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  1. #1
    Join Date
    Jul 2012
    Posts
    6

    Default 5.7 vs 8.1 in a 2006 @4ssv

    I just sold my 1987 Supra Sunsport and loved it, now i'm needing some info before i buy my next supra.

    i'm looking to buy a 2006 24ssv, my last Supra was direct drive and now i want more room for people and storage.

    what i would like to know is what is the fuel consumption on the 5.7L and the 8.1L in that boat, and secondly would the 8.1 with a prop upgrade be pretty much the same consumption.

    I mostly wakeboard and wakesurf and when i cruise around it's mostly 30-35mph, not a very big lake. we're usually 6-7 in the boat and when we wakesurf i usually put an 1100lb in the rear with front bags 100% full

    it's not a question of not being able to afford the gas..... i'm just wondering if the 8.1 is overkill, or if i can tune it a bit to be a little less of a gas guzzler. i'm not familiar with the transmission gear ratios, but i'm guessing the 5.7 would run at higher RPM than the 8.1 at the same speed.

    any help anyone can provide would be much appreciated,
    thx

  2. #2
    Join Date
    Aug 2010
    Location
    NJ
    Posts
    1,393

    Default

    Smaller engine will have to run at higher RPM when weighted down. You'll have less top speed, so with the small block propped for surfing 30-35 may be pretty near wide open. Personally I'd never do a small block again, in a boat, a car, or a truck. Everything I own has a big block. Fuel consumption should be slightly higher with a big block, comparable or possibly slightly less than a small block when heavily weighted. Biggest thing is a big block will likely last more hrs before rebuild when weighted heavily.

  3. #3
    Join Date
    Jul 2012
    Posts
    6

    Default

    thanks for the input, i've also heard that the big block tends to jam up if only running low speed heavily weighted, is there a serious difference between regular gas and super, i can understand super if i was trying to win a race, but i think the 8.1 has more than enough hp to go around,
    any idea about type of fuel or do you recommend 1 tank of super for every 3 tanks regular?

  4. #4
    Join Date
    Jul 2006
    Location
    Baton Rouge, LA / Hattiesburg, MS
    Posts
    93

    Default

    my buddies 08 XStar has big block 8.1L . IT is STROOOOONG....but THIRSTY.
    We were out on it a few weeks ago. after a few sets each, i was in driver seat and asked, DUDE, is your gas gauge correct??? YEP. it had burned that much gas.

    No question, it has more than enough power, but it does drink fuel.
    Brad
    2011 Supra 21V
    Big Bay Lake, Mississippi / Baton Rouge, LA

  5. #5
    Join Date
    Aug 2010
    Location
    NJ
    Posts
    1,393

    Default

    Don't know what you mean by "jam up", but if you run low speed heavily weighted, the more displacement the better. What we do on the water requires torque at low RPM. Small blocks are torqueless wonders and require gear reduction transmissions and small pitch props so they can spin to the moon to do teh same work a big block can happily do at 1000-2000 RPM less.

    As for octane... An engine requires a certain octane rating fuel based on dynamic compression ratio, chamber design, and several other factors. Bottom line is if it needs 87 octane you are just wasting money putting anything higher in it. If it needs 89 or higher and you put 87 in it, even just once, you may hammer your rod bearings, crack rings, or even crack pistons. Use the required fuel for the engine. If you're unsure (old boat, non factory engine, blah blah) just put higher octane than you think it needs if in doubt. A new boat like you're talking about, just use the fuel the engine manufacturer calls for... Likely 89 octane but possibly 87.

  6. #6
    Join Date
    Jul 2012
    Posts
    6

    Default

    cadunkle, i had heard that it was not so much the octane, but more the new ethanol blend fuel that was hard on seals and gaskets, i know it's an issue with 2 stroke engines but i'm not familiar how it is with an 8.1, i'll try and download the owners manual to see what grade they recommend.

  7. #7
    Join Date
    Jul 2012
    Posts
    6

    Default

    hey brad is your buddy running with a stock prop, or upgrade, also when you say drinks gas, are you talking a $200, $300, $400 day of intensive riding?

    thx

  8. #8
    Join Date
    Jul 2006
    Location
    Baton Rouge, LA / Hattiesburg, MS
    Posts
    93

    Default

    Munday
    He has upgraded prop to max pull power. because of the lake we use on, it never gets run above tow/wake speeds.. sometimes up to maybe 30.. but we ride from and to the launch aas my buddy has a private launch.
    20 gals for 2-3 hours riding is not uncommon. We used about 25 gals last trip for 3 hours of wake and surfing.. That was 2 sets each for 3 people of wakeboarding and 1 set each surfing..
    SO $80-100 in fuel for 3 of us riding..
    NO question, the motor is AWESOME. I have 340 ETX Cat in My 21V and full ballast and crew and you can feel a little coming out of the hole, 8.1 loaded, its a hammer and its like towing a trailer empty vs having the boat on it!!

    The comments about Jam Up... his has been known to shut off at low RPM's.. but that was more when new than lately.
    Brad
    2011 Supra 21V
    Big Bay Lake, Mississippi / Baton Rouge, LA

  9. #9
    Join Date
    Sep 2009
    Location
    Western PA
    Posts
    491

    Default

    Having the 5.7 in the 22ssv, I would definitely get the 8.1 for the 24. Like everyone says, won't be enough motor if you get weighted down and full of people to capacity.
    2004 Supra Launch 22 SSV
    5.7L Indmar Assault
    "One More Hour"

  10. #10
    Join Date
    Jul 2012
    Posts
    6

    Default

    Brad thanks for the feedback, i used to run $100 days on average with my last supra, Carburated so when it on 4 barrels it got thirsty as well,

    do you mind giving me the prop dimensions your buddy is running on his x-star,

    thanks,

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