vtown

The LS is not a good choice to replace a big block in a BOAT above about 550 hp. Its a great choice below 550hp.

the advantage to the LS is the volumetric efficiency and lower weight of an alum block and heads.

The bore that works the best to unshroud the valves is 4.065...the biggest crank to live in the alum block is 4" so thats 416ci. The combo I would build is the alum ls3 with ls3 heads, incolnel and stainless valves, forged internals, closed cooling, with variable valve timing to increase the low end power needed in a 1 speed boat. That makes about 550 hp at 6k rpm.

any more power than that will be with rpm at the expense of torque...again a boat is like a car stuck in 4th gear...so the boat auto comparison does not work well here.

boost will give more power across the rpm band but kills longevity, price, and fuel economy compared to a N/A bbc...you will want an iron block to run boost so there goes alot of the weight savings.

There is a good reason that Raylar, MAST, ILMOR all make mid-upper 500hp marine LSx engines.

Merc tested the off the shelf GM ls engines but in stock auto form they are not as good as a BBC. either not enough torque (stock ls7), not strong enough to live in a boat (stock ls3), drinks too much fuel and has a short life (stock lsa).

weismann marine has done very well with stock ls7's but that is due to the 6spd TRANSMISSIONS. stronger build and low end power are needed in a boat build compared to a car/truck...thats why the LSx engine that is ruling auto drag racing only has a small place in marine compared to BBC.

Pismo10

LS has its place and will find it. One would be perfect in my 22 donzi classic.

GTOKILLER

iTrader: (1)

IMO smaller cats should be the candidate for LS engines, light weight, high RPM high torque is required as much as high RPM.

tomcat

Most marine BBC in the 700-800 HP range are supercharged engines that make 500-550 HP NA. If the LS is a better choice up to 550 HP NA why not supercharge it and be the better choice at 800 HP?

rmbuilder

Katech LSX 500 CID, 600 lbs/ft from 3000 RPM, 675 HP @ 5900 RPM, mild cam. Affordable, reliable, complete with an accurate SAE dyno sheet. Makes for an interesting comparison stacked up with a conventional 502 BBC.
http://youtu.be/aE576x32yJA

KRAUSMOTORSPORTS

iTrader: (2)

Wow this is some good information and answered the question i woke up today thinking as I looked out at my engineless 25.5 IMP Eleganza (yea old boat i know compared to you guys) But I was considering this as a alternative to weight loss on the Pig with the LS2 Stroker 408. Which I have readily available. But looks like i'll continue with my 454 rebuild and exhaust worth more than the boat build! I also agree with the big block producing more torque at low end then the under 416ci. engines. But i'm also not up to par as to whats available to the LS world. But catching up!

C_Spray

iTrader: (2)

Remember to factor in the usable rpm ranges between an LS and BB package when making flywheel torque comparisons. A 10% or 15% gearing (or prop) change can make a big difference. The availability of variable cam-timing on the LS is a big factor as well.

wannabe

I don't agree the LS is limited to 416. The intake valve is 2.20 inches and with a 4.185 bore and 4.125 stroke you are at 454 cu. inches- the same as the venerable BBC. The increased efficiency of the LS ports will give you MORE torque, better rpm range also. The way I would go is with the iron LSX block for durability and it will still be lighter than a BBC.

Wannabe

KRAUSMOTORSPORTS

iTrader: (2)

I know the LSX isn't limited to 416 as I've only owned a couple ls2's and one LS3. But I have never had the opportunity to work on anything bigger. I know the LSX427 are some awesome runners! But pricey too- at least for me. Not to the thread either as I may wonder with running LSX/2/3. I know some of these especially Running forced induction have had great success on E-85. Anybody tried this even though fuel consumption i know is horrible and e-85 also has moisture issues?

Plowtownmissile

I agree 100%.

While I agree the aluminum blocks would be good in a light and efficient cat, a stroker iron block motor can be done for the heavier Vees that you can throw tons of boost to reliably. There are also tons of twin turbo LS7s out there throwing down 1,000+hp. As far as the reliability of LSX engines go, just remember where there design came from. For all the naysayers, just wait til Skate gets his new boat dialed in.