A few thoughts on Mercury outboard fuel economy.

[Tom Brown]

I hope this post stimulates some discussion.
I've rigged the same boat with four different engines. The boat is a 1977 Glastron/Carlson CVX-16. 16'. About 750 lbs. Pad-V.
Here are the engines:
- 1977 Mercury 1500. 1.5 liters. 150 hp at the crank. Ferocious on fuel.
- 1989 Mercury XR-4/150. 2.4 liters. 150 hp (I've heard 175ish at the crank?). Over twice as efficient on fuel (seat of the pants wise) as the 1500 and lots more power.
- frankenstein based on a Merc 260 EFI. 2.5 liters. Unknown horsepower. EFI.
- 1977 Mercury 1750. 2.0 liters. 175 hp at the crank.
Here's how they compare. The 1500 seemed to burn more fuel than any other engine by a wide margin. When I put the XR-4 on, it was 18 mph faster and what felt like quadrouple the bottom end power. The fuel economy seemed better than twice as good. The boat had an 18 gallon tank, at that time, and I could boat for the better part of an hour on a tank of fuel. I have no doubt the XR-4 has paid for itself in fuel savings alone. It is now enjoying life on a different hull.
When I rebuilt the boat, I added two 13 gallon tanks to the original 18 gallon tank. My goal was to be able to cruise to Penticton from Kelowna. At the time, I didn't realize there were a couple of fuel docks between those two locations. The distance, as I understand it, is about 70 miles.
I suspect I would have been able to make the Kelowna->Penticton run with the XR-4 and the original 18 gallon tank. It would have been close. I know I can cruise roughly 55 miles on my local lake, starting with a full tank, and still have about ¼ tank showing on the fuel gauge.
There is a pretty standard tour I take people on. It starts at our pier and then goes to the dam, to the north end of the lake, through the channel to the next lake, up the length of the next lake on the east side to the city of Fort Qu'Appelle, and then back to the pier via the other side of the lake. The trip looks to be around 55 miles on GPS.
The curious thing is that the 1750 is about the same as the XR-4, fuel economy wise. Maybe it's a little worse but not much. It's tough to tell with only the fuel gauge to go by but the same 55 mile run leaves me with about ¼ tank of fuel.
When I got the 260, I was braced for horrible fuel economy. It turned out to be just fine. I have no doubt it's the worse of the three V6 engines I've had on the boat but not by a lot. I can make the 55 mile run on the stock 18 gallon tank and I can do it going faster than the XR-4 or 1750's max speed.
If you look at the engines, they are designed quite different. The XR-4 has a tiny little exhaust can (in comparison to the XR-4 and 260) and when you take the heads off, the ports look pretty small. I've heard the tuner is deliberately restrictive to get the 2.4 liter engine down to 150 hp (the other 150 hp Merc V6 was 2.0 liter in 1989). Perhaps this is the case. Perhaps with tiny porting like that, it doesn't need a big tuner. Maybe one day I'll throw a drag tuner on the XR-4 and see what happens.
The 260 has a big exhaust can and massive ports (and more of them). This comparison uses nothing more than my eyes but it's clear to see, it is set up completely differently than the XR-4.
The 1750 falls between the XR-4 and the 260. It has a really big exhaust tuner and what looks like more porting than the XR-4, but lots less than the 260.
... and yet the three V6 engines seem to get pretty similar economy at cruise speeds. I cruise the XR-4 at about 60 mph and the 260 at about 80 mph.
I don't know what's going on with the 1500. It really sucked fuel. We used to ski with it and it would go through the 18 gallon tank in 30 minutes with little trouble. My cousin's 1150 doesn't seem a lot better.

[stoker2001]

i love our new "green two stroke motor" did a 105 miles on delta yesterday (gps verified).only used around 27 gallons averaging 50mph :sqeyes: http://forums.screamandfly.com/forum...chmentid=92649

[You Te]

Interesting.

[Tom Brown]

Interesting.
The discussion is really cooking now.

[votech]

my sanger with efi 225 merc is WAY worse than old warrior with 150xr4 and the thing is it doesn't feel like pulls as hard, but it looks good :rollside:

[Tunnel Vision]

My Mach22 DCB with twin 2.5 Drags holds 54 gallons and is good for about 50' beyond the ramp docks! And then just refill it...
Tv

[Screaming Pete]

I have the 300 straped on back and get all the way out to the channel than have to turn around and refuel... i have 52 gallons and can run wot for 3.5-4hrs before having to call sea tow