LS3 6.2 transplant

QBhoy

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So being from the UK and not too familiar with the US engines and automotive industry....and there is likely a good answer to my question, but;

why dont people drop in an LS3 6.2l 500hp engine in as a direct replacement to their short block 5.0, 5.7 and 6.2 mpi engines ? Am I right in thinking it’s also a GM engine and logic would perhaps suggest be fairly easy to do and might even be genetically set up to drop straight in without too much problems ?
why can’t we get this kind of power from Mercruiser instead of the 310hp. I understand the marine environment is harsh and reliability is key, but come on. The power from these big lumps is pretty pathetic...especially when I think of European power figures from modest engines half the size.
Has anyone done this ? If it is compatible, why go to the bother of 383 stroker etc ?
thanks
 

Scott Danforth

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They do.... However the marine motors are limited to about 420hp (prop rated).
they are paired with dual prop drives

They require closed cooling and a few other things such as cats and are only EFI

A simple 383 doesnt need closed cooling and many are carbureted
 

alldodge

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This has come up a couple times on OSO but from what I remember (Suffer from CRS) this is a car motor, HP is higher but torque is lower. There are a few folks which are starting to install the LS motors, but not wide spread yet.

Similar to a Indy race 12 to 1500HP motor, they produce that HP but only at 10K RPM
 

QBhoy

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Ah. Good points from both. Just thinking why have the 8.1 HO mpi at 400hp or there abouts, if the 6.2 LS3 (which is surely derived from the base 6.2) can comfortably produce these figures.
I know mercury and VP seem to be going their own way with engines, but why break away from what’s tried and tested over decades. I’m not for it. The 4.5 v6 replacing the small block V8....telling us that more modern materials are used etc. The LS engines now have the same more modern materials. Why not follow their development ? The fuel economy difference is tiny.
Or why not develop the 4.3 ? Has this been taken further in the automotive industry ? Are we seeing 300hp from a 4.3 GM in a car ? We only hear and see the cars like camaro Z models etc over here. Some mad people actually buy them because they are so much cheaper than the equivelant powered BMW or Mercedes. Despite the crazy fuel costs, haha.
 

QBhoy

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I mean, who would rather a 4.5 V6 250hp over a 5.0 V8 260hp ? Not me.
 

QBhoy

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I digress slightly, but if the change to in house engines is about fuel economy and progress (as stated by Merc) then the below pictures show wot figures on new 4.5 vs old 5.0 mpi engines. The 4.5 is actually worse and only marginally better further down the revs. One might argue that the 5.0 and it’s extra torque and hp might even see the same boat going the same speed at less RPMs and less fuel used.
Point being, why not just follow the car industry gm engines and use the same tech and advancements to see tried and tested improvements ?
these in house engines have yet to be trusted over decades of use. Let the motor industry make the mistakes first.
 

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Rick Stephens

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Small engine+high horsepower = higher RPM for power range. Boat motors don't have gears. Now if they did...... turbos and 10K RPM would be the ticket.
 

Scott Danforth

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Ah. Good points from both. Just thinking why have the 8.1 HO mpi at 400hp or there abouts, if the 6.2 LS3 (which is surely derived from the base 6.2) can comfortably produce these figures.
I know mercury and VP seem to be going their own way with engines, but why break away from what’s tried and tested over decades. I’m not for it. The 4.5 v6 replacing the small block V8....telling us that more modern materials are used etc. The LS engines now have the same more modern materials. Why not follow their development ? The fuel economy difference is tiny.
Or why not develop the 4.3 ? Has this been taken further in the automotive industry ? Are we seeing 300hp from a 4.3 GM in a car ? We only hear and see the cars like camaro Z models etc over here. Some mad people actually buy them because they are so much cheaper than the equivelant powered BMW or Mercedes. Despite the crazy fuel costs, haha.

8.1 motors were big block torque monsters and could produce well over 550hp in a boat. the LS 6.2 will never produce that amount of torque without a blower sitting on top of it. in a car you can spin it to 9000 RPM. in a boat, the outdrive limits it to about 6000.

a car only needs 5 hp to maintain speed on a road. so a 300 hp motor in a car is all High RPM power, no significant low end torque.

a boat is similar to a dump truck traveling fully loaded up hill in sand while stuck in 4th gear..... so a 300 hp motor in a boat is all low end and mid-range torque and some hp.

comparing HP is meaningless unless you know the RPM. HP and RPM reference is simply comparing Torque.....and Torque is what makes the propeller go round

believe what you want about the in-house design at Mercruiser. however the truth is they wanted more in-house proffit...... but that doesnt make good marketing
 

Maclin

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QBhoy , Typical pleasure boating is like a truck/tractor pull in reverse as the engine sees it. And with only one gear ratio + prop combination to work with. To the manufacturer(s) it is fraught with compromises.

The high winding high HP/Torque ratio engines can have their place in purpose-built racers, automotive or marine. Basically the longer the duration of the "race" the more higher HP wins out. In recreational boating, multiple holeshots in a typical day make for somewhat tamer engines over the high performance ones.
 

QBhoy

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Guys, I’m just talking about a standard ls3 found in a camaro or something. Peak torque at 4000rpm and peak power anything from 5100-6000 from what I can see.
Surely easily useable in a marine application. Perhap slightky differently cam’d.
 

Rick Stephens

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Guys, I’m just talking about a standard ls3 found in a camaro or something. Peak torque at 4000rpm and peak power anything from 5100-6000 from what I can see.
Surely easily useable in a marine application. Perhap slightky differently cam’d.

Who cares what it's doing at 6K? What is it doing at 1k?
 

Scott Danforth

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Guys, I’m just talking about a standard ls3 found in a camaro or something. Peak torque at 4000rpm and peak power anything from 5100-6000 from what I can see.
Surely easily useable in a marine application. Perhap slightky differently cam’d.

nope, the came lobe centerline in the stock camaro motor is all wrong for marine use, and the stock valves are not set up for long-term loading. you could change the cam and change valves to inconnel on the exhaust, etc. but because of the alloy block you still need raw water cooling and cats.

can it be done, yes, some people are doing it. can it be done as cheaply as an iron motor......no.

GM sells the motor in a marine config..... you still need to add all the other stuff to it. price out a set of LX exhaust manifolds and a heat exchanger

http://www.gmpowertrain.com/engines/6-2l-l86.html
 

QBhoy

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Scott. This is the kind of answer I was after. Nice one.
Rick...at 1000 rpm....bugger all ! Haha.
 

QBhoy

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But...again...an argument might be that Merc and VP have followed these GM engines throughout decades of development and marinised and marine proofed versions of the most popular variants....slightly behind the times of advancements in auto. Why not follow on and marinise and follow trend ?
 

Scott Danforth

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Merc and VP use the motors from GM's marines specific line of industrial engines. That way they get a warranty.
 

Maclin

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I was on a sleuth recently on VP engines, looks like they stuck with the 4.3 displacement for their V6 but in aluminum block and heads. Theirs has 200 and 240 and 280 horsepower configurations. They have retired the 3.0. One boat review for a Stingray Cuddy said that even in the 200hp "version" the full 280hp was available at takeoff. That was what I was sleuthing, no real satisfaction on that claim as yet.

VP went with the 5.3 displacement in the small V8 offering, and 6.2 displacement for the next step up V8. So seems like they went more along with current but updated GM stuff, while Merc went with the "all new" ones when just looking at displacement. Maybe?

Both 4.3 V6 and 5.3 V8 use VVT and are catalyst engines with wideband Oxy sensors in use with direct injection for more precise a/f. Seems to me that VVT with the aluminum block/heads allowing the 11/1 compression ratio, most of the Marine-induced problems have been addressed and mitigated to a huge degree. I did not look at their 6.2 in detail yet.

I am still poking around... :ranger:
 

99yam40

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Back in the 70s I worked for a place that the owners son had too much money.
He had a few special 454s built in Cal and shipped to Tx where we installed 2 of them into a cigarette boat just running around in a lake.
he kept ripping the flex plate up between motor and out drive.
we put in solid flywheels and then he just ripped up the outdrives.
upgraded HP needs drive trains that can handle the HP also.
he sold that boat and then installed the spare he had in a 16 foot boat.
I was not around if and when he got that on into the lake
 

QBhoy

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Interesting stuff guys. I just hope they are doing it for the right reasons.
I keep thinking back to when VP tried to go high tech...using the horrendous 4 cylinder 16v 151 and 171 engines. Came from the Volvo cars (not that that’s a problem in general) but they just weren’t suited for the marine environment. Timing belts...yuk.
I have long considered the GM 4.3l the best marine engine in the world. Pound for pound superb. Simple, cheap to maintain and run. Yet to hear of one fail, that wasn’t down to poor maintenance.
Lets hope these new engines can compare in years to come.
 
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