350 Magnum engine - what is it...

ontheplane

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Strange question perhaps, but can someone explain to me what this engine is....

3.0 - 135 hp 4 cyl
4.3 - 190 hp 6 cyl
4.3efi - 220 6cyl - single point efi
4.3 mpi - 250? hp multipoint efi
5.0 - 220 hp v8
5.0

and so on.....

But there is a 5.7EFi engine (which afaik is about 270HP)
there is a 7.4 carb (approx 270HP afaik) and EFi (330HP)

so what is the 350 magnum? I am sure it's not 350 litres!! and it doesnt' say MPi or anything on it.

I see a few of these in boats, and don't know where it fits the range - i.e. is it a very powerful 5.7 (small block) or a pretty standard big-block (7.4)

I assume it's fuel injected?

Does it produce 350HP (which in some of the boats i've seen that would make for quite a rocketship....)

Ta
Anyone know what sort of fuel it burns at tickover? (less than 1gph? or significantly more?)
 

Beamishken

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350 magnum= 350 cubic inch displacement it's the high performance version of the 5.7 I think it comes in different hps depending on year but it was always higher hp than the standard engine for a given year
Think origionaly the magnum had 4 bolt mains & other strength upgrades but not sure if that continued
 

ontheplane

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But theoretically then it's probably a better bet than a standard 5.0 or 5.7 as it has more power same weight, and better than a 7.4 as it has less weight and same power - PLUS theoretically it could be more efficient at mid-throttle.

Would it be better at running at low speeds than a carb as the fuel better metered?
 

mlines

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We have the 350MAG in our boat. Its a 5.7 litre (350 Cu) engine and is rated at 300Hp.

Ours is the EFI, early ones have carbs.

You will also see the 320Hp Thunderbolt version which is an overbored engine (5.8 litre) and is often the result of a factory re-condition on the 350MAG.

They are derivatives of the small block Chevy engine.

According to the data from the engine management on the SmartCraft output from the engine ours burns 2.8 litres per hour at idle. When at just under 5 knots (Thames river speed) it burns just under 6 litres (about a gallon) an hour.

Martin
 

AndieMac

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?.........You will also see the 320Hp Thunderbolt version which is an overbored engine (5.8 litre) and is often the result of a factory re-condition on the 350MAG.

They have been boring and stroking the same small block engine for many years, afaik the original small block many years ago started at around 292 cubic inch, bore to get more width, then stroke for more depth, increasing capacity for each new model.
Mercruiser marinise small blocks, 6.1 or 6.2 from memory these days.
 
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AndieMac

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But theoretically then it's probably a better bet than a standard 5.0 or 5.7 as it has more power same weight, and better than a 7.4 as it has less weight and same power - PLUS theoretically it could be more efficient at mid-throttle......

Depends how big and heavy the boat is. The big block 7.4 litre delivers lots of torque on a heavier boat for down low work, on and off the plane (excuse the pun :))

The EFI and MPI are wonderful things, instant start etc, but still use plenty of fuel just like a good, well maintained carb set-up.
For the average, less than fifty hour per season recreational trailer boater, you probably won't see a huge difference in fuel money saved.
 

spannerman

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I have a 350 Magnum with a carb and knock sensor ignition, at 3300 rpm I get 33 lph consumption and at 4500 rpm its heading towards 70 lph, guess which speed I cruise at!
 

ontheplane

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All good though thank you - and interesting that at tickover it will use as little as 3l per hr - that means a 5 hour day on the river would cost about £20 in fuel - that's perfectly ok with me!

Even 33lph at 3300 rpm is quite bearable.... 70lph getting less so! I would imagine that 3300 rpm in a 21-23' sportsboat / cruiser with that engine is still 22 - 35 mph though, so a good fast cruise
 

AndieMac

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...Even 33lph at 3300 rpm is quite bearable.... 70lph getting less so! I would imagine that 3300 rpm in a 21-23' sportsboat / cruiser with that engine is still 22 - 35 mph though, so a good fast cruise

MPI 350 MAG, 23' boat, 19" prop @ 25 knots will use approximately (in fair conditions) 35 LPH @ 3300 rpm, just as spannerman says.
 

spannerman

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My 350 is in a Draco 2400 which is a very solid boat and 3300rpm gives me 24 knts when its clean, with on a stainless 17" prop.
 

AndieMac

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Ours measured off the SmartCraft feed: 3250 rpm, 26 knots - 33LPH 22ft boat with 350MAG on Bravo III drive

That 3250 rpm is a nice sweet spot in this engine, the speeds of course vary with the prop pitch's and gear ratio's of the drives.
As most of us living in relatively short summer period countries will appreciate, the cost of fuel in an average year is not a lot of money, running a recreational trailer boat.
 
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