cam specs?

[Guest]

Can anyone tell what the cam specs are for a 1964 300. motor with a 4 barrell carb. I need the the specs at .50 not the advertised specs? I have a origanal servive manual but it dosesnt list them. Thanks Tim

[BUICK RACER]

Email Sean at buick3001964@yahoo.com maybe he can help you.

[NTX5467]

Starting in '65, Peterson Publishing Company put out an annual "Complete Book of Engines" that covered all of the production engines for North American built cars. It also included ALL of the SAE specs for the engines plus had a write up on each engine family. In the back were some articles on modifications, historical information, and such. Quite nice items to have! They continued doing one each year up until about '75.

The "advertised" cam specs are or should be to the SAE procedures, which should be (if I remember correctly) at .006" lobe lift on intake and .008" lobe lift on the exhaust. Going by the specs of some repro cam manufacturers that offer "equivalent" cams will not yield the EXACT same specs as the factory cams as to do so without a license would be copyright infringement--therefore, all of the "equivalent" cams will have a little more duration and/or lift and/or lobe centerline changes. That's why a Melling 350/350 cam for a Chevy small block sounds so much wilder than the stock GM 350/350 cam does in the same motor.

As for the .050" duration numbers, the Chrysler guys claim that you can generally take the factory's advertised total duration numbers and multiply them by .80 on normal stock cams and .85 on higher performance cams to approximate the .050" duration numbers.

As mentioned, the factory numbers are according to SAE specified procedures. The .050" numbers were developed by the aftermarket cam vendors to standardize how their cams were spec'd out so you'd know what you were getting. The general orientation is that by the time the lifter has moved .050" higher than the base lobe circle of the cam, it's past any clearance or transitionary ramps on the lobe profile and into the "meat" of things. On some Chevrolet cams, they allegedly used to include these ramps in their specs and generate some very large duration numbers for otherwise mild cams. The .050" orientation came along in the '70s or thereabouts so the only way to get these numbers for a factory cam would be to find one and degree it to determine the lift and timing event numbers.

I happen to have the '69 edition (#5) close by and here are the numbers on the '69 Buick 350 2bbl & 4bbl V-8. The numbers for the 300 might be similar, but until I find the earlier version, you can use these as a general guide.

Intake -- Opens BTDC -- 24 Closes ABDC -- 78 Total -- 282 degrees

Exhaust - Opens BBDC -- 70 Closes ATDC -- 38 Total -- 288 degrees

Overlap -- 62 degrees

Lobe Lift -- Intake/Exhaust >> .243"/.247"

Rocker Ratio -- 1.55

Valve Lift = Lobe Lift x Rocker Ratio

Hope this might help you in your search,

NTX5467

[Guest]

Thanks for your help.The reason Im trying to find out is not to replace the cam but to replace the carb.and the one Im looking at ask for duration at. .50 to be no greater than 210. Just trying to get it right the first time. Thanks again for your help.

[NTX5467]

Thanks for that additional information.

Remember that it's VERY EASY to over-carb a small motor. I suspect that with a stock cam with a stock intake manifold (or even an aftermarket aluminum dual plane), stock exhaust manifolds, and stock exhaust, something in the range of 550 cfm would be about right. Even then, if the secondaries are controlled by air flow, they might not open all of the way at WOT (or until about 5000rpm).

The earlier Carter AFBs that GM used had manual secondaries but also had counterweighted "air valves" just above the secondary throttle plates to keep too much air from getting inside too quickly (and lowering power output) and bogging the motor. Chrysler used some in the middle '60s that were full manual secondaries and even at about 525cfm, they were on the verge of bogging a stock 383cid 325 horsepower V-8 from a dead stop.

The cam duration deal is an indication of just how "hot" the motor is and what its intended use might be. In order to make a 210 degree at .050 aftermarket cam work in my '77 Chevy 305 with 2.56 gears, I had to recurve the distributor from stock and also had to seriously play with the idle mixture to get it right. I initially used an emission spec Holley 4160 for a '76 350 V-8 on a Holley Z-Line intake. The whole package, being more conservative as it was, got me more power with no loss in fuel economy. When I finally put a 650 cfm 4175 spread bore Holley on it (emission spec for a '79 L-82 Corvette), the mileage went up 2 mpg and felt like another 20 lbs/ft or torque suddenly appeared. That made every day mileage average right at 20mpg in mixed driving. That extra air flow might have come in handy when I totally peeved-off a new '87 Mustang on the Interstate one day (with no traffic in front of us). I know his car was stock as it still had the paper tag in the rear window, hehe.

Email me if you have any other concerns on your proposed combination.

NTX5467