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10-30-2020, 03:27 PM | #101 |
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Re: "Old School" Stocker Cams
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.
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10-30-2020, 03:39 PM | #102 | |
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Re: "Old School" Stocker Cams
Quote:
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10-30-2020, 06:26 PM | #103 |
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Re: "Old School" Stocker Cams
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.
Last edited by Greg Reimer 7376; 10-31-2020 at 10:39 AM. |
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10-30-2020, 07:14 PM | #104 | |
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Re: "Old School" Stocker Cams
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10-30-2020, 08:03 PM | #105 | |
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Re: "Old School" Stocker Cams
Quote:
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. |
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10-30-2020, 10:09 PM | #106 | |
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Re: "Old School" Stocker Cams
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10-30-2020, 11:59 PM | #107 | |
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Re: "Old School" Stocker Cams
Quote:
cam ) with much better service life!
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10-31-2020, 10:36 AM | #108 |
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Re: "Old School" Stocker Cams
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.
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10-31-2020, 11:23 AM | #109 |
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Re: "Old School" Stocker Cams
Ford 292 lifter:
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10-31-2020, 02:41 PM | #110 |
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Re: "Old School" Stocker Cams
Seems that many an engine assembler putting together a 292 or a 312 would get his bare block on the stand, stick in the cam, the crank, the front cover and balancer, then put in the pistons and the rods, button things up, install the pan, pickup and the pump, then turn the engine over and start to install the lifters and then discover one of Ford's better ideas. It was the FE engine that went with a conventional lifter which Ford stayed with ever since. The lifters went into the block on the Y block first, then the cam slid in, then the rest of the bottom half went together. Lots of Ford line mechanics had a set of spring clothespins in their toolbox to hold those lifters up so they could replace a camshaft in the car if need be.
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