Re: Cam Specs for Mercruiser 260hp?
Duration 260 advertised 212 @ .050 both intake and Exhaust
Lobe lift .293 Total Lift .440 both Int. and Exh.
110 Lobe Center Angle
106 Intake Centerline
Installed Straight up.
Seams to work fine but with my 2800lbs 20foot, Searay SRV195 I was expecting it to pull to 4500+rpm even with the 21p prop. I though 50mph without having to trim up would be no problem. Don't really care how fast it goes just want to make the engine is making the power it should. I have a new ignition system with 12 degrees initial timing and 24 mech advance all in by a high 4000rpm(being safe) and I have ruled out valve float. Maybe I am over propped but with the small boat shouldn't turning a 21p prop @ 4500+rpm's be no problem. Thanks again for your information and help.
what I have says stock merc flat tapet cam pn 431-5943 that was put in most 350s is: 0.05 duration (intale/exhaust) 200/212, lift .400/.410, centerline 108/112, lsa 110.
off the top.. that's a decent cam and should make a good amount of power, but if you've got factory heads that'll be the main bottleneck to making much additional power... I agree on single pattern cam - especially with anything that looks remotely like a factory exhaust system... spit pattern would probably be a good bit better. dry headers and aftermarket heads are a different story.
The factory bump stick in a marine engine really isn't so bad that only a different cam is going to make a dramatic change by itself.
last thing to consider. if gear ratio is constant and we assume that slip doesn't change much, a change from a 17" prop to a 21" prop and pulling the same engine rpms equates to somewhere around 12 miles an hour increase in top speed. that would require an increase of over 100 horsepower... incremental changes in power don't make major changes in speed in a boat... the load required to displace water and overcome the friction is just too great...
Also, the thunderoblt ignition system is a good ignition. and adding aftermarket really isn't worth much if anything in terms of power. I also think if you're running your stock heads that your timing may be too far advanced if it's 36 degrees total advance based on your post... I would think you're going to be on the money at more like 32 or 33 degrees... but I could be wrong