Good cam choice for a Mercruiser 5.0LX

[mudweiser]

Looking for a cam for a 89 Mercruiser Chevy 305 4bbl for a 21ft Bayliner. It's ran about 1,000ft in elevation. I was thinking a Edlebrock #2102 which is a performer for the street 305/350. Any thoughts or has anyone found a cam that works well?

 

[Coors]

Re: Good cam choice for a Mercruiser 5.0LX

Only use a marine cam, as otherwise you will end up engesting water into your engine.

 

[180shabah]

Re: Good cam choice for a Mercruiser 5.0LX

What Coors said, you don't want to suck water from the exhaust.

Edelbrock is usually very helpful, give 'em a call. They should point you to a good one. You can tell them you are 1000 up, but that really isn't high enough to make a difference.

Good luck

 

[John_S]

Re: Good cam choice for a Mercruiser 5.0LX

Assuming you are replacing a worn stock cam, the rest of the motor is stock, and you want something with mild improvement, look at:

Xtreme Energy XE250H Hydraulic Flat Tappet Camshaft
Lift: .432''/.444''
Duration: 250?/260?
RPM Range: 600-4600

249-12-230-2
Very strong torque, excellent mileage, smooth idle.

Operating Range: 600-4600 RPM
Duration Advertised: 250? Intake / 260? Exhaust
Duration @ .050'' Lift: 206? Intake / 212? Exhaust
Valve Lift w/1.5 Rockers: .432'' Intake / .444'' Exhaust
Lobe Separation Angle: 110?



Dennis Moore recommends this in his SBC Marine Perf book. Says it is good for 15hp over stock.

 

[SuperNova]

Re: Good cam choice for a Mercruiser 5.0LX

Only use a marine cam, as otherwise you will end up engesting water into your engine.

That is a fallacy.

 

[Coors]

Re: Good cam choice for a Mercruiser 5.0LX

I guess you don't have thru-hulls, 6 inches above the waterline.

 

[Coors]

Re: Good cam choice for a Mercruiser 5.0LX

That is a fallacy.

So, how far beyond 112 degrees overlap is possible?

 

[Bondo]

Re: Good cam choice for a Mercruiser 5.0LX

A Marine Cam has it's LSA between 109*s,+ 112*s,..........

Anymore, or Less,..... Isn't a good grind for a Marine motor.........

 

[Matt S]

Re: Good cam choice for a Mercruiser 5.0LX

Ok another marine motor curiosity on my part. I always see "don't do this" and "do that" with regards to differences between marine and automotive engines. 99% makes sense. BUT....overlap increases cylinder scavenging no?

Under what condistions would the dreaded overlap cause water to be sucked into my motor? I can see a few but to my brain it's a stretch..

1) water pressure at exhaust outlet exceeds exhaust pressure and water travels up exhaust (assume engine running). In this case you'd have to be swamped at the transom for the water level to be above the exhaust riser..long enough and strong enough to overcom the running motor's exhaust.

2) motor is off, valve is partially open, water swamps the rear of the boat.
a) but wait..this can happen with any cam since there's no way for me to ensure my motor stops without an exhaust valve open (pretty impossible even if I could).

3) When motor is turned off the compression on one cylinder causes a 1/4 turn reverse in the crank..sucking water in. This is most plausable in my head.

So can I get some edumacation here on how I would get water up my tailpipe far enough into my motor..and enough of it to hydrolock a cylinder?

Also, how do outboards get away with radical high revving cams? Is this because the powerhead is never below the waterline and can't be (theoretically of course)?

 

[SuperNova]

Re: Good cam choice for a Mercruiser 5.0LX

I agree with Bond-o, but I believe the reason has more to do with power band placement than with water ingestion. The design of the exhaust system is supposed to protect the engine, not the design of the cam. You have to remember, the water and exhaust do not mix until they exit the riser and at that point, on a properly designed exhaust system, the mixture should be running downhill at least six inches to the exit point, be it thru-hulls or the Y-pipe. The engine would have to have some very powerful reversion to suck water in and I would daresay that reversion that strong would give you some problems with running qualities. But, like I've said before, I'm not a designer or an engineer so this is all just opinion.
--
Stan

 

[Bondo]

Re: Good cam choice for a Mercruiser 5.0LX

Also, how do outboards get away with radical high revving cams?

Where the Redline is,... Is pretty much Irrevelant......

Valve Overlap causes Reversion........

And,..... Until recently,.....
Outboard Motors are/were 2-strokes,.....
No Cams,+ No Valves......

 

[Matt S]

Re: Good cam choice for a Mercruiser 5.0LX

Where the Redline is,... Is pretty much Irrevelant......

Valve Overlap causes Reversion........

And,..... Until recently,.....
Outboard Motors are/were 2-strokes,.....
No Cams,+ No Valves......

Please elaborate!? How?
But 4 stroke outboards do exist, with very different cams. If I can get a 1500cc Honda to spin at 6500rpms sideways on top of a shaft..why not mounted on an outdrive in a boat? Redline is revlant..does not cam design play in the decision of redline? Of course it's not ALL of it....

Don't get me wrong, I'm not wanting to start a feud. Think of me as the 3 year old "why" LOL!

 

[Coors]

Re: Good cam choice for a Mercruiser 5.0LX

why not mounted on an outdrive in a boat?
That would be an outboard?

 

[Matt S]

Re: Good cam choice for a Mercruiser 5.0LX

why not mounted on an outdrive in a boat?
That would be an outboard?

If I took a BF90 powerhead and found a way to mount it to my volvo SX-A outdrive that would be an I/O now.....

Notwithstanding all the design changes in oiling etc of the motor..it's a theoretical question.

 

[CharlieB]

Re: Good cam choice for a Mercruiser 5.0LX

Major differences between marine/industrial motors and 'standard' automotive motors;

1. Corrosion of core plugs and impeller
Automotive engines and industrial motors with radiators usually run an anti-freeze solution with inhibits corrosion. Marine motors run primarily raw water. Standard automotive water mump impellers ant core plugs would begin to rust away in the marine environment, the reason for brass core plugs and stainless impeller.

2. Peak torque vs peak horsepower
Marine/industrial motor are built to operate at peak torque. Period. From idle on, it' torque nessessary to turn that prop.

 

[jastacey]

Re: Good cam choice for a Mercruiser 5.0LX

I'd just would install a chevy truck cam in the motor, the grind is very close to the marine version, and really no one would be the wiser

 

[Zackman]

Re: Good cam choice for a Mercruiser 5.0LX

Per the Crane Cam Website... http://www.cranecams.com/?show=newsLetters&no=92 under Marine Tech Tips

"Camshafts with a wider centerline like 112 to 114 are better for marine use because they idle better during docking or shifting in and out of gear. Also wider centerline camshafts have less valve overlap, so you have a lesser chance of water reversion in the exhaust system (i.e. water sucking back into the engine at idle)."