Effects on cam advance/retard
 

If you had a cam that was properly matched to the engine and it had 5 degrees of advance ground in, what would be the real life effect of retarding it 2 degrees, so essentially you have 3 degrees of advance now?

Say intake closing goes from 42 to 44 abdc...

Thoughts?
Thanks

Usually engine builders with piston clearance issues on big dome pistons for valve to piston clearance issues.. Im not sure on reversion for marine . This link from comp cams may help you

http://www.compcams.com/Pages/413/ca...ion-angle.aspx

Thanks for the link. I do know the theory, I guess I was thinking more real world in the boat. Would I be able to feel a little less low end, more top end or is 2 degrees negligible assuming the engine doesn't desparetly need more advance/retard to begin with.

I'm guessing about the same effect as the timing chain breaking in, slightly less bottom end slightly higher power band. I would think you would have to go 4 degrees to even notice it.

Apparently my cam likes 4* retard to the tune of almost 47 hp on top . Does not like advance one bit. Same for Mild thunderer . (per desk top dyno, thanx Mild Thunderer)
Will know for sure at dyno time.
Retarding makes the cam 'bigger'

Retarding makes the cam 'bigger' How ?

My cam has 5 degrees of adance ground in. I have it retarded 2 degrees. Timing chain is already been used so no initial stretch. I think I will leave it. Intake closing went from 42 to 44.

IVC and EVO are the two most important events. IMHO.

Retarding makes these (and all events) later. Advancing, thus obviously makes these earlier.

Most 'typical' cams are installed (many are even ground this way) 4° advanced.

Most of the Merc/Crane Marine HR's are 5° advanced.

SB, yeah, so going from 5 to 3. I always seem to run out of cam on the top end.

it has been my experiance that it moves the peak power either higher or lower a little in the rpm band but no hp difference to speak of.i always install them straight up for marine use,espically in a supercharged deal.i am looking forward to moving it around on the dyno dan.we need to keep in mind that when we change cam timing it also changes piston to valve clearance.

ooops sorry, got sidetracked.

Not a big deal IMHO, unless a build you are willing to make everything exactly spot on.

If you run out of cam on the big end as you say, then get a bigger cam. Seriously.

My cam is sized correctly, I guess I was looking for real world feed back on effects of a couple degrees. I think I'll leave them at 3 degrees advanced.

couple things,1/ if you are running out of cam how can your cam be sized correctly?2/ is it maybe you are running out of head?also,moving the cam 2 deg either way probibaly won,t be noticeable.

Mike,
I was generalizing, and talking about past engines rather than this one. I am running dart 308s on a 462 with a custom cam. I didn't mention names because I didn't want to get into it.
Thanks for your thoughts and input. Based on this feedback looks like I should be fine.

:cool:

altering cam timing is just another tuning factory as long as you have piston to valve clearance to do so, advancing will give more lower end power, while retarding it sends the power in at a higher RPM, and yes it will also effect the H/P, just depends on heads/cam/intake etc. In drag race setups we would advance cam on good traction tracks and retard on slippery ones...now we do the same thru a computer and ignition timing...slightly easier

what king of et gain did you see from altering the cam timing at the track.my guess is very little.i will stand by my statement that in a pleasure boat the difference will not be notacible,in other words not even 1 mph.

we would retard to kill off a slight bit of power to be able to get down a iffy track, the only gain was being able to hook the car vs not, and yes on a boat retarding would only hurt a boat I would think

Never know unless you try.

I've seen guys swap out their current cams, for "custom" cams , that have less of a timing event change, than what advancing or retarding their current camshaft would have been.

Many things are going on withh camshafts. To suggest advancing a certain cam, will make more torque, is vague. Where ? From idle to 2500? From 2500 to 3500? From 3500 to 4500? Retarding a cam, to say that upper rpm power will be gained, is also vague. Just because you advance a cam, doesnt simply mean more torque, and just because you retarded it, doesnt mean more upper rpm power. It all depends on the individual applicstion.

A simple thing like a trick valve job, increasing low lift airflow, can change what the engine "wants" for cam timing. What may have been the "perfect" cam, is no longer perfect. I think we can argue theories on this all day, but the only way to tell if you made a change for the better, is on the dyno.

Who knows, depending on the current setup, you just might see an increase in peak torque, and peak horsepower. I wouldnt expect much on a 400hp engine. Things change though when you get into nearly 2hp per ci builds . Jmo.

Piston to valve clearance needs to be checked as others stated.

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

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.

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.

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.

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.

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.

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.

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.

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?

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.

Ignition timing and cam (valve) timing are two separate entities.

that cam has 4 deg of advance ground into it and i can assure you it was properly timed when installed.it is not uncommon on a blown engine to see max power above the projected rpm,as the rpm goes up so does the boost.boost=power.

I wish I researched a little more about camming my 540's to move a heavy mistress, too late now to change things but my results are off, the issue is some guys say I have too much cam, others say not enough to keep the Tq to move the boat. I do plan to dyno in Feb. that will also tell me things I guess

I was talking to Cigrocket last year he moved a mistress to nice speeds with his 540's I should have build identical to that build, I thought about moving cams around on dyno but does not seem the effort will produce great results in N/A application.

tim,the wrong camshaft sure could be the root of your problem.i forgot your cam specs.can you refresh my memory?

241/[email protected] duration, 681/663 lift, 112 LSA was informed to install dot to dot, we degreed it in also, I would have to look for that spec, I wanna say 108.5? been a while....

241/246 @ .050
.681/.663

112 lsa

109 icl
115 ecl

haha DITTO!!

i am no cam expert but i think that should be a good choice for your engines.

Some say yes, some say no, I have no idea, it's not getting changed right now anyway $$ but Cigrockets builds pushed his boat to easy 75 with more to go, I am struggling to see 73, same exact boat and props... he had similar builds with 741 cams 687 on Dyno..I think he said, 540, AFR315's

i know for a fact that the afr 315 is a hell of a good head.