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Discussion Starter · #1 ·
Alrighty then, after dropping a valve and consequently grenading a piston and cracking the block on one of my NON-Mag motors a few weeks ago, I have acquired a set of 454MAGS from a member here.

I have my blown motor pulled and dissected, looking to start swapping accessories tomorrow.

My goals are simple, I am looking to end up with a RELIABLE package that will get me the best results for a heavy boat that wants to just cruise. I'm not looking to keep up with the proverbial Joneses or make it anywhere in a real hurry. I have looked into the Merc 420 specs and am finding them very interesting.
Couple of questions on where I should (could) go for total rebuilds at the end of this season.

1) My boat currently has single plane aluminum intakes, not completely sure WHY, but it does. I am learning that they are more designed for power in the higher RMP ranges (which, I am thinking I DON'T need). So, the mag motors I picked up running the stock intakes for that vintage, should I just stay with those?

2) The old Merc 420, I understand that was considered a "reliable" set up, can anyone elaborate on that? I can't see just freshening up these motors without getting some more "Umph" and a better sound out of them. Something else I should be considering other than these specs?

3) Stock manifolds. I know, they are crap, but cost wise, headers just aren't in the budget so far.
I have stainless risers on (will be new) cast manifolds right now. Is that going to be a huge problem with what I am trying to accomplish?


I am attempting to complete one build during the summer, have the other one done and installed in the fall.
Thanks in advance!

Phil
 

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You BLOT that schit!
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Discussion Starter · #2 ·
Remember, the boat is fat, heavy and will never (I repeat) NEVER be a "fast" boat. If I can attain a decent cruise speed at 3200-3500 rpms I will be happy. ;)
 

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I would start with the 454 mag engines as is since they are well built. And yes, that intake is a respectable piece for what you intend to do. That exhaust will work with the stock cam as well.

Improving on them with doing the top end only would consist of better head gaskets (cometic) and some high quality exhaust valves like the ferria super alloy. They would be a great candidate for blowers at that point.

Blowers aside, a good roller cam of your choice would be in order. Maybe a 731 crane. I would also consider going to a 800cfm holley carb.

If a fountain is your boat, I would think it would respond well to power. I would suggest building the engines for super charging down the road.

BT :cool:
 

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I built my motors to 420's and loved them. Ran great sounded great and the only thing I did to them was change oil. Had @ 200 hours on them when I sold the boat.
 

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You BLOT that schit!
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Discussion Starter · #5 ·
jetmech said:
Run the stock 365 Mags . You should see many trouble free hours of use.
That is still an option. Just trying to maximize the opportunity of having them on the ground in the fall.

I was just figuring that if Merc built up the 420's off of this same base, I could still get a reliable set up with some extra power too. (correct)?
 

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I could be wrong on this, but wasn't the primary change from 420hp to 365hp the way they rated the hp? I thought I read that back when I was working on my 365hp engines.
 

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Discussion Starter · #7 ·
jetmech said:
More power is always a good thing. I don't think you'll see any performance gains building 420's.

Where are you located in Port?



Bob
Really? Consider this though, I am going from 330's.....

In simple numbers that would be around ~180HP gain.

From my crude calculations it is going to cost around $1800-$2000 per motor to upgrade.


I'm about 2 miles down from the track on the opposite side. I would really like to tell people I live in North East or even Rising Sun, but alas, my address is Port. Got these motors from a buddy of yours, heck of a nice guy to deal with.
 

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Discussion Starter · #8 ·
Blue Thunder said:
I could be wrong on this, but wasn't the primary change from 420hp to 365hp the way they rated the hp? I thought I read that back when I was working on my 365hp engines.
The 420's had a different Crane cam, gold 1.7 roller rockers, Holley 750 double pumper, single plane Weiand.

Note, I'm getting ALL of my info from here and OSO, absolutely none is first hand experience. I'm in uncharted territory here. :rolleyes:
 

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Discussion Starter · #9 ·
PJDiesel said:
The 420's had a different Crane cam, gold 1.7 roller rockers, Holley 750 double pumper, single plane Weiand.

Note, I'm getting ALL of my info from here and OSO, absolutely none is first hand experience. I'm in uncharted territory here. :rolleyes:
Yes, there was a change in the late 80's early 90's from crankshaft to prop HP.

That didn't have everything to do with the differences between the 420 and later 454 MAG (365)
 

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PJDiesel said:
The 420's had a different Crane cam, gold 1.7 roller rockers, Holley 750 double pumper, single plane Weiand.

Note, I'm getting ALL of my info from here and OSO, absolutely none is first hand experience. I'm in uncharted territory here. :rolleyes:
Close i think It ran the 800 holley carb and i think iwas the 365 mag intake (dual plane). It did have the crane cam and the gold rockers. That cam was run in a bunch of merc motors. I think the 400,420,465,470,and the 525SC all ran that cam. BTW Crane is proud of that cam as well if you go and buy one :rolleyes:
 

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