Buying a automotive engine to replace my mercruiser, need opinions

[2550SX]

I have an older 25' cuddy which has the original 330hp 454 from 1992. She still gets up and goes and seems to have decent compression with minimal oil consumption but I was considering pulling the motor this winter and stroking it to 496 and throwing some better heads on it than the current peanut ports. I feel like putting work into a 30 year old cast iron block from a boat bought from Florida may result in some corrosion and pitting in the water jackets.

Then I started looking at crate motors. I have a GM employee discount and this 502 caught my eye:

502 HO 461HP 558 LB.-FT. TQ

Check out the deal on 502 HO 461HP 558 LB.-FT. TQ at GM Performance Motor

www.gmperformancemotor.com

The cam specs are below:

•Steel Hydraulic Roller
•Duration Lift( Deg): Intake: 211 / Exhaust: 230
•Maximum Lift (in): Intake: .510 / Exhaust: .540
•Lobe Centerline (deg): 112


I notice the NOT INTENDED FOR MARINE USE note so I started doing a little poking around the internet and I see this is a pretty common question.


The first thing I notice people say is that you need a USCG approved starter, alternator, carburator and ignition. This engine is void of all of those components so I would either be reusing my current starter, alternator, carburator and Thunderbolt IV ignition or simply buying new USCG components for peace of mind.

The second thing I noticed is that people say is you need stainless head gaskets and brass core plugs. I only use my boat in a fresh water lake. Regardless, if this engine does not already have brass plugs and stainless head gaskets those would be easy enough to swap out upon receiving the crate engine if I really wanted to.

The third thing I notice that people say is that the cam would need a lobe separation of 112 or more. The cam in this engine has a cam with 112 degrees of lobe separation.

Is there anything that I am missing? What are your opinions of this particular engine?

A couple other notes are that the current 454 in my boat is carburated but does not have a mechanical fuel pump boss. I currently use that seawater pump fuel pump combo. This 502 also does not have the mechanical fuel pump boss so I would reuse the pump. Both the existing 454 and this 502 are 1 piece rear main seals I think I can reuse the coupler.

 

[alldodge]

454 and 502 is same size block, only difference on the outside is where the holes for brackets might be.

Use all the stuff from your 454 on the 502 (starter, ALT, etc). You do want brass or stainless core plugs even with fresh water, otherwise they will rust out. Also use a marine circulating water pump not a auto

The issue with auto motors is torque comes in higher on the rpm band. You want a marine or truck cam so torque is at the bottom in.

 

[2550SX]

454 and 502 is same size block, only difference on the outside is where the holes for brackets might be.

Use all the stuff from your 454 on the 502 (starter, ALT, etc). You do want brass or stainless core plugs even with fresh water, otherwise they will rust out. Also use a marine circulating water pump not a auto

The issue with auto motors is torque comes in higher on the rpm band. You want a marine or truck cam so torque is at the bottom in.

What is different about the circulation pump that comes with the engine vs. a marine circulation pump? Stainless components?

Here is the dyno graph for this 502

 

[Bondo]

Ayuh,..... Marine cirulatin' water pumps usually have a cast impeller, rather than a stamped steel impeller,.....

Scott is steerin' you straight,.....

My take on the boat motor Vs car motor is it's somewhat overblown, like most internet memes,....
The biggest thing is you don't want a Hot Rod car motor,......
A standard production car or truck motor is very close to a boat motor, other than what Scott is tellin' ya,.....

 

[Scott06]

What is different about the circulation pump that comes with the engine vs. a marine circulation pump? Stainless components?

Here is the dyno graph for this 502

View attachment 351912

In addition to the cast impeller a marine water pump is bi-directional not sure which belt configurations drive it the opposite way than it would be in an auto configuration.

Normally a truck cam would be ok but I think this is bigger than a truck cam.
I think the 230 deg duration @.050" would be too much for a wet exhaust/reversion . @Scott Danforth may be able to better to comment on the cam specs.

 

[achris]

In addition to the cast impeller a marine water pump is bi-directional not sure which belt configurations drive it the opposite way than it would be in an auto configuration.

A cast BRASS impeller is inherently bi-directional, but a marine circ pump also has a SS shaft seal and a SS back plate.

Chris......

 

[Scott Danforth]

@2550SX do you have the cam duration and the LSA for the cam?

many marine cams are between 108 and 214 lobe centerline, however need to know the overlap (marine engines you do not want any overlap)

post the complete cam card with duration at both 0" and the published 0.050" as well as the lobe separation angle

it will look something like this



the 211 and 230 duration are relatively mild however, however need the cam card to know the whole story

the cam in the 502 may be fine

I know I suffered reversion and had to have a custom exhaust system made to handle the reversion

 

[tank1949]

If I understand you, the motor has been heavily used in salt water off and on since 1992. If so, unless it is FW/antifreeze cooled, I'd pitch it and start with something only used in fresh water for cooling. Just my 2 cents...

 

[2550SX]

@2550SX do you have the cam duration and the LSA for the cam?

many marine cams are between 108 and 214 lobe centerline, however need to know the overlap (marine engines you do not want any overlap)

post the complete cam card with duration at both 0" and the published 0.050" as well as the lobe separation angle

it will look something like this

View attachment 351919

the 211 and 230 duration are relatively mild however, however need the cam card to know the whole story

the cam in the 502 may be fine

I know I suffered reversion and had to have a custom exhaust system made to handle the reversion

Good info here. So far I only have the cam specs listed in my first post from the GM Performance site. I don't think I would get a cam card unless it came with the engine if and when I purchase it.

Let me ask you this. What marine cam would you recommend for a 502 in a 5000lbs cuddy with a Bravo1?

I would consider swapping the cam before installing the motor .

 

[Scott Danforth]

Good info here. So far I only have the cam specs listed in my first post from the GM Performance site. I don't think I would get a cam card unless it came with the engine if and when I purchase it.

Let me ask you this. What marine cam would you recommend for a 502 in a 5000lbs cuddy with a Bravo1?

I would consider swapping the cam before installing the motor .

I would suspect you need to pull that motor down and swap head gaskets.

you will also need a marine circulating pump

you should also look at the core plugs to ensure they are stainless or brass, or you need to swap to HX cooling

per the link above, you should be fine with the cam

Cam # 24502611
@ 0.050
ID 211
ED 230
LSA 112
ICL 108


IVO -2.5 BTDC (- indicates ATDC)
IVC 33.5 ABDC
EVO 51 BBDC
EVC -1 ATDC (- indicates BTDC)
ECL 116
Overlap -3.5


This steel roller is for the 502 and 454 H.O.crate engines.
The duration at .050" tappet lift (intake/exhaust) is 211/230;
Lift with 1.7:1 rocker ratio (intake/exhaust) is 510/540.
Valve lash is zero/zero
Lobe centerline is 112 degrees.
Lifter are not included
For Use in Gen VI Blocks.Can be used in Mark IV and Gen V blocks if aftermarket tie-bar type roller lifters are used along with a Gen VI timing set and thrust plate (Older blocks may need to be drilled and tapped for thrust plate mounting.
Technical Notes: Distributor P/N 1104067 or melonized distribtor gear P/N 10456413 must be used

 

[harringtondav]

All of this engine discussion is great learning, but a mile over my head.
My input is while you have the engine out is a great opportunity to update hard to get at parts. Particularly the flywheel engine coupler and front and rear engine mounts. Especially if these are original. Transom assembly parts like the gimbal bearing, bellows etc may need attention.
Also get yourself an alignment tool for reassembly. The pros above can walk you through this when the time comes.