Mr Maine

When I first degreed the cam in, I used the intake center line. The cam card showed it at 107 (5 degrees of advance ground in). I set it at 107.5. After I put it together, I realized that measuring it that way was not the best because the lobe is probably asymmetrical. So I measure the intake at .050, and it shows its actually 2 degrees retarded, so the intake centerline is on a 109 (3 degrees advanced).

I can run it here, and always advance it a bit when on the dyno, or in the boat to see what change it makes.

I didn't want to make a big deal out of it, that's why my original post was just asking for thoughts on real world effects of 2 degrees of cam timing change.

Thanks

MILD THUNDER

iTrader: (3)

If you havent purchased a timing cover yet. The cloyes hex adjust cover and toming set will make it very easy to change cam timing on the dyno. Plus setting the end play is really easy with that cover.

MILD THUNDER

iTrader: (3)

Personally, i would lean towards a retarded cam in a boat myself. Well, offshore boat that is. Advancing the cam closes the intake valve sooner, and will help build cylinder pressure down low. Which is why usually one sees an increase in low speed power when advancing.

Maybe my boat is different, but i certainly dont need more cylinder pressure while getting on plane , as my throttle levers are not even halfway while planing a 10k lb boat. Last thing i want is a bunch of low end cylinder pressure at low rpm, not only from a detonation standpoint, but how manyvguys out there are worried about low end torque with their bravo drives ? Lol.

As far as once my boat is up and running, if theoretically, i can pick up some upper rpm power , you know, when the throttles are pegged to the dash and your watching the speedo stop climbing, then yes, i want power there . I have no interest in drag racing my boat from 45mph to 90mph.

Also. Lets say you tell your cam guy, you want peak power at 6000rpm. You go to the dyno. Engine makes peak hp at 6000. You nut in your pants, and go all over the interweb telling everyone your cam guy nailed it, and is better than jesus christ himself at cam design. My opinion is different, in that another cam that may have peaked at 6300rpm, may make more power at 6000 than the other cam, as well as 6300, and have a better power curve for which you operate in.

My buddy Joe specifically asked for a cam that makes max power at 6000rpm for his engine build. On the dyno, we pulled it to 6700rpm, and still never saw hp fall off. Does that mean his cam was all wrong? Imo, no. In some peoples, yes it would.

Im not suggesting everyone goes around retarding their cams. I do agree that if you must move the cam more than 4 deg, youre better off with a new cam usually. 2 deg i really wouldnt waste my time.

mike tkach

iTrader: (3)

i think some people think,i want to keep my max rpm at 6000rpm as not to over rev their engine might be the wrong train of thought.if you have the right combination of parts and the properly sized oil and water cooling that 6500 rpm max won,t hurt the engines.i also believe that we should prop the boat so your max rpm is slightly under the max hp rpm of the engine.

MILD THUNDER

iTrader: (3)

If your valvetrain can handle it, and you dont mind a reduction in cruising speed, then i dont see why not.

Generally speaking, i would rather make 1000hp at 6000, than 1030 at 6500. Id take advantage of a larger pitch prop to put me at 6000 wot, which results in a faster cruise speed. Id rather cruise at 80mph at 4000, than 80mph at 4500 for example. Might now sound like much, but after say 100 hours of cruise time, those 500 revolutions per minute, add up to alot less cycles on parts. Thats 30,000 revolutions per hour difference. At the 100 hour point, the engine with the larger pitch prop has had 3 million less revolutions. The valve springs, lifters, pistons, rockers, all have covered less ground.

Kinda like comparing 100k miles on an engine thats been in a truck with a 4.10 gear with no overdrive, vs an engine that was in a truck with 100k miles and overdrive. Every part in that overdrive equipped engine has cycled much less during those 100k miles.

I think mercury marine knows this, and generally , thats why their engines are 5200ish rpm max. The technology is certainly there is they wanted to build a 650hp version of a 502 spinning 6000 rpm, but i believe they keep it down, in order to get decent life out of the engines.

mike tkach

iTrader: (3)

i believe merc kept the rpm down so they could use cheeper parts.i don,t think merc cares how long the engines last once they get past the warranty period.

SB

iTrader: (1)

Just as a note, retarding a cam moves some more of the overlap period after tdc. ie: that's when the piston is going down. Another reason why I think the blue merc Crane cams are 5° advanced.

ezstriper

I would think the extra low end would be a + getting a 10k boat on plane...just me...moving the cam around mainly just moves the power band, as in your friend Joe, said his 6000rpm cam pulled to 6700, bet if he advanced it 4 deg might be close to the 6k he was looking for...maybe was not degreed in correct on the built or cam just missed a bit...getting down to splitting hairs at this point.

230lx434

In theory lets say, if the cam had 3-4 degrees of advance ground into it from a tuning perspective would this amount of advance be adding to initial timing at idle and also WOT timing at WOT? Example initial timing straight up would be 22* and WOT 33-34*. would the advance need to be taken into consideration when setting these parameters up in FAST Xfi on commanded spark?

HaxbySpeed

Cheap parts like forged cranks, forged rods, forged pistons, crank trigger ignition with coil packs, billet cams, crane lifters, crane gold rockers, custom designed efi intakes, stainless headers, etc.? Just sayin.