65 327/365hp motor rebuild--Solid or roller cam/lifters?
11-28-2015, 11:32 PM
#101
Le Mans Master
Note that the limitation with flat tappet cams is related to the lobe contact pattern running off the edge of the tappet face. One way to allow faster ramps is to use a larger diameter tappet. This is why some racing classes that require flat tappet cams allow for the use of larger diameter tappets.
11-28-2015, 11:41 PM
#102
Melting Slicks
I agree with the main point that Critter1 is making, but I think some readers are getting it confused with another, related factor. So, I'm going to try to clearly separate the two factors:
1) Visual Differences Between Flat Tappet Lobes and Roller Lobes
If you take any stock GM flat tappet cam and you *exactly duplicate* the valve lift profile with a roller cam, the lobes on the roller cam will be visually much fatter than the flat tappet lobes, even though the lift profiles at the valve are *exactly the same.* The reason is that for a roller cam, the tappet contact with the lobe is always dead center on the axis of the lifter bore. However, for a flat tappet lobe, the contact pattern with the lifter starts near one edge of the lifter face and sweeps across toward the opposite edge. The result is that roller cam lobes are visibly fatter than flat tappet lobes even when the lift profiles at the valve are *exactly the same.*
2) Maximum Ramp Speeds
With a flat tappet cam, if you try to lift the tappet too-far-too-fast, the contact pattern on the face of the tappet will go off the edge of the tappet, resulting in immediate damage to the lobe and tappet. All flat tappet cams have this limitation.
With a roller cam, this limitation is eliminated, so the designer of the roller cam can use faster ramps that are physically impossible with a flat tappet cam. Note that I said "can use," not "will use." However, most roller cams take advantage of this option, resulting in "more area under the curve" for a roller cam that has the same duration at .050" lift as a similar flat tappet cam.
Summary
For a given lift profile, a roller cam implementation will always have a fatter looking lobe than a flat tappet cam that has the exact same lift profile. This is simply a fact that is related to the two different mechanical arrangements. There is no way to visually compare a roller cam to a flat tappet cam and determine which one has greater duration.
That being said, most performance roller cams take advantage of the option to use faster ramps, increasing the "area under the curve" compared to what can be achieved with a flat tappet cam.
Another way to describe the situation is that it is always possible to design a roller cam that exactly duplicates the lift profile of an existing flat tappet cam, but the reverse is not true. There are some roller cam lift profiles that simply can not be achieved with a flat tappet cam.
Note that the limitation with flat tappet cams is related to the lobe contact pattern running off the edge of the tappet face. One way to allow faster ramps is to use a larger diameter tappet. This is why some racing classes that require flat tappet cams allow for the use of larger diameter tappets.
1) Visual Differences Between Flat Tappet Lobes and Roller Lobes
If you take any stock GM flat tappet cam and you *exactly duplicate* the valve lift profile with a roller cam, the lobes on the roller cam will be visually much fatter than the flat tappet lobes, even though the lift profiles at the valve are *exactly the same.* The reason is that for a roller cam, the tappet contact with the lobe is always dead center on the axis of the lifter bore. However, for a flat tappet lobe, the contact pattern with the lifter starts near one edge of the lifter face and sweeps across toward the opposite edge. The result is that roller cam lobes are visibly fatter than flat tappet lobes even when the lift profiles at the valve are *exactly the same.*
2) Maximum Ramp Speeds
With a flat tappet cam, if you try to lift the tappet too-far-too-fast, the contact pattern on the face of the tappet will go off the edge of the tappet, resulting in immediate damage to the lobe and tappet. All flat tappet cams have this limitation.
With a roller cam, this limitation is eliminated, so the designer of the roller cam can use faster ramps that are physically impossible with a flat tappet cam. Note that I said "can use," not "will use." However, most roller cams take advantage of this option, resulting in "more area under the curve" for a roller cam that has the same duration at .050" lift as a similar flat tappet cam.
Summary
For a given lift profile, a roller cam implementation will always have a fatter looking lobe than a flat tappet cam that has the exact same lift profile. This is simply a fact that is related to the two different mechanical arrangements. There is no way to visually compare a roller cam to a flat tappet cam and determine which one has greater duration.
That being said, most performance roller cams take advantage of the option to use faster ramps, increasing the "area under the curve" compared to what can be achieved with a flat tappet cam.
Another way to describe the situation is that it is always possible to design a roller cam that exactly duplicates the lift profile of an existing flat tappet cam, but the reverse is not true. There are some roller cam lift profiles that simply can not be achieved with a flat tappet cam.
Note that the limitation with flat tappet cams is related to the lobe contact pattern running off the edge of the tappet face. One way to allow faster ramps is to use a larger diameter tappet. This is why some racing classes that require flat tappet cams allow for the use of larger diameter tappets.
That's what I've been trying to say all along but you did a much better job of explaining it.
11-29-2015, 12:04 AM
#103
any well equipped engine shop can bore the block for larger diameter lifters. back in the day we used mushroom shaped tappets to get a larger face without enlarging the lifter bores
Last edited by PAmotorman; 11-29-2015 at 12:09 AM.
11-29-2015, 08:36 AM
#105
when installing .875 dia ford lifters or using mushroom lifters in a chevy you need a special cam with narrower lobes to prevent interference with the next llfter in line.
11-29-2015, 09:26 AM
#106
Safety Car
The subject was changed to divert attention away from the argument which arose after the OP's question was answered in post #41.
Most of us know that the shape of a roller lobe is more U shaped than a flat tappet lobe having the same lift, duration and ramp speed. That difference is based on the different contact patterns for the two types of followers as they traverse the lobe.
I'd like to know what the "real" reason is, that OEMs went to roller lifters.
Most of us know that the shape of a roller lobe is more U shaped than a flat tappet lobe having the same lift, duration and ramp speed. That difference is based on the different contact patterns for the two types of followers as they traverse the lobe.
I'd like to know what the "real" reason is, that OEMs went to roller lifters.
Last edited by 65tripleblack; 11-29-2015 at 09:28 AM.
11-29-2015, 09:26 AM
#107
Le Mans Master
Exactly. A trip to the machine shop. So before anyone chimes in and suggests how this is a viable means of getting a flat tappet camshaft with steeper ramps we need to establish that the cost of the machine work alone would likely be more than a roller camshaft and a set of roller lifters.
11-29-2015, 09:57 AM
#108
Melting Slicks
The subject was changed to divert attention away from the argument which arose after the OP's question was answered in post #41.
Most of us know that the shape of a roller lobe is more U shaped than a flat tappet lobe having the same lift, duration and ramp speed. That difference is based on the different contact patterns for the two types of followers as they traverse the lobe.
I'd like to know what the "real" reason is, that OEMs went to roller lifters.
Most of us know that the shape of a roller lobe is more U shaped than a flat tappet lobe having the same lift, duration and ramp speed. That difference is based on the different contact patterns for the two types of followers as they traverse the lobe.
I'd like to know what the "real" reason is, that OEMs went to roller lifters.
11-29-2015, 12:43 PM
#109
Safety Car
So back to the question you haven't answered:
What is the REAL reason OEMs went to roller lifters. Was it to gain another increment of fuel economy, or was it something else?
Please provide proof to back up your argument.
Last edited by 65tripleblack; 11-29-2015 at 12:44 PM.
11-29-2015, 01:00 PM
#111
maybe they went to rollers to get away from warranty problems with flat tappet cam. rebuilders now just change out the lifters and use the same cam over again as they show no wear.
11-29-2015, 03:45 PM
#113
Melting Slicks
From what I understand, there are two issues.
One is the increase in fuel mileage because of the reduction of oil flow requirements to roller lifters/rockers and the reduction in pumping losses. Also, the reduction in oil viscosity recommendations over the last decade.
And the other is the diminishing amount of ZDDP in motor oils over the last decade or two. That will eventually destroy a flat tappet cam lobe.
Last edited by Critter1; 11-29-2015 at 03:50 PM.
11-29-2015, 04:49 PM
#114
I think that's a big part of it Clem.
From what I understand, there are two issues.
One is the increase in fuel mileage because of the reduction of oil flow requirements to roller lifters/rockers and the reduction in pumping losses. Also, the reduction in oil viscosity recommendations over the last decade.
And the other is the diminishing amount of ZDDP in motor oils over the last decade or two. That will eventually destroy a flat tappet cam lobe.
From what I understand, there are two issues.
One is the increase in fuel mileage because of the reduction of oil flow requirements to roller lifters/rockers and the reduction in pumping losses. Also, the reduction in oil viscosity recommendations over the last decade.
And the other is the diminishing amount of ZDDP in motor oils over the last decade or two. That will eventually destroy a flat tappet cam lobe.
11-29-2015, 04:55 PM
#115
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Do you know anyone that had OEM cam problems with flat tappets other than GM in the '70's when they tried to do a cost save? I don't except the the 2.0/2.3L four cylinder Pinto engines that failed due to ???????? I forget the fix but it wasn't changing over to rollers. The Ford engines worked directly on a rocker arm that pushed the valves down.
Who cares why the OEM's went to rollers on today's engines. The fact remains, it's an expensive proposition to change over a Gen I SBC to roller cams just to gain horsepower. There's far cheaper ways to do it.
Last edited by MikeM; 11-29-2015 at 05:00 PM.
11-29-2015, 07:04 PM
#116
Last I checked, a huge rebuilder like Jasper Engine Exchange just reground the existing cam core. Same core, new surface ground on it.
Do you know anyone that had OEM cam problems with flat tappets other than GM in the '70's when they tried to do a cost save? I don't except the the 2.0/2.3L four cylinder Pinto engines that failed due to ???????? I forget the fix but it wasn't changing over to rollers. The Ford engines worked directly on a rocker arm that pushed the valves down.
Who cares why the OEM's went to rollers on today's engines. The fact remains, it's an expensive proposition to change over a Gen I SBC to roller cams just to gain horsepower. There's far cheaper ways to do it.
Do you know anyone that had OEM cam problems with flat tappets other than GM in the '70's when they tried to do a cost save? I don't except the the 2.0/2.3L four cylinder Pinto engines that failed due to ???????? I forget the fix but it wasn't changing over to rollers. The Ford engines worked directly on a rocker arm that pushed the valves down.
Who cares why the OEM's went to rollers on today's engines. The fact remains, it's an expensive proposition to change over a Gen I SBC to roller cams just to gain horsepower. There's far cheaper ways to do it.
11-30-2015, 05:08 AM
#117
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That's been too long ago to remember.
11-30-2015, 01:02 PM
#118
Le Mans Master
I think initially the Ford used a stamped steel rocker arm that was hardened and it kept failing then the fix was a new rocker arm that had a hardened pad inserted into the stamped steel rocker arm the hardened pad was about 1/8 thick by 1/2 inch x 3/4 inch made out of a much harder steel alloy. You could look and see if it was the original type or the newer replacement. The replacements worked but the first gen did not. I hope my memory is correct on this. In the early to mid 80's we sold a lot of those engine parts and the early designs would be rejected by customers if we shipped them. We had to scrap the older design, nobody wanted them.
11-30-2015, 02:11 PM
#119
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I think initially the Ford used a stamped steel rocker arm that was hardened and it kept failing then the fix was a new rocker arm that had a hardened pad inserted into the stamped steel rocker arm the hardened pad was about 1/8 thick by 1/2 inch x 3/4 inch made out of a much harder steel alloy. You could look and see if it was the original type or the newer replacement. The replacements worked but the first gen did not. I hope my memory is correct on this. In the early to mid 80's we sold a lot of those engine parts and the early designs would be rejected by customers if we shipped them. We had to scrap the older design, nobody wanted them.
11-30-2015, 02:51 PM
#120
Drifting
Do you know anyone that had OEM cam problems with flat tappets other than GM in the '70's when they tried to do a cost save? I don't except the the 2.0/2.3L four cylinder Pinto engines that failed due to ???????? I forget the fix but it wasn't changing over to rollers. The Ford engines worked directly on a rocker arm that pushed the valves down.
My wife had a Pinto that needed a new cam before 30Kmi. I think they were called "cam followers". I changed the cam and all the followers but the new ones looked just like the old ones. If I remember correctly, the dealer guy said they were known for those failures and he said it was an oiling problem.
Verne