Assuming it came from a car, this will be pretty close:
Duration at 050 inch Lift:184 int./194 exh.
Advertised Duration:260 int./270 exh.
Intake Valve Lift with Factory Rocker Arm Ratio:0.368 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio:0.398 in.
if it came from a truck you can take about 10 degrees off both the 0.050 and advertised duration. Lift is about the same, but I’m having a time trying to find the exact measurements for a 305 TBI truck cam.
Try to read the partial VIN under the engine assembly code. 305’s in 1986 had several assembly options between 2 bbl or 4 bbl carbs. This is the year before the LO3 TBI engine. Needless to say non of the engines produced in the mid early 1970’s through the later 1980’s produced much power. The emphasis was on NOx reduction as the catalytic technology at an affordable price didn’t yet exist. So compression ratios were reduced, cam timing significantly shrunk, ignition advance reduced and delayed. Part of the cam timing reduction was impacted by the factory eliminating Parkerizing the cam which was a wear reduction process that is way not environmentally friendly, that and the reduction in ZDDP and other metallic EP chemistry in the oil to aid cat converter longevity. Plus fuels going unleaded and alcohol adulterated.
The 1970’s and for the most part the 80’s was a dismal period for factory performance. The emissions mandates pretty much killed the performance aftermarket. Most any medium size town could boost 3 or 4, sometimes more, performance shops in 1970, by 1990 nearly all, if not all, of that was gone.
It took the 3 way cat converter, fuel injection, factory roller cams, and modern heads to restore the performance industry to what it is today. Basically from the 1972 oil imbargo to the mid 90’s LT1 and LT4 the performance market was dead except for us die hard. Even the early EFI was of little help, those systems were ‘point designed’ and while not impossible to hop up we’re difficult to do so.
The fallout of all of that completely changed combustion chamber design to put the chamber to work on mixture quality, better flame propagation, and faster burns. Cams went roller which offers better wear and higher lifts that are more compatible with cylinder filling on less duration.
The end product of this is today the average guy in his garage can build a very street mannered 400 horse 350, 351, or 360 depending on brand choice with a carburetor. Where even back in the late 1960’s and very early 70’s you’d sweat blood to get 350 maybe 375 horses out of an engine that would not run with an automatic nor very long between tune ups as 2500 to 5000 miles for a rod dead engine where a stock grocery getter could go 10,000 maybe 15’000 miles between tune ups. I lived through this period where if someone got a 100,000 miles on an engine all the guys in the neighborhood came over to marvel at the feat and get pointers on how to do it. Most didn’t and couldn‘t simply because of the discipline and maintenance cost of frequent oil and filter changes and staying up on the tuneup.
So enjoy the technological fruits of modernism, no matter how much you hear guys complain about unleaded alcohol infused modern gasoline, it is way ahead of scraping lead off the spark plugs every few weeks.
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