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Old 10-29-2012, 08:34 AM
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JimN JimN is offline
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Join Date: Jul 2004
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Originally Posted by Surfer View Post

thanks for the answers!

So my original engine has got a cam, which is stardard in GM marine engine?
-> Indmar EFI computer is programmed for this.

Rossterman, you meant in comparison to vortech car engine cam is different in marine engine?
JimN, yes I just need basic replacement, no customization.

If so, the GM base marine engine will do ok? Even the replacement has got a roller cam,
as the original engine has got flat tappet cam.
Ok, flat tappet cam is maybe an option, but roller cam would be better I understand; E.g. a bit more power.

The valve timings seem to be different with different cams, that is why I am wondering if the original EFI computer would do ok with roller cam?

I do not know EFI working principles yet so closely, and I am not able to tune EFI computer, and don't want to buy a new one.


If you call Jasper, they'll ask for some numbers that are on the block- they're usually in the rear and could be hidden by the transmission/bell housing. Sometimes, they're on the heads. Using this info, they can tell which engine you have. One easy way to tell if it's a Vortec or non-Vortec engine is by looking at how the intake manifold bolts go in- if they're perpendicular to the head/intake manifold mating surface, it's non-Vortec. The Vortec bolts go in vertically.

This info will also tell them which cam it has and, having replaced engines in MC boats of similar vintage to yours, they did get it right. All that was needed was to remove the accessories from the old engine and transfer them to the new engine. The roller cam isn't necessarily as different WRT valve timing just because it's a roller cam- it's because of a lot more than that. The air/exhaust characteristics of Vortec heads are different from non-Vortec and changing the cam allows more/faster intake and exhaust gas movement. If you get the same kind of block as the OEM, you won't need to make any changes to the calibration.

You can recover a bit of power by using roller rocker arms, too. This adds about 15 HP. Roller lifter/cam adds a similar amount and both allow more power because they add less resistance through friction. The intake manifold may be another place to look for more power but you might have to watch out for excessive height- some intake manifolds are a lot taller than what came with it, although you may be able to find a newer TBI manifold from an MC (a little better than the original TBI, but not a tremendous difference).
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