Being new to the boating world I found the most difficult decision after settling on a brand and model was what type of engine to get. With all the different engine options it'll make you Finally I decided on a Big Block, but which one? The MAG or HO? My Baja dealer wanted $7,500 for the HO upgrade. I found this to be outrageous. Having done some work on GM cars previoulsy I opted for the regular Mag496 375hp version instead, thinking that it would be cheaper to upgrade it in the long run.

So after my purchase I bought all the manuals from Mercruiser, including the Parts Manual. I took a highliter and went through every page hilighting only when there were different part numbers for the same part. Here is what I found.


Decal HO pn#37-863307 vs. Decal Base pn#37-863306
PCM HO (Mechanical Throttle & Shift) pn#866091T01 vs. PCM Base pn#866090T01
Throttle Body Assemble HO pn#863379A06 vs. Base pn#863078A06
Camshaft HO pn#431-881628 vs. Base pn#431-881627

That's it boys & girls! A whopping 4 different pn#'s for and entire engine assembly and one of them's a sticker!

Some notes of interest. Same pn#s for ; fuel injectors, crank ( I was afraid that one might be forged while the other not), fuel rail and fuel pressure regulator kit. Different pn# for the throttle bodies but same hardware. (Source: Ray from Raylar)

So now all I need is a solid contact for Mercuriser Parts to start arriving at my doorstep. Can anybody recommend somebody who sells parts cheap, like 10% over cost.
Sebastien

Before you go wasting a lot of money upgrading your 375 mag to a 425HO, check out our website at www.raylarengine.com for some decently priced upgrades that will give you 525HP.
Ray @ Raylar

Looks like the php/mysql dbase on the forum went down today. I'm going to repost some of the answers to questions which were posted on this thread earlier.

The PCM is a different pn# hence different programming. I recall reading from other members that the HO redline was 5,4xx rpm vs. the 5,000 rpm redline on my regular 496 MAG.

Raylar,
I have already bookmarked your web page. Congrats on a great product!

However, I have to disagree with your original post as it being a waste of money to upgrade my 375hp to 425hp. If by replacing 3 factory parts I can gain 50 hp including a properly tuned factory PCM to match the cam and power output for the upgrades, then how am I wasting money? Your $5,800 package, a good tune, add $799 and now your at $6,500, or $65 per horsepower.

So far I have acquired 2 of the 3 pieces (cam and new throttle body) I need for the puzzle and have only spent $250. Let's say worse case scenario the 3rd piece costs me full retail ($1,200) So thats $1,200 plus $250 equals $1,450 or $29 per horsepower. So how am I wasting money now? Also my 50 hp package has been tested on thousands of boats so it is safe to say it is a very proven upgrade. With all the 496 MAG owners doing supercharger upgrades, engine builds etc there will be a lot of manifolds, heads, camshafts, etc.. on EBAY or in various other classfieds that can be picked up at a very substantial discount over purchasing them from Mercruiser. In my case I have a forum member who is shipping me the entire intake manifold, pcm harness, throttle body, injectors, camshaft, 496MAG HO engine cover for $250 !!! This is why I love the internet baby!

Happy Boating!

Sebastien

Sebastien

The big difference is 50hp will net you about 1 mph.

So on my 24 foot Baja that weights 4,400lbs I'm only going to see 1mph on the top end?

Shirley you can't be serious?

I took a 1992 350 mag about 270hp out of my boat and replaced it with a 2000 502 mag 415hp went from 54mph w/labbed 3 blade to 70.6 mph w/labbed 4 blade in this swap we also changed to a bravo from a alpha. speeds were recorded with GPS

I dont know about you but 145hp made a huge difference to my boat at 4500lbs

Actually, you'll probably 2-4mph on the top end with 50hp. Been there, done that on a 24 Outlaw. Bumped a tired 365hp up to about 420hp and saw a 4mph gain.

Griff,

2-5 is more inline with what I'm expeting. If at the end of the day I only get 1mph I'll be a little bummed but will post my results nonetheless.

replace the prop w/ a lab finished prop.

While you are doing all that work look into porting the heads.

Wannabe