454 vs 454 Magnum

[ericcarr2000]

I recently purchased a 87 Sea Ray Sundancer. The motor was rebuilt back in 2004 and I was told that it is the Magnum version, it does say Magnum on the flame arrestor. My question is this, what is the difference between the standard 7.4 and the 454 Magnum motors. Is there a difference in Horse power, and how can I tell the difference to see if I have the Magnum?
Thanks.

 

[Mischief Managed]

Re: 454 vs 454 Magnum

The last of the 454MAGs have 365 or 385 HP (can't recall) versus 310HP for the last of the "regular" 7.4 engines, not sure about your vintage. They used very different internals and the cylinder heads/intake manifold have bigger ports on MAG. The MAG is designed to rev much higher and is built to do so.

I suspect you have the regular 454 with 330 crankshaft HP.

 

[ericcarr2000]

Re: 454 vs 454 Magnum

So I guess pretty much the only way I can tell if I have the Magnum version is to take the intake off and take a look at the head ports then?

 

[tpenfield]

Re: 454 vs 454 Magnum

The intake manifold would probably be the best way to tell as MM mentioned. The Magnums were known as having 'rectangular' intake ports, whereas the the standard 454 is commonly referred to as 'oval' port.

There may still be a serial number on the engine (look near the starter), and that could be more telling.

For the vintage that you are looking at (1987), I think the differences are 330hp for the std and 365hp for the Mag. Later models of the engine went more like 310hp for the std and 385hp for the Mag.

Usually you would see the 454 Mag on go-fast boats that can take advantage of the higher RPM. A cruiser would be more fitting for the std 454.

 

[ericcarr2000]

Re: 454 vs 454 Magnum

Well I do know the serial number on the motor it is-B522432.

 

[tpenfield]

Re: 454 vs 454 Magnum

That serial number comes up as a 454 Mag w/ Alpha1, which was an offering prior to the Bravo outdrive introduction in 1988.

 

[ericcarr2000]

Re: 454 vs 454 Magnum

So according to the S/N, I do have the Magnum then?

 

[Tail_Gunner]

Re: 454 vs 454 Magnum

So according to the S/N, I do have the Magnum then?

Nope while merc can call it a mag there are other mag's made also..They have stronger internals and better flowing head's..Good motor though

 

[Bondo]

Re: 454 vs 454 Magnum

So according to the S/N, I do have the Magnum then?

Ayuh,.... Accordin' to the serial number, yer Lucky it's a 330hp, 'n not a 365hp,...

Alpha's done like that kinda power,...

 

[Fun Times]

Re: 454 vs 454 Magnum

Since your engine model was made in 1987 your serial number and the service manual and since the engine came in a sea ray, your engine model is a magnum but only rated at 330 HP and with one exception, Most of the engine internals should be cast aluminum for the 87 model, in 88 the magnums started using forged aluminum and upped to 365 HP. Studying over the links below should help you with some questions you may have.

Boatinfo - Mercruiser Service Manual nr. 9 - 1985-1988 - GM V8 Engines

Boatinfo - Mercruiser Service Manual nr. 9 - 1985-1988 - GM V8 Engines

Long Block Marine Engines, Marine Longblocks, New 454 7.4 Marine Long Block Engines and Rebuilt Mercruiser Long Blocks | Performance Product Technologies

Engine serial number 0B522432 is an MERCRUISER MAGNUM ALPHA 454 PARTS CATALOG 90-14296 - 454 MAGNUM ALPHA ONE ENGINE MERCRUISER - (454 H.P. (1987) Serial No: 0B522432 Model No: 04544347

Post #2,
Mercury Tech 454 magnum vs 7.4 litre Mercruiser

https://www.google.com/search?q=198...%2F210223-454-mag-s-build-ideas.html;1024;768

 

[Walt T]

Re: 454 vs 454 Magnum

Keep in mind 20-30 extra HP wont really be felt in that boat. I really do like those older Sundancers. I liked the teak they used to use.

 

[ericcarr2000]

Re: 454 vs 454 Magnum

Ok so let me ask this, how much work is involved in changing over from Alpha one to a Bravo outdrive, do I have to replace the transom assembly?

 

[thumpar]

Re: 454 vs 454 Magnum

Ok so let me ask this, how much work is involved in changing over from Alpha one to a Bravo outdrive, do I have to replace the transom assembly?

Yes. Inside and out.

 

[ericcarr2000]

Re: 454 vs 454 Magnum

Do you think that the Alpha one would be able to handle a few more horse power, like maybe 10 or 15 more?

 

[thumpar]

Re: 454 vs 454 Magnum

Be gentle with the right hand. There is a reason Merc stopped that combo.

 

[Bondo]

Re: 454 vs 454 Magnum

Do you think that the Alpha one would be able to handle a few more horse power, like maybe 10 or 15 more?

Ayuh,... The drive is Already over-powered,.... yet ya wanta add more,..??

Be gentle with the right hand. There is a reason Merc stopped that combo.

 

[ericcarr2000]

Re: 454 vs 454 Magnum

Ok but if I were to ease into the throttle I should be ok though right? I rarely just hammer them anyways.

 

[Bondo]

Re: 454 vs 454 Magnum

Ok but if I were to ease into the throttle I should be ok though right? I rarely just hammer them anyways.

Ayuh,..... It's a BBC, with an Alpha drive,....

It'll run just fine,..... til it Don't,.....

 

[tpenfield]

Re: 454 vs 454 Magnum

Ok but if I were to ease into the throttle I should be ok though right? I rarely just hammer them anyways.

Yup, but the good part is you can still brag to your boating buddies . . "yea, its got a Magum in it" :thumb:

 

[alldodge]

Re: 454 vs 454 Magnum

Ok but if I were to ease into the throttle I should be ok though right? I rarely just hammer them anyways.

+1 with Bondo and will add

A buddy picked up a Fountain with a 600HP motor (Org motor was a 415HP). The boat use to belong to a high end rebuilder and he pumped the boat up to the 600HP blower motor. My buddy babied the boat and very slammed the throttles. The drive was a standard Bravo 1. The drive did finally give out and now it has a XR drive.