Cam and valvetrain longevity....??? low duration high lift...
#1341
Registered
Heres a thread I had started about tims combo, in another forum. If anyones interested.
http://www.speedtalk.com/forum/viewt...hp?f=1&t=47746
http://www.speedtalk.com/forum/viewt...hp?f=1&t=47746
Mild what cam specs are you running now? I might as well copy you...
#1342
ok so from beginning to date of this thread there has been a lot discussed. Some off the subject in question but mostly involving input with combos, cam specs, lobe flaws with premature failure etc. To me it's evident something has changed drastically over the last couple years with rmbuilder but perhaps much longer. Difficult to say as we don't have all input going back several years (decade or more). Especially when we upgrade our builds, sell engines and lose track of the long jevity of the said engine and valvetrain. Just saying we're constantly changing builds, going bigger, adding SC's, procharger's, tunnel rams and so on which in most cases involves cam and valvetrain in most cases. So in a nutshell who's to say how long who's cam last and who's doesn't.
Other thread MT started may shed shed some more light on that. List is growing without a doubt. Good bad indifferent.
What I have come to the conclusion for the most part here is without a doubt duration goes up with cubic inch to maintain peak hp at a given rpm. (Pretty common knowledge for most part). Also obviously short duration higher lift cams are causing valvetrain stability all over. You'd think after all the years of techknowledgey and R&D there would just be a simple ratio rule of thumb (lobe/duration). Yet most likely there is that's why you don't see cams similar to the ones in question being sold by most all cam companies.
I will have to admit I am shocked to learn how much duration is needed to achieve peak hp let's say 6,000-6,200 on a 540-548. What I am understanding for the most part is on a 540-548 build with 315-325 cc heads is you should be looking at a cam 250/260-700/690 plus or minus. Heads being 100% professionally set up is crutial. If in doubt send them out... Every single moving part pertaining to valvetrain including lifter bore alignment, size, etc all equally important.
I recall MT posting some CI's vs duration differences but would be kinda of neat to really narrow it down with most common builds. Runner cc can change up duration so formula would never be a 100% accurate but at least get many people in the ball park. Head runner 305-335 (probably average based on CI below)
Just keep 6,000 rpm as a guideline for all engines.
496-509
540-548
555-565
572-598
Some variables may apply such as same CI with different stroke but just looking for general duration. Might be best for another thread however I think would be helpful for many individuals as well as builders. Example when you look up a cam in cam book it's not real specific with 396-454 or some 396-502. I have seen 540 plus occasionally however I think what we could do here would be helpful. Lift rates easier to determine based heads and flow at various lifts.
As many cam threads that come up I think this would be helpful for many.
Other thread MT started may shed shed some more light on that. List is growing without a doubt. Good bad indifferent.
What I have come to the conclusion for the most part here is without a doubt duration goes up with cubic inch to maintain peak hp at a given rpm. (Pretty common knowledge for most part). Also obviously short duration higher lift cams are causing valvetrain stability all over. You'd think after all the years of techknowledgey and R&D there would just be a simple ratio rule of thumb (lobe/duration). Yet most likely there is that's why you don't see cams similar to the ones in question being sold by most all cam companies.
I will have to admit I am shocked to learn how much duration is needed to achieve peak hp let's say 6,000-6,200 on a 540-548. What I am understanding for the most part is on a 540-548 build with 315-325 cc heads is you should be looking at a cam 250/260-700/690 plus or minus. Heads being 100% professionally set up is crutial. If in doubt send them out... Every single moving part pertaining to valvetrain including lifter bore alignment, size, etc all equally important.
I recall MT posting some CI's vs duration differences but would be kinda of neat to really narrow it down with most common builds. Runner cc can change up duration so formula would never be a 100% accurate but at least get many people in the ball park. Head runner 305-335 (probably average based on CI below)
Just keep 6,000 rpm as a guideline for all engines.
496-509
540-548
555-565
572-598
Some variables may apply such as same CI with different stroke but just looking for general duration. Might be best for another thread however I think would be helpful for many individuals as well as builders. Example when you look up a cam in cam book it's not real specific with 396-454 or some 396-502. I have seen 540 plus occasionally however I think what we could do here would be helpful. Lift rates easier to determine based heads and flow at various lifts.
As many cam threads that come up I think this would be helpful for many.
#1344
Charter Member#568
Charter Member
I am not so sure about that small of runner head on a 540+CI marine engine. My 548s have Dart 360s speced by Teague and made great numbers. Bob recommended AFR 305s for my 502ci 575sci, I thought that was small as well, or was it just what he had on the shelf? As far as my cams they are Crane Hydraulic Roller 254/262 680/680. 982 and 984 a side at 8psi
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Last edited by bck; 10-06-2016 at 08:28 PM.
#1346
Charter Member#568
Charter Member
If I could do it over again no doubt. Seems like it'd be much easier. The only reason I didn't was because I had just paid to remove the blower scoops and fill in the opening in the bulkhead for the drive belt. Oops
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Straight bottoms and flat decks
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#1347
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oh man do I have "if I did it again" thoughts.. DAILY.... my buddy bolted on 5 lb M3's to his TRS mistress, my twin... went from 66-76 mph with no real tuning.... for 10,000.00... talk about regrets....
#1348
Registered
I am not so sure about that small of runner head on a 540+CI marine engine. My 548s have Dart 360s speced by Teague and made great numbers. Bob recommended AFR 305s for my 502ci 575sci, I thought that was small as well, or was it just what he had on the shelf? As far as my cams they are Crane Hydraulic Roller 254/262 680/680. 982 and 984 a side at 8psi
I did see the cam 12.1 comp min recommended. Obviously with the numbers you pulled it didn't apply to your build.
Last edited by getrdunn; 10-06-2016 at 08:50 PM.
#1349
Charter Member#568
Charter Member
I'm fortunate that I have a light boat so I don't need crazy power to run fast. But it's always nice to have and for the time, effort and money I have into the n/a motors I probably could've added blowers and made about 200 more hp.
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Straight bottoms and flat decks
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#1350
Nice combo especially for a supercharged cat. That thing must scoot... Now that size of runner in a heavy deep V NA app would be very questionable. How fast you running? Also meant to ask you what rpm your propped for?
I did see the cam 12.1 comp min recommended. Obviously with the numbers you pulled it didn't apply to your build.
I did see the cam 12.1 comp min recommended. Obviously with the numbers you pulled it didn't apply to your build.