Hello,

I'm trying to figure out what I have for a camshaft without actually taking it out if that's possible? I have a 71 350 and was told by the previous owner that the owner before him rebuilt the motor with a w31 type cam. Is there anyway by the sound of the motor at idle or some other method to know if my cam is stock or not?

Thanks in advance,

Pete

 

No

 

With a 360* timing tape and a dial indicator on a rocker arm you could get some crude measurements of the cam itself. Then you would have to cross reference that somehow to know factory grinds. If you suspect it's an after market cam you'd just drive yourself nuts trying to figure it out due to the multitude of available grinds out there.

 

If the engine is running good, how about a vacuum reading, because factory is going to be way above 15 to 19??? More radical less of a reading.

 

Runs good and has a nice lope at idle, thanks for the replies

Pete

 

Vacuum at idle will tell you. A very mild or stock cam will idle 15-20 inches at idle. I would bet a W31 cam will be closer to 10 inches at idle, they only had manual brakes from the factory.

 

Technically a W31 cam would be a "stock" cam. That is why you wouldn't know unless you pulled the cam.
Olds installed some pretty aggressive cams back then.

 

But it won't have 15 or up vacuum. 308 duration will be under 10 on the vacuum gauge.
Basically if your under 12 on the vacuum gauge in gear consider timing is way off or you have a cam with more than 280 duration.

 

My point was you wouldn't be able to tell a "stock" cam from an aftermarket one based solely on the vacuum reading.

 

If you know how to read a vacuum gauge you can.
Were not talking about a stock GM cam verses a Mellings stock replacement, we understand that but if you read the gauge and its under 12 you know its a larger cam than stock becuause we know a 72 Cutlass Supreme is not going to have a stock W31 cam in it so it must be an after market performance cam just from the sound and vacuum reading. Or at least I could tell it.

 

OK, let me put it another way.....I know how to read a vacuum gauge as well, but again, that was not my point.

It could have been a stock replacement cam for a W31, who knows. It could have even been re-purposed from a W31 that blew up but the cam survived. You can't tell unless you physically look at the camshaft.

I get that it wouldn't be stock for 1972, but it could still be a "stock" Oldsmobile camshaft. That is all I'm saying.

 

You are purposely swaying away from the obvious answer he is seeking.
He doesn't care who made it, yes we know by a gauge we can't tell if its a Crane cam or a Comp Cams from stock, jeeze really?
I'll type it 10000 times if need be, if you can't look at a vacuum gauge hooked to a 1972 Cutlass Supreme and see its under 12 and know it has a different spec cam than stock or listen and it has an obvious racket to it, then I believe you can't tell anything about an engine.

 

This will only tell you the vacuum level. Many, many aftermarket cams will produce similar vacuum levels. Plus, you don't know if low vacuum is caused by the cam, vacuum leak, or other mis-adjusted setting.

 

Good point on the vacuum leak. Yes, what exact cam can't be told by vacuum readings but anything over the generic 204/214 will produce less vacuum, even it produces slightly less. I know there are many factors but a W31 replacement cam will produce low vacuum as will other larger cams. How low depends on all the cam specs.