What makes a marine cam different??
Can they be used successfully in a car?

 

Anyone heard of these people?:

PREDATOR CAMS / MIDWAY PERFORMANCE WHSE
United States /Philadelphia

 

Some marine engines are reverse rotation engines, so the cams are ground for it.

 

Marine cams tend to be ground with a wider lobe seperation angle (LSA) for increased low end torque. Boats need more low end than cars because water is a constant resistance (Until the boat planes out).

A marine cam would probably work well in a heavier car with a tall rear highway gear.

 

Go here and do a search on cams (Forums: Technical Q & A). You'll find enough threads on marine engines/cams to keep you reading for a year: www.offshoreonly.com

D. Ocean
Miami, FLA

 

Thanks!
I've been poking around in there!
Interesting stuff....and lots of it.

 

Some Marine engines do turn the wrong way. The torque curve is also way wrong for a street car!!!

 

Stupid question, but here goes:
1)Isn't the torque curve just like bolting in a 411 rear or something like that....getting LOTS of torque at very low RPM's?
2)How quick will it run out of steam.....when you hear those boats go it sounds like they rev right up there!

Not that I want to put one in my car, but I would like to know the physiology behind the grind madness.
What do the increased LSA do physically?

 

You gotta realize boats only have one gear and pretty much run at a constant RPM. Having owned several cabin cruisers, you want lots of power is at low RPM to get you on plane then you just cruise at max of 3500 most of the time. If you ever see 5000 rpm, you're probably out of the water! The constant RPM also isn't really good on an engine but that's the way they run. Of course, that's for a cruiser and not an offshore race prepped boat (hopefully my next big purchase!).

 

If you have 2 cams that are exactly the same other than the LSA, the wider LSA will produce more low end torque. The original LT-1 mech cam had lots of duration so it could make tons of HP upstairs, but it also had a wide LSA (I think it was 116 deg) - so it would have some street manners.

Just to add on the reverse rotation motors; They also produced regular-rotation marine motors with reverse-rotation cams...Why? Because GM thought a 2-gear drive setup was more reliable than a timing chain at continuous high rpm operation (and more cost effective than reinventing the wheel on a 3-gear arrangement) The only way to make 2 gears work is to spin the cam the opposite direction.

 

Do you then have a reversed firing order?....

.....81463527??

 

Just to be a smart *** , no, 2 gears can be setup to spin in the same direction if one gear spins within the other gear. The outter gear would have its teeth along its inside perimeter. This could be applied to automotive use, but is probably not practical as it would require a major re-design.

 

Right. That's why they call them reverse rotation cams. Not a big deal, it's just reground the opposite way. Firing order and everything else stays the same.
EDIT: A new reverse-rotation distributor gear is required - available from the supplier of the reverse rotation cam.

 

I talked to the original owner of my '70 the other night. He's the guy that built the engine, and to drag. It's a 454 running a boat cam. He didn't remember the lift/duration but let's just say it has a very hefty lope. The block has been bored twice, 11:1 TRW pistons, different heads, C396 intake, big double pumper Holley, magneto, Hooker headers/sidepipes (no baffles), different (lower) 1st and 2nd gear in the auto trans, shift kit, 411 rear end. It will jump.

On the boat cam, mostly used for low end torque. Mine works very well. I do wish I knew the specs on it but probably never will.

VaporLockd

 

1)The question that follows is whether one would be able to take advantage of the wider LSA for lower end torque.....

..when using large intake runner rectangular port open chamber heads and a single plane high rise intake?

2)Would one benefit from a marine cam, where you usually have to go with more cubes with that type of combination in order to compensate for the losses due to reduced flow velocity at lower rpm's?

3)Would you still be able to take advantage of your top end combination by being able to rev higher or will a marine cam cause your bottom end to run out of steam due to inefficiency at higher rpm's

4)I'm trying to put a lot of thoughts into as few as possible words for fear of boring everyone with lengthy posts that sound stupid.....and is probably stupid. It does however put little pieces into a big puzzle for me

 

Has no one heard of these people?

 

Selecting a cam is not easy to do. It's hard to say what will or won't work. I would contact several cam manufactures & see what they recommend...Might be a marine cam who knows. Never heard of Midway Performance

 

Actually there is not such a thing as a Marine Cam . It's just a section in a catalog for cam maker to market some of the cams commonly used .

Now here n there you'll see GM cams for sale that come out of the Marinised engines " over the counter crate motors " These are low lift and pretty much just long , heavy paper weights

When choosing cams think of it this way , all boats are not created equal . Some are Jet Drives , some V-Drives and then enter the Mercruiser or other brand outdrives so the engine builder or cam selector should have been there n done that to be able to give best advice ... anything less is guessing

All three of the type drives like specific series of cams . All three of these drives can be regeared like the impeller size of the pump , the prop size and pitch on the outdrive and both the v-drive case gears and props of the v-drive be them the negative lift for the flat bottoms or positive lift style props for the Hydro's in both diameter and pitch .

Stern Drives need a solid idle unless they are using a blown engine . Then when the blower roam is on the low side you can cram them in gear .

V-Drives with compression just cam them like a light drag car for the most part

Jet Drives with compression just cam them like an oval track car for the most part

Take into consideration how good the exhaust is when choosing a cam on any of them and yes , tuning with LCA's and intake-Exhaust centerlines properly is what gets one boat 4 lenghts ahead of the one with a poor choice in cam and other engine components

 

First of all, not even Merc makes reverse rotation anymore. BTW, they reverse the rotation of the crank only by using a gear rather than chain drive.
Second, marine cams are generally made for a broader torque range and usually only good to about 5000 rpm. They are also designed with less overlap of talve timing to prevent reversion. Water is generally introduced into the exhaust to quiet it. If your exhaust valve is open too long after TDC of the exhaust stroke, water will be sucked in.