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View Full Version : Milage difference between 5.7 and 7.4 motors



Jeff U.
07-08-2008, 06:04 PM
Hi all,
For those that have had both (or know someone who has), I'm wondering if the milage difference between the two is significant? I'm looking at a 1998 21 Lavey Craft that has the 7.4 mag w/ Bravo. I was hoping for thte 5.7 mag package because of the price of fuel these days. I'm considering the 454 a deal breaker unless you guys tell me there's very little difference between the two.
Thanks in advance.

deltaAce
07-08-2008, 10:56 PM
At cruise speed they should have similar GPH fuel consumption, as it takes the same amount of fuel to make the same amount of HP.
Ultimately though, you will consume more fuel in the BB because of the enjoyment in the application of power:D

Unitek
07-09-2008, 09:52 AM
At cruise speed they should have similar GPH fuel consumption, as it takes the same amount of fuel to make the same amount of HP.
Ultimately though, you will consume more fuel in the BB because of the enjoyment in the application of power:D
Not True.
The 350mag is a MUCH more efficient motor than the 310hp 454. I had a 310 454 in my 22 scarab and that thing drank gas like it was free. IMHO, the 310 454 is a very poor performer, I think the 350mag is a way better choice.

justfloatn
07-09-2008, 12:08 PM
I have the 310HP 454 in a 23' boat and the fule cosumption is fine. I filled up before Shasta. Ran the Poker Run and boated around a litte, Went to a local lake for the day boated, took the kids tubing(huge fuel waster) and I still have a little under half of one tank and 1/4 of the other left. Basicly depending on the ammount of boating we do I can get two to five trips out of every fill-up. It holds 50gal. So it's about $75.00 a day average. If you can't afford that I don't think you can afford any boat in todays fuel prices. IMO:D

TCHB
07-09-2008, 08:15 PM
I had a 350 Merc Package a couple years back and was real happy with fuel usage compared to out 454 410 HP package.

Jeff U.
07-09-2008, 11:13 PM
Wow, what a mixed review :D I had a 350 mag in a 21 Baja about 10 years ago and it did great on gas. Seems like I could run a whole weekend at Havasu on one tank. I just can't imagine the 454 big block doing anywhere near that. I'm thinking I might wait for a 350 mag to present itself again.

Legal Chemistry
07-10-2008, 11:02 AM
so a bit of a fact, my buddies 22' Scarab ('98?) w/454 (310hp) will get 3mpg at 35mph (25 pitch mirage)

Legal Chemistry
07-10-2008, 11:03 AM
why not go with the 383? light and the power at the 454?

Trash
07-10-2008, 09:40 PM
I've got a 350 Mag EFI/MP and get 3 mpg at 3000 rpm (30-32 mph). Most boat reports from the various magazines show the big blocks getting nearly the same. My rule of thumb is 3.5-4.0 mpg for a V6 package, 3-3.5 mpg for a SBC package and 2.5-3.0 mpg for a big block. All those numbers are for a 2500-3000 rpm cruise speed.
If you're making the decision based on fuel mileage I think it would be a waste of time for boats. They all get lousy mileage, its the nature of the beast.

Ziggy
07-11-2008, 07:20 PM
I've got the 6.2 (377) EFi motor in my 23'. 5 straight days of boating, boarding and tubing barely consummed 50 gal.
I couldn't be happier with the (s)miles per gallon :D :D

HDF WATERDOG
07-13-2008, 11:57 AM
I've got the 6.2 also. I average less than 4 GPH at 3000 RPM. Props a 19 pitch.

twobobz
07-13-2008, 02:06 PM
:D :D I've got the 6.2 (377) EFi motor in my 23'. 5 straight days of boating, boarding and tubing barely consummed 50 gal.
I couldn't be happier with the (s)miles per gallon :D :D

hkunz
07-14-2008, 07:41 PM
You can always pull back on the throttle to get better mileage. However, if you get a raise/promotion, you can't swap in a BB because you now can afford the gas.
Our 502 blower motor gets about 2 MPG. Our 377 stroker small block gets about 3 MPG in a boat that weighs half what the blower motor boat does. The big motor loafs most of the time, the small motor has to be on the power band most of the time.
You can slow down and get better mileage, if that is a real concern. If you have lots of family in the boat and want to get off the water before your daughter's water breaks, your SBC can't go fast enough.

Riverbass
07-16-2008, 12:31 AM
If you are Worried about the price of fuel then you should not own a boat.