what the difference between 5.7 mag and 5.7

[bobboater1]

question i want to know the difference between 350 gm marine and 350 mag
thank bob

 

[Don S]

Re: what the difference between 5.7 mag and 5.7

In a nutshell, In the Mercruiser line, the Magnum was the higher performance line of the 350/5.7 line.
How it became the high performance version has a lot to do with year and rather carbed or EFI.

 

[bobboater1]

Re: what the difference between 5.7 mag and 5.7

don the boat came with a 350 mag new . i brought a 350 260 hp marine long block. think their is a big h/p difference??
bob

 

[Don S]

Re: what the difference between 5.7 mag and 5.7

Like I said, it depends on the year. I don't have a clue what year boat you have, or what year your old motor is, or anything about it.
Get the OEM service manual and look at the specs for your original engine, and then compare them to the specs of whatever long block you just bought. I also don't have a clue what that is.
All you have to do is compare specs.

 

[bobboater1]

Re: what the difference between 5.7 mag and 5.7

sorry don its an 89 glastron boat but the engine is a replacement
thanks for all your help. ready to go to my local merc. dealer(nice people) next week as we planned on saving money by installing the motor in dec..winter here. pa.hes dead slow here he's a small dealer, so that hurts some vrs the giant dealers. i am going to see how much stuff i can get him to do. i can do a lot but if he's fair and i know he is. i will give him lots to do then winterize it. so when weather breaks i wont have to do as much. stuff. getting to old for this 44...got new manifolds , water pump. getting a starter and will let him sell me what i need..as the watt. is 2 yrs dealer installed up to $3500 for repairs. gasket . oil leaks pistons etc..at least they will pay for dealer to remove and fix problem
thanks bob

 

[bobboater1]

Re: what the difference between 5.7 mag and 5.7

don the manual say's mag is still 260 hp

 

[Bondo]

Re: what the difference between 5.7 mag and 5.7

I Don't know this for a Fact,...
But I believe the Magnum motors are built alittle Heavier on the bottom end,......
You Might find 4 bolt Mains,+ Possibly a Forged Crankshaft.......

What's ya doin' with the Take-out,..??....

 

[FreeBeeTony]

Re: what the difference between 5.7 mag and 5.7

Didn't the mag also have the roller cam and the highrise manifold?

 

[bobboater1]

Re: what the difference between 5.7 mag and 5.7

well i got amotor witha 4 bolt main and have my old manifold , so the worst case i could be missing the diff. crank and the roller cam
thanks
bob

 

[crazy charlie]

Re: what the difference between 5.7 mag and 5.7

The heads on a Mag are of a heavy casting

 

[Zackman]

Re: what the difference between 5.7 mag and 5.7

The Mag has some stronger components (e.g. steel crank) that allows for higher max revs. Hp difference is 300 for the Mag vs 260 for the standard mpi. I believe both have the same amount of torque, but with the increase max rev the Mag gets a higher Hp rating.

 

[Don S]

Re: what the difference between 5.7 mag and 5.7

Hate to tell ya this BSMan, but in 89 (The year of his engine) they didn't have MPI, but they did have Mag and standard 5.7. They both used the same crankshaft. Only difference I can see is there were different cams used (both flat and roller) in that time, but there is nothing that says which is on a Mag and which is on the Std 5.7. Same with carbs, there are 2 bbl carbs used and both Qjet and Weber carbs, but it doesn't say which is use on what.
Both are same HP rating and RPM rating for WOT rpm.

 

[Zackman]

Re: what the difference between 5.7 mag and 5.7

Don, no problem; my bad. But you'll see the boat is an 89 and the motor is a replacement. You're probably right about the mpi issue although it's never stated that it carburated.

Are you sure about the crankshaft being the same in that vintage? I know that more recent vintages uses the steel crankshaft. Based on your comments, it would make sense that the Mag would have the roller cam.

 

[Don S]

Re: what the difference between 5.7 mag and 5.7

Bobboater would be the one to tell us what the old motor was like, As he said early on, the old engine was a 350 mag, I don't know if he pulled the intake and looked for roller lifters, he never said what carb it had or anything, all he ask is what the difference was.
In Mercs parts, the crank is the same, and any of the items that are listed with more than one option are not designated Mag and Non Mag,

We can all assume what caused the engine to be designated as Mag or not, but there is no way of knowing for sure because Merc doesn't evey say what the differences are. In 89, the only difference may have been the price and the decals. Who knows.

 

[bobboater1]

Re: what the difference between 5.7 mag and 5.7

WELL I WILL KNOW SOON ABOUT the lifters i hope to get the motor in within 2 weeks at the shop
bob

 

[John_S]

Re: what the difference between 5.7 mag and 5.7

From going through MercruiserParts.com and Dennis Moore's book, no 5.7L, 5.7LX or 350 Mag had 4 bolt mains or a steel crank. As Don stated, the flat and roller hyd cam produced the same hp. The main differences of the mag was the high-rise intake, 4brl carb jetting (over LX), and advance ignition curves (some years same as LX, but more agressive than L, and sometimes by drive - alpha or bravo).