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There have been several questions recently about how these two cams compare, including one recently in response to a sale by a GM dealer offering "take-off" 839s from crate engines for ten bucks.
I've completed a detailed review and analysis of the lobes on both cams and have come to the following conclusions.
1. The duration at .050" for both is 194/202 degrees and the points of maximum lift are the same at 108 ATDC/116 BTDC. The 839 gross lift is .25654/.26902" versus .26000/27333" for the 929, but this difference of a few thou is not at all significant.
2. There are some slight differences in the dynamics, particularly at the point of acceleration inflection, but, again, they are not significant, and it's not at all clear why the slight changes were implemented. Many are small even relative to production allowable tolerance.
3. The 839 drawing appears to have been done on a CAD system, and the old 929 drawing, though digitized, would have to be changed manually, and it was getting pretty cluttered, notwithstanding the fact that the original 929 velum was nearly 25 years old in 1991 when the 839 drawing was completed and released.
My conclusion is that the decision was to redraw and renumber this basic cam since it was (and is) still a production item - at least for crate engines - and having it on a CAD system with all the various new drawing standards that have been implemented since the sixties will make it easier to read and maintain. I suspect the responsible engineer saw a few minor "flaws" in the dynamics and "corrected" them, but as I said, they are very minor.
Consider the 1808839 to be a fully fit, form, and functional replacement for the 3232798 camshaft used on all hydraulic lifter SBs from '57 to '66, except L-79, and the 3836929 used on all base engines from '67 to '79.
This is the "new" "300 HP" cam and it will be a proper restoration replacement for any engine originally equipped with the 798 or 929 cams. Given that it's basic timing dates back nearly forty years is testiment that it is a good design. Relative to a SHP cam on an other wise identically configured SB, this cam will provide stump pulling off-idle torque and make more power up to somewhere in the mid 3000 rev range, so it's an excellent cam for the way most of us use these cars nowadays and is happy with tall gears for relaxed highway cruising, and massaging the OE heads will allow it to pull strong all the way to 5500, which is close to the valvetrain limiting speed.
Duke
I've completed a detailed review and analysis of the lobes on both cams and have come to the following conclusions.
1. The duration at .050" for both is 194/202 degrees and the points of maximum lift are the same at 108 ATDC/116 BTDC. The 839 gross lift is .25654/.26902" versus .26000/27333" for the 929, but this difference of a few thou is not at all significant.
2. There are some slight differences in the dynamics, particularly at the point of acceleration inflection, but, again, they are not significant, and it's not at all clear why the slight changes were implemented. Many are small even relative to production allowable tolerance.
3. The 839 drawing appears to have been done on a CAD system, and the old 929 drawing, though digitized, would have to be changed manually, and it was getting pretty cluttered, notwithstanding the fact that the original 929 velum was nearly 25 years old in 1991 when the 839 drawing was completed and released.
My conclusion is that the decision was to redraw and renumber this basic cam since it was (and is) still a production item - at least for crate engines - and having it on a CAD system with all the various new drawing standards that have been implemented since the sixties will make it easier to read and maintain. I suspect the responsible engineer saw a few minor "flaws" in the dynamics and "corrected" them, but as I said, they are very minor.
Consider the 1808839 to be a fully fit, form, and functional replacement for the 3232798 camshaft used on all hydraulic lifter SBs from '57 to '66, except L-79, and the 3836929 used on all base engines from '67 to '79.
This is the "new" "300 HP" cam and it will be a proper restoration replacement for any engine originally equipped with the 798 or 929 cams. Given that it's basic timing dates back nearly forty years is testiment that it is a good design. Relative to a SHP cam on an other wise identically configured SB, this cam will provide stump pulling off-idle torque and make more power up to somewhere in the mid 3000 rev range, so it's an excellent cam for the way most of us use these cars nowadays and is happy with tall gears for relaxed highway cruising, and massaging the OE heads will allow it to pull strong all the way to 5500, which is close to the valvetrain limiting speed.
Duke