69 L72 CAM

[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.

[olredalert]

-----The 450hp engines were simply rated at a higher RPM than the 425HP motors. GM claimed that the insurance companys were screaming so just rated the engines at a lower RPM......Bill S

[LS6 RAT]

Bill,

In Karl Ludvigsen's Corvette book both the '65 L78 & the '66 L72 were rated at 6400rpms.

However the later engines such as the '67, '68 & '69 L71 which also was a 11:0 to 1 compression rated engine, did indeed rate their 435hp at 5800 rpms. I don't know what rpm's the '70 LS6 used for their factoring with a 11:25 to 1 compression, but the '71 454/425hp rating was also rated at a low 5600 rpms, and this with a factory compression rating of 9:0 to 1.

[olredalert]

Warren,

----Good to hear from you!!!
----Nolands book (PG.354) says that 450hp engines were rated at 6400rpm while 425hp engines were rated at 5600rpm. Both the 450hp and the 425hp were L72s. I believe Ludvigson was referring to the much more common 427/425 rating that was prevalent most of the production year of 1966........Bill S

[Keith Tedford]

From my experience, these engines are not making more horsepower at the higher rpm above 6K. About all you are going to do shifting up there is drop a valve, if you are running stock valve springs. A friend's L78 with more cam shaft and head work, ETs best shifting at 6K. Our L78 and L72 are both 4 speed with 4.10 gears. The 427 is a ton stronger in all rpm ranges. The bottom end torque and the extra hp on the top end make a bigger difference than the 31 cubic inches would indicate. Perhaps the bigger bore unshrouds the valves allowing for better breathing. The minor differences in cam shafts would make an insignificant difference. I wouldn't put much credence in factory ratings. The numbers look good on the breather though.

[LS6 RAT]

Keith,

I had a '69 L78 engine in a SS Camaro Convertible, and had this car restored completely. I was disappointed in this engines performance, it did not feel very strong, and many people had extolled stories on how powerful these 396 engines were. This car ran a M20 transmission and a 3:55 ratio axle. My LS6's with their low compression seemed to pull harder and run stronger. Heck, my friend Larry Weymouth, last year at the Pure Stock Drags ran a 13:12 with his stock '71 LS6, and this was with a 3:36 axle ratio.

[nuch_ss396]

Warren,

There was a recent thread here about our beloved SHP engines,
the vast manufacturing tolerances employed back in the day,
and how these tolerances effected the compression ratio,
and ultimately the power output of that particular engine.

Indeed, one member here posted that an L/72 ( 11:1 compression )
actually spec'd in under 10:1 compression. Another member
wrote about deck heights being different by as much as 0.020

So, you can possibly see why your particular BB ran less than steller.

Needless to say, I will never build another engine without blueprinting it first.

[Keith Tedford]

The two L78 cars that we have/had would probably run mid to low 13s. They both had headers and appropriate tuning. Nothing spectacular considering all the good equipment involved. The gas mileage was no better that our 427 which did perform pretty well. The actual compression ratio tended to be about a point lower than that listed. I was told by a fellow with several COPO cars, that these engines were honed to the outer limit. This is what accounted for their free revving at higher rpms. Ours certainly didn't fall off over 6K like the L78s did.