496 vs 540 BBC

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Rbode
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496 vs 540 BBC

Post by Rbode » Mon Apr 16, 2018 11:48 am

I am building a new boat and am at the point of engine selection. The boat is a 20x8 and will be used for seasonal hunting transport. I am deciding between a fresh build 496 BBC(w/ Scat, grumpy Jenkins heads, Comps magnum marine cam, stud girdle) and a HIGH quality built 540 BBC, which I am told has around 150 hours. I can get these for similar money and trust the 540 seller. I was considering re-using a 2:1 reduction but could change it to 2.3 if I need to. Also, both these have single plane intakes and wonder if I should just change the one I get to dual plane right away to capture lower RPM power? Which one would you go with and why?

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digginfool
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Re: 496 vs 540 BBC

Post by digginfool » Mon Apr 16, 2018 12:19 pm

First, no substitute for cubic inches. Second, I would go with the 2.3 ratio. That's a big boat and you'll be able to turn more prop with the higher ratio. Also, it seems the 496 is built for higher RPM performance which is not necessarily what you're looking for in an airboat engine. You want a wide torque curve with plenty of low end grunt. I'm sure others will weigh in.
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loudmouse
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Re: 496 vs 540 BBC

Post by loudmouse » Mon Apr 16, 2018 10:03 pm

540 no brainer as long as the engine is a matched combo(heads, cam, intake , carb) I disagree with lady on the intake for a heavy ride boat operating at 5600 or less. Dual plane opened up over the single every time will have more bottomend, better cold cranking, better fuel economy, better throttle response below 4000 rpms. A 4.375 stroke crank (582) would be even better yet.
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Rbode
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Re: 496 vs 540 BBC

Post by Rbode » Tue Apr 17, 2018 10:45 am

Thanks guys, going w/ 540 and 2.3!

Should I consider lowering Carb from current 1050 cfm? I guess I've read something about lowering to 750 or say may be better? I also have an old MEFI 1 I thought about re-using?

Also, since it is used, would it be worth looking at heads, springs or replace bearings, seals in assembly? Guess now would be the time since I will have on cradle (vs on boat). What would that normally cost?

Sounds like different schools of thought on single or dual plane intake... :scratch:

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Re: 496 vs 540 BBC

Post by loudmouse » Tue Apr 17, 2018 11:45 am

I would not change the carb. A 4150 1050 is perfect. Not knowing history of engine, could not recommend what should be done. If low hrs prob nothing but if it is a well used engine then lifters, and vavle springs, retainers and locks as a minimum. Ask previous owner how it was used , hours, oil pressure and if there is anything that should be replaced ect?
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digginfool
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Re: 496 vs 540 BBC

Post by digginfool » Tue Apr 17, 2018 12:01 pm

I was in the middle of a little more involved answer but mouse is correct; the 1050 is probably your best bet between the two. But, one way to look at it is that a BBC is probably not going to be set up to turn more than 5,400 RPM. With that in mind, every two revolutions will have completed the cycle for all cylinders then, assuming a volumetric efficiency of 85% and doing some number crunching, your motor is ingesting 717 cfm. That's a little too close to the 750. Yes, you could run the 750 most of the time and possibly get better fuel consumption but not enough to risk choking your engine for air. Another good choice would be an 850. You won't be running high RPM that often and the larger carb has its own issues at lower RPM. Since you already have the 1050, I say let her ride and see how it goes.
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Re: 496 vs 540 BBC

Post by RJC5778 » Wed Jul 18, 2018 12:55 pm

Rbode, i can shed some light on this as i have both engines, first one is a 498 airboat built engine, i have specs and dyno test to prove all this on my build thread, its on here somewhere "robicheaux hull rebuild". boat is a 14x7.5 robicheaux work boat hull, built a new 498 stroker with all good parts, k1 crank, k1 rods, mahle pistons, brodix heads, inconel exhaust valves, comp cams, sniper junior single plane intake, quick fuel 850 carb. ran the engine on the dyno and made 597 hp at 5400 rpm and 603 lb ft trq at 4300 i believe if memory serves me correctly. long story short ran this motor for 3 years with no issues and i can point the boats anywhere and it would go, on recent hog hunt, the old tires block (reused from the original motor that broke a lifter) decided that it wanted to crack while running at 5k, boat never overheated and was running fine that day, just think the block finally gave up. well now we are building a 540 block with all the same parts, crank, rods, new mahle pistons, same cam, same heads, intake and carb but with a new big m dart block for a true 540 CU in BBC airboat engine. i can tall you that it will be just as reliable if not more than what i had before and a boost of about 90-100 hp. the block will be in in a week or so and then the same guy who built the engine before is building this one is going to assembly it all together. i will keep you posted on this in the near future whens its done, i can tell you that you have to go with your gut on this issue, i loved the 498, it was a great motor, but when being forced to upgrade, no subsitute for cu inches in a work/boat application, torque is the name of the game here, you dont turn ab engines high enough see the high hp numbers, torque torque and more torque is what you need. my $.02 on this would be the 540, the single plane dual plane issue is negligible on a built engine IMO, i run a single plane sniper junior and it made those numbers, throttle response is awesome on this setup too for when you need to make a tight turn or avoid something in the water/land pm me if you need more details or have questions, ill be happy to talk

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Re: 496 vs 540 BBC

Post by Sniper » Thu Jul 19, 2018 7:35 am

Just Curious why go with a BBC when a LS engine will out preform them they are way more reliable and lighter my team mate on my SAR team used to run 502 BBC and then Farron with American Airboats and I got him to try an LS engine and need less to say he has never run another BBC he is now running the MAST 750 hp LS and loves it, not here to start a fight just wondering why not when the LS has such a great reputation even Dave Hartz does not run BBC any more so I'm just wondering the new LSX engine you can get well over 500 ci out of it
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Joe
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Re: 496 vs 540 BBC

Post by Joe » Thu Jul 19, 2018 1:00 pm

Sniper you been stuck on them ls motors for years now. You say Dave doesnt run them any more but if you look back through his posts even he agrees there's a point where a BBC is just a better choice.
If my memory is right he said it was around 18 foot and this thread involves a 20ft boat. ALL engines have there place.
Long thread short, an ls is not the end all be all airboat motor, never will be. But it damn sure has its place.
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Sniper
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Re: 496 vs 540 BBC

Post by Sniper » Fri Jul 20, 2018 9:16 am

Ok got it was not trying to start anything was just wondering why, was thinking more of the weight end of it than anything else and I agree there is no replacement for displacement but with LS engines being built over 500 ci now and their design being so much better than the older motors and I used to run the older motors, the 6 bolt main and great flow on heads and intake and a strong valve train thats what I was basing my question on that the LS engine has
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loudmouse
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Re: 496 vs 540 BBC

Post by loudmouse » Sun Jul 22, 2018 11:23 am

Having both LS And BBC, IMHO, the LS is a better choice because of weight and $$$. Coming from someone who can build either very cost effective, HP for HP on a boat the LS will accomplish a better performing boat at less $$. Unless the BBC is getting some high $$ parts turning more than 6200 rpm. 600hp from a stockish LS is very easy to do and will do it on less fuel.
Back to the dual vrs single intake, if I was to set up a boat with BBC to work or ride, about 54-5600 would be max rpm. Heads would be sized for airspeed first then flow, at that rpm. The dual plane will make more average power and torque than the single everytime in this rpm range. The longer divided runners will minimize reversion which is increased when a high load at low rpm(prop) resulting in more torque down low(below 5000 (faster cruz lower rpm) while consuming less fuel. Peak hp doesn't matter except for when braggin.
15' Alumitech deckover LSX TT Oxbox 84" JX 4-blade
Gas required Water optional :dontknow:
Built and Tuned by Me
14'X8' JW, Chevrolet 122CID LNF Turbo Engine, Ox box, 80" NGR 3 blade

Life is short, eat your dessert first! :downtown:

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