Built HR *Broken Cam* Part 2
04-07-2011, 07:49 AM
#23
^ well they both play a role since rate of change of engine rpm and the resulting force acting on the cam will be proportional to the torque transmitted through the chain and gears, but I also feel that it is the resistance to turning that is the larger part of the equation in this case (just as you are more likely to break an axle on sticky tires on a dry prepped track vs street tires in the rain - clearly horsepower is also part of the equation).
I do have a hard time believing that stock Nissan cams are somehow weaker than any other aftermarket cam. In fact, I wouldn't be surprised if aftermarket cams used blanks from the same source. Perhaps just being torqued down twice is enough to weaken the cam?
04-07-2011, 08:08 AM
#24
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no, you would be surprised. OEM cams can be pretty weak compared to aftermarket bits.
knew a guy localy that did a cam shootout for SR20s years ago. dyno tests, etc... the final element (which is retarded, but i *did* learn something) the cams had to endure was whacking them across a bench vise. for him, it was just because 'he could'. obviously, i would never do something like this. any route, the OEM cams snapped immediately. one of the aftermarket cams (couldnt tell you which one, i had no idea) took one hell of a beating and just wouldnt snap, so forth and so on. HAHAHA it's just one of those things where, well... i would never even have thought to subject a cam to, but damned if i didnt want to watch it and see what would happen.
knew a guy localy that did a cam shootout for SR20s years ago. dyno tests, etc... the final element (which is retarded, but i *did* learn something) the cams had to endure was whacking them across a bench vise. for him, it was just because 'he could'. obviously, i would never do something like this. any route, the OEM cams snapped immediately. one of the aftermarket cams (couldnt tell you which one, i had no idea) took one hell of a beating and just wouldnt snap, so forth and so on. HAHAHA it's just one of those things where, well... i would never even have thought to subject a cam to, but damned if i didnt want to watch it and see what would happen.
04-07-2011, 01:50 PM
#26
already went over this in the other thread with a very long explanation as to why hp being delivered to cams dosnt go up with horsepower. the only thing that will increase the amount of hp being delivered is stronger springs which require more power or increase of friction from higher rpms/tighter chain. again like i said in the previous thread if increase of horsepower also increased the power being delivered to the accessory's then we would have broken a/c compressors and broken alternators which we do not have. reason being is that those items take no extra power to turn so no extra power is delivered =/ comparisons to the drive train are also included in the other thread. i don't think you will find any engine builder that disagrees with me.
my only question had been why it snapped there instead of the pin but that was answered, i had thought the stock cams where billet steel like most of the roller cams used with ohv engines are today and i was wrong. *shrug*
back on topic though it seems that anytime somebody gets an engine built now it should be recommended against stronger springs, and if they want a higher rev limit they should simply be told they have to get different cams or it wont work right. seems like a step forward for the community in my book
my only question had been why it snapped there instead of the pin but that was answered, i had thought the stock cams where billet steel like most of the roller cams used with ohv engines are today and i was wrong. *shrug*
back on topic though it seems that anytime somebody gets an engine built now it should be recommended against stronger springs, and if they want a higher rev limit they should simply be told they have to get different cams or it wont work right. seems like a step forward for the community in my book
^ well they both play a role since rate of change of engine rpm and the resulting force acting on the cam will be proportional to the torque transmitted through the chain and gears, but I also feel that it is the resistance to turning that is the larger part of the equation in this case (just as you are more likely to break an axle on sticky tires on a dry prepped track vs street tires in the rain - clearly horsepower is also part of the equation).
I do have a hard time believing that stock Nissan cams are somehow weaker than any other aftermarket cam. In fact, I wouldn't be surprised if aftermarket cams used blanks from the same source. Perhaps just being torqued down twice is enough to weaken the cam?
I do have a hard time believing that stock Nissan cams are somehow weaker than any other aftermarket cam. In fact, I wouldn't be surprised if aftermarket cams used blanks from the same source. Perhaps just being torqued down twice is enough to weaken the cam?
04-07-2011, 02:09 PM
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^ well they both play a role since rate of change of engine rpm and the resulting force acting on the cam will be proportional to the torque transmitted through the chain and gears, but I also feel that it is the resistance to turning that is the larger part of the equation in this case (just as you are more likely to break an axle on sticky tires on a dry prepped track vs street tires in the rain - clearly horsepower is also part of the equation).
Last edited by rh_334; 04-07-2011 at 02:10 PM.
04-07-2011, 05:27 PM
#29
^ both you and jerryd87 are overlooking simple physics. The springs didn't break the cams all by themselves. The force to break the cam came via the CRANK. If the crank turned over at say 1 rpm, do you really think you'd be able to get that cam to break?
The force that broke that cam is a function of BOTH engine torque and the resistance provided by the springs. Increased engine torque doesn't usually hamper accessories because there is very little resistance to turning, that we all agree on.
I guess I missed the explanation there, but horsepower isn't really the correct term to be using anyway. The rate of change of speed of the crank is angular acceleration. That acceleration directly translates into increased acceleration of the cam via the chain and cam gear. So with increased "horsepower" the cam is being accelerated more quickly than it otherwise would. There is no way to get around the fact that increased acceleration results in additional angular force on the cam.
Not really interested in arguing - just clarifying what I think is an inaccuracy given my understanding of the physics involved. I understand what you're trying to say about accessories not being adversely affected with increased hp/tq.
Keep in mind I didn't say that engine torque was the only force - only that it factored into the equation. And yes if being under load doesn't increase one of the relevant forces (such as forcing a valve open when it's trying to close which would resist the cam from turning with the crank) then I think that's correct in this case for the cams.
I try to keep an open mind - let me know if you think this logic is flawed.
The force that broke that cam is a function of BOTH engine torque and the resistance provided by the springs. Increased engine torque doesn't usually hamper accessories because there is very little resistance to turning, that we all agree on.
Not really interested in arguing - just clarifying what I think is an inaccuracy given my understanding of the physics involved. I understand what you're trying to say about accessories not being adversely affected with increased hp/tq.
If that was the case, and if the increase acceleration caused it then this would be more likely to happen during free reving, when the engine is not under load, since the rate of change of the rpm is by far the fastest when free rev'ed. Thats why i say this is not the cause.
I try to keep an open mind - let me know if you think this logic is flawed.
Last edited by rcdash; 04-07-2011 at 05:51 PM.
04-08-2011, 04:50 PM
#31
over time? yes it would break the force that broke the cams came from the crank BUT only because the cams demanded it. Tell me do you really think those cams would have broken will zero spring pressure if a power source was driving them with the same rpms and power as the engine? i can tell you they wouldnt have. better yet i would love to hear your explanation why more power isnt delivered to the ac unit or alternator? Based on your thinking they would recieve extra power as well. However there are dynos all over the internet of various a/c power intercoolers that show only 3-10hp drain on the engine wih the system on or off. the exact same as what the draw at stock power levels. please explain why there are no broken alternations? those are cast iron shafts that are even smaller in diameter then the cams.
Bottom line is no the springs dint break them by themselves, the friction of rpms, the tension from the timing chain and the tougher spings all caused it to be harder to turn the cams, thus they needed more power to turn so the crank delivered the extra power. The other thread had people reporting they have seem this at STOCK power levels with upgraded springs and stock rev limits. If there was very little resistance to turning on an alternator or a/c compressor then they wouldnt draw measurable power, however have you seen the pressure coming out of an a/c compressor? no 5 hp isnt much in the grand scheme of things but 15 hp which is what would be exerted if things increased like you say if a substantial amount. hell a half horsepower electric motor will break your arm if your not careful. so i hadly think that is considered very little resistance.
Another thing you must remember is the cam is only moving at half the rate of speed when compared to the crank, so these cams are seeing very little acceleration i dont care how fast you rev the engine. and like what was pointed out before the fastest acceleration would be during free rev which these did not break during. a perfect example would be do you think the engine makes full power at free rev? or how about cruising speeds? the answer is no for the same reason the engine will only deliver power if it is demanded that is how load works. same thing go dyno a car with a 1:1 final drive(thats including the rear and and transmission ratio) if that car makes 500 hp i guarantee you it will make less then 2500 with a 5:1 gear ratio it will probably be closer to the 2k mark. why? beacause there is less demand on the engine therefore it delievers less. like i said its not going to magically say omg i make more power so i must deliever more power to the cams.
Better yet go talk to mechanics for top fuel dragsters/funny cars. they will tell you it takes 500 hp to turn those blowers at full boost. then ask em how much it takes to turn at idle and i bet you they walk over to one of there spares and turn it by hand. why? again because of demand or load. there is no resistance turning it by hand so you can turn it, however there is immense resistance at full boost. put that blower on a regular fuel engine(that engine on regular fuel makes 2k hp switching just) still draws 500 hp. so that would require some explination as well why a blower delivering the same amount of air to an engine at the same boost level draws the same power despite one engine making 2000hp and another making 6000-7000 the only difference between them is fuel.
I mean no disrespect but your argument contradicts everything known in the world of motor sports, it contradicts efi tuning, and i have yet to see any of the shops say it was because of increased engine power. in fact they said it was because of the springs and the cams being a weak casting. again i mean no disrespect but hen 9/10 people tell you your wrong you usually are(same goes for me look in my tech thread where i changed the content on oil i was wrong so i changed it.)
Bottom line is no the springs dint break them by themselves, the friction of rpms, the tension from the timing chain and the tougher spings all caused it to be harder to turn the cams, thus they needed more power to turn so the crank delivered the extra power. The other thread had people reporting they have seem this at STOCK power levels with upgraded springs and stock rev limits. If there was very little resistance to turning on an alternator or a/c compressor then they wouldnt draw measurable power, however have you seen the pressure coming out of an a/c compressor? no 5 hp isnt much in the grand scheme of things but 15 hp which is what would be exerted if things increased like you say if a substantial amount. hell a half horsepower electric motor will break your arm if your not careful. so i hadly think that is considered very little resistance.
Another thing you must remember is the cam is only moving at half the rate of speed when compared to the crank, so these cams are seeing very little acceleration i dont care how fast you rev the engine. and like what was pointed out before the fastest acceleration would be during free rev which these did not break during. a perfect example would be do you think the engine makes full power at free rev? or how about cruising speeds? the answer is no for the same reason the engine will only deliver power if it is demanded that is how load works. same thing go dyno a car with a 1:1 final drive(thats including the rear and and transmission ratio) if that car makes 500 hp i guarantee you it will make less then 2500 with a 5:1 gear ratio it will probably be closer to the 2k mark. why? beacause there is less demand on the engine therefore it delievers less. like i said its not going to magically say omg i make more power so i must deliever more power to the cams.
Better yet go talk to mechanics for top fuel dragsters/funny cars. they will tell you it takes 500 hp to turn those blowers at full boost. then ask em how much it takes to turn at idle and i bet you they walk over to one of there spares and turn it by hand. why? again because of demand or load. there is no resistance turning it by hand so you can turn it, however there is immense resistance at full boost. put that blower on a regular fuel engine(that engine on regular fuel makes 2k hp switching just) still draws 500 hp. so that would require some explination as well why a blower delivering the same amount of air to an engine at the same boost level draws the same power despite one engine making 2000hp and another making 6000-7000 the only difference between them is fuel.
I mean no disrespect but your argument contradicts everything known in the world of motor sports, it contradicts efi tuning, and i have yet to see any of the shops say it was because of increased engine power. in fact they said it was because of the springs and the cams being a weak casting. again i mean no disrespect but hen 9/10 people tell you your wrong you usually are(same goes for me look in my tech thread where i changed the content on oil i was wrong so i changed it.)
^ both you and jerryd87 are overlooking simple physics. The springs didn't break the cams all by themselves. The force to break the cam came via the CRANK. If the crank turned over at say 1 rpm, do you really think you'd be able to get that cam to break?
The force that broke that cam is a function of BOTH engine torque and the resistance provided by the springs. Increased engine torque doesn't usually hamper accessories because there is very little resistance to turning, that we all agree on.
I guess I missed the explanation there, but horsepower isn't really the correct term to be using anyway. The rate of change of speed of the crank is angular acceleration. That acceleration directly translates into increased acceleration of the cam via the chain and cam gear. So with increased "horsepower" the cam is being accelerated more quickly than it otherwise would. There is no way to get around the fact that increased acceleration results in additional angular force on the cam.
Not really interested in arguing - just clarifying what I think is an inaccuracy given my understanding of the physics involved. I understand what you're trying to say about accessories not being adversely affected with increased hp/tq.
Keep in mind I didn't say that engine torque was the only force - only that it factored into the equation. And yes if being under load doesn't increase one of the relevant forces (such as forcing a valve open when it's trying to close which would resist the cam from turning with the crank) then I think that's correct in this case for the cams.
I try to keep an open mind - let me know if you think this logic is flawed.
The force that broke that cam is a function of BOTH engine torque and the resistance provided by the springs. Increased engine torque doesn't usually hamper accessories because there is very little resistance to turning, that we all agree on.
I guess I missed the explanation there, but horsepower isn't really the correct term to be using anyway. The rate of change of speed of the crank is angular acceleration. That acceleration directly translates into increased acceleration of the cam via the chain and cam gear. So with increased "horsepower" the cam is being accelerated more quickly than it otherwise would. There is no way to get around the fact that increased acceleration results in additional angular force on the cam.
Not really interested in arguing - just clarifying what I think is an inaccuracy given my understanding of the physics involved. I understand what you're trying to say about accessories not being adversely affected with increased hp/tq.
Keep in mind I didn't say that engine torque was the only force - only that it factored into the equation. And yes if being under load doesn't increase one of the relevant forces (such as forcing a valve open when it's trying to close which would resist the cam from turning with the crank) then I think that's correct in this case for the cams.
I try to keep an open mind - let me know if you think this logic is flawed.
04-08-2011, 05:25 PM
#32
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..... same thing go dyno a car with a 1:1 final drive(thats including the rear and and transmission ratio) if that car makes 500 hp i guarantee you it will make less then 2500 with a 5:1 gear ratio it will probably be closer to the 2k mark. why? beacause there is less demand on the engine therefore it delievers less. like i said its not going to magically say omg i make more power so i must deliever more power to the cams.
Here's a hint, the HP output of a 5:1 gear reduction fed 500HP will be ~500HP minus frictional losses.
Torque is multiplied, HP is not.
Onto the broken cam, if you look, it broke right at the oiling hole, there were also threads cut into the ID of that bore. Huge stress risers. Probably a flawed casting, it was dropped or impacted in some manner. Even improper install can break some of the hollow shaft cams. You are also not taking into account the constant cyclic forces on the cams from forcing the valves open against the valve springs, and the valve springs trying to accelerate the cams when on the closing ramp of the cam.
I say a failure like this is pick of the draw. If it's going to happen, there is nothing that can be done to cause or prevent it, it's just going to happen. This is disragarding the cam siezing in the bores or something else failing and jamming it.
04-08-2011, 06:06 PM
#33
^ But there seems to be a developing pattern of stock cams breaking in conjunction with the use of aftermarket valve springs.
Can you explain a logical or legitimate reason for installing aftermarket springs on stock cams when the rev limit is not being raised above stock redline? Cuz nobody else has...
Can you explain a logical or legitimate reason for installing aftermarket springs on stock cams when the rev limit is not being raised above stock redline? Cuz nobody else has...
04-08-2011, 06:22 PM
#34
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^ But there seems to be a developing pattern of stock cams breaking in conjunction with the use of aftermarket valve springs.
Can you explain a logical or legitimate reason for installing aftermarket springs on stock cams when the rev limit is not being raised above stock redline? Cuz nobody else has...
Can you explain a logical or legitimate reason for installing aftermarket springs on stock cams when the rev limit is not being raised above stock redline? Cuz nobody else has...
Wall-o-text stirred my grey matter and caused me to miss that this engine had aftermarket springs.It makes no sense to me to change to heavier springs and stay with stock cams and stock redline. Being that the stock cams lay over at higher RPM, if you're not doing it all, you're gaining nothing but potential issues it seems.
How many cases like this have there been with stock cams and heavier valvesprings?
04-08-2011, 06:30 PM
#35
I think the pattern is coming from a lack of knowledge or understanding of the stresses on the cams... Cam companies have closed and open seat pressures that need to be speced out when installing aftermarket springs. You take your installed height and measure that pressure, the you add your lift to the installed height and you have your open pressure. Now if you have room to go higher in both catagories, and assuming you dont have coil bind on the spring, you can shim the spring to get as high of a pressure without going over the cam copmanies specs and getting coil bind. Also in the reverse...if it is too high spring seat machining or valve facing is needed.
I would have to look at all the specs, but im willing to guess that the BC( a company known for running higher spring pressure then probaly needed) spring pressures closed and open are well over stock values. So plain and simple... the cam broke at the weakest link...
I feel that some shops and individuals install aftermarket springs on stock cams cause when the motor is apart and they are performing a valve job they figure..."why not..it doesnt take much more extra labor to do it....and if i upgrade cams in the future it will make it that much easier.." Then shortly after the Cam breaks and here ya are.
Maybe I missed it but why did the shop pull the motor. If the cam just broke I probaly would have just yanked the cams on that side(cause they have to come apart anyway) and do a quick leak down test to see if any valves are bent... If ya got lucky then just toss some cams in there...ya already have upgraded springs... and button it back up...
I would have to look at all the specs, but im willing to guess that the BC( a company known for running higher spring pressure then probaly needed) spring pressures closed and open are well over stock values. So plain and simple... the cam broke at the weakest link...
I feel that some shops and individuals install aftermarket springs on stock cams cause when the motor is apart and they are performing a valve job they figure..."why not..it doesnt take much more extra labor to do it....and if i upgrade cams in the future it will make it that much easier.." Then shortly after the Cam breaks and here ya are.
Maybe I missed it but why did the shop pull the motor. If the cam just broke I probaly would have just yanked the cams on that side(cause they have to come apart anyway) and do a quick leak down test to see if any valves are bent... If ya got lucky then just toss some cams in there...ya already have upgraded springs...
and button it back up...
Last edited by Vince@R/TTuning; 04-08-2011 at 06:33 PM.
04-08-2011, 06:36 PM
#36
Sorry a slip of words, but in reality hp dosnt break things anyway its torque. You are right hp will be the same due to lower rpms of the components but torque will be multiplied. so 500 ft lbs of torque with a 1:1 ratio would not be 2500 ft lbs with a 5:1 gear ratio. Not counting mechanical losses which would account to a portion of the lower torque output the majority would be due to simply having lower load on the engine. the rest of your post pretty much agrees with what i have been saying that springs, friction and tension will be the only things that cause the crank to deliever more power to the cams as it will cause them to be harder to turn. anyway i think everyone gets the point i was trying to get across i just dint fully finish my thought and allowed a slip of words.
I will definitely put in my thread not to use bc springs on stock cams, i already have in there to not try and "one up" what is recommended for springs to try and increase reliability. As we can see thats a bad idea.
op should be a little quieter to drive once you get this thing fixed up and those exhaust leaks taken care of
i dont wanna mention anything else on the cam as it seems pretty cut and dry at this point so if anyone wants to continue pm me so we dont clutter the thread anymore. I think the upgraded springs where just to make a bit more money at this point rude unless he asked for em =/
I will definitely put in my thread not to use bc springs on stock cams, i already have in there to not try and "one up" what is recommended for springs to try and increase reliability. As we can see thats a bad idea.
op should be a little quieter to drive once you get this thing fixed up and those exhaust leaks taken care of
i dont wanna mention anything else on the cam as it seems pretty cut and dry at this point so if anyone wants to continue pm me so we dont clutter the thread anymore. I think the upgraded springs where just to make a bit more money at this point rude unless he asked for em =/
If you're saying a 500HP engine fed through a 5:1 gear reduction will make 2K HP, you have a severe misunderstanding of how power works.
Here's a hint, the HP output of a 5:1 gear reduction fed 500HP will be ~500HP minus frictional losses.
Torque is multiplied, HP is not.
Onto the broken cam, if you look, it broke right at the oiling hole, there were also threads cut into the ID of that bore. Huge stress risers. Probably a flawed casting, it was dropped or impacted in some manner. Even improper install can break some of the hollow shaft cams. You are also not taking into account the constant cyclic forces on the cams from forcing the valves open against the valve springs, and the valve springs trying to accelerate the cams when on the closing ramp of the cam.
I say a failure like this is pick of the draw. If it's going to happen, there is nothing that can be done to cause or prevent it, it's just going to happen. This is disragarding the cam siezing in the bores or something else failing and jamming it.
Here's a hint, the HP output of a 5:1 gear reduction fed 500HP will be ~500HP minus frictional losses.
Torque is multiplied, HP is not.
Onto the broken cam, if you look, it broke right at the oiling hole, there were also threads cut into the ID of that bore. Huge stress risers. Probably a flawed casting, it was dropped or impacted in some manner. Even improper install can break some of the hollow shaft cams. You are also not taking into account the constant cyclic forces on the cams from forcing the valves open against the valve springs, and the valve springs trying to accelerate the cams when on the closing ramp of the cam.
I say a failure like this is pick of the draw. If it's going to happen, there is nothing that can be done to cause or prevent it, it's just going to happen. This is disragarding the cam siezing in the bores or something else failing and jamming it.
what is it putting down?
04-08-2011, 08:08 PM
#38
The shop involved hasn't addressed these points and has yet to explain why they recommended aftermarket valve springs.
04-08-2011, 08:17 PM
#39
Question: were all the cams that have reportedly broken near the threads as in this case been installed more than 1 time into an engine (always a rebuild)? Put another way, has a new cam (stock or aftermarket) failed in an engine after the original install? Probably too few data points to generate a statistically meaningful conclusion...
Last edited by rcdash; 04-08-2011 at 08:20 PM.
04-08-2011, 09:34 PM
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I think the pattern is coming from a lack of knowledge or understanding of the stresses on the cams... Cam companies have closed and open seat pressures that need to be speced out when installing aftermarket springs. You take your installed height and measure that pressure, the you add your lift to the installed height and you have your open pressure. Now if you have room to go higher in both catagories, and assuming you dont have coil bind on the spring, you can shim the spring to get as high of a pressure without going over the cam copmanies specs and getting coil bind. Also in the reverse...if it is too high spring seat machining or valve facing is needed.
I would have to look at all the specs, but im willing to guess that the BC( a company known for running higher spring pressure then probaly needed) spring pressures closed and open are well over stock values. So plain and simple... the cam broke at the weakest link...
I feel that some shops and individuals install aftermarket springs on stock cams cause when the motor is apart and they are performing a valve job they figure..."why not..it doesnt take much more extra labor to do it....and if i upgrade cams in the future it will make it that much easier.." Then shortly after the Cam breaks and here ya are.
Maybe I missed it but why did the shop pull the motor. If the cam just broke I probaly would have just yanked the cams on that side(cause they have to come apart anyway) and do a quick leak down test to see if any valves are bent... If ya got lucky then just toss some cams in there...ya already have upgraded springs... and button it back up...
I would have to look at all the specs, but im willing to guess that the BC( a company known for running higher spring pressure then probaly needed) spring pressures closed and open are well over stock values. So plain and simple... the cam broke at the weakest link...
I feel that some shops and individuals install aftermarket springs on stock cams cause when the motor is apart and they are performing a valve job they figure..."why not..it doesnt take much more extra labor to do it....and if i upgrade cams in the future it will make it that much easier.." Then shortly after the Cam breaks and here ya are.
Maybe I missed it but why did the shop pull the motor. If the cam just broke I probaly would have just yanked the cams on that side(cause they have to come apart anyway) and do a quick leak down test to see if any valves are bent... If ya got lucky then just toss some cams in there...ya already have upgraded springs...
and button it back up...Motor was pulled just to make it easier.There was also some other things have need to be fixed,.. Such as the exhaust with no gaskets that I posted above
Last edited by Jasonvs2146; 04-08-2011 at 11:31 PM.