Roller Rockers/ Are they really that important
03-26-2009, 10:20 PM
#1
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Roller Rockers/ Are they really that important
Roller Rockers... are they that important?
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This might seem a little out there however I have been up reading late night and even sometimes into the early morning. Several articles from very reputable engine builders that have been around for a long time and still going at it. (Even in the HP BBC books) Many claim what little good R/R's really do and sometimes even what damage they even can cause. Studs Breaking, Rockers themselves breaking, needle bearing failure and then of course the expense that comes along with them. 250.00 Rockers, sometimes resulting in new valve covers 100.00- 250.00. Then if you have twin's, trips?? I've never really have given it much of a thought however lately I've been in a bit of a cruch and then came across this. I always figured with the newer profile cams and higher lifts, just put them in. But really what do you gain. A little less friction. I understand that less friction may result in more HP however that friction seems very minor when you think of all the other rotating parts as well valve springs. I din't realize how high of RPM they twist the stock rockers 7,500 plus RPM's. Just really think about this and share your thoughts. I'm certain I will hear the flip to this but that's OK.
I think there are definitely applications for them but just wondering if we make them out to be more than what they really are. I would be very curious as to dyno results on the subject with various engine sizes and HP.
Take care for now.
Maybe I just need more sleep. Lately when I do sleep it seems like I've been going on those camshaft lobe roller coaster rides. LOL. Getting close to summer, boat in the water...
John
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This might seem a little out there however I have been up reading late night and even sometimes into the early morning. Several articles from very reputable engine builders that have been around for a long time and still going at it. (Even in the HP BBC books) Many claim what little good R/R's really do and sometimes even what damage they even can cause. Studs Breaking, Rockers themselves breaking, needle bearing failure and then of course the expense that comes along with them. 250.00 Rockers, sometimes resulting in new valve covers 100.00- 250.00. Then if you have twin's, trips?? I've never really have given it much of a thought however lately I've been in a bit of a cruch and then came across this. I always figured with the newer profile cams and higher lifts, just put them in. But really what do you gain. A little less friction. I understand that less friction may result in more HP however that friction seems very minor when you think of all the other rotating parts as well valve springs. I din't realize how high of RPM they twist the stock rockers 7,500 plus RPM's. Just really think about this and share your thoughts. I'm certain I will hear the flip to this but that's OK.
I think there are definitely applications for them but just wondering if we make them out to be more than what they really are. I would be very curious as to dyno results on the subject with various engine sizes and HP.
Take care for now.
Maybe I just need more sleep. Lately when I do sleep it seems like I've been going on those camshaft lobe roller coaster rides. LOL. Getting close to summer, boat in the water...
John
03-27-2009, 01:04 AM
#3
Charter Member # 55
Charter Member
The need for roller rockers is often dictated by the amount of cam lift. Anything over about .550 lift will need them.
STOCK MERC VALVE COVERS WORK JUST FINE WITH ROLLER ROCKERS!!!!!!!
STOCK MERC VALVE COVERS WORK JUST FINE WITH ROLLER ROCKERS!!!!!!!
03-27-2009, 08:33 PM
#4
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R/R's
I'll post a couple of articles regarding this. I'm going down to Grand Rapids next week and will be helping out in the shop/Dyno room at More Power Racing and post the results on what I come up with.
03-28-2009, 06:35 AM
#5
VIP Member
VIP Member
I'm sure an argument can be made for anything, I've had regular rockers on small blocks mushroom out as well because of a stuck valve. even though they are more expensive, I personally would rather have rollers, even with the complexity and more moving parts they help dissipate valve train harmonics and help center and take wear off, freeing up horsepower.
03-28-2009, 10:05 AM
#7
Registered
gertdunn,
This is a really good question with many answers , but let's go down some of them.
Stock rockers will last much longer than roller rockers ever will, this is proven everyday by all the car & trucks that run up and down our highways daily. A car driven daily back and forth to work with 100,000 miles on it has approx 3,000 hours on it. A big truck with 750,000 miles has approx 17,000 hrs on it - neither have roller rockers. Your typcal stud mount roller rockers can't come close to those hours - period.
Why have them?
Typically when you run rpm's that are above stock you need a 2 things to do that with:
- larger cam (lift and duration)
- stiffer valve springs (as you go even higher they get bigger in dia as well)
The stock stamped style rocker has trouble with larger dia springs as the area from the stud to the tip is a very gradulau slope compared to a roller with a steep rise that allows larger springs.
The valve contact area on a stamped rocker is not constant so as the rocker pivots the area that makes contact with the stem will change in size. The roller tip aside from less drag because it rolls along the face of the tip provides a constant contact area size.
As you increase cam lift the rotation of the stock rocker goes past a certian point it will start to push the valve stem because your going off it's contact patch, the roller tip eliminates this.
Your comment about breaking studs comes into play because of the extra degrees of rotation of the rocker with a high lift cam that it will push the stud over instead of just straight up, that is one reason for girdles or shafts.
The other problem stock rocker have is with higher rpms it means th chronological time for the valve to go from seated to open to seated becomes shorten, the higher the rpms the shorter the time you have to accomplish that. That is why with more rpm's comes more spring pressure.
Valve spring pressure has nothing to do with anything other than the shortening of the valve close-open-close cycle becoming shorter. As this time frame shortens the weight of the valve, rocker and pushrod will continue to throw the valve open further when it goes to open, you need to stop that from happening because your valve lash will get to great and you have slap - things break then. Also the pressure of the piston traveling upward will push the valve closed faster and if the springs can't keep up you have valve float, again to many lose parts floating around makes things break.
With all those dynamics happening at once the metal to metal contact area between the stock rocker arm and ball create drag because with the bigger cam your going past it's normal contact area and pushing of the valve stem and etc and make the rocker move slower and it can't keep up with the speed/velocity of the valve train. The extra spring pressure will start to squeeze the oil out of the this area and again make drag which binds the valve train and things get lose from not being in constant contact and break!
I can keep going but I'm pooped now!
So, you answer is stocker rocker are better with stock engines, once you drastically exceed those stock design parameters you've changed the dynamics such that the stock parts just won't cut it. The HP losses due to friction are very small compared to the valve train damage that can result and the longeveity will decrease by many times of the stock parts once you over work them.
This is a really good question with many answers , but let's go down some of them.
Stock rockers will last much longer than roller rockers ever will, this is proven everyday by all the car & trucks that run up and down our highways daily. A car driven daily back and forth to work with 100,000 miles on it has approx 3,000 hours on it. A big truck with 750,000 miles has approx 17,000 hrs on it - neither have roller rockers. Your typcal stud mount roller rockers can't come close to those hours - period.
Why have them?
Typically when you run rpm's that are above stock you need a 2 things to do that with:
- larger cam (lift and duration)
- stiffer valve springs (as you go even higher they get bigger in dia as well)
The stock stamped style rocker has trouble with larger dia springs as the area from the stud to the tip is a very gradulau slope compared to a roller with a steep rise that allows larger springs.
The valve contact area on a stamped rocker is not constant so as the rocker pivots the area that makes contact with the stem will change in size. The roller tip aside from less drag because it rolls along the face of the tip provides a constant contact area size.
As you increase cam lift the rotation of the stock rocker goes past a certian point it will start to push the valve stem because your going off it's contact patch, the roller tip eliminates this.
Your comment about breaking studs comes into play because of the extra degrees of rotation of the rocker with a high lift cam that it will push the stud over instead of just straight up, that is one reason for girdles or shafts.
The other problem stock rocker have is with higher rpms it means th chronological time for the valve to go from seated to open to seated becomes shorten, the higher the rpms the shorter the time you have to accomplish that. That is why with more rpm's comes more spring pressure.
Valve spring pressure has nothing to do with anything other than the shortening of the valve close-open-close cycle becoming shorter. As this time frame shortens the weight of the valve, rocker and pushrod will continue to throw the valve open further when it goes to open, you need to stop that from happening because your valve lash will get to great and you have slap - things break then. Also the pressure of the piston traveling upward will push the valve closed faster and if the springs can't keep up you have valve float, again to many lose parts floating around makes things break.
With all those dynamics happening at once the metal to metal contact area between the stock rocker arm and ball create drag because with the bigger cam your going past it's normal contact area and pushing of the valve stem and etc and make the rocker move slower and it can't keep up with the speed/velocity of the valve train. The extra spring pressure will start to squeeze the oil out of the this area and again make drag which binds the valve train and things get lose from not being in constant contact and break!
I can keep going but I'm pooped now!
So, you answer is stocker rocker are better with stock engines, once you drastically exceed those stock design parameters you've changed the dynamics such that the stock parts just won't cut it. The HP losses due to friction are very small compared to the valve train damage that can result and the longeveity will decrease by many times of the stock parts once you over work them.
Last edited by HabanaJoe; 03-28-2009 at 04:16 PM.
