63 L84 engine with an L79 cam

[Michael G.]

I was talking to a guy today who told me he had an L79 cam in his 63 L84 engine. He said it runs very well. I'm just looking for some other comments on this combination, if any one has done it, etc.

thanks,

[Duke W.]

Re: 63 L84 engine with an L79 cam

It's a good cam - broader torque bandwith than the Duntov and much better low end torque than the 30-30, but the LT-1 cam is the best overall for a SHP/FI small block.

With massaged heads and careful setup of the OE second design valve springs, the L-79 cam will make useable power to the lifter pump up speed of about 6700-6800, but the LT-1 cam will make useable power to about 7200, which is the point of incipient valve float.

However in lieu of using the L-79 cam on a 327 I recommend the L-46 cam installed with four degrees advance to bring the inlet POML back to 110 ATDC - same as the L-79. The L-46 cam has better lobe dynamics. It's the best SHP hydraulic lifter cam Chevrolet ever offered, but it's still tick behind the LT-1 cam if you want to exploit maximum useable revs.

Duke

[Michael G.]

Re: 63 L84 engine with an L79 cam

Thanks Duke, as I've mentioned here a few times, the L84 engine in my black car has had few mysterious valve train problems since it was rebuilt a several years ago. I've never been quite comfortable that it was done right, and even after I swapped out the springs and rockers with new correct ones, the valves still constantly clatter, no matter how well I adjust them (my other L84 car just sings when the valves are correct). I'm kind of fed up, so I'm thinking about pulling it this winter and re-doing it.

I'm looking for street performance, not track racing. I drive this car a lot and adjusting the valves is a pita on a fuelie, so hydraulic lifters are preferreable. I've always liked the way 327-350's drive, so I thought maybe I'd swap out the cam with the L-79 hydraulic one while I'm at it. I've driven a few 350-350's - they didn't seem much different that 327-350's. Can you tell me why you have a preference for the lobe dynamics of the 350-350 cam?

Thanks,

[Joe L.]

Re: 63 L84 engine with an L79 cam

It's a good cam - broader torque bandwith than the Duntov and much better low end torque than the 30-30, but the LT-1 cam is the best overall for a SHP/FI small block.

With massaged heads and careful setup of the OE second design valve springs, the L-79 cam will make useable power to the lifter pump up speed of about 6700-6800, but the LT-1 cam will make useable power to about 7200, which is the point of incipient valve float.

However in lieu of using the L-79 cam on a 327 I recommend the L-46 cam installed with four degrees advance to bring the inlet POML back to 110 ATDC - same as the L-79. The L-46 cam has better lobe dynamics. It's the best SHP hydraulic lifter cam Chevrolet ever offered, but it's still tick behind the LT-1 cam if you want to exploit maximum useable revs.

Duke

Duke------


... and the L-46/L-82 cam, GM #3896962, is still available from GM to this very day over 45 years since it was first released. In fact, this camshaft is still used in some SERVICE Gen I small blocks still being manufactured today. So, one might say it's "tried-and-true". I think it's very likely the longest-produced camshaft in the history of GM.

The curious thing about this camshaft is that it has a part number that implies a late 1966 or early 1967 release. However, I've never been able to find a PRODUCTION application for it prior to the 1969 model year.

[Duke W.]

Re: 63 L84 engine with an L79 cam

I always wondered why the L-46 cam was so close in high level specs to the L-79 cam, and it wasn't until I saw the detailed lobe lift data from the engineering drawing and did a dynamic analysis to determine the velocity, acceleration, and jerk profiles that the reason became somewhat apparent.

Though .050" durations are nearly the same (224 deg. vs. 222 for the L-79) on both lobes, the lobes are actually different as can be seen in the slightly higher exhaust lift. The primary difference is in the jerk profiles. They are a bit milder, which reduces dynamic valve train loading and probably allows slightly higher revs for the same valve spring.

GM learned a lot about valve train dynamics in the early to mid-sixties, so all cam designs after about 1964 offer superior dynamics compared to previous similar designs.

As Joe said, this cam has part numbers for finished cam/cam assy. w/ pin that are very close to the second design 300 HP cam, so it was probably released in 1966. It could be that they originally planned on using it in the L-79, but waited for the longer stroke L-46 because the four degrees retarded events on both the inlet and exhaust side would hurt low end torque on the L-79.

Also, as Joe said, the L-46 cam is still available from GM under the original part number, and it is used in the current 350/290 HP crate engine. It's also available from Sealed Power and Clevite - exact same cam built to the GM drawing, but likely cheaper than what most guys would pay from GM.
]
Maximum revs can be achieved for a hydraulic cam by setting valve spring installed height to allow .090-.100" coil bind margin according to the following formula; 1.44 is the typical actual maximum true ratio achieved by OE rocker arms at maximum lobe lift, and shims are typically available in .030" and .010" thicknesses.

Installed spring height min/max = coil bind height + 1.44(lobe lift) + .090/.100

This may result in so much shimming that the spring comes out of the pocket. In these cases install at least a .030" shim under the retainer.

The L-79 and L-46 cams offer a slightly tamer idle and more low end torque than any OE mechanical lifter cams due to their less effective overlap. The idle is a little tamer, but still has some "attitude". Installing one of these cams in OE mechanical lifter engine makes sense if you drive a lot and don't want to be bothered with valve adjustments, and with careful spring height setup you can still attain the 6500 tach redline.

Duke

[Tim S.]

Re: 63 L84 engine with an L79 cam

Thanks Duke, as I've mentioned here a few times, the L84 engine in my black car has had few mysterious valve train problems since it was rebuilt a several years ago. I've never been quite comfortable that it was done right, and even after I swapped out the springs and rockers with new correct ones, the valves still constantly clatter, no matter how well I adjust them (my other L84 car just sings when the valves are correct). I'm kind of fed up, so I'm thinking about pulling it this winter and re-doing it.

I'm looking for street performance, not track racing. I drive this car a lot and adjusting the valves is a pita on a fuelie, so hydraulic lifters are preferreable. I've always liked the way 327-350's drive, so I thought maybe I'd swap out the cam with the L-79 hydraulic one while I'm at it. I've driven a few 350-350's - they didn't seem much different that 327-350's. Can you tell me why you have a preference for the lobe dynamics of the 350-350 cam?

Thanks,

Mike, have you checked pushrod length for proper geometry? When it is not right, they can get real squirrely. What problems were you having? Quite frankly, I usually only lash my cars because I get bored. (I know, sounds stupid) Tim

[Michael G.]

Re: 63 L84 engine with an L79 cam

Tim,

Lashing the valves is not terribly difficult, but on a fuelie you've got to take off the air cleaner elbow and disassemble the air meter to take off the left hand valve cover. Since this car makes a lot of noise with the valves correctly adjusted, it really sounds bad when they get a bit off. To prevent this I'm now adjusting more often than you'd expect, so its more that a bit of work. I think I'm now on a first name basis with all of the valves....

I've had several problems since the engine was rebuilt. It started with excessively strong springs pulling the rocker studs out and bending pushrods. I sorted all that out and it really runs OK, but, the problem is excessive engine noise. I just can't adjust the valves to get rid of it: they just don't remotely compare to my other car. I was so frustrated that I even took push rods and rockers from another L84 and compared them dimensionally in our lab. No difference.

Since I didn't re-build this originally, I don't really know everything that was done, but I do know that I have no confidence in anything that was done by the rebuilder (and I'm certainly not going to give him another shot at it). As of now, I think a total rebuild of the heads, with replacement of the cam and lifters, is the only thing that will give me confidence that whatever screw-ups he made, they are gone. I probably won't change anything in the block except the cam and lifters.

Mike

[Timothy B.]

Re: 63 L84 engine with an L79 cam

Michael,

From you description of the valve lash getting loose it almost sounds like the rocker studs are not holding.

[Stuart F.]

Re: 63 L84 engine with an L79 cam

Did anyone mention that the cam might be a tooth off? I recall a friend's 348 335hp from 1959 that had been built by a most respected engine builder and we tried everything to get it to run right. One constant was noisy valves leading us to revisit the adjustment frequently. We also found it was bending pushrods - oh so little that you could only detect them by rolling them on glass. We just could not face the possibility that the builder screwed up. The thing would rev like a banshee to about 5800, then shut down. We tried everything we could think of until we finally checked the cam.

Stu Fox

[Michael G.]

Re: 63 L84 engine with an L79 cam

That's interesting Stu, as this engine doesn't pull strongly in the upper revs like my other L84... That information, combined with the fact that I had to reverse the distributor gear, makes me think there's something wrong with the cam or its gear orientation. In any case, I guess the re-build will sort that out.

[Joe L.]

Re: 63 L84 engine with an L79 cam

Tim,

Lashing the valves is not terribly difficult, but on a fuelie you've got to take off the air cleaner elbow and disassemble the air meter to take off the left hand valve cover. Since this car makes a lot of noise with the valves correctly adjusted, it really sounds bad when they get a bit off. To prevent this I'm now adjusting more often than you'd expect, so its more that a bit of work. I think I'm now on a first name basis with all of the valves....

I've had several problems since the engine was rebuilt. It started with excessively strong springs pulling the rocker studs out and bending pushrods. I sorted all that out and it really runs OK, but, the problem is excessive engine noise. I just can't adjust the valves to get rid of it: they just don't remotely compare to my other car. I was so frustrated that I even took push rods and rockers from another L84 and compared them dimensionally in our lab. No difference.

Since I didn't re-build this originally, I don't really know everything that was done, but I do know that I have no confidence in anything that was done by the rebuilder (and I'm certainly not going to give him another shot at it). As of now, I think a total rebuild of the heads, with replacement of the cam and lifters, is the only thing that will give me confidence that whatever screw-ups he made, they are gone. I probably won't change anything in the block except the cam and lifters.

Mike

Mike------


How did the rocker stud problem get resolved? Did you replace with screw-in type studs?

[Michael G.]

Re: 63 L84 engine with an L79 cam

Joe, yes, I replaced the springs with correct ones, then removed the press-in studs and tapped the holes. The new studs don't loosen now.

[Duke W.]

Re: 63 L84 engine with an L79 cam

Do you have a real Duntov cam? Manufacturer/part number?

What are the "correct springs?" Manufacturer/part number?

Duke

[James B.]

Re: 63 L84 engine with an L79 cam

Michael, I cannot enter this discussion from a technical standpoint. However, many years ago I restored a 1966 L72 car. I didn't want the pain of adjusting valves and got talked into a hydraulic cam. That changed the character of the engine and i regretted it for as long as I owned the car. The lope at idle was about gone as was the clatter of the solids. People always questioned, was it really a 425 horse motor (asked if maybe it was rebuilt by 'bubba'). It also hurt me on resale several years later even though I had dyno sheet and list of component changes, machining, etc.
i think for most of us part of what a "Fuelie" is is the cam be it a Duntov or a 30-30. My 64 L84 was rebuilt in 1984 when the LT1 cam was the best available. The engine runs great, sounds good but you can tell at idle it doesn't have the lope of the 30-30.
I'm sorry that I'm going counter to advise here and what you want to hear, just suggesting you give it some thought and consider the possibility that you might be able to correct the current problems & keep the cam and solids.

[Michael G.]

Re: 63 L84 engine with an L79 cam

Duke, the springs are Sealed Power VS-677. The cam is a supposed clone of the Duntov, made by Elgin, I don't know the part number. Believe me, I've given up on that cam and will be replacing it with either the L-89 or L-46 cam. Its likely, now that I know the L-46 is still available, that it will be the L-46.

Another option I've been considering is to just buy a GM crate engine, put the FI unit on it and drive it that way for now, then the put the current engine back sometime later, after I've fixed it. Maybe Joe can tell me if any of the current crop of GM crate engines have the proper head angle to allow the FI base plate to be installed....