I’m mostly an internet mechanic but I’ve never heard of an LS as low as 9:1 so I’d double check that.

Many people on here haven’t had the best luck without an intercooler. It may work but you’re leaving a ton of performance and reliability on the table without one. The heat in the bilge and demands on the engine compared to a car are big contributors to the issue.

i plan to use the 5.3L gen3 LS engine. One of articles I read referred to the cast iron block 5.3 325ci engine as an LS1. I’m sure I can get the compression down to 9 to 1 using the stock pistons if I run a thicker cometic head gasket.
my goal is to build a twin turbo set up to run in these engines as they are the least expensive ls eng to buy at the boneyards as most guys don’t want the gen3 engines.
check my other thread on the LS Eng


a guy wanted to see how much hp a stock 5.3 Ls coulda handles. They ran 76mm turbos. And ran a bunch of Dyno pulls increasing boost each pull. It made 695hp @ 5.5 lbs of boost and they made over 1300hp on the last pull. I think they should have kept going until they blew up the engine lol

say you want 700-800 ponies. You can buy a merc for all the money and when you blow it up it’s big money to fix. Or I think a twin turbo set up for the LS 5.3 will live a long life at that hp level as It’s under 8lbs And will make that hp. It was proven in the Dyno tests Buy a junkyard engine hone the cylinders install new rings gapped for turbo set up and Shim up the oil pump spring, arp rod bolts, cometic head gaskets and you have a 1500 buck or less 800hp engine if you do your own freshen up work it would be closer to a grand! I would set mine on kill for 1,000 ponies and so what if i puke a motor. At that price I would keep a couple spare bullets in my garage lol.
Just tryna build a better mouse trap

Rm you seemed to have it all figured out!!! Set on kill and let us know how you make out. 😁

Im sure ls engines with good rods will hold up at that hp level.

I would be doing it with stock rods. The motor made 350hp more than that. It sucked That they didn’t keep going until it failed. To see what would fail and when. My guess is the powdered rods.

I think the LS is a much better engine design than the bbc platform. With A/m rods and forged slugs they make insane hp. The block is serious reinforced and has the six bolt mains.

the guy above said over 9 to 1 Cómp I would have detonation issues I was just saying I’m sure a stock ls motor is 9 to 1 or above. Which you just confirmed. As a result I would definitely Run on intercooler.

aren’t most currently built blower motors in the 8.5 to 1 range?

I never ran an intercooler for years on my 8lbs 10-71.
Intake temps never went over 150* at speed.
An intercooler dropped it down 30* (summer weather)
I don`t recall any speed increase but probably a safer set up with less chance of detonation.

what size are your engines?

well does it accelerate harder? Did you try spinning more prop?

thanks for the info, RM

The ls platform has been beat to death. It is well know what breaks at what hp/rpm/boost in a stock ls engine. Search the internet and you will find all the info you will need.

It is hard to compare a bbc to an ls engine or any other. Modern engines can run more cylinder pressure (in general) than an older designed cylinder head. It is not uncommon for a stock modern engine to run compression of 10:1-12:1 on pump gas from the factory. Try that with a bbc.

where are all the twin turbo LS engines in offshore power boats? I haven’t seen one.

comparing a blower motor to a turbo motor on how much boost it can take is like comparing apples to oranges. The added ho an engine needs to make in a blower motor and the added stress in the front of the crank for the blower drive add a huge load on the bottom end that a turbo doesn’t. Say a 1000hp. Lower motor how much ho does it take to spin the blower 125hp?

I look at the new turbo packages from merc and others, I think that is the future. Don’t see anyone one offering twin turbo set ups for an LS anywhere.

merc gets close to 40k for a 600sci. I think a reliable 600-800hp twin turbo kit for the LS would sell very well especially knowing that when it gets tired you can replace the engine very affordably.

Turboed ls engines are nothing new. Like I said, beat to death. Yes that is in the automotive world. Marine environment is another story. You think there aren't many for no reason?