I have a budy who has an ls7 in a jet boat with very low hrs (35hrs) and he wants more power. I have a few options. 1. I have a ls3 block that I can get sleeved and make him a 454ci and get him approx 650 hp at the rpm level that he will run. I can make him a 416 ci ls3 from the block and throw a procharger on it and make him 700-750 at the same rpm. 3. I can change out the pistons in ls7,throw a procharger on it and make 750-775 at his rpm. All of them being on 93 octane fuel. Any thoughts?

 

How much is he looking to spend is the first question? All those choices will easily break 10k if not more...

 

Money with this guy isn't really the issue. He has lots but ya he's cheap. (I guess thats why he has lots). One problem is hood clearance. It may be dificult to get a non fuel injected version of any of the engines in the boat. Problem with fuel injection is that it is a dumb system and not having a dyno within 500 miles of here to set it up can be a problem along with the water cooled exhaust makes it a little hard to tune it on the water using an o2 sensor.

 

For cheap you can do some headwork, cam and headers and get over 600hp for half of a forced induction build.

Or forge the engine and do the procharger as you said for a lot more.

 

I think putting a Procharger on an LS7 block is a recipe for disaster. They go pop in a car...worse a boat where high RPM is sustained for a long time. Sleeve the LS3 or LS7 block then throw a Procharger on it.

 

^^^^WERD^^^^

Why do you think they developed the LS9 and it is 376ci???? Because the LS7 cylinder walls are to thin for boost that's why.

 

A properly sleeved LS7 block with aftermarket sleeves will be stronger than GM's LS9 version. RED or ERL can make a very nice foundation out of an LS7 or any other LS block.

 

How about a J/Y 5.3 and a pair of turbos? Run it 'til it blows and then upgrade the long block...

 

Jet boat stuff is different. This thing will only turn 5500 rpm and if supercharged only run less than 8 lbs of boost. 600 hp is easy but try and do it at 5000 rpm with a 416. Can be done but I would like to see close to 700 at that rpm. Typically on NA engine for jet boats the heads are small and the cam is a little biger than what you would see in a car. Bottom end doesn't matter but peak torque and were it occurs is the ticket.

 

How about sleeving the LS3 for 440ci, then supercharging it?

 

Correct.... but I was under the impression he didn't want to drop the roughly 2 grand to sleeve the block.......

 

If I supercharge then I don't need to sleeve it to get the power i need. If it is NA it needs to be at least a 454 ci to get the power I need. I think it is going to get put on the back burner for a while anyhow now.