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FUEL CONSUMPTION

C

COLD

Well-known member
I was just looking at the American Airboats site and they are posting 350 SBC fuel burn at 5-8 GPH. I was just wondering what kind of fuel burn you guys are averaging for your different engines. If I can average that kind of burn I think I could afford more HP (after watching the videos I have a yearning to be able to run dry). I have built SBC 350's and 400's and love the torque of the 400 so if I go SBC it would be 383. Does anybody build a 4.25" stroke crank for the 4.3 V6 yet?
 
Fuel Consumpions are very hard to quote. Depends on size of boat, size of prop, amount of weight in boat, the foot of the person driving, ect...

I drove 90 miles on 33 gallon of fuel on an all day 8 hr run. THat was with a big block 502 with 2 people in the boat at 2800 to 3000 rpm no stop and start.

No matter what number someone throws out there are just way to many factors to take into consideration to be accurate in order to duplicate it into your boat.


You can buy identical trucks off the lot that get totally different fuel consumption.
 
Yeah, I know that but just trying to get an idea. I guess I am trying to figure out what kind of consumption I would get at a satisfactory cruise speed. There are a lot of factors, If the prop is set up for climbing hills you might be pulling 6000 RPM at my satisfactory cruise. If it's set up for speed you might pe pulling 2800 rpm so I do agree lots of factors. I you all could mention those factors when posting I think I could get an idea of what to expect!
 
Faron, I looked at your post again and that is exaclty the kind of information im looking for. Looking at your burn for that trip, its no more than my outboard. The thing im trying to figure out is like is smaller V6 tuned to the nuts crusing at 4500/5000 rpm for that acceptable cruise speed and not much left on tap going to be cheaper or more expensive to operate than say a caddy cruising along at 2500/3000 RPM with lots left on tap. Just something I have to check into before I build! I can sell the 100 HP engine I got for free and I can get 350 SBC cores for nuthin, Don't know if my buddy has anything bigger or not! I would like the ability to fit my family on board (4 of them for a total of less than 350 lbs) and take friends and kids out so I can convince them to build a boat. More fun with more boats!
 
COLD-EH'":2wyrk579 said:
Does anybody build a 4.25" stroke crank for the 4.3 V6 yet?
Click to expand...

You'd still only have 325 cubic inches. Not to mention you can't fit a 4.25 stroke crank in a standard 4.3 block, you'll hit the cam.
 
Bummer! would be a cool little engine. Only thing about the little engines is HP parts non existent or expensive. While you have less pistons they still want over $100.00 bucks each while SBC you can go to Summit or someone and gat a Hyperutecic kit for about $200.00 or forged for $400.00. What do you guys run? 383 cranks are inexpensive and im thinking cast is good enough. If I decide on bigger engine it will end up with cast. Engines I've built that I like, 460's, BBC, Windsors and even the 360 dodge on propane. Also built a 11-1 460 on propane that ran really nice.
 
Hey Cold,

Faron is right on with his fuel consumption quote. I believe that was the trip I was on with him (in my own boat). Sadly, my fuel consumption was just a little higher than his (identical engines, boats etc...) and I ran out of fuel in the middle of the river, during a downpour and at sunset... I'm sure Faron remembers the ride back after they brought me fuel... :shock: :shock:

Another thing to keep in mind is water depth.. Shallower the better for fuel economy.. I can cut my fuel consumption by up to a 1/4 by just staying in 2 or so inches of water while up on plane..
 
Interesting, shallow water acts like ground effect on a wing? Don't have that 460 anymore. had it in a 78 3/4 ton 4x4, 6" body lift and big tires on propane. Ran reel sweet but had moved to Vancouver and kept running over the little cars! (just kidding).
 
Cold - That is exactly how it functions. When running with a GPS on some shallow flats you can see the mph change as water depths change while the RPMs are kept the same. It is a good thing to file away and can be useful at times to get home.
 
I've got a 502 on a 16' Diamonback with a 45 gal. fuel tank and a 4 blade whirlwind. I bought used from a guy at Kissimmee. The day after we bought it we filled it up, put in at Grape Hammock and headed south following the bank, drove all the way around the lake and lapped every Island along the way at least once. It took all day, however many miles that is, it was 8-10 hours. We had about 5 gals. of fuel left when I refilled that night. That was with 500lbs. of passengers and big ice chest loaded to the top on board.

We ran shallow water around 3200 rpm most the day with some idling around and an occasional outburst, opened it up once coming back on the west side of Brahma island, hit 73mph on the gps and still had some throttle left. Then we ran a little ground up on Brahma island before we put it back on the trailer. I was satisfied.

The boat consistantly runs all day on the fuel in the tank, I'm sure I could run it out in a day if I was trying to... I try not to open the secondaries except to push it up on plane, I think it really is pretty economical running on the front two barrels between 3000-3500 rpm. I've quit carrying an extra can just in case.

I posted this same story about fuel consumption a a while back and there were several doubters, kinda made me feel like they didn't think I knew what I was talking about. Funny how the responses depend on who is making the claim.
 
COLD-EH'":3kly5tto said:
383 cranks are inexpensive and im thinking cast is good enough. If I decide on bigger engine it will end up with cast.
Click to expand...

Cast is excellent for an airboat. Cast cranks deal with harmonics better than forged. There's a lot of harmonic vibrations present in an airboat.

For about 900 bucks you can get a whole rotating assembly from Summit (Eagle crank and rods, Keith Black pistons and Clevite 77 bearings, along with a damper and flex plate). That's what I bought and the quality seems very high. For the money, it's hard to piece together a kit with the same quality of parts, and the kit comes already balanced.
 
Yeah im checking out there stuff to figure what engine to build. I didn't see lots for cheap for caddy 500's. 460 was better, can even get some nice Trick flow heads if I think I need them later. Like BBC, (built a wicked 12.5/1 427 once) or 383 SBC. BBC commands a higher price, see what my buddy has in his yard.
 
There isn't much cheap about a Cadillac except maybe getting the enine itself.

SBC is the cheapest motor to build, and has the most parts available for it. The only disadvantges I can see is that it's easier to pick combinations of parts that are not as likely to work well together, and that some of the cheaper parts available are just that: cheap, and not of high quality.

A 383 is an excellent choice, and if the budget is there, you can build an even bigger SBC that is sure to impress
 
Yeah, I spent some more time on thier website tonight and I could probably even get into a nice set of heads if I built a 383. I like the looks of those Trickflow's, anybody try them yet? It's alot to shell out for those big block aluminum heads so I probably would have to run factory heads. Nothing wrong with that either. I built an oval port BBC that was real nice to drive, and actually another one that just plain scared me! Shouldn't have traction problems in a straight line at 60 MPH! So if I build a big block it will be pretty simple. Probably a set of Hyperuetectics, little higher compression, (flat tops instead of dished) cam thats nice to 5000 RPM, aluminum intake and a Holly. Thanks!
 
Cold, I can't help but notice how far you've come from a 100hp Toyota, or a 35hp Briggs & Stratton :lol: . Torque and horsepower are addictive, aren't they? I've been talkin to Faron about my next boat and I'm lookin at a 350 or 383 w/tuned port fuel injection ..... that could be done for about the same money as heads if you use GM take-off parts, and up there where you live it would make starting and running a lot simpler when that old thermometer is down low, and should help the fuel economy too. Just a thought.

BF
 
if you realy want torque in a small block configuration go to a 400 small block big block torque and horsepower in a smallblock form and weight Copperhead.
 
John - Keeping those secondaries closed will save lots of fuel. But most people never learn to keep the foot out the throttle. I am impressed with your comsumption, that is amazing. Beats the 540 I run. :(

They were doing some seismic work around the house this summer and they all were running 454s. They were using 45 or 55 gallon fuel tanks and had 3 fuel hauler boats with 90 to 120 gallon tanks set in the hull that ran all afternoon refueling guys to keep things arolling along. But they were turning 4000+ all day. Guess I have never been around BBC being used for just cruising around, but always as work boats.
 
100 HP to much more, It's your fault! If you guys didn't put those videos on this site, but oh well! It will only hurt when I fill up. Stroker 4.3, looks like I went a little long on that arm, but why? I was in weight saving mode at that time but it's not really that much lighter> I am really interested in factory fuel injection for a 383. Still have to give my buddy a call, has his own personal junk yard. Why would I chose 383 over 400? I dont mind the idea of water flowing between the cylinders and a lot of the 400's I have taken apart have had quite a bit of core shift resulting in scalloped bores at the bottom. They still ran nice. I really have to start on a hull though. That gets me to the point of no return.
 
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