C2 Camshaft Identification

[Dave K.]

I’d like to determine if the cam in my 66 327/300 hp 4speed roadster is the stock cam or a performance replacement. The engine was overhauled by a speed shop about 10 years ago (and the cam replaced) when the car was owned by the previous owner. There is no documentation that specified what cam was installed.

I’m trying to get the engine to idle smooth below 650 rpm. I’ve carefully checked the distributor map, VAC performance, timing and carb idle setting. I performed a vacuum leak test using the unlit propane torch method but detected nothing. Below 650 rpm, it will idle rough (mild vibration) and occasional surge +/- 50 rpm. I’m doing all of this in preparation for a PV where the book calls for a smooth hot idle speed of 500-600 rpm for the 66 base engine (327/300 hp).

Is there any way to determine what cam is in the engine short of engine disassembly and inspecting the removed cam?

Regards,
Dave Kitch
33108

[Dave K.]

Re: C2 Camshaft Identification

I should have also reported that manifold vacuum is 19-20 in. Hg @ 600 rpm.

[Duke W.]

Re: C2 Camshaft Identification

The base engine cam used from '57-'66 was replaced by the 3896929 in 1967, but I defy anyone to discern a difference in idle characteristics.

Your engine should idle essentially butter smooth at 500 @ 18-19" Hg manifold vacuum.

Typical engine rebuilders install high overlap aftermarket camshafts, which foul idle quality, and that's probably what you have.

You should set the idle at 500 and take a manifold vacuum reading and compare to the above that I listed and note the degree of stability. Or, if it just won't idle that low, take a reading at the lowest that it will idle without stalling. That will be a good indicator of whether or not you have an OE or equivalent camshaft.

Given your description of the idle charateristics/quality, I would not give you a very good chance of passing a PV unless you replace the camshaft with a proper OE replacement.

There is no practical way to positively ID an aftermaket camshaft without removing it and looking at any identifying codes. Even then, with literally hundreds of aftermarket camshaft "grinds" out there with each manufacturer using their own ID method, many defy identification.

Duke

[Duke W.]

Re: C2 Camshaft Identification

That's encouraging. If it pulls that much vacuum at 600, it should be in the 18-19 inch range at 500, so perhaps your idle quality/stability problem is something else.

Initial timing should be 6-8 degrees and the OE VAC provides 16@12" so you should be able to read total idle timing in the low to mid-twenties.

Also adjust the mixture for maximum idle speed/vacuum.

If the ignition map/carb are to OE spec, do a compression or leak down test.

Duke

[Ken A.]

Re: C2 Camshaft Identification

First thing you should do is to let us know what you're using to measure RPM.
If it's the original tach, then that could be your problem. The OEM tach accuracy below 1000 RPM is questionable, and over time, because it is a magnetic device, becomes even more inaccurate. In addition the lubricant that the tach was assembled with dries out over time. Also the design of this tach prohibits "rock steady" readings. The PV should allow for a range of readings in order to be accurate. You may have to have your tach rebuilt in order to satisfy a judge.

[Dave K.]

Re: C2 Camshaft Identification

The tach that I used was part of an engine analyzer, tach/dwell, etc. meter.. I compated to the car's tach. It varied about 50 rpm. The tach cable is a brand new inner/outer cable assembly that I just installed and lubricated.

[Joe R.]

Re: C2 Camshaft Identification

Hi Dave:

I went through this same drill with my 67 327/300. It turned out that a previous owner had substituted the 327/350 cam.

If you really want to determine whether you have the correct cam, you can do so by installing a "degree wheel" on the front of the balancer and then using a dial guage to measure the lobe lift of the cam as a function of the crankshaft position. You'll have to pull off the pulleys on the crankshaft to install the degree wheel and pull off one valve cover to get the dial gauge in place, but it's not major surgery. It's probably a few hours of work start to finish.

If you decide to do this I can provide more details on the procedure offline, and I can even loan you the equipment if necessary.

From the vacuum data you have provided, it sounds like there is a chance that you have the correct cam but something else is misbehaving. Be sure to check all the easy things first before you invest the time to degree the cam.

[James H.]

Re: C2 Camshaft Identification

Dave.........The cam can be checked using the method we used when I worked for the NHRA. It's much easier than a degree wheel with no need to take off your pullys. Overlap and duration can be checked. However, without pulling your intake and installing a solid lifter, lift can only be aproximated but you can come close. Since I recently retired and going stir crazy with this weather,
give me a call.

Jim Henderson