5.7 vs 8.1 in a 2006 @4ssv

[munday]

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

[cadunkle]

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.

[munday]

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?

[webbbrad]

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.

[cadunkle]

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.

[munday]

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.

[KG's Supra24]

Its a perfect reference point. I don't track mine though. Id put money on mine being higher than that, though, without a doubt.

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[Monroeyd]

We have an '06 with the 8.1 and OJ 466 prop and have averaged 6.87 GPH from March 2011 to present day. We are closer to 6 GPH now cause we dropped 600 lbs to 2600 lbs and speed to 23.7 MPH at 75', RPM's are right around 3000. Overall it's a great boat. We've put 350+ hrs on ours since 2/10 with 1 minor issue. Hope this helps. Good luck with the purchase.