GM Cams

[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.

[Chevy454]

Here is a link to the very page of the GM Performance parts site selling the "143" cam: 143 cam page

You can either order it online from GMPP off the above page, or go to your local Chevrolet dealer and order it there, or call Crane and get it from there...whichever you choose, you will end up with the same cam.

Just curious, any specific reason you are needing an EXACT "143" cam? I've got a couple of "original" 143 cams (already broken in![img]/ubbthreads/images/graemlins/naughty.gif[/img]) that I would GLADLY put in a GM box and sell to you!

[69L89396]

I was just curious. I have a new one I bought from Comp Cams. It shows the same specs as the original. I was wondering if there was any real difference in the actual measurements.

[1969L78Nova]

Previous owner of my L78 had GM install PN 3904362 a few years back. My research indicates this cam is for an LS 6. The specs. are very close to the original cam. [img]/ubbthreads/images/graemlins/dunno.gif[/img]

Martin

[Chevy454]

I believe it's the exact same cam. Same specs, same casting symbol, just different part number.

It's listed as being used in the L-78/L-71 in '67, the L-78/L-72/L-71 in '68, and the L-78/LS-6 in '70, but in '69 they changed the part number for the L-78/L-72/L-71 cam, even though it had the same specs in ALL the years?

[Chevy454]

For my fellow engine builders out there, while I was on the phone with Crane yesterday I asked them about how the "143" was ground (straight up, or retarded/advanced), and they said the original cams were ground with 6 degrees of advance and their (Crane) cams are exact duplicates. Might be something to think about for those of us who race on the skinnies...

[69L89396]

I asked the same question when I bought mine from Comp Cams and they said the same thing. [img]/ubbthreads/images/graemlins/biggthumpup.gif[/img]