Help with camshaft selection for 350 SB

[Duke W.]

Re: Help with camshaft selection for 350 SB

The previous posts have provided some useful information about flat tappet versus roller cams. I recently wrote an article on this topic for the New England Chapter newsletter. A copy of the article is attached.

I think that the OEM flat tappet designs were well engineered as a system, and held up well. They held up well because they combined three key features:

1) The lobes used comparatively gentle, slow ramps that minimized inertial stress on the valve train.

2) The valve springs were comparatively soft.

3) The oil contained a sufficient amount of the zinc-based ZDDP friction modifier additive.

As long as you keep all three of these features, I think you can still run a flat tappet cam with good results. However, if you fail to meet any one of these criteria, you increase the risk of a flat tappet failure.

These days you have to do some extra work to make sure that you meet all three of these criteria. When I had my heads rebuilt, I told the rebuilder that I wanted stock springs. Nevertheless, he installed a set of Comp Cams springs that were significantly stiffer than the OEM springs. These were the softest springs available from Comp Cams, but they were still much stiffer than the OEM springs.

Also, some of the aftermarket flat tappet cams have faster ramps than the OEM cams, even if their stated duration and lift are the same as the OEM cam. So, you have to be careful when you select an aftermarket cam.

Using a roller cam allows you to be less careful about the above criteria with regard to lifter-cam interface. However, if you use an aggressive roller cam, the rest of the valve train will probably need some upgrades. I think that a mild roller cam can probably be used with an otherwise stock (or near stock) valve train.

Regarding the performance benefits offered by a roller cam, it is well established that at the limits of what each technology can achieve, a roller cam can provide more lift than a flat tappet cam, at least for durations over about 220 degrees at .050” lift. Below 220 degrees duration, the comparison is less clear.

...good article on the pros and cons of roller cam installations in vintage engines, Joe, however, I do take exception to the following statement:

"In recent years there has been much talk about the removal of ZDDP (a zinc-based friction modifier additive)
from passenger car engine oil, and the possible effects on flat tappet cams. ZDDP has been phased out of
passenger car oils because if fouls catalytic converters."

This statement is not accurate, but it is a persistent internet myth that won't die. ZDDP has NOT been removed, but limits have been established using phosphorous (P) as a surrogate for the amount of ZDDP. This limit is .08% (800 ppm) for current SN and .12% (1200 ppm) for current CJ-4. Guys also talk about "ppm ZDDP" and "ppm zinc", but these are both wrong, so I repeat, the specification for the level of ZDDP is the PHOSPHOROUS concentration.

Prior to the establishment of P limits the concentration was about 0.12-0.13% for typical engine oils that were dual-rated for both gasoline and diesel engines, so the P reduction is C-category oil is insignificant, but significant for S-category, which is why for the same price, C-category is a better choice for vintage engines with sliding surface valve trains.

I've attached the 2011 revision of my 2008 engine oil article as I think many may need a refresher.

The long lived CJ-4 spec is being replaced by two new specs, and you will probably see these show up on retailer shelves in the first quarter of next year. CK-4 is designed to be "backward compatible with prior C-category oils", which implies the P concentration limit has not been reduced, but I am still trying to verify it. The new FA-4 category is designed for new engine designs due out in 2017 and is generally NOT backward compatible with previous C-categories, so CK-4 will be the best choice for vintage gasoline engines with sliding surface valve trains.

When I get it fully sorted out, I'll start a thread on the subject.

Duke

[Joe L.]

Re: Help with camshaft selection for 350 SB

...good article on the pros and cons of roller cam installations in vintage engines, Joe, however, I do take exception to the following statement:

"In recent years there has been much talk about the removal of ZDDP (a zinc-based friction modifier additive)
from passenger car engine oil, and the possible effects on flat tappet cams. ZDDP has been phased out of
passenger car oils because if fouls catalytic converters."

This statement is not accurate, but it is a persistent internet myth that won't die. ZDDP has NOT been removed, but limits have been established using phosphorous (P) as a surrogate for the amount of ZDDP. This limit is .08% (800 ppm) for current SN and .12% (1200 ppm) for current CJ-4. Guys also talk about "ppm ZDDP" and "ppm zinc", but these are both wrong, so I repeat, the specification for the level of ZDDP is the PHOSPHOROUS concentration.

Prior to the establishment of P limits the concentration was about 0.12-0.13% for typical engine oils that were dual-rated for both gasoline and diesel engines, so the P reduction is C-category oil is insignificant, but significant for S-category, which is why for the same price, C-category is a better choice for vintage engines with sliding surface valve trains.

I've attached the 2011 revision of my 2008 engine oil article as I think many may need a refresher.

The long lived CJ-4 spec is being replaced by two new specs, and you will probably see these show up on retailer shelves in the first quarter of next year. CK-4 is designed to be "backward compatible with prior C-category oils", which implies the P concentration limit has not been reduced, but I am still trying to verify it. The new FA-4 category is designed for new engine designs due out in 2017 and is generally NOT backward compatible with previous C-categories, so CK-4 will be the best choice for vintage gasoline engines with sliding surface valve trains.

When I get it fully sorted out, I'll start a thread on the subject.

Duke

Duke------


If one uses an hydraulic roller cam, one does not have to be concerned about zinc or phosphorous concentrations in the oil. In fact, one can even use modern, low viscosity engine oils (e.g. like those that are Dexos-compliant). Lower viscosity oils = more horsepower and better MPG.

[Joe R.]

Re: Help with camshaft selection for 350 SB

...good article on the pros and cons of roller cam installations in vintage engines, Joe, however, I do take exception to the following statement:

"In recent years there has been much talk about the removal of ZDDP (a zinc-based friction modifier additive)
from passenger car engine oil, and the possible effects on flat tappet cams. ZDDP has been phased out of
passenger car oils because if fouls catalytic converters."

This statement is not accurate, but it is a persistent internet myth that won't die. ZDDP has NOT been removed, but limits have been established using phosphorous (P) as a surrogate for the amount of ZDDP. This limit is .08% (800 ppm) for current SN and .12% (1200 ppm) for current CJ-4. Guys also talk about "ppm ZDDP" and "ppm zinc", but these are both wrong, so I repeat, the specification for the level of ZDDP is the PHOSPHOROUS concentration.

Prior to the establishment of P limits the concentration was about 0.12-0.13% for typical engine oils that were dual-rated for both gasoline and diesel engines, so the P reduction is C-category oil is insignificant, but significant for S-category, which is why for the same price, C-category is a better choice for vintage engines with sliding surface valve trains.

I've attached the 2011 revision of my 2008 engine oil article as I think many may need a refresher.

The long lived CJ-4 spec is being replaced by two new specs, and you will probably see these show up on retailer shelves in the first quarter of next year. CK-4 is designed to be "backward compatible with prior C-category oils", which implies the P concentration limit has not been reduced, but I am still trying to verify it. The new FA-4 category is designed for new engine designs due out in 2017 and is generally NOT backward compatible with previous C-categories, so CK-4 will be the best choice for vintage gasoline engines with sliding surface valve trains.

When I get it fully sorted out, I'll start a thread on the subject.

Duke

Hi Duke:

I figured you would call me on that over-simplification!

I knew when I wrote it that technically, there is still some ZDDP in modern passenger car oils, but I think most people agree that the amount is lower now and that this is cause for concern. I was just trying to keep things simple.

I probably should have said "reduced" instead of "phased out," but I did not want to get into a discussion of percent content.

For the upcoming version of that article that has been submitted to the Restorer, I will try to modify the wording to make it more accurate.

[Duke W.]

Re: Help with camshaft selection for 350 SB

The trouble with trying to "simplify" an issue is that the simplification can totally change the message to something that is erroneous.

Duke

[Duke W.]

Re: Help with camshaft selection for 350 SB

Duke------


If one uses an hydraulic roller cam, one does not have to be concerned about zinc or phosphorous concentrations in the oil. In fact, one can even use modern, low viscosity engine oils (e.g. like those that are Dexos-compliant). Lower viscosity oils = more horsepower and better MPG.

Unless you also use roller trunnion rocker arms (most of which won't fit under the OE valve covers without spacers or double gaskets) there are still sliding surfaces in the valve train, namely the OE rocker arms/balls, so I recommend CJ-4 if the engine still has the OE rockers even with a roller cam.

BTW, 15W-40 CJ-4 is about the same price as any SN oil, so the choice is not a cost issue.

Duke

[Michael L.]

Re: Help with camshaft selection for 350 SB

Guys,
thanks for a spirited debate. I should have been a little more specific about what I was asking. What I was looking for specifically was the pros and cons of a roller vs flat tappet REGARDLESS OF PRICE. I have been restoring this car for almost 10 years with countless hours into it personally and probably 100k in cash when m done. Another 1k on a roller valve train means almost nothing to me. What I wanted to know was are there risks with going with a roller? I have heard parking lot talk of valvetrain failure with rollers but not from anybody I would necessarily trust to make a decision on so I figured I would ask here. Given that all the car companies switched to rollers tells me that when done right they are at least as, if not more durable, than flat tappet setups. I realize that flat tappets were used for decades with minimal problems but that was in a different time. Rotors and drums used to last forever too and now they're disposable. Bottom line: I wasn't asking if flat tappet is sufficient or adequate; I was asking, regardless of price, which is best and I have my answer. I'm going with a roller. Thanks to all who took the time to weigh in.

Mike

[Joe R.]

Re: Help with camshaft selection for 350 SB

Guys,
thanks for a spirited debate. I should have been a little more specific about what I was asking. What I was looking for specifically was the pros and cons of a roller vs flat tappet REGARDLESS OF PRICE. I have been restoring this car for almost 10 years with countless hours into it personally and probably 100k in cash when m done. Another 1k on a roller valve train means almost nothing to me. What I wanted to know was are there risks with going with a roller? I have heard parking lot talk of valvetrain failure with rollers but not from anybody I would necessarily trust to make a decision on so I figured I would ask here. Given that all the car companies switched to rollers tells me that when done right they are at least as, if not more durable, than flat tappet setups. I realize that flat tappets were used for decades with minimal problems but that was in a different time. Rotors and drums used to last forever too and now they're disposable. Bottom line: I wasn't asking if flat tappet is sufficient or adequate; I was asking, regardless of price, which is best and I have my answer. I'm going with a roller. Thanks to all who took the time to weigh in.

Mike

Hi Michael:

If you are going to install a roller cam into a non-roller block, you should read the "Part 2" portion of my Chapter newsletter article. That should be coming out any day now. I will try to post it here after the newsletter comes out.

There is a lot of confusing and contradictory information on the web regarding the three technical problems I listed in Part 1. I found this very frustrating. Part 2 describes why I think this available information is confusing, and what I decided to do in the end. I don't claim to be an expert on the technical issues, but I think Part 2 will help you understand what the issues are, so that you can make up your own mind about how to address them.

BTW, the Comp Cams 280HR is an off-the-shelf roller cam that has about the same .050" duration as the L79 cam (224 degrees), but has .525" lift as compared to the .447" lift of the L79 cam. The LSA is a bit tighter at 110 degrees compared to 114 degrees for the L79, so there is more overlap and idle might be a tad lumpier. If you want, you can have Comp Cams do a custom cam that changes the LSA to 114 degrees to match the L79 LSA.

I think the L79 cam is a fantastic OEM cam for all-around street driving, so I would not deviate very far from that cam in terms of duration and overlap.

[Joe R.]

Re: Help with camshaft selection for 350 SB

Unless you also use roller trunnion rocker arms (most of which won't fit under the OE valve covers without spacers or double gaskets) there are still sliding surfaces in the valve train, namely the OE rocker arms/balls, so I recommend CJ-4 if the engine still has the OE rockers even with a roller cam.

BTW, 15W-40 CJ-4 is about the same price as any SN oil, so the choice is not a cost issue.

Duke

Hi Duke:

FYI, the problem with fitting roller rockers under stock valve covers is rarely due to interference between the rocker and the valve cover. Usually, the only problem is the height of the stud and the locking nut. Often these are far taller than they need to be.

With some careful modifications to the stud and the locking nut, it is usually possible to clear the stock valve covers. I did this on my recent 383 build, and the cover cleared the roller rockers even with no gasket at all.

[Joe C.]

Re: Help with camshaft selection for 350 SB

Duke------


If one uses an hydraulic roller cam, one does not have to be concerned about zinc or phosphorous concentrations in the oil. In fact, one can even use modern, low viscosity engine oils (e.g. like those that are Dexos-compliant). Lower viscosity oils = more horsepower and better MPG.

Joe,
Like you, I'm a fan of roller cams but for a different reason. In my opinion, you are being overly conservative in your approach, but I respect your opinion. The reason that I prefer roller cams (solid rollers, to be more specific), is for the performance benefits. Solid rollers are more fragile than hydraulic rollers, but if proper precautions are taken, including the installation of a rev kit, then if properly designed and sprung, an engine equipped with one will outlive us in a car driven on the order of 3-4,000 miles/year.

I see no reason to use a roller in the interest of durability alone. If you GOOGLE CK-4 motor oil, you'll see numerous websites which indicate that the phosphorous content of proposed CK-4 motor oil will be more than sufficient to ensure proper lubrication of vintage engines' cam lobes and tappets. Further, if one wants a lower viscosity API rated CJ-4 motor oil, then Shell Rotella and Chevron Delo-Delvac can be special ordered in multivis 10W-30 weight. Is there a need for a lower viscosity motor oil in a vintage engine which uses 50 year old ring technology? I think not.

[Joe L.]

Re: Help with camshaft selection for 350 SB

Hi Michael:

If you are going to install a roller cam into a non-roller block, you should read the "Part 2" portion of my Chapter newsletter article. That should be coming out any day now. I will try to post it here after the newsletter comes out.

There is a lot of confusing and contradictory information on the web regarding the three technical problems I listed in Part 1. I found this very frustrating. Part 2 describes why I think this available information is confusing, and what I decided to do in the end. I don't claim to be an expert on the technical issues, but I think Part 2 will help you understand what the issues are, so that you can make up your own mind about how to address them.

BTW, the Comp Cams 280HR is an off-the-shelf roller cam that has about the same .050" duration as the L79 cam (224 degrees), but has .525" lift as compared to the .447" lift of the L79 cam. The LSA is a bit tighter at 110 degrees compared to 114 degrees for the L79, so there is more overlap and idle might be a tad lumpier. If you want, you can have Comp Cams do a custom cam that changes the LSA to 114 degrees to match the L79 LSA.

I think the L79 cam is a fantastic OEM cam for all-around street driving, so I would not deviate very far from that cam in terms of duration and overlap.

Joe------

The 1969 L-46 did not use the L-79 cam. It used the GM #3896962 which was also used for 1973-81 L-82. I actually think this is a better cam than the L-79, especially for 350 cid or larger engines.

I don't think I would use the Comp Cams 280HR. I think I'd prefer the the 276HR-14. This cam has an intake duration (@ 0.050") of 210 degrees and an exhaust duration of 220 degrees. Lift (with 1.5:1 rocker arms) is 0.500" on the intake and 0.510" on the exhaust. Lobe separation is 114 degrees. This cam (or the 280HR) requires more valve spring pressure than stock. However, the GM #10134358 should work nicely, fit in standard spring pockets, use stock retainers, and appear as stock.

The really big advantage of roller cams which Joe Ciaravino mentioned earlier but which has otherwise been pretty much left out of this discussion is LIFT. Increased lift with equivalent duration (or, even slightly less duration) than stock = FREE HORSEPOWER with similar or even better driveability and idle quality. Flat tappet cams cannot match this because a flat tappet lifter cannot follow the lobe profile that an hydraulic roller can accommodate. Flat tappet cams and lifters constrain engine builders in lobe profile by the limitations of what a flat tappet lifter can follow.

[Joe C.]

Re: Help with camshaft selection for 350 SB

Hi Duke:

I figured you would call me on that over-simplification!

I knew when I wrote it that technically, there is still some ZDDP in modern passenger car oils, but I think most people agree that the amount is lower now and that this is cause for concern. I was just trying to keep things simple.

I probably should have said "reduced" instead of "phased out," but I did not want to get into a discussion of percent content.

For the upcoming version of that article that has been submitted to the Restorer, I will try to modify the wording to make it more accurate.

Hi Joe,

The current level of phosphorous in CJ-4 motor oils is sufficient for the protection of flat tappet camshafts having stock dynamics; the same will hold true for the proposed CK-4 API category and that's why they can boast "backwards compatibility".

If you have a more aggressive flat tappet camshaft installed, like the "High Energy" or "Nostalgia Plus" series', then you would be correct in your statement. Remember that the phosphorous is sacrificial during high pressure sliding friction cam/lobe duty cycles................so no content amount can be said to be "sufficient" unless one specifies one's oil change intervals. For a vintage car owner who changes his oil at the "old standard" 3000 mile interval, along with the filter, then a CJ-4 motor oil will be more than sufficient, even with a more aggressive flat tappet camshaft from Howards, Comp, Lunati, Crane, or any other. The more frequent one's oil change intervals, the less one would have to ruminate about this issue.

[Joe C.]

Re: Help with camshaft selection for 350 SB

Hi Michael:

If you are going to install a roller cam into a non-roller block, you should read the "Part 2" portion of my Chapter newsletter article. That should be coming out any day now. I will try to post it here after the newsletter comes out.

There is a lot of confusing and contradictory information on the web regarding the three technical problems I listed in Part 1. I found this very frustrating. Part 2 describes why I think this available information is confusing, and what I decided to do in the end. I don't claim to be an expert on the technical issues, but I think Part 2 will help you understand what the issues are, so that you can make up your own mind about how to address them.

BTW, the Comp Cams 280HR is an off-the-shelf roller cam that has about the same .050" duration as the L79 cam (224 degrees), but has .525" lift as compared to the .447" lift of the L79 cam. The LSA is a bit tighter at 110 degrees compared to 114 degrees for the L79, so there is more overlap and idle might be a tad lumpier. If you want, you can have Comp Cams do a custom cam that changes the LSA to 114 degrees to match the L79 LSA.

I think the L79 cam is a fantastic OEM cam for all-around street driving, so I would not deviate very far from that cam in terms of duration and overlap.

In that case then your head technician made the right choice by using less compliant valve springs in your heads. He probably went with the valves recommended by Comp to complement your camshaft. Your hydraulic roller has harsher dynamics and valve control will not be achieved with stock "marshmallows" because it lifts the valves .078" higher than the 151 cam within the same duration. The cam degree/lift graph in your excellent article illustrates that. You never get nothin' fer nothin' and there ain't no perpetual motion machine.

In order to have a meaningful comparison of camshaft dynamics one must, among other things, compare the lobe lift at at least 2 points on the lobe: At advertised duration (or SAE J604d), at .050 lift, and/or at .200 lift.

[Joe R.]

Re: Help with camshaft selection for 350 SB

In that case then your head technician made the right choice by using less compliant valve springs in your heads. He probably went with the valves recommended by Comp to complement your camshaft. Your hydraulic roller has harsher dynamics and valve control will not be achieved with stock "marshmallows" because it lifts the valves .078" higher than the 151 cam within the same duration. The cam degree/lift graph in your excellent article illustrates that. You never get nothin' fer nothin' and there ain't no perpetual motion machine.

In order to have a meaningful comparison of camshaft dynamics one must, among other things, compare the lobe lift at at least 2 points on the lobe: At advertised duration (or SAE J604d), at .050 lift, and/or at .200 lift.

Hi Joe C:

My previous reference to a head rebuilder putting in stiffer springs than I requested was referring to an earlier build that I did with the stock heads on the original engine. The cam I used in that build was a flat tappet cam very similar to the original 300 HP cam. So, I think the OEM springs would have been fine for that application.

I used the 280HR roller cam in my 383 build, which was an entirely different project. The valve train on that build uses the modern beehive springs that Comp Cams recommends for the 280HR cam. Just for extra margin in the valve train dynamics, I used stronger push rods and roller rockers. To reduce weight, I used titanium retainers and a hollow stem intake valve to get the intake weight down to about the same as the exhaust valve. I think the resulting valve train will hang in there well beyond 6000 RPM where the engine's power peak occurs.

I agree that some sort of valve train upgrade is usually required when converting to a roller cam that has faster ramps. In most cases, probably just the springs need to change. I just did the other stuff for extra margin and because it was technically interesting to me. Probably none of the extra stuff was necessary for the RPM range I plan to use.

[Joe R.]

Re: Help with camshaft selection for 350 SB

Joe------

The 1969 L-46 did not use the L-79 cam. It used the GM #3896962 which was also used for 1973-81 L-82. I actually think this is a better cam than the L-79, especially for 350 cid or larger engines.

I don't think I would use the Comp Cams 280HR. I think I'd prefer the the 276HR-14. This cam has an intake duration (@ 0.050") of 210 degrees and an exhaust duration of 220 degrees. Lift (with 1.5:1 rocker arms) is 0.500" on the intake and 0.510" on the exhaust. Lobe separation is 114 degrees. This cam (or the 280HR) requires more valve spring pressure than stock. However, the GM #10134358 should work nicely, fit in standard spring pockets, use stock retainers, and appear as stock.

The really big advantage of roller cams which Joe Ciaravino mentioned earlier but which has otherwise been pretty much left out of this discussion is LIFT. Increased lift with equivalent duration (or, even slightly less duration) than stock = FREE HORSEPOWER with similar or even better driveability and idle quality. Flat tappet cams cannot match this because a flat tappet lifter cannot follow the lobe profile that an hydraulic roller can accommodate. Flat tappet cams and lifters constrain engine builders in lobe profile by the limitations of what a flat tappet lifter can follow.

Hi Joe L:

You are correct that the L48 cam is not identical to the L79 cam. I had a mild brain fade because I think of them as being functionally identical in terms of duration, lift, and LSA. The L48 cam has a different (and less desirable) intake centerline, but that can be adjusted with a timing gear set that has multiple key positions.

I fully agree with your view that the main advantage of a roller cam is that you can get more lift for the same duration. That's the reason I used the 280HR roller on my most recent project. I have not seen a flat tappet cam that has as much lift for a 224 degree duration.

BTW, I have read various technical articles that suggest this advantage of the roller cam (more lift for the same duration) is only true for durations above about 220 degrees. The implication is that for smaller durations, a flat tappet cam can pretty much match a roller cam. I have not been able to determine whether or not this is true, but if it is, the lift advantage of a roller cam does not apply for durations that are well below 220 degrees.

[Joe L.]

Re: Help with camshaft selection for 350 SB

Hi Joe L:

You are correct that the L48 cam is not identical to the L79 cam. I had a mild brain fade because I think of them as being functionally identical in terms of duration, lift, and LSA. The L48 cam has a different (and less desirable) intake centerline, but that can be adjusted with a timing gear set that has multiple key positions.

I fully agree with your view that the main advantage of a roller cam is that you can get more lift for the same duration. That's the reason I used the 280HR roller on my most recent project. I have not seen a flat tappet cam that has as much lift for a 224 degree duration.

BTW, I have read various technical articles that suggest this advantage of the roller cam (more lift for the same duration) is only true for durations above about 220 degrees. The implication is that for smaller durations, a flat tappet cam can pretty much match a roller cam. I have not been able to determine whether or not this is true, but if it is, the lift advantage of a roller cam does not apply for durations that are well below 220 degrees.

Joe------

It's L-46, not L-48. The L-48 cam is essentially the same as the base engine cams used from 1962-70.

You won't see a flat tappet cam that has as much lift for 224 degrees of duration. A flat tappet lifter could not follow the lifter profile for such lift at such duration.

I kind of doubt assertions that that the lift advantage of a roller cam does not apply at durations below 220 degrees. It might not be as much of an advantage, but I think there's still an advantage for street engines.