69 L72 CAM

[RS69]

Could someone plz post the specs. for the L72 cam. lift/duration. thanks

[Chevy454]

This should be the cam card: Crane/GM 143 blueprint

[RS69]

thanks

[LS6 RAT]

RS69,

There are 2 GM camshafts that have been used for 1965 thru 1971 solid lifter high performance big blocks. And there has been a fair amount of confusion as to their applicability to which RPO option. The two camshafts are 3863143 and 3904362. My understanding is that 3863143 was used originally with L78, L72 options during the model years 1965 & 1966. Camshaft 3904362 was used originally with L71, L72, L78, L89 & LS6 during the model years 1967, 1968, 1969 1970 & 1971.

Where the confusion exists is that camshaft 3904362 was used with the re-designed oiling system incorporated with the 1967 and later big block. This camshaft (3904362) was discontinued shortly after the last high performance big block, the 1971 LS6 option in Corvette.
GM issued the earlier 3863143 camshaft to be the service replacement unit for all applications using the original 3904362 camshaft. There was a one way relationship between these two cams. 3863143 could be used in '67 and later blocks, although a GM technical bulletin was issued recomending a modification to be performed before installing this cam in a '67 & later block. However, camshaft 3904362 should never be used in '65 & '66 year blocks, because a oil starvation condition would occur, since this camshaft did not incorporate the grooved rear journal necessary along with the grooved cam bearing that was part of the earlier blocks oiling design. Hence the decision to discontinue the 3904362 camshaft to prevent catastrophic failure due to incompatibility of the two cams between the two re-designed cylinder cases.
Further confusion abounds because the GM parts books and Colvins books show incorrect part numbers for some of these applications. An example would be the 1953 thru 1971 Corvette parts book, this shows camshaft 3863143 as the part for a LS6 application. Another example is Colvins book, which shows 3863143 camshaft as the part for a 1969 L71.

In some applications camshaft 3863143 & 3904362 are shown with the same specifications, while other applications show 3863143 to have different specifications. I think most on this board think these cams are identical except for the groove, I am not sure this is true.

Specs for 3863143 & 3904362 have been shown to be .520 intake lift, .520 exhaust lift, 316 intake duration, 302 exhaust duration.

Camshaft 3863143 specs for 1965 are also shown as .497 intake lift, .503 exhaust lift, 348 intake duration, & 348 exhaust duration.

Camshaft 3863143 specs for 1966 are also shown as .520 intake lift, .520 exhaust lift, 336 intake duration, & 336 exhaust duration.

As you can see there is some conflicting information out there. I also believe that Cranes "blueprint series" cams are not exactly the same as GM's, they are close, but I would suspect that Crane, as well as any other manufacturer would improve upon the GM's specs, as camshaft technology has obviously advanced since the 35 years of the previous design.
I have had both of the above camshafts, NOS, however I did not take them to someone knowledgeable to do a comparison. I have since sold the 3863143 cam and kept the 3904362, as I believe this is the true original GM camshaft used in production LS6 engines, which I have 2 of.

[nuch_ss396]

Warren,

I don't want to confuse the issue here, but I seem to remember
that the '66 427 Vette was actually rated at 450hp, not 425.
So, perhaps the earlier cam was slightly different.

Steve

[396/425blr]

not sure but i think the 450 HP was due to the high flow exhaust manifolds in the corvette for the increase rating? DOC

[Keith Tedford]

Back in the '60s, the car companies seemed to put whatever hp rating they liked on the various engines. For drag racing Ford decided to low ball the 428 Cobra Jet at 335 hp, the same as the 390. A definite advantage in NHRA. The '66 L72 cars came down the line for a short time with the 450 hp stickers and then they were changed to 425 hp. This according to a friend who worked on the line in Oshawa at the time. Same engine. Different numbers. 425 hp was probably a lot more accurate for an L72 engines and they would probably need a little help at that. Not that they couldn't make a lot more power with a few changes. Ask Rob.

[LS6 RAT]

Steve,

The L72 option for the model year 1966 for the Corvette did indeed begin with a rating of 450hp. This rating was used during the Aug, Sept & Oct production build out. It was changed to 425hp thereafter. A very well written article about this subject was published in The Corvette Restorer magazine by a man named Ogilvie. The article goes on to prove that this hp rating was a paper change only and that no physical changes were made during the L72 production during the entire years build out.

[LS6 RAT]

396/425blr,

This may well be one reason for the difference in ratings initially between the Corvette and Camaro, since the more streamline freer flowing manifolds would not clear the engine bays of the Camaro, Chevelle, Nova models without slight modification.
However these larger manifolds were also used on the full size models, such as Caprice, Biscayne, Impala and their ratings were still 425hp. My opinion is that the Corvette was considered the flagship of the Chevrolet division, and as such would certainly merit the title of highest hp rating.

[LS6 RAT]

Keith,

Very interesting point. A good example would be the L78 of 1965 and the L72 of 1966 for Corvette. Here we have a 396/425hp and a 427/425hp both rated the same, however the 1966 engine has a 31 cubic inch advantage, with both engines having all other factors the same. So either the 396 is over rated or the 427 is under rated.

To further confuse things, both engines are purported to use camshaft 3863143, however the specifications in Colvins book show differences in these cams for these two years. I don't know if his information is incorrect, or that GM would actually use the same part number for two different specifications? And again this same camshaft 3863143 uses different specs in later applications. Although camshaft 3904362 is called for use, in these same later applications.