L79 Camshaft (GM # 3853151); who makes what

[Joe L.]

Re: L79 Camshaft (GM # 3853151); who makes what

Joe,
Just as a piece of information to anyone replacing L79 pistons. The forge L79 piston configuration is difficult to obtain even in standard over size. Even the engine shop in our area was only able to come up with configurations of bigger and smaller L79 dome sizes in forged style. But there were several L79 in hypereutectic pistons. A good alternative to the original forged for the average person. No enhancement here. There is also weight difference. But understand, make no mistake the wall clearance in definitely different from hypereutectic pistons vs forged pistons.

I could care less what timing chain one uses. (That timing chain thing really weakens your argument). There is no change in the way the Corvette performs as there would be by changing a stock hydraulic L79 cam to a solid lifter LT1 camshaft. The tappet noise alone is major. No you can't see the timing chain, but you sure as hell can hear and feel the performance of a solid lifter LT1 cam shaft installed in what was a hydraulic lifter engine.

Gene------


Yes, there is definitely a difference in wall clearance between hypereutectic cast pistons and forged pistons. However, I was talking about the difference between conventional cast and hypereutectic; there is no significant wall clearance difference between them. I consider hypereutectic cast pistons to be an excellent choice for engines originally equipped with forged pistons. They're almost as strong and provide better oil control, among other benefits.

I never said or implied that there was no difference in the sound or performance if an L-79 cam was replaced with an LT-1. I would say it would be very detectable. However, I am certain that no one could detect the difference in an L-79 versus an L-46 cam. There also wouldn't be any detectable difference between the L-79 cam and other aftermarket hydraulic cams, including roller cams. That's primarily what I was talking about, not a change to a mechanical lifter cam.

[Gene M.]

Re: L79 Camshaft (GM # 3853151); who makes what

Gene------


Yes, there is definitely a difference in wall clearance between hypereutectic cast pistons and forged pistons. However, I was talking about the difference between conventional cast and hypereutectic; there is no significant wall clearance difference between them. I consider hypereutectic cast pistons to be an excellent choice for engines originally equipped with forged pistons. They're almost as strong and provide better oil control, among other benefits.

I never said or implied that there was no difference in the sound or performance if an L-79 cam was replaced with an LT-1. I would say it would be very detectable. However, I am certain that no one could detect the difference in an L-79 versus an L-46 cam. There also wouldn't be any detectable difference between the L-79 cam and other aftermarket hydraulic cams, including roller cams. That's primarily what I was talking about, not a change to a mechanical lifter cam.

Joe,
I have to agree the hypereutectic piston is a good choice of replacement for the L79 dome forged version. There about one step down to the forged if put to heavy duty life but for the average NCRS guy he would be happy. In fact for street use they may be a better choice. No difference that can be detected nor will there be any adverse effects.

But after market cams (off the shelf versions) for the most part will be of some detectable difference. The lobe centers are generally tighter and gives a stronger burble to the idle. And as far as rollers there would be a required special grind to mimic the L79, as most rollers, again (off the shelf versions) are much more area under the curve profiles for the 222 degree duration.

[Joe R.]

Re: L79 Camshaft (GM # 3853151); who makes what

[QUOTE=Joe Lucia (12484);

Actually, I don't know of an available hydraulic roller camshaft that's equivalent to the L-79. However, there may be one out there by now as lots of retrofit hydraulic roller grinds have been added since I shopped for one. If not, though, most of the major cam grinders offer custom grinding to just about any specification you want---I suppose the wonders of CNC machining. If I were building an L-79 and I wanted to maintain L-79 characteristics and I could obtain an hydraulic roller camshaft with equivalent L-79 characteristics, I'd use that hydraulic roller without a moments hesitation regardless of what it cost. I don't think that Duke would, though.[/QUOTE]


Hi Joe:

I have an engine build underway where the goal is to have the external appearance of an L79 but with modern performance upgrades internally. This engine is not the original engine from my car and it will *not* be used for NCRS judging. I'm just building it for fun and for the technical challenge of keeping a stock external appearance while using modern performance upgrades internally.

From the outset it was a given that I would use a roller cam. One off-the-shelf hydraulic roller cam that comes close to the L79 is the Comp Cams 280HR, which is 224/224 duration, .525" lift, and 110 degrees LSA. The stock L79 cam is 222/222 duration, .447 lift, and 114 degrees LSA.

In terms of the "sound" of this cam, the idle would likely show a bit more attitude than the L79 cam, since the L79 cam has a 114 degree LSA and a correspondingly lower overlap. However, my engine is stroked to 383 cubic inches, so it can tolerate a bit more overlap than a 327.

I considered ordering a customized version of the 280HR that has the same 114 degree LSA as the L79 cam (I have heard that the charge for a custom cam is minimal these days). As it urned out, my simulations in Engine Analyzer showed a slight performace loss from this change in my particular engine, so I stuck with the off-the-shelf cam. However, I think that someone trying to make a roller equivalent of the L79 cam that "sounds" like the L79 could come very close by using the 280HR lobes with the phasing and LSA of the L79 cam.

Duke is correct that the faster ramps of roller cam lobes typically require corresponding upgrades to the valve train, such as the springs, rockers, and pushrods. This is an added cost associated with a roller implementation, and some people would argue that overall, a roller conversion isn't worth all this trouble and expense. I think the final choice is just a personal preference, with the roller cam offering slightly better performance and freedom from worries about the access to oils with sufficient ZDDP.

Since my project is technology-driven, I made a complete set of upgrades including full roller rockers, beehive springs, and high strength pushrods. This added several hunderd dollars of cost on top of the already-higher cost of the roller cam and roller lifters. I'm not sure whether all the valve train upgrades were absolutely necessary for this particular cam, but it was fun solving all the little problems such as fitting everything under stock valve covers. And, I don't have to worry at all now about the strength of the valve train.

For someone trying to specify a roller cam that is equivalent to the stock L79 cam, there are other lobes that could be considered that are less aggressive than the lobes on the 280HR. Some of these lobes would probably do okay with a closer-to-stock valve train. Following are some example lobes from the Comp Cams lobe catalog, with the duration values at .050" lift and lift values based on rockers with a 1.5 ratio:

(Stock L79: 222 degrees, .447 lift)
CC Lobe 3161: 220 degrees, .428 lift
CC Lobe 3051: 220 degrees, .480 lift
CC lobe 3109: 220 degrees, .510 lift
CC lobe 3110: 224 degrees, .500 lift
CC lobe 3119: 224 degrees, .525 lift (used in the catalog 280HR cam)

In summary, I think it would be pretty easy for someone to have a custom roller cam that comes pretty close to matching the L79 cam. The only thing I'm unsure of is what the minimum level of valve train upgrades would be for each of the various lobes listed above.

[Joe L.]

Re: L79 Camshaft (GM # 3853151); who makes what

Hi Joe:

I have an engine build underway where the goal is to have the external appearance of an L79 but with modern performance upgrades internally. This engine is not the original engine from my car and it will *not* be used for NCRS judging. I'm just building it for fun and for the technical challenge of keeping a stock external appearance while using modern performance upgrades internally.

From the outset it was a given that I would use a roller cam. One off-the-shelf hydraulic roller cam that comes close to the L79 is the Comp Cams 280HR, which is 224/224 duration, .525" lift, and 110 degrees LSA. The stock L79 cam is 222/222 duration, .447 lift, and 114 degrees LSA.

In terms of the "sound" of this cam, the idle would likely show a bit more attitude than the L79 cam, since the L79 cam has a 114 degree LSA and a correspondingly lower overlap. However, my engine is stroked to 383 cubic inches, so it can tolerate a bit more overlap than a 327.

I considered ordering a customized version of the 280HR that has the same 114 degree LSA as the L79 cam (I have heard that the charge for a custom cam is minimal these days). As it urned out, my simulations in Engine Analyzer showed a slight performace loss from this change in my particular engine, so I stuck with the off-the-shelf cam. However, I think that someone trying to make a roller equivalent of the L79 cam that "sounds" like the L79 could come very close by using the 280HR lobes with the phasing and LSA of the L79 cam.

Duke is correct that the faster ramps of roller cam lobes typically require corresponding upgrades to the valve train, such as the springs, rockers, and pushrods. This is an added cost associated with a roller implementation, and some people would argue that overall, a roller conversion isn't worth all this trouble and expense. I think the final choice is just a personal preference, with the roller cam offering slightly better performance and freedom from worries about the access to oils with sufficient ZDDP.

Since my project is technology-driven, I made a complete set of upgrades including full roller rockers, beehive springs, and high strength pushrods. This added several hunderd dollars of cost on top of the already-higher cost of the roller cam and roller lifters. I'm not sure whether all the valve train upgrades were absolutely necessary for this particular cam, but it was fun solving all the little problems such as fitting everything under stock valve covers. And, I don't have to worry at all now about the strength of the valve train.

For someone trying to specify a roller cam that is equivalent to the stock L79 cam, there are other lobes that could be considered that are less aggressive than the lobes on the 280HR. Some of these lobes would probably do okay with a closer-to-stock valve train. Following are some example lobes from the Comp Cams lobe catalog, with the duration values at .050" lift and lift values based on rockers with a 1.5 ratio:

(Stock L79: 222 degrees, .447 lift)
CC Lobe 3161: 220 degrees, .428 lift
CC Lobe 3051: 220 degrees, .480 lift
CC lobe 3109: 220 degrees, .510 lift
CC lobe 3110: 224 degrees, .500 lift
CC lobe 3119: 224 degrees, .525 lift (used in the catalog 280HR cam)

In summary, I think it would be pretty easy for someone to have a custom roller cam that comes pretty close to matching the L79 cam. The only thing I'm unsure of is what the minimum level of valve train upgrades would be for each of the various lobes listed above.

Joe------


Valve spring GM #12551483, the 1996 LT4 stock spring, or equivalent would work just fine with any of the above cams. This spring is just slightly larger in OD than the stock Corvette small block springs and is 101 LBS @ installed height of 1.780

[Joe R.]

Re: L79 Camshaft (GM # 3853151); who makes what

Joe------


Valve spring GM #12551483, the 1996 LT4 stock spring, or equivalent would work just fine with any of the above cams. This spring is just slightly larger in OD than the stock Corvette small block springs and is 101 LBS @ installed height of 1.780

Hi Joe:

What is the open pressure of the 12551483 spring? For the 3119 lobe that I'm using, Comp Cams wants about 120 pounds on the seat and about 280 pounds over the nose.

I've heard there is also a GM beehive spring, used on certain LS engines, that has a 1.29" diameter that is easily retrofitted to vintage heads designed for 1.25" springs.

Regarding the other valve train components, such as the pushrods and rockers, do you think these would need to be upgraded? Qualitatively, I know that the faster ramps on performance roller cams add stress on the valve train because the valve is being opened much more quickly than the OEM flat tappet cams open the valve. What I'm unclear about is how far the stock components can go before they become unstable and/or broken.

I suspect that the stock pushrods and rockers might be okay for some of the milder lobes I listed, but my sense is that the 3119 lobe with 224 duration and .525 lift might be pushing things with the stock pushrods and rockers.

The fact is that I simply don't know the answer to this question, so I played it safe and upgraded the entire valve train. That's okay for a project where cost is not a key consideration, but it would be nice to know what can be done with a budget build.

[Gary B.]

Re: L79 Camshaft (GM # 3853151); who makes what

...But after market cams (off the shelf versions) for the most part will be of some detectable difference. The lobe centers are generally tighter and gives a stronger burble to the idle. And as far as rollers there would be a required special grind to mimic the L79, as most rollers, again (off the shelf versions) are much more area under the curve profiles for the 222 degree duration.

Gene,

But don't you think there's a way to spec a custom hydraulic roller cam that wouldn't be easily detectable except to some savant-type who has memorized car idle sounds? And even for the savant, the benefit during judging is supposed be to given to the owner, so unless the cam sound is clearly off I think a judge would be hard pressed to take a deduct based on anything that falls into the subtle or questionable difference category.

Gary

[Gene M.]

Re: L79 Camshaft (GM # 3853151); who makes what

Gene,

But don't you think there's a way to spec a custom hydraulic roller cam that wouldn't be easily detectable except to some savant-type who has memorized car idle sounds? And even for the savant, the benefit during judging is supposed be to given to the owner, so unless the cam sound is clearly off I think a judge would be hard pressed to take a deduct based on anything that falls into the subtle or questionable difference category.

Gary

Gary,
If you spec the profile so the area under the curve is not enormous (making a deeper power sound) compared to the L79 profile and the lobe centers are at or close to the L79's 114 degrees (so it idles smooth) then yes it should sound and perform like a L79. But why would one do that?

[Gary B.]

Re: L79 Camshaft (GM # 3853151); who makes what

Gene,

I think there are just going to be folks who choose a roller cam and other folks who choose a flat tappet cam. Some want the newest technology; some want time-proven technology. To each his/her own is my view.

Gary

[Joe L.]

Re: L79 Camshaft (GM # 3853151); who makes what

Gene,

I think there are just going to be folks who choose a roller cam and other folks who choose a flat tappet cam. Some want the newest technology; some want time-proven technology. To each his/her own is my view.

Gary

Gary------


I like time-proven technology, too. However, I was among the first to "jump on the bandwagon" for hydraulic roller cams because I believe the technology is so vastly superior to flat tappet. To be honest, I never liked flat tappet technology when it was, essentially, "the only game in town". So, when hydraulic roller technology appeared, I leaped on it.

Also, by now, hydraulic roller systems are definitely time-proven. Consider that GM has been using hydraulic roller systems for 28 years now. I don't know of any current OHV engine from any manufacturer that uses flat tappet systems.

[Joe L.]

Re: L79 Camshaft (GM # 3853151); who makes what

Hi Joe:

What is the open pressure of the 12551483 spring? For the 3119 lobe that I'm using, Comp Cams wants about 120 pounds on the seat and about 280 pounds over the nose.

I've heard there is also a GM beehive spring, used on certain LS engines, that has a 1.29" diameter that is easily retrofitted to vintage heads designed for 1.25" springs.

Regarding the other valve train components, such as the pushrods and rockers, do you think these would need to be upgraded? Qualitatively, I know that the faster ramps on performance roller cams add stress on the valve train because the valve is being opened much more quickly than the OEM flat tappet cams open the valve. What I'm unclear about is how far the stock components can go before they become unstable and/or broken.

I suspect that the stock pushrods and rockers might be okay for some of the milder lobes I listed, but my sense is that the 3119 lobe with 224 duration and .525 lift might be pushing things with the stock pushrods and rockers.

The fact is that I simply don't know the answer to this question, so I played it safe and upgraded the entire valve train. That's okay for a project where cost is not a key consideration, but it would be nice to know what can be done with a budget build.

Joe-----


I don't have specs on the open pressure of 12551483 spring. However, I am very confident that it's at least 280 lbs.

The beehive spring of which you speak is likely GM #12625033. This spring is 1.25" OD, 90 lbs @ installed height of 1.80", 295 lbs open pressure and works with lift up to 0.550".

There is another spring of GM #12621428. This spring is 101 lbs @ 1.96" installed height, 310 lbs open pressure and will work up to 0.600" lift. I don't have OD specs on it, though.

I don't think that the push rods or rocker arms would need to be upgraded with any of the cams you mention. However, keep in mind that retrofit hydraulic roller lifters usually require a special length push-rod. There is no stock GM pushrod that I know of that will work. So, one has to use an aftermarket pushrod. A high quality 5/16", 0.060" wall push rod should work just fine. However, you can't really go wrong using upgraded parts but I really don't think it's necessary even with the 3119 lobe cam.

[Joe R.]

Re: L79 Camshaft (GM # 3853151); who makes what

Joe-----


I don't have specs on the open pressure of 12551483 spring. However, I am very confident that it's at least 280 lbs.

The beehive spring of which you speak is likely GM #12625033. This spring is 1.25" OD, 90 lbs @ installed height of 1.80", 295 lbs open pressure and works with lift up to 0.550".

There is another spring of GM #12621428. This spring is 101 lbs @ 1.96" installed height, 310 lbs open pressure and will work up to 0.600" lift. I don't have OD specs on it, though.

I don't think that the push rods or rocker arms would need to be upgraded with any of the cams you mention. However, keep in mind that retrofit hydraulic roller lifters usually require a special length push-rod. There is no stock GM pushrod that I know of that will work. So, one has to use an aftermarket pushrod. A high quality 5/16", 0.060" wall push rod should work just fine. However, you can't really go wrong using upgraded parts but I really don't think it's necessary even with the 3119 lobe cam.

Hi Joe:

It sounds like GM has used springs in regular production that are very similar to what Comp Cams recommends for the Comp Cams hydraulic roller cams. That implies that some of the production GM roller cams have similar dynamics. I find that rather reassuring in terms of the expected reliability of a Comp Cams hydraulic roller retrofit into a Gen 1 small block.

I think the LS engines have better rockers than the Gen 1 small blocks, but maybe even the Gen 1 rockers are okay for these applications. If so, that would greatly reduce the total cost of converting to a roller cam. I wasn't sure what I needed in a rocker, so I took the conservative path and upgraded to roller rockers. They are very handsome to look at and I'm sure they will perform well, but they are expensive.

[Joe L.]

Re: L79 Camshaft (GM # 3853151); who makes what

Hi Joe:

It sounds like GM has used springs in regular production that are very similar to what Comp Cams recommends for the Comp Cams hydraulic roller cams. That implies that some of the production GM roller cams have similar dynamics. I find that rather reassuring in terms of the expected reliability of a Comp Cams hydraulic roller retrofit into a Gen 1 small block.

I think the LS engines have better rockers than the Gen 1 small blocks, but maybe even the Gen 1 rockers are okay for these applications. If so, that would greatly reduce the total cost of converting to a roller cam. I wasn't sure what I needed in a rocker, so I took the conservative path and upgraded to roller rockers. They are very handsome to look at and I'm sure they will perform well, but they are expensive.

Joe-------

The stock GM rockers are very strong. For example, stamped steel rockers were used on the L-88. The main problem with them is friction (and heat) generated at the ball socket. But, as far as strength, I don't think there's a problem.

GM has not offered a non-guided type rocker for small blocks in many years. If I were going to use a stock type, non-guided rocker arm, I'd use the Crane Nitro-Carb rockers.

[Joe C.]

Re: L79 Camshaft (GM # 3853151); who makes what

Hi Joe:

What is the open pressure of the 12551483 spring? For the 3119 lobe that I'm using, Comp Cams wants about 120 pounds on the seat and about 280 pounds over the nose.

I've heard there is also a GM beehive spring, used on certain LS engines, that has a 1.29" diameter that is easily retrofitted to vintage heads designed for 1.25" springs.

Regarding the other valve train components, such as the pushrods and rockers, do you think these would need to be upgraded? Qualitatively, I know that the faster ramps on performance roller cams add stress on the valve train because the valve is being opened much more quickly than the OEM flat tappet cams open the valve. What I'm unclear about is how far the stock components can go before they become unstable and/or broken.

I suspect that the stock pushrods and rockers might be okay for some of the milder lobes I listed, but my sense is that the 3119 lobe with 224 duration and .525 lift might be pushing things with the stock pushrods and rockers.

The fact is that I simply don't know the answer to this question, so I played it safe and upgraded the entire valve train. That's okay for a project where cost is not a key consideration, but it would be nice to know what can be done with a budget build.

Hi Joe,

Did you use Comp valve train components? I would stay "all Comp" since their parts are matched to each other. I have done so and valve train is very reliable. Now running a solid roller which easily revs to 8000. I'm now using their 26055 spring.

Look at Comp's 26915 spring. It's 1.290 - 1.055 and should fit into the stock spring pockets. Seat pressure is 121 @ 1.750, 277 @ 1.250, and 293 @ 1.200. You might need + 0.050" locks for the increased seat height, and you have "room" for an additional .025" valve lift.

[Gary B.]

Re: L79 Camshaft (GM # 3853151); who makes what

Did you mean to say that the OD is 1.25" or the open height at 295 lbs? Typically beehive springs give a top OD and a bottom OD, since they are different.

Gary

[Joe R.]

Re: L79 Camshaft (GM # 3853151); who makes what

Hi Joe,

Did you use Comp valve train components? I would stay "all Comp" since their parts are matched to each other. I have done so and valve train is very reliable. Now running a solid roller which easily revs to 8000. I'm now using their 26055 spring.

Look at Comp's 26915 spring. It's 1.290 - 1.055 and should fit into the stock spring pockets. Seat pressure is 121 @ 1.750, 277 @ 1.250, and 293 @ 1.200. You might need + 0.050" locks for the increased seat height, and you have "room" for an additional .025" valve lift.

Hi Joe:

Nice to see you weigh in here (note that we now have three different Joes on this thread...). You are the guy who first told me about the LS beehive spring that fits into the stock spring pockets. I really like the attributes of beehive springs, so I think this is a great idea.

In my case I'm using aftermarket heads that have been carefully reshaped on the outside to resemble '462 heads so that I can maintain a stock appearance in the engine compartment (I call this "NCRS disease"). The spring pockets in my heads are 1.55" in diameter, so there is room for just about any spring. The spring that I'm using is the Comp Cams 26986, which has a 1.412" diameter at the base. The only down side of the big spring pockets is that I had to use a spring locator on the base of the spring, which lifts the spring by .060." I compensated for this with +0.050 valve locks.