GM Cams

[Chevy454]

Nope.

[69L89396]

I quess if they make it to the exact original specs there's no difference.

[Chevy454]

Well, if I had to guess, there WILL be a difference, as the new GM/Crane is probably a lot closer to specs than the originals were! I haven't found a cam doctor (yet!) to check my new cam, but I think Jim Lerum had a friend run an original cam on a cam doctor, and the specs were all over the place. He was surprised, as was I.

[Rowdy Rat]

Rob,

I had Jere Stahl run several "178" LT-1 cams (all three GM - two original and one current replacement) on his equipment about a year ago... Absolutely no difference other than some minor (reduced lift slightly) wear on one of the original cams.

I would imagine that checking the acceleration and lift curves for the "143" cam would yield similar results.

Regards,

Stan Falenski

[Chevy454]

Stan:

Here were Jim's results:

Cylinder # 1 .050 check height
Part Number 3863143

Intake & Exhaust
Lobe center separation = 111.4 cam degrees
Valve Overlap = 13.9 crank degrees

Intake
Valve Opening = 8.6 œBTDC
Lobe Center = 111.4 œATDC
Valve Closer = 53.1 œABDC
Duration = 241.7 Crank Degrees
Max Cam Lift = .30516 In
Net Valve Lift = .500 In
Lobe Area = 27.36 In * DEG

Exhaust
Valve Opening = 57.5 ŒBBDC
Lobe Center = 111.4 ŒBTDC
Valve Closer = 5.3 ŒATDC
Duration = 242.8 Crank Degrees
Max Cam Lift = .32126 In
Net Valve Lift = .524 In
Lobe Area = 27.6 In * DEG


Notes: Intake .024 hot lash/ Exhaust .028 hot lash
Net Valve Lift=(Max Cam Lift x 1.72)- hot lash
Rocker Arm ratio= 1.72



I thought it was very interesting that a cam that is suppose to have a lobe center separation of 114 degrees cam out to 111.4. This car would idle a little rougher than a cam with 114 degrees. If you noticed that the camÃs exhaust lobe is a little taller than itÃs suppose to be. In a perfect world with a perfect cam the hot lash it should come out to .492. net valve lift. This imperfect grind on the exhaust side should be beneficial to some performance. I have the numbers of this cam at .020 which I'll post in the near future.

Like Jim, I am curious about the LSA difference, and the pretty big difference in intake/exhaust lift is worth noting as well.

Stan, any chance that you have a new "143" laying around that you could get checked @ .024"/.028" ? I haven't been able to locate a cam doctor in this part of the world yet...

[69L89396]

Do you know who made the cam what was checked?

[Chevy454]

Jim tested an original GM cam purchased in 1982.