I'm still trying to figure out the details on our new boat. I know the fuel guage is useless, 2nd time out we ran out of gas, luckily at the ramp, due to the level going from full to empty in a couple miles. Today we ran about 2 1/2 hrs on what I figured to be a full tank. We didn't run out of gas but came pretty close, not many fuel stops available around here. It appears we are using around 25 GPH while cruising between 3200 & 3500 RPM. We only ran it up to 4400 for a very short distance so I wasn't blasting her all day. The Gaffrig shows about 42 @ 3200 and 52 @ 3500. 3000 is about 40.
The engine is 502 Mag EFI procharged, 27p Hydro prop. The boost doesn't come up until around 4000 RPM so I assume it's not sucking gas when not on the boost. Any ideas on what rpm/spped will give me some range? We like to travel down river a bit and hate to stop for fuel going out and coming back.

Mate 229-

You just have to get used to the fuel gauge. The gauge stays on full for a long time. Wen you see it come off full you need to start paying attention to it. When it reached 1/2 you only have a quarter of a tank remaining. When it reaches 1/4 you only have about 5 gallons left.

Hey Mate229, I did run out of gas on my boat a couple of weeks ago. My gauge was reading 1/4 to 1/2 full. So i thought i was alright but was i wrong. Today it was reading 3/4full when i took it to the pump and she took 51 gallons of full.

When you consider the technology of the hull and the quality of construction you would think they could devise a gas guage that would work. My company has a division that designs and builds industrial control systems. I'm going to talk to some of those folks to see if they have any ideas. If I get anything good I'll post it.

I have a 99 with a 502 EFI and my gauge is crazy too. It stays on full for a long time then as soon as it moves it starts to bounce from full to empty while under way. I have kind of gotten used to it now. When it statrs bouncing from full to e I have refueld and put in 30 gals or half the tank capacity. So when its going from full to e its really half full. Then I waited untill it was bouncing one half to e and refueled and it took 45 galons so I had a quarter tank. This is as far as I will let it go down now.

The 27 really needs a bigger tank.

As far as fuel consumption with the procharger I have no idea.

Ron

Mate 229,
I average 1.5 gallons per mile. I always reset the GPS mileage after filling. Never trust the gauge. I ran out once with the gauge still showing a quarter of a tank. By my calculations I should have had 10-15 per tank left. NOT! Fountain put smaller tanks in for half a year in 97! When the boat took 60 gallons at the pump I figured there was 20 gallons still in the tank. My tanks were 11 gallons smaller than listed on the spec sheet. Also the pickups are not to the bottom of the tanks. I have 64 usable gallons in each of my tanks not 80. Do your calculations off of how many gallons it took to refill the tank when you ran out. That is your useable gas.
Dan
BTW, a 35 Fountain will not stay on plain much less get on to plain with one engine.

RJ, my guage is similar to what you described. It didn't bounce but could almost watch it going down once it came off full. What do you consider a good cruise speed / RPM? I was running 3200 to 3500 which showed low 40's to 50 on the speedo. The boat came with a Garmin GPS/MAP color unit but I need to get the instruction book. It's a little more complecated than what I was used to.

Mate, I'm getting 1.8 mpg when cruising at 2900 rpm @ 40. With a 509 bm 250, w/2x 750 holleys. A friend with a 98 hp 500 w/bm 250 with stock carb is getting 1.9 to 2 mpg. Another friend with stock hp 500 is getting 2.2,2.3. These numbers are all gps and pretty accurate.