Help with camshaft selection for 350 SB

[Duke W.]

Re: Help with camshaft selection for 350 SB

The primary difference between the L-46 and L-79 cams is the inlet POML, the former being 114 deg. ATC, the latter is 110 deg. ATC. The L-46 cam's additional two degrees .050" lifter rise duration is not significant, but what's interesting is that even though the inlet and exhaust .050" durations are 224 deg., they are actually different lobes with slightly different lifts and dynamics. Chevrolet optimized the dynamics for the differing masses of the inlet and exhaust valves!

The above is why I recommend the L-46 cam for L-79 restorations, but installed four degrees advanced to equal the inlet POML of the L-79 cam. Installing it at the as-manufactured inlet POML will reduce low end torque and increase top end power, but that additional top end power on the short stroke 327 may be beyond lifter pump up speed, especially with massaged heads.

Later indexing is better for long stroke engines. In fact I recommend installing a L-46 cam retarded four degrees for a 3.75" stroke configurations, and with typical OE induction and exhaust systems, it should make useable power to about 6000, and the long stroke/large displacement yields plenty of low end torque.

Duke

[Joe R.]

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.

Hi Michael:

The Part 2 article for my Chapter newsletter just came out today. Attached is a copy of that article.

I found it very frustrating to get reliable information about the cam button and the distributor gear, and I also learned a few things about fitting roller lifters under stock valve covers. Hopefully some of this info will be helpful to you and others who are planning to install a retrofit roller cam.

BTW, if anyone sees any errors or issues with this article, I would be interested in the feedback. A merged version of Part 1 and Part 2 has been submitted to the Restorer, so there is still time to improve that version.

[Gene M.]

Re: Help with camshaft selection for 350 SB

Joe R
I read your article last night in the news letter. Again well written. But in your post do you not intend to say:
................fitting roller rocker arms under stock valve covers. ................

The roller lifters are in the valley under the intake manifold.

Again liked you presentation.

[Joe R.]

Re: Help with camshaft selection for 350 SB

Joe R
I read your article last night in the news letter. Again well written. But in your post do you not intend to say:
................fitting roller rocker arms under stock valve covers. ................

The roller lifters are in the valley under the intake manifold.

Again liked you presentation.

Hi Gene:

Yup, I used the wrong word there.

[Joe L.]

Re: Help with camshaft selection for 350 SB

Hi Michael:

The Part 2 article for my Chapter newsletter just came out today. Attached is a copy of that article.

I found it very frustrating to get reliable information about the cam button and the distributor gear, and I also learned a few things about fitting roller lifters under stock valve covers. Hopefully some of this info will be helpful to you and others who are planning to install a retrofit roller cam.

BTW, if anyone sees any errors or issues with this article, I would be interested in the feedback. A merged version of Part 1 and Part 2 has been submitted to the Restorer, so there is still time to improve that version.

Joe------


Your Part II looks fine to me. Just a few comments:

I, too, am not sure that the cam button is really necessary. However, I'd never install a roller cam in a block not originally designed for a roller cam without using a cam button. It's really not a big deal to install the button, anyway. GM engines originally equipped with a roller cam used a camshaft thrust plate which mounted to the front of the block with 2 screws. While this is the best solution, it's not practical to retrofit such a plate to earlier blocks.

When I built my first roller cam engine about 15-20 years ago, I brazed a reinforcement/button stop into the timing cover. A photo of that very installation is attached below. It looks similar in function to what you fabricated.

As you mention, most hydraulic roller cams are ground from steel billet cores. Those require a melonized distributor gear. GM has been using these for almost 30 years now and they have proven to be highly reliable and durable. However, some hydraulic roller cams are made using an austempered ductile iron core. Those made by Federal Mogul/Speed Pro are among these. These cams can use a standard distributor gear. Never, ever use a brass or bronze distributor gear on ANY street cam no matter what anyone says.

[Joe R.]

Re: Help with camshaft selection for 350 SB

Joe------


Your Part II looks fine to me. Just a few comments:

I, too, am not sure that the cam button is really necessary. However, I'd never install a roller cam in a block not originally designed for a roller cam without using a cam button. It's really not a big deal to install the button, anyway. GM engines originally equipped with a roller cam used a camshaft thrust plate which mounted to the front of the block with 2 screws. While this is the best solution, it's not practical to retrofit such a plate to earlier blocks.

When I built my first roller cam engine about 15-20 years ago, I brazed a reinforcement/button stop into the timing cover. A photo of that very installation is attached below. It looks similar in function to what you fabricated.

As you mention, most hydraulic roller cams are ground from steel billet cores. Those require a melonized distributor gear. GM has been using these for almost 30 years now and they have proven to be highly reliable and durable. However, some hydraulic roller cams are made using an austempered ductile iron core. Those made by Federal Mogul/Speed Pro are among these. These cams can use a standard distributor gear. Never, ever use a brass or bronze distributor gear on ANY street cam no matter what anyone says.

Hi Joe L:

Thanks for the feedback. In my research, I did see the term "austempered ductile iron" and came to the conclusion that this is what most "cast iron" flat tappet cams are made of. I wondered whether this basically what is called "nodular iron" or possibly something else.

I have looked at several stock distributor gears that were used with stock flat tappet cams for 100,000 miles and the distributor gears show virtually no visible wear. So, whatever that material system was, it worked very well.

As you note, GM used the Melonized gear with their roller cams with good success. I don't understand why the cam manufacturers don't simply tell people to use the GM gear on their steel roller cams. And, I don't understand why the cam manufacturers don't make it really clear when the cam they are selling you is a steel cam and requires a special gear.

BTW, I did see one internet posting where the author claimed that the steel alloy used by the aftermarket manufacturers is different from the steel alloy that GM used. He suggested that this was a possible risk factor when using the Melonized gear with aftermarket steel cams, but said he had not seen evidence of problems. Just another thing to worry about....

This is why I said that if I had it to do over again, I might just pay the extra cost to get an iron gear on my steel roller cam.

[Joe L.]

Re: Help with camshaft selection for 350 SB

Hi Joe L:

Thanks for the feedback. In my research, I did see the term "austempered ductile iron" and came to the conclusion that this is what most "cast iron" flat tappet cams are made of. I wondered whether this basically what is called "nodular iron" or possibly something else.

I have looked at several stock distributor gears that were used with stock flat tappet cams for 100,000 miles and the distributor gears show virtually no visible wear. So, whatever that material system was, it worked very well.

As you note, GM used the Melonized gear with their roller cams with good success. I don't understand why the cam manufacturers don't simply tell people to use the GM gear on their steel roller cams. And, I don't understand why the cam manufacturers don't make it really clear when the cam they are selling you is a steel cam and requires a special gear.

BTW, I did see one internet posting where the author claimed that the steel alloy used by the aftermarket manufacturers is different from the steel alloy that GM used. He suggested that this was a possible risk factor when using the Melonized gear with aftermarket steel cams, but said he had not seen evidence of problems. Just another thing to worry about....

This is why I said that if I had it to do over again, I might just pay the extra cost to get an iron gear on my steel roller cam.

Joe------


I do not think that standard, flat tappet cams use an austempered ductile iron core. It may be that some do but I do not think this is generally the case.

The pressed-on iron gear on a steel cam is, without a doubt, the best solution and I've thought so ever since that's been available. I think it's the ultimate solution and have no problem with extra cost. The one thing that has given me a little pause, though, is that for the cam manufacturer to do this the rear cam bearing journal or the entire rear of the cam has to also be pressed on or otherwise attached after the gear is pressed on. However, that really should not be a problem.

[Michael L.]

Re: Help with camshaft selection for 350 SB

Hi Michael:

The Part 2 article for my Chapter newsletter just came out today. Attached is a copy of that article.

I found it very frustrating to get reliable information about the cam button and the distributor gear, and I also learned a few things about fitting roller lifters under stock valve covers. Hopefully some of this info will be helpful to you and others who are planning to install a retrofit roller cam.

BTW, if anyone sees any errors or issues with this article, I would be interested in the feedback. A merged version of Part 1 and Part 2 has been submitted to the Restorer, so there is still time to improve that version.

Joe R.,

Is it possible for me to contact the company you had make that plate and request they make one for me?

Mike

[Joe R.]

Re: Help with camshaft selection for 350 SB

Joe R.,

Is it possible for me to contact the company you had make that plate and request they make one for me?

Mike

Hi Mike:

I had a mechanical engineer create a Solidworks CAD file that allows any well-equipped machine shop to make the part by simply loading the file into a computerized water-jet cutting machine. I can send these file to anyone contacts me by PM.

[Michael L.]

Re: Help with camshaft selection for 350 SB

Mike,
Joe L is 100% spot-on.......................power and torque are a function of how fast and how high the valves are lifted. I have experienced the effect of swapping in a roller cam with no other modifications done, and the torque/power increase is substantial, on the order of 20% using a pair of 2.02/1.6 double hump heads. The immediate effect is that with two cams of equal duration, the faster ramps of a roller lobe can be used to provide higher valve lift than a flat tappet cam of the same duration. That is one reason modern engines make so much power using small duration camshafts. The second reason is that they use higher ratio rocker arms, which increase valve lift but have no effect on duration.

The problem here is that it will be expensive since there are no valve springs suitable for a roller cam, including beehive springs which will fit within the stock spring pockets, so you'll need to have them opened up, as well as having the pushrod guides enlarged. You should also back cut both intake and exhaust valves. No need to forward cut the exhausts unless you plan on a lot of valve overlap.

Since you'll have to remove the heads for machining, IT WOULD BE WISE FOR YOU TO HAVE THE PORTS BLENDED INTO A "PERFORMANCE" MULTI ANGLE VALVE JOB. This modification will get the very best power increase from your fast action valves.

You'll also need a new distributor gear made of melonized iron to replace the original plain iron gear. This gear is available from GM, and was used on all 1st Gen smallblocks originally equipped with roller cams, beginning in 1987. If you don't do this, you will quickly wipe the distributor gear because some cam blanks are steel rather than iron. Milder hydraulic rollers, as well as some solid rollers are made of iron as well, but these are hardened and will destroy a stock, non-hardened iron distributor gear as well.

You'll also be wise to install a double roller timing chain, which requires clearancing of the block. Some people insist that it's necessary to install a cast aluminum timing cover to handle the froward thrust forces developed by a roller cam. I have never seen the need for this, as I always braise in a plate on the inside of a stock cover against which the cam button bears. You MUST set the cam end play with gasket installed on the timing cover. End play can vary, and .005" is a safe bet. It's also a good idea to use a Torrington bearing between the timing gear and the block.

Joe,

I'm getting my distributor restored and need to tell them what type of distributor gear to use. On previous roller motors I've used a bronze gear, but you recommended a "melonized iron" gear. Is there a difference or are these equivalent?

Mike

[Jeff P.]

Re: Help with camshaft selection for 350 SB

[Joe L.]

Re: Help with camshaft selection for 350 SB

Joe,

I'm getting my distributor restored and need to tell them what type of distributor gear to use. On previous roller motors I've used a bronze gear, but you recommended a "melonized iron" gear. Is there a difference or are these equivalent?

Mike

Mike------


I absolutely do not recommend the use of bronze distributor drive gears. These are relatively short-lived pieces in a street application.

I recommend using a melonized gear as also recommended by GM for use for all roller cams manufactured from a steel core.The gear is GM #10456413.

[Joe L.]

Re: Help with camshaft selection for 350 SB

Jeff------

This is the OEM GM L-79 camshaft. It was never used by GM for any 350 cid application but it may be OK. A better choice is the L-46/L-82 camshaft GM #3896962.

[Joe C.]

Re: Help with camshaft selection for 350 SB

Joe,

I'm getting my distributor restored and need to tell them what type of distributor gear to use. On previous roller motors I've used a bronze gear, but you recommended a "melonized iron" gear. Is there a difference or are these equivalent?

Mike

Michael,

Bronze gears are so short lived that you might call them "sacrificial". If your cam core was steel, as used in a more high performance shaft, then you'd be using a steel or composite gear. Since I ASSUME THAT your cam is iron, the best choice is a melonized iron gear, which is a good match.

Here is a good primer on gear matching:

http://www.enginebuildermag.com/2009/07/properly-matching-your-camshaft-and-distributor-gear/

FYI: GM has been using melonized iron dist gears since they began installing roller cams in production engines. GM has been using iron shafts, which are excellent for camshafts that don't require super stiff valve springs. They are not subject to extremely high torsional loads where a steel shaft would be required.