Late Model GM Engine - Pros & Cons

[willysnut1959]

I have searched 11 pages of this forum and have found no prior posts on using newer, lighter, and more efficient, (and more easily huffed), motors in our old jetboats. In some posts, some of respondents suggested using these engines but that was all that was said. The $4 per gallon gas from 2 years ago has me gun shy about building a BBC and I think this can be built cheaper.

I have a accumulated three 20.5' Sleekcraft Aristocrat tunnel hulls in the last couple of years and want to use a late model General Motors LQ9 engine with 6.0 liter displacement for power. I plan on using this engine with the factory fuel injection, computer, and wiring. Buildups in Car Craft and Hot Rod magazines show that this engine can easily produce 400 HP, and 400 ft-lbs torque, normally aspirated. This is more HP than the Olds and Ford engines in my last two boats. I did have a twin turbo Gale Banks setup with a BBC and that was fun, but unreliable. It spent many a summer in the shop with blown head gaskets and eroded blocks/heads. I wasn't smart enough back them to tune in the right combination of pressure, fuel, and ignition.

The factory fuel pump will be mounted in a small fuel cell next to the engine and feed the cell from the existing two saddle tanks. I have a lead on the complete engine including accessories, computor, wiring, etc, out of a running 2001 Chevy pickup for $1000. I've read where the PROM will need to be modified so that the engine will run without the 02 sensor. I will use a water-to-water heat exchanger for cooling and retain the stock water pump.

I spoke with a boater in Texas that who is running this same engine in his jet except his motor is carbuerated and he uses a MSD LS ignition. His only problem has been the the hull was built for a 455 Olds and now runs nose down with the lighter engine. His boat runs much better with the late model engine that his Oldsmobile. He used OT headers, but I want to use water cooled exhaust so that I can retain the engine cover. This guy mentioned that his brother-in-law's, sister's, friend's, mechanic said that a Ford 351 Cleveland exhaust manifold could be adapted to fit these aluminum heads by just drilling and threading new holes in the head. I have acquired a set of those exhaust manifolds and plan on machining an 1" - 2" thick aluminum spacer to address the exhaust bolt pattern and port differences.

My plan is to install and sort out the engine in stock configuration and after getting it lined out start upgrading with power adders such as more aggressive cam, ARP rod bolts, Melling oil pump, LS 6 intake, heavier duty valve springs, and finally turbocharger or centrifical blower. Initially I'd like to turn this engine at 5000 to 5500 rpm

I'll be using a Dominator pump where the bowl is flush with the inside of the transom. I know that I'll need to trim the impellor to match my new power curve.

My questions include:
1) Has any of you done this and what problems did you run into?
2) Should I use an all aluminum engine like the 5.7 LS1 instead of the iron block LQ4 engine to save weight?
3) How much cheaper would it be to convert to carb and MSD LS1 ignition system instead of the factory injection and computer?
4) Should I be considering sliding the engine and jet towards the rear to compensate for the lighter engine? How do I know how much to move it? I assume I could also fix any "attitude" issues with trim tabs.
5) Should I start with the AA impeller?
6) Does anyone know where to find water jacketed manifolds to fit this engine or who could build them?
7) And finally, why are these engines not being used by the major marine engine builders like Inmar. I scares me that they know something that I have not considered.

Any help or suggestions would be appreciated.

Marty , St. Louis, MO

[thompy]

get on it, i think the only reason they are not more popular is the lack of aftermarket exhaust at reasonable prices, i would bet when some headers become available they will explode in popularity

[Duane HTP]

I personally believe the BBC will end up running the most economically, IF the pump is set up with todays later techonology. Better cams, better pumps, better impellers, better ect. It takes so much HP to move the boat through the water. This does not change with engine swap unless you loose a teriffic amount of weight. A properly set up BBC does the job with ease. Sometimes a smaller engine has to work so much harder to do the job that it uses more fuel than the BBC.
Duane HTP

[njj502]

Contact WastedIncome. He just finished a 6L swap into an Avenger. Got a cam and some other goodies in it. He's running the stock ECM tuned for no O2 sensors. He did use the Ford manifolds too and moved the bolt holes. I think he's spinning it just under 5K. He said it runs much much better than the old 454 that was warmed up. He's def an LsX guy. Got a turbo'd 5.3 in his 69 C-10.

[carykard]

I've been running mine for a while, but mine is a v-drive. I was the one who turned everyone onto the 351C exhaust. What kind of exhaust do you have, I've only seen three sets and I own two of them?

[njj502]

My buddy welded up a set of Hardens for his 6 OH

[DanielC]

PCM is offering a 409 HP 6.0 liter engines in ski and wakeboard boats. Depending on where you live, you might be able to find one with freeze damage you could get a lot of the parts, or maybe just the computer you would need to run a modern fuel injection engine, without O2 sensors.

They are also starting to make marine engines with catalytic converters on them. The catalytic converter may not be the best thing for getting power of of an engine, but having the O2 sensors could be an advantage.

[njj502]

O2 sensors are not needed if you tune with speed density. Go to the local junkyard and get one. Last one I knew went for 900 bucks with ECM, harness, starter, p/s pump and the manifolds on it.

[carykard]

I would of ran injection but I bought my intake and carb for $200 and my msd for $85. Easy to tune too. If you are buying everything new it cost about the same for injection or carb. There is a company in Australia that makes exhaust logs for the LS but they are about $900 without shipping or elbows. There is also a company that makes exhaust risers for the LS but they are even higher. If you have any questions about my setup just ask, I done alot of research figuring it all out.

[biohzrd]

LSx engines are starting to work thier way into the marine industry. GM is puting out the 6.2l supercharged engine right now for it. I think it is 500 or 600 hp!!! You really do not have to do much to get 400hp and 400lb out of an LSx engine. My cam only LS1 puts 442hp to the wheels with the torque above 400lb from 2200rpm all the wat yo 5500rpm in my Camaro. That is around 525hp at the crank!!!! If you decide to stay fuel injected don't worry about swapping out the truck intake for your desired hp levels. The truck manifold flows just as good as the ls6 intake, produces a little more torque, but is just ugly w/o the cover. Stock injectors are good to that level aswell.

It all comes down to the tune. For 400hp you can tune it to were you won't even realize it is a 400hp engine. You can't compare a 454 to a LSx engine. LSx engines have 50yrs newer technology in them over the 454's, and are able to handle 600hp from the factory on stock internals with nothing more than rod bolts.

Check out www.ls1tech.com. There are a few guys over there doing it.

[willysnut1959]

Thanks for all the encouragement and leads to others who have made this swap. I was hoping that Duane had done one of these swaps as he seems to be the "go to" guy for jets. Unless your going to race it or need obsene amounts of horsepower, the newer engines will produce just as much horsepower and torque as the stock BBC, Fords, and Oldsmobile. A jet pump doesn't care whether the torque is from a BBC or SBC. My buddy had a 350 Olds engine in his jet and it ran in the mid 50's. I'd be happy with 65 mph. I understand that the better valve angle makes hellava difference. Besides, where can you buy a 400 HP BBC complete for under $1500? Then compare the cost to supercharge. The LS motor would be much cheaper. After looking a Carykard's photo of his LS V-drive, I see that his exhaust manifolds are not the same as those I purchased. My exhaust mainifolds are Mercruiser cast iron with rear riser. They must be off of an I/O. Do you think they will still work?

I've tried researching posts on LS Tech, but found little information dealing with boats.

Between the all aluminum LS1, 5.7L and the LQ4, 6.0 L motors, which do you think would make the best motor for my boat? The larger motor would obviously make more torque, but the other has less weight and better heads.

What's the downside of running dry, stock exhaust manifolds? Could riser humps and water injection be added to stock manifolds?

[njj502]

Don't rule out the iron block/ alum head 6L truck motors. Much MUCH cheaper and still lighter than the ole BBC and just as much power!

Dry exhaust = very loud = Tickets from the water po po.

[carykard]

I would run an iron block not just because of the price but the strength that you gain. If you read on some of the forums you'll see that the iron blocks can hold up to more abuse when you boost them. Your riser exhaust will work just fine they're just heavy. You could run the stock exhaust with some type of water injection just make sure you don't get inversion and the exhaust manifolds are going to be very hot ahead of where the water goes in. Big block logs could be made to work with a spacer.

[willysnut1959]

Do you have any suggestions regarding setting the motor further back to compensate for the lighter motor.

I have a set of Hardin manifolds for an Olds motor. I investigate their ports versus the LS1 to see if they could be modified to work. I expect that an adapter plate will be needed in order to use 351C, Olds, BBC or SBC mainifolds.

I have posted wanted ads on the local Craigslist and have found a complete 5.3L iron block for $500, a complete 6.0L for $3500, and a complete, low mileage, aluminum block 5.7 for $3500. The 6.0L truck engine from my local salvage yard for $1000 appears to be the best deal.

Who sells water-to-water heat exchangers? I've seen them on Indmar engines, so I assume they're available.

[carykard]

If you use 351C exhaust you just need to drill and tap a few holes, the others would take alot of fab work especially the olds and sbc. Don't know about the setback, I just put mine as far foward as possible. I would go with the 5.3 or 6.0 truck motor because of availability and cost. You can get just as much power out of them. Go to ebay for your heat exchanger, just sold one to a guy putting an LS in a jet boat. Look for mercruiser 4" heat exchangers, they'll do the trick. Most can be had for about 100 bucks used just make sure its good.