OMC marine 5.8 GT40 compatability

[94oxfordL]

Does anyone know if this is the same or close enough I could put my Lightning accessories on and run it in the stock computer.

My motor has a coolant leak and oil pan leak, if I could swap this in and it would work, it would save my summer driving.
Thanks for any advice and information.

 

[Raymond_B]

The lower intake will be cast iron, you'll also want to check injector size to make sure they are 19's. Most of it **should** work, but you'll need your truck's wiring harness, headers, balancer, flexplate etc. Not sure what kind of timing cover the boat engine would have.

 

[oilwell1415]

On the OMCs I'm not sure, but on the Mercury Marine engines all of the main castings were the exact same as the auto castings. Some had different water pumps and distributors, but that's easily enough changed. I think I remember that some of them were balanced differently as well, but it's only been 30 years. Back in the mid 90s half the street machines in Stillwater, OK were running a Merc engine from the employee sale with no issues, but at that time Merc was using GM stuff. If you swap out everything you possibly can from your current engine it should work OK for you.

 

[rusty_408]

the ECUs are completely different... i was helping folks retrofit automotive ECUs with a j3 chip and the stock marine program when PCM and OMC stopped carrying replacement units.

some differences..
no O2s, marine runs full time open loop, cant get O2s wet with wet manifolds,
no emissions or egr, (tab, tad , purge, etc)
no trans controls (all lightnings have electronic trans controls in the eec-iv)
marine 5.8s mostly uses 24lb injectors, Lightnings have 19lb
fuel pump and wiring pins are all different, i have a excel file with some of that
Marine ECUs actually share the same board and hardware as early 90s 4 cyl mustangs

can do a lot more reading here:

Hope for GT40 EFI ECU - PlanetNautique Forums

I was going to wait till spring to announce this, but I have some possible good news for those of you worried about lack of replacement ECUs. I was working

www.planetnautique.com

PCM GT-40 Marine Engine ECU Replacement

The PCM (Pleasure Craft Marine) GT40 marine engine, famed for powering the CorrectCraft Nautique, was a popular choice in high-performance ski boats throughout the 1990s and early 2000s. This robust engine relied on the EFI-MA39 ECU, which is integral to managing the engine’s electronic fuel...

www.tiperformance.com.au

https://eectuning.org/forums/viewtopic.php?f=2&t=22155&sid=5e0498f8862e6e64eba979d839314c0c&start=60

 

[rusty_408]

forget all i said above, I think i misunderstood what you were trying to do.... if you're just trying to swap the marine block and intake into a Lightning, just use the L computer, accessories, harness and injectors. the intake and heads are close to the same specs, only thing i can think of that wont work is EGR and the air injection (no ports on the rear of the heads). I dont recall the shape of the marine oil pan if it will clear the truck crossmember, I can check my boat if that helps.

I have a ton more info on the marine setups if needed. i have a 2001 Nautique 210 with the 5.8L gt40.

 

[94oxfordL]

I am thinking to swap my lightning accessories on to the marine motor and using it in my truck.
My real question is how different are the cams from one to the other. I know the L speed density does not like much difference.

 

[Raymond_B]

I am thinking to swap my lightning accessories on to the marine motor and using it in my truck.
My real question is how different are the cams from one to the other. I know the L speed density does not like much difference.

I would almost bet money that marine cam would be fine.

 

[rusty_408]

they're both speed density... this is what i had saved on the stock marine cam

MARINE
HO 351w
Duration 210 int./221 exh. @ .050
Valve Lift 0.453 int./0.453 exh
115.5°

351w cam upgrade?

Just curious if anyone has upgraded their camshaft on these reverse spinning engines? I've got...

www.correctcraftfan.com

Quick search on here for the stock L cam.... they look close, a little more duration on the marine setup. I think it'd be fine

LIGHTNING
LOBE SEPARATION ANGLE= 114 degrees
VALVE OVERLAP at .050 = -24.4 crank degrees
INTAKE: Valve opening= -12.2 BTDC
LOBE CENTER = 111.1 ATDC so cam has 2.9 degrees advance built in
Valve Closure= 28.4ABDC
DURATION= 196.2 CRANK DEGREES
MAX. LIFT (LOBE)= .25846"
NET VALVE LIFT (1.6 rocker ratio)= .41354"
LOBE AREA= 18.5 IN DEGREES

EXHAUST: VALVE OPENING= 40.4 BBDC
LOBE CENTER 116.8 BTDC
VALVE CLOSURE= -12.2ATDC
DURATION= 208.2 DEGREES
MAX. LIFT (LOBE)= .27634"
NET VALVE LIFT= .44214"(1.6 ratio)
LOBE AREA= 20.67"

specs on a 351 lightning cam and a 302 H-O cam

Does any one know the specs on a lightning cam and a 302 H-o cam:tu:

www.nloc.net

 

[rusty_408]

little blurb from AI.... take it with a grain of salt

---

Camshaft Specs Comparison​

Spec	Marine HO 351W Cam	Lightning 351W Cam
Intake Duration @ .050	210°	196.2°
Exhaust Duration @ .050	221°	208.2°
Intake Valve Lift	0.453"	0.4135"
Exhaust Valve Lift	0.453"	0.4421"
Lobe Separation Angle	115.5°	114°
Cam Advance	Not specified	2.9° advanced
Valve Overlap @ .050	Not specified	-24.4° (negative = no overlap)

---

Performance Differences​

1. Duration​

• The Marine camhas longer intake and exhaust durations, which means it holds the valves open longer.
  
  • Effect: Better high-RPM breathing and power, but potentially rougher idle and less low-end torque.
• The Lightning cam has shorter durations, favoring low-end torque and driveability.

2. Valve Lift​

• The Marine cam has higher lifton both intake and exhaust.
  
  • Effect: More airflow at peak valve opening, which supports higher RPM horsepower.
• The Lightning cam’s lower lift is more conservative, again favoring torque and efficiency over peak power.

3. Lobe Separation Angle (LSA)​

• Marine: 115.5°
• Lightning: 114°
  
  • A wider LSA (Marine) generally smooths idle and reduces overlap, which is good for marine applications where idle stability and vacuum are important.
  • The Lightning cam’s slightly narrower LSA increases overlap slightly (though still negative at .050), which can help scavenging and mid-range torque.

4. Cam Advance​

• The Lightning cam has 2.9° advance, which moves the powerband lower in the RPM range — again, favoring torque.
• The Marine cam doesn’t specify advance, but if installed straight up, it likely favors a broader powerband.

 

[Raymond_B]

TLDR

Send it

Seriously good info though.

 

[Ovals Only]

Anybody have any experience with the holman moody 289's that came in Donzi Sweet 16's in an automotive application?

 

[oilwell1415]

4. Cam Advance

• The Lightning cam has 2.9° advance, which moves the powerband lower in the RPM range — again, favoring torque.
• The Marine cam doesn’t specify advance, but if installed straight up, it likely favors a broader powerband.

So is the Lightning cam actually advanced 2.9 degrees? Or is it just retarded 2.9 degrees less than the normal cam?

 

[FMOS Racing]

The firing order is the same?

 

[rusty_408]

same firing order 1-3-7-2-6-5-4-8... i dont think any of these early 90s were reverse rotation, if it were it should be stamped on the motor and would be 1-8-4-5-6-2-7-3

 

[RPM289]

Are any of the marine engines roller set ups?

 

[oilwell1415]

Are any of the marine engines roller set ups?

Yes. They largely transitioned inline with the auto manufacturers. Maybe a year or two behind, but not much.

 

[rusty_408]

my understanding is that most were roller blocks, but i dont think any marine setups actually had roller cams.

 

[FMOS Racing]

I have a neighbor that bugs me a lot about what to do with his marine 351W for more this or that. I tell him, "Turbocharge it" and other than that, "No idea..." LOL!

 

[rusty_408]

I would love to stroke mine. i ballast my boat with over 2500lbs when we take it out for wakeboarding. the torque from a 393 or 408 would be a dream. I got the tuning definition too. just short on cash and time.