"Old School" Stocker Cams

[SSDiv6]

Originally Posted by Greg Reimer 7376

Back in the scary days of the early '70's, I worked at a Chevy dealer beginning in 1975 up till about mid 1980. The cars they made between those years were not exactly exciting as to drivability and gas mileage. Beginning in 1971, the typical 4 barrel 350 that you got in most cars, came with 9.0 to 1 compression by using a piston with a small dish and a large CC combustion chamber in the heads. The '71 engine had the same camshaft as the 67-70 engines, .390" intake lift, .410" exhaust lift. Those cars still ran pretty well. It seemed that NOX emissions were a real concern, and excessive heat or combustion produced it, so the quick fix was to drop the compression down to 8.5 or so to 1, pull ignition timing out of it, and they ground a different cam with more lift,.398I,.430E, as per the NHRA engine specs in the guide. The problem was that the exhaust valve opened early and closed late. Also, the exhaust system in the car was quite restrictive. The sleeve on the right side exhaust manifold where the exhaust do-nut went had a noticeable restricted opening. This was an attempt to cause back pressure in order to trap a portion of the exhaust in the combustion chamber as a precursor to the EGR systems that came out in '73. Also, the presence of an inert gas in the mix combined with the retarded timing (4-6 degrees initial ) was designed to get the NOX emissions low enough to pass some federal standard. This resulted in a car that just didn't have it compared to its predecessors. This also was the start of a rash of 350 Chevy motors that used to get flat camshafts in about 20-30,000 miles. The factory replacement cam was the earlier cam, so when the line mechanics at the local dealer got one of these cars,'72-80 for a camshaft and lifter replacement, the earlier cam went in, and the customer got his car back with a noticeable improvement in drivability. We always set the timing to the factory specs and marked it so that the state smog gestapos wouldn't come visit the dealership and fine us for "tampering". In 1970-72, we had no idea the horrors awaiting the auto industry regarding upcoming emission control constraints! Now, if you have a Stock Eliminator car, all attention is being paid to making all the cylinder pressure and thermal efficiency you can for maximum power at the wheels when the car needs it most. The whole science of camshafts and their effect on engine performance is a huge field, and sometimes understanding what it takes to make an engine work better is to review why some engines didn't work right in the first place.

You are correct. There are many variables from one engine manufacturer and year to the other. One limiting factor, especially in Stock Eliminator is the lifter diameter. The lifter diameter on GM engines limits the lobe and ramp when compared to Ford, Chrysler and AMC that uses a larger diameter lifter, hence, allowing more aggressive lobes.

[Greg Reimer 7376]

Maybe, that could explain why so many small block Chevy cams went flat all through the '70s and 80's. It's also a possibility that a cam vendor had problems with quality control that caused a lot of problems. Seems to me that some Ford engines in the late '50's and early '60's had a bunch of issues like that, too. I think it was with the onset of the FE engine and the MEL engine, 352,390,430's, etc.

[Ralph A Powell]

Originally Posted by Greg Reimer 7376

Maybe, that could explain why so many small block Chevy cams went flat all through the '70s and 80's. It's also a possibility that a cam vendor had problems with quality control that caused a lot of problems. Seems to me that some Ford engines in the late '50's and early '60's had a bunch of issues like that, too.

It was the Ford Y-Block (272 292 312s) they had a nail head (mushroom) style solid lifter.

[Dave Gantz]

Originally Posted by Greg Reimer 7376

Maybe, that could explain why so many small block Chevy cams went flat all through the '70s and 80's. It's also a possibility that a cam vendor had problems with quality control that caused a lot of problems. Seems to me that some Ford engines in the late '50's and early '60's had a bunch of issues like that, too.

It wouldn't surprise me if Chevy tried to save a penny or two by changing the "recipe" of the steel or iron that the cams were made from. The vendors only adhered to the provided spec. Short term quality problems were more likely a vendor issue.
I say this from my experience working at a vendor that provided tooling and stampings for the big three. We would order steel that was to the customers spec ("recipe"), and it was checked by QC. It would then rust through in a few years until Japanese competition magically made UAW stuff better (late 80's,early 90's). If there was a vendor QC issue, we worked to get it back to the customer's standard, whatever that may have been.

[Paul Precht]

Originally Posted by Dave Gantz

It wouldn't surprise me if Chevy tried to save a penny or two by changing the "recipe" of the steel or iron that the cams were made from. The vendors only adhered to the provided spec. Short term quality problems were more likely a vendor issue.
I say this from my experience working at a vendor that provided tooling and stampings for the big three. We would order steel that was to the customers spec ("recipe"), and it was checked by QC. It would then rust through in a few years until Japanese competition magically made UAW stuff better (late 80's,early 90's). If there was a vendor QC issue, we worked to get it back to the customer's standard, whatever that may have been.

The Chevy blocks, cams and lifters were all soft and brittle iron back in the 60s and 70s. The cams didn't have the large oil drain back area the Mopars had directly over the lobes nor the larger lifters and with the rocker/stud setup always loosening up they didn't last long. Back in 72 I rebuilt a 65 283 for a friends 62 Corvette and a 60 413 for myself. After removing the 283 cam which was missing a few lobes, I threw it up in the air on the asphalt road and it broke into about 50 pieces. I did the same with the 413 cam but it just bounced around without a break, I then at 17 yo using a good amount of force took it over the concrete curb with my hands and whacked it at least 20 times and couldn't even break it in half, the only way that 413 cam was coming apart was with a saw or a torch.

[GTX JOHN]

Originally Posted by Paul Precht

The Chevy blocks, cams and lifters were all soft and brittle iron back in the 60s and 70s. The cams didn't have the large oil drain back area the Mopars had directly over the lobes nor the larger lifters and with the rocker/stud setup always loosening up they didn't last long. Back in 72 I rebuilt a 65 283 for a friends 62 Corvette and a 60 413 for myself. After removing the 283 cam which was missing a few lobes, I threw it up in the air on the asphalt road and it broke into about 50 pieces. I did the same with the 413 cam but it just bounced around without a break, I then at 17 yo using a good amount of force took it over the concrete curb with my hands and whacked it at least 20 times and couldn't even break it in half, the only way that 413 cam was coming apart was with a saw or a torch.

The Mopar had a much better camshaft core (Stamped CWC on the
cam ) with much better service life!

[Greg Reimer 7376]

We received new camshafts back in the day in a cardboard tube with the GM logo and part number on them. Once in a while, we would open the tube and find the camshaft was broken in two right in the package. Also, dropping a camshaft was a real sure fire way to break it. If one rolled off a workbench and hit the ground it was usually done for as well. When Chevy went to the steel hydraulic roller cams, that ended a multiplicity of problems. Actually, a flat tappet camshaft was kind of antique technology even a long time ago.