Gm always liked to recycle ,when you select a cam look at what you want to use the vehicle for, im still a big fan of a 350hp cam in the 327s. some guys don't like them, old school but it works. I like a high lift , dual pattern and not to big a duration at .050, with a 112 lobe center, it works well with 10.1 to 11.1 compression, just me I guess. I use it for towing to goofing around.

its a very big two barrel, Duntov was a very good engineer

Are you saying Zora Arkus Duntov designed the carb I grew up with on my 250hp 350cid Laurentian?

Looks like 3896929 was the go-to cam for most of the common smallblocks back to 1962. In fact it's the broadest part I've ever seen listed:

1963 - 69/ALL WITH 283 - 307 - 327 - 350 ENGINES

So basically all pedestrian small blocks of all displacements from about 1962 through at least 1971!

I assume that's what you mean by the 280/288, which must be "advertised" duration because the real specs @ 0.050" are 195/202 duration and .390/.410 lift.

The wildest smallblock cam seems to have been the 370hp cam (3849346) - 254/254 and .485/.485 which is bigger than all the big block cams save the L88.

Are we sure that the listing of applications for that cam was the same for service replacement as it was for factory install?

Here's some more analysis of the small block cam:

"The 3896929 hydraulic grind; a cam that has been used as standard equipment in everything from the low-horsepower 283 to the medium output 350-ci engine. Its a perfect example of the ideal street cam for production vehicles. The timing is versatile enough to work in a wide variety of engines without hurting performance in any of them. Notice that it follows the game plan by opening the intake valve early: 26 degrees before TDC to be exact. This gets things moving and we can start adding up event timing to arrive at the number of degrees (duration) that the intake valve is open. To the initial 26 degrees of crankshaft rotation before TDC, we can add 180 degrees for the entire intake stroke and 90 more degrees for the amount of time the valve remains open after BDC. The total of these figures is 296 degrees, and thats listed as duration (in crankshaft degrees) at the lash point. This actually means the number of degrees between the point at which the valve lifts off and then returns to its seat. It is not, however, the true effective duration of the intake event. At extremely low valve lifts there is little significant flow, so we have to look at the timing from a point where the charge actually begins to gather momentum. Manufacturers disagree on just where this point occurs. This is understandable, since this initial point can be affected by a variety of factors, the most obvious of which are carburetor venturi area, intake manifold design, and cylinder head efficiency. It is generally agreed that significant flow begins somewhere between 0.010- and 0.050-inch valve lift and most manufacturers use a figure in this range as their reference checking point. The most common figure is 0.050 inch, although 0.020 and 0.030 inch are sometimes used for published specs.

At 0.050-inch valve lift, the intake event on the 3896929 cam is reduced to only 195 degrees. But this is not as bad as it seems. Recalling that the theoretical intake stroke is only 180 degrees, it provides an additional 15 degrees of duration in which significant flow can continue to fill the cylinder. And all is not lost with the low-lift flow, because the valve is physically off the seat during this period and some charge movement does occur (a certain amount of lead-time inertia isestablished for each event).

The 0.050-inch checking point is an excellent means of comparing camshafts, but only if the published figures for each cam are rated at the same 0.050-inch figure. If they differ, it will be difficult to arrive at a meaningful comparison without physical testing. If we move down the chart to one of the early race profiles (PN 2927140, for example) we can observe how the timing events are realigned to work at higher engine speeds. Where the hydraulic street cam opened the intake valve at 26 degrees BTDC (before top dead center), the 2927140 cam opens it at a much earlier 44 degrees BTDC. You have to remember that as engine speed increases, there is less time for each event (cycle) to occur. Therefore, a longer period (in crankshaft degrees of duration) is used to make up for it. You may notice that while the intake opening is significantly earlier, the closing point is nearly the same. This is because the designers wished to maintain a flat torque curve since this cam is intended for use in short-track racing, where superior torque is required to accelerate heavy cars out of low-speed turns. Cams listed below the 2927140 cam have a later closing point because they are intended for longer tracks and higher speeds where it is beneficial to move the torque curve higher in the RPM range.

When you examine the chart you will find that the 0.050-inch specification for the 2927140 cam provides 48 degrees more duration that the 3896929 cam. This is a significant breathing increase for the faster running engine. All of this is, of course, general and any cam grinder will tell you that the success of the overall combination depends greatly on the compatibility of the rest of the engine components and even the gearing, tire diameter, car weight, and a hundred other factors. With the basic information offered here, you should be able to study various cam profiles and observe how each is designed for a particular application. It may take considerable study before you are able to approximate the timing required for your engine. But before you get too engrossed, there are several other factors that can affect your selection. Chief among them is the lobe displacement angle, sometimes called the lobe-center angle.

davepl wrote:

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One other random observation kind of related: If you add a four barrel to the base 250hp 350, you pick up only 5 hp. So that tells me that 2bbl is plenty big enough for 250hp.

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Thinking the 4 bbl only added 5 H.P. on the short lived 1969 LM1, 255 H.P. is incorrect.

It was advertised at 255 H.P. to give non SS Camaros and Novas an edge in NHRA drag racing.

They're still competitive in stock classes today.

It was replaced with the L65 250 H.P. Engine after a few short months of production.

Only Canadian Pontiacs had the L65 Engine available from the start of 1969 production, along with the LM1 and L48.

Chevy had to wait until around Jan. 1969 to start using the L65. 250 H.P., after the LM1 was gone

In 1971 the very same Engine, with .5 less compression, was rated at 270 H.P. though it was coded L48.

I consider Chevy H.P. ratings to be more of an "Engine I.D." than its place in the "pecking order"

Similar thing with the 1970 360 HP 454, it got less compression and was re rated to 365 H.P. for 1971.

 

Thanks

Randy

I noticed that this ubiquitous cam was superseded by part number 14060651 which is still available from GM:

www.gmpartsdirect.com/oem-parts/gm-camshaft-14060651

But they list it as fitting vehicles as late as 1995. The specs for it at 194/202 and .383/.401 so almost identical to the 1963 original.

So cars from 1963 to 1995 used the same cam? That's amazing... either they got it really right the first time or didn't care too much!

Good point, was there any mechanical difference between the 385 and 390?

Also didn't most of these motors switch from closed to open chambers without changing rating?

And of course there's the 396, which I never fully memorized - 375 one year, 425 the next, mechanical cam then a hydraulic, and numbers all over the place it seemed.

So why the 430 and 435 charade if the Vette wasn't subject to the AMA limits anyway? Or was the 435hp motor fairly rated and then the L88 stuck just below it to stop people from blithely picking the "top" option?

Obviously the L88 made more than 430, but the did L71?