. With the stress a boat engine is under the EFI will only give a slight advantage at cruise. Most will be noticed at idle speeds. At WFO an EFI, carbed, DI, etc will all burn the same as horsepower is horsepower. In outboards at WOT they burn roughly 10% of stated hp, I/O's run a bit less(.085?). Look at 2 stroke VS 4 stroke outboards, 4 strokes are roughly 40+% better at cruise but at WFO a 200 4S is burning the same as a 2 stroke.

joseph m. hahnl
08-02-2013, 06:51 PM
There's a GPH chart floating around this site on the 22. My memory seems to recall 3200 as the best . Boat on plane aired out and 3/4 throttle works for me in the Minx:drive:

gcarter
08-02-2013, 08:38 PM
Look at 2 stroke VS 4 stroke outboards, 4 strokes are roughly 40+% better at cruise but at WFO a 200 4S is burning the same as a 2 stroke.

Actually, it's the other way around.
At WOT, the 2 stroke does the best it can and uses only a little more than a 4 stroke instead of twice as much.
I remember reading an SAE paper stating a 2 stroke (outboard or otherwise) ran a fuel burn rate of about 1.25 lb/hp/hr vs .55 (or so) for a 4 stroke.
At WOT, the 2 stroke was at .9 lb/hp/hr vs. .75 lb/hp/hr for the 4 stroke.
In other words, at WOT, the 2 stroke gets quite a bit better, and the 4 stroke gets a lot worse.

joseph m. hahnl
08-03-2013, 09:07 AM
Actually, it's the other way around.
At WOT, the 2 stroke does the best it can and uses only a little more than a 4 stroke instead of twice as much.
I remember reading an SAE paper stating a 2 stroke (outboard or otherwise) ran a fuel burn rate of about 1.25 lb/hp/hr vs .55 (or so) for a 4 stroke.
At WOT, the 2 stroke was at .9 lb/hp/hr vs. .75 lb/hp/hr for the 4 stroke.
In other words, at WOT, the 2 stroke gets quite a bit better, and the 4 stroke gets a lot worse. Must be the timing advance curve. 2 cycle Outboards use a variable stator. Where as most other 2 stokes the stator is set and locked. I think the new Direct Injected 2 strokes are a bit more efficient than the yester year motors:rolleyes:

Pismo
08-03-2013, 09:59 AM
I remember in a PowerBoat review, 2500 was the best mpg.

fysis
08-04-2013, 06:30 AM
I just measured the fuel consumtion for my 22 c. Carb 540cu.in
32 Q4X . My cruising speed is a comfortable 33 mph. At 2200 rpm.At that speed the drive is fully in .No tabs. No porpoising.100% soft ride. At that level the consumtion is 3.22 mpg. Before i did the test i thought it would be higher. I was pleased with the result.

biggiefl
08-05-2013, 01:28 PM
2500 would be your best if your boat is really fast. With a boat that does 60-65 it seems 28-3200 is ideal as you are airing the hull properly. Once you get above 40+ drag starts to eat away at your efficiency. The 22 starts to fall off plane a 22mph w/o tabs so cruising at 28-30 is probably not the most efficient speed. The only write-ups I found on 22c's are the one with a 270hp Cobra that did like 53mph and the other extreme one that ran like 80(plus the diesel one but...). If somebody could find a write-up on a 330-385hp B1 that would be awesome but I don't think one exists.

joseph m. hahnl
08-05-2013, 06:08 PM
2500 would be your best if your boat is really fast. With a boat that does 60-65 it seems 28-3200 is ideal as you are airing the hull properly. Once you get above 40+ drag starts to eat away at your efficiency. The 22 starts to fall off plane a 22mph w/o tabs so cruising at 28-30 is probably not the most efficient speed. The only write-ups I found on 22c's are the one with a 270hp Cobra that did like 53mph and the other extreme one that ran like 80(plus the diesel one but...). If somebody could find a write-up on a 330-385hp B1 that would be awesome but I don't think one exists.


:yes:

http://img.photobucket.com/albums/v637/Rokketmania/thumbs_up_smiley.gif~original

ssozonoff
08-07-2013, 03:11 AM
Hi All,

Here is what I observed.... contrary to my question I did not look for the optimum but rather just drove and observed the results.

We filled the boat up before leaving to our destination we then drove 30min at around 60mph@~4000rpm with a short run at WOT and a few miles between 50-55mph. When we arrived at our destination I filled up the tank again.... we put in 15.8 gallons (60 litres). This seems to confirm the spec. for the 496 of ~135 litres per hour at WOT.

I would be keen on finding a fuel consumption meter to hook up to the engine to find the sweat spot.

Thanks,
Serge

Sidney073
08-07-2013, 07:14 AM
Search fuel flow meters, there are several on the market, they are placed inline with your fuel line. I think they can be placed anywhere in the fuel line from the tank to the carb or injection. You should be able to get either or both Litre's Per Hour and or Gallon's Per Hour.
This is iteresting, curious of results also,
Sid

biggiefl
08-07-2013, 11:27 AM
The best way Serge is to have a GPS and hook the meter up to it. This way it shows you MPG as well as GPH so you can actually see it show you that 2850 rpm at 36.2mph fetches the highest cruise of 3.87mpg. Then you can also decide that at 3275rpm at 44.8mph fetching 3.58mpg is not hurting your wallet for a faster cruise. The last thing they do is because they measure fuel you no longer need to look at your gas gauge because once you synchronize it a couple of times it will show your tank level within 1/2 a gallon. Should be able to pick one up for under $200.

BUIZILLA
08-07-2013, 12:44 PM
FloScan

Conquistador_del_mar
08-07-2013, 12:55 PM
Before you get a Flowscan or any other GPH device, make sure it can flow enough for your application. Years ago, I installed a Flowscan on my 1971 Donzi with an LT-1 engine (350CID/350HP) and it would not quite allow WOT so I had to remove it. Just a heads up. Bill