1981 L81 Camshaft spec?

[Vader]

I've done the search, both on the sites and www, and I can't seem to find a definitive set of specs (nor even a part number) for the mysterious cam grind of the '81 L81. Any help?

 

[GerryLP]

Vader,

My GM 1981 Corvette Shop Manual shows the following data.

Lobe lift at +/- 0.002 Intake = 0.2600 0.3000

Exh. = 0.2733 0.3067

Journal Diameter 1.8682 - 1.8692

Camshaft end play 0.004 - 0.012

This imformation is in page 6A4-24. The second lobe lift number is probably the total lift of the lobe when the tappet is at its highest point.

 

[Jack]

My GM 1981 Corvette Shop Manual shows the following data.

Lobe lift at +/- 0.002 Intake = 0.2600 0.3000

Exh. = 0.2733 0.3067

The lift looks a lot like an L82 cam. Although the L81 cam isn't listed ... here's a link to a table of other vette cam specs.
http://www.geocities.com/MotorCity/Downs/3000/cmspec.html
JACK:gap

 

[Jack]

My GM 1981 Corvette Shop Manual shows the following data.

Lobe lift at +/- 0.002 Intake = 0.2600 0.3000

Exh. = 0.2733 0.3067

On second thought ... if you look at the first lift numbers ... then multiply by 1.5:1 RAR ... to get lift at valve. Then ... those numbers look very similar to L48's 3663152 .390"/.410" valve lift cam. Simply a wild guess here, but maybe the second lift numbers have some relationship to the overall play in hydraulic lifters? I know they run at zero-lash. I just dunno about the second lift numbers.

Referencing the other thread in the L81 registry ... http://corvetteactioncenter.com/forums/showthread.php?s=&threadid=30101 ... I agree w/ Tom Bryant ... the L81's cam sure don't lope like L82's 3896962 .450"/.460" cam.
JACK:gap

 

[Vader]

Cam specs measured!

Well, I got a little bored and dropped the cam in 'V' blocks with a degree wheel. Some of the lobes were worn (not surprised) and the best lobes I could measure yielded these numbers:

(SPEC-INT-EXH) Lobe Lift .253" / .266", Gross Lift .381" / .402", Total Duration 306° / 323° (crank degrees), Duration @ .050 196° / 204°, LSA 113°.

Also, after a trip through the parts washer, the cam does have some numbers "GM 54 6930" I couldn't find a reference to that anywhere.

The next time the question arises, hopefully someone who searches will be able to find this thread.

 

[Jack]

Re: Cam specs measured!

(SPEC-INT-EXH) Lobe Lift .253" / .266", Gross Lift .381" / .402", Total Duration 306° / 323° (crank degrees), Duration @ .050 196° / 204°, LSA 113°

Good Job Based on lift alone ... looks a lot like an L48 cam having nominal wear.
JACK:gap

 

[JohnZ]

Casting #6930 was used exclusively for the #3896929 cam, in all 327 and 350 base engines (except the 1980 California 305), from '67 -'81.

 

[Vader]

JohnZ,

Thank you for that clarification. I strongly suspected that the "0.450/0.460" numbers for an L81 I've seen tossed about some web sites was grossly incorrect.

Go buy yourself a cold Big Orange drink on me...