Danimal182

Its coming into winter time and i want to start working on my Bandit, I have a few options and curious of opinions. 6.2 with cathedral heads or gen 6 454. I have both engine currently in my garage sitting. The LS has a smaller truck cam with 228 deg. @ .050 and options for either Edelbrock or Fast intake, and Hardine exhaust. The 454 is a .030 22cc dome piston, Brodix 312cc Rec ports 9.9:1 CR and would get a Hardine cam. It already has a IMCO Thumper exhaust on it as well. The BBC would get 750 quick fuel and the 6.2 would get a Holley Terminator X. I boat rivers so no matter what im going closed loop cooling. I appreciate any replies and opinions.
Dan

Tartilla

Dan, you're not going to save as much in weight with the LS vs BBC. LS are lighter, but if your Brodix BBC heads are aluminum, any increased weight of the BBC is makes it stronger.

BBC block with caps: 220lbs
​Iron LS Block with caps: 200lbs

The 228° LS cam is rather large for a peak HP at 5000+ power band. You get a good advantage with the larger LS cam tunnel.

BBC has the abundance of new/used marine parts.
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The BSFC can be similar for both engines. You can run FI on the BBC or a carb and digital timing.
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I used to be all over getting rid of the of the BBC in favor of an LS or healthy SBC. After crunching the numbers, I'm now pro BBC for performance boats.

I'll still put a 400 SBC on my Formula 233, but thats a fishing boat with focus on reliability and economy.

My suggestion is go the path of least resistance, to get the Bandit burning fuel.

Danimal182

So my 6.2 is all aluminum and plastic intake, it's quite a bit lighter than the 454. The 6.2 is also a running engine with the Holley already there and fuel parts, I sold my truck as a roller and kept everything for a future project. The 454 I wouldn't buy a whole EFI setup for, there's already good carb and ignition on the existing 454 coming out. The cost between the two is close since I have to buy the parts to assemble the new big block and some machine work. The LS cost factor is the exhaust and cooling system parts. Oh and I looked up an old picture of the cam, misspoke on the size, it's slightly smaller at 223/226

Tartilla

Aluminum blocks are nice, and you're not going to be stressing it enough to make it benefit from an iron LS block.

Closed cooling as you mentioned would be the way to go for sure.

223° Int LS cam is certainly more in the ballpark of where you want to be.

LS marine exh manifolds are far more plentiful now compared to even a few years ago.

How will the Bandit handle choppy water with reduced weigh in the stern?

Feels like you're leaning to LS. Be sure to doc your install a bit and share it on here.

What engine would be more reliable? Resale value?
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Looking forward to the results.

Danimal182

What I like about the LS is the EFI and ease of tuning, what I love about the big block is the the deep sound and capabilities. What makes it tough is not knowing how the LS does in a boat application and it puts me at a crossroad.

As for the Bandit handling choppy water, that's not an option. Its for flat water only on days with low wind. I also have a 272 for majority of my boating, my wife definitly likes that one more since its not quite the boobie bouncer the Bandit was when that's all we had.

As far as reliability, I feel like ones as good as the other.

TomZ

Many have gone the LS route with so-so results.

I think you’ll be disappointed with the LS unless you supercharge it. And even then, it still wont have the torque production of a good big block Chevy at the RPM needed to run a boat.

Just my two cents.

plavutka

Torque will be ok, if you find drive with 2:1 gear. Classic 1.5 or 1.6 it is not enough for LS engine. In this case it is better to take BB, but with 2:1 it is LS better choice.

BB have ca 5.000 rpm and LS have 6.200 rpm. To turn prop with 3.000 to 3.300 rpm you need 2:1 or at least 1.9:1 by LS. In this case you have better torque curve on the propeller than BB with same power. Good LS with enough prop torque. https://i.postimg.cc/jjTkKhHP/47713064-3.png

Tartilla

The potential CID of a BBC can give some great tq numbers.

SBC/LS engines if built correctly are not shy in the tq department either.
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It's all about engine/drive/prop to hull weight.

A 400 ftlb SBC/LS is pretty common and easy to produce NA.

Would I put an LS in my 9000 lb 30 ft twin engine hull...prob not. The BBC is naturally stronger and more reliable for performance marine use in that application.

plavutka

Would be Merc. 8,2 HO any better in your 9000 lbs hull than Volvo Penta V8- 430?
No way. VP have beter efficiency and it has a better torque curve on the propeller and in VP it is classic LS3 (Ok, now LT) with 2:1 gear.

Inadequate drive ratio is the main reason for the poor success with LS engines reported in this forum. It is understandable that the industry will not develop drives with a gear ratio of around 2:1, if it has a solid solution in the BB, which rotates more slowly and therefore has more torque on the main shaft. They did develop outboards 300, 400, 500 hp, which have wery similar rpm-torque engines like LS. And work good for heavy boats if you put a lot of them on the transom.
I have a 5,000 lbs 30 ft speedboat with LS 376/480. With a 1.6:1 gear, it pulled like a snail and was only conditionally usable. With a 2:1 gear shift, it's at least on par with the old Merc. EFI 500 engine, maybe even more powerful. I don't know, I'll see about that next summer when I get more familiar with the speedboat and can safely run it up to full speed.
I already wrote somewhere on this forum that the propeller takes power from the shaft with the fourth potency of the diameter (This is why it is sometime better to have more slip and smaller prop diameter, but even better it is to change gear ratio to have smaller prop rpm and bigger diameter.) , the third potency of the revolutions, the scuare of the pitch and the first potency of the working area. This applies to all propellers rotating in any fluid. Even a quick look tells that there is a whole potency difference between the revolutions and the step, and this bothers you with the LS!
With a classic B1 drive, you get around 4,000 rpm on the prop shaft, which is way too much, so there is no torque to turn the propeller. If you reduce the pitch, you are affected by the square, and the revolutions punish you by the cube...
It is necessary to go to a gear ratio around 2:1 and then no BB can beat an equally powerful LS engine in acceleration, top speed and consumption.

Tartilla

OP isn't likely to change his drive gear ratio.

BBC properly prepped will always beat an LS for reliable power production.

Optimal prop diameter is all based on intended use.

OSO generally focuses on high speed performance hulls, where larger diameter props become less efficient than smaller faster props.

On Volvo drives, the elephant ear props are very efficient, but they aren't going to win any races.

I don't have any issues with LS engines in boats. I considered putting one in my Formula 233 with TRS. But it's not any better than the 400 SBC block I have with RHS Vortec heads. To match the 400 cubes, the LS ends up having piston skirts come out of the bore. I've even considered using a Volvo 290 drove on the 233, as the TRS and Merctrans are becoming difficult to maintain.