Mercruiser 454 into chevy with a 454

willness33

willness33

Here for the memes
Joined
May 3, 2005
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Alexis,NC
Just kicking this idea around here. I have a friend that has a line on a 330hp mercruiser 454 out of an early 90's boat. I've got a '95 chevy with a non-vortec 454 that I believe was originally rated at 195hp or something embarassing like that. See what I'm thinking here? The two should be very similar with differences being in the freeze plugs and gaskets. After reading a bit it looks like the cam grinds are very similar between the marine engines and the truck engines. Of course the marine engine is carbed but the throttle body should bolt right on using either intake. Anyone have any personal experience with this or ideas of why this wouldn't be a good swap?
 
you need to check out mounting bosses and dowel locations of the rear of the block, starter mount locations as well.

Marine and "industrial" engines may not cross directly over to an automotive platform

it's an emissions thing, the OEM is required to make it difficult if not impossible to keep "industrial" type engines from being installed in automotive applications
 
A friend of mine swapped a marine 350 into his truck. It got horrible gas mileage until he changed the cam. I think it also didn't run quite right until he changed the cam too. This was about 12-15 yrs ago, so my memory is foggy.
 
Keep in mind the 454 TBI will not support that higher power 454. There are very few mods to improve it. On a small block, sure you can throw the 454 TBI and injectors on and build a little more, but with the 454 you are limited in what you can improve.
 
I'm thinking the exhaust manifolds on that 454 may have water passages going through them, I would think that would either cause issues when you block those passages to run the stock manifolds, or if you (not likely) use the boat manifolds it would probably run the coolant temps up too high.
 
Tacoma747 said:
I'm thinking the exhaust manifolds on that 454 may have water passages going through them, I would think that would either cause issues when you block those passages to run the stock manifolds, or if you (not likely) use the boat manifolds it would probably run the coolant temps up too high.
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Marine exhaust manifolds take the water exiting the block (from the t-stat housing) and cycle it through a set of water jackets in the manifolds. They do not receive water straight from the block however, they are hosed.

The biggest issue, other than aforementioned physical constraints, is going to be the cam. Marine engines are set up for running mostly at WOT and as such their cam grinds are not happy for variable RPM running below WOT. For example, the marine 305 4-bbl in my Four Winns is happiest between 4000 and 4400 RPM. Below that it does not have good economy. Lots of bottom end to get out of the hole and up on plane but I would not run it around below 2000 rpm much, which is where a truck engine lives a lot of the time.
 
OnlyOneDR said:
Marine exhaust manifolds take the water exiting the block (from the t-stat housing) and cycle it through a set of water jackets in the manifolds. They do not receive water straight from the block however, they are hosed.

The biggest issue, other than aforementioned physical constraints, is going to be the cam. Marine engines are set up for running mostly at WOT and as such their cam grinds are not happy for variable RPM running below WOT. For example, the marine 305 4-bbl in my Four Winns is happiest between 4000 and 4400 RPM. Below that it does not have good economy. Lots of bottom end to get out of the hole and up on plane but I would not run it around below 2000 rpm much, which is where a truck engine lives a lot of the time.
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You're right about the exhaust manifolds. They are "watered" by hoses off the t-stat housing. Everything I've read is that the marine 454 is the same exact block as the truck engine. Something else I've read is that the cam is very close to the grind of the truck cam. Still, 100hp increase for just a proper cam is a good bit cheaper than finding vortec heads for the 454 I have in the truck now. Still thinking about this....
 
the 7.4 330 hp is basically a dually motor with a marine grind cam. They are pretty mild. I'd just strip the marine exhaust and cooling off of it and run it as is. You could probably step up with another cam, but you're going to start spending money and opening a can of worms(where do you stop). The hp difference is mostly due to the way the engines are measured(SAE specs, accessories, emission equipment, exhaust, etc). The 330 has a bunch of bottom end, it will push some heavier boats up on plane that the higher hp magnum engines won't. They offered the same engine for two years with a bolt on TBI set up with basically no differences in performance over the q jet. The only thing I'd recommend is replacing that boat anchor of an intake with an aftermarket aluminum intake. This engine should be a Mk IV type big block so all the "classic" accessories should bolt on. The heads are the small "peanut port" style that work well for making bottom end. These heads also don't require extensive head work to use aftermarket rocker arms like the Mk V, VI heads do. Should be a pretty easy swap.
 
GCncsuHD said:
Keep in mind the 454 TBI will not support that higher power 454. There are very few mods to improve it. On a small block, sure you can throw the 454 TBI and injectors on and build a little more, but with the 454 you are limited in what you can improve.
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You're kidding, right? :rolleyes:

The fuel pressure can be turned up, the BPW (base) injector pulse widths and the fuel curves can be adjusted in the BIN (the injectors will likely have a LOT more flow left over after the stingy-arse factory tune)... just like every other SBC sporting mods and running the stock TBI hardware
 
Damn. I was about to abandon the idea until the last 2 posts..... Still undecided if I should do it..... The price will be "right" on the merc engine and I will have a solid (albeit underpowered) 454 for sale.

So spareparts and Carver, in your opinion, would it be worth it assuming not a lot of money is going to be spent? Or should I look at just letting the current 454 breathe better via a good cold air intake, open the exhaust, an alum intake manifold and a "chip" for the obdI?

I've been using this truck for years and it's rock solid as a tow rig or whatever I ask of it, but it does lack a bit of HP. Anyone that has one of these trucks will agree to that.
 
it would be nice to be able to swap engines rather than to tear into the one in the truck, also nice to have a spare. I always equate having a big block around is similar to having a big ass hand gun, you hope you never need that kind of power, but it gives you a warm feeling just knowing its there. In all seriousness, the mercruiser motor isn't too different form the engine you have. good thing is you can play with one, and keep the other as a back up. Keep in mind, big blocks are getting scarce, depending on what you have to pay for the mercruiser, it may be worth having just to hang onto. Before you go spending any money on it, do a compression test, if you can, pull the exhaust manifolds and look for signs of water getting back in the exhaust ports. If it checks out, swap out to a performer intake, put a good set of rockers on it, and ride
 
spareparts said:
it would be nice to be able to swap engines rather than to tear into the one in the truck, also nice to have a spare. I always equate having a big block around is similar to having a big ass hand gun, you hope you never need that kind of power, but it gives you a warm feeling just knowing its there. In all seriousness, the mercruiser motor isn't too different form the engine you have. good thing is you can play with one, and keep the other as a back up. Keep in mind, big blocks are getting scarce, depending on what you have to pay for the mercruiser, it may be worth having just to hang onto. Before you go spending any money on it, do a compression test, if you can, pull the exhaust manifolds and look for signs of water getting back in the exhaust ports. If it checks out, swap out to a performer intake, put a good set of rockers on it, and ride
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THat's the thing here, I really don't need to actually tear into the current engine. It's been good to me and still runs perfect. I'm just looking to get more out of it or swap for something that has more grunt with minimal mods. Since vortec 454s aren't falling out of the sky anytime soon, this merc engine seemed to be a good idea at the time. I can get access to the engine for a compression test and pull the manifolds pretty easily. Ok, I'm back on with thinking I may do this.
 
one thing you may need to consider, your existing 454 may be a MK IV or MKV(95 was the intro year), if its a MK V, it may require a different flywheel/flex plate. If you're running a manual, just keep the one with the Mercruiser engine, if you're running an auto, you may have to buy another flex plate if your current engine is a MK V
 
Mk IV will have a 2 piece rear main seal and a flanged crankshaft, tin timing cover, and a fuel pump boss. MK VI has a one piece rear main, cast timing cover, no fuel pump boss, provisions for roller cam. MK V is where it gets tricky and I may be wrong on some of this. should have 1 piece rear main with non flanged crankshaft(only thing I'm sure of), I've seen them with tin and cast timing covers, with and without fuel pump boss, if it had the fuel pump boss, some times it not machined. To be sure between MK V and VI, you should run the casting numbers. MK V and VI have a different head gasket water jacket pattern from a MK IV, you can swap them all around but it takes special head gaskets. All kinds of story's about MK V blocks not having enough metal in them and not maintaining the crank bore after use. I know one boat engine builder that won't build a MK V, but he's got stacks of MK VI stuff laying around to use anyway
 
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