[Caligirl]

I'm trying to find out the specs on a cam. I've been told its GM based on the stamp and a purple
paint mark (?) A local auto shop
machinist mic'd it at a 501 lift but was unable to inform me of anything else. the numbers (part # ?) stamped on the cam are of no help as they are either outdated or obsolete. It is a part of a rebuild to my 396 375hp 69 SS. The restoration is 10 yrs in the making and in the final stages. The friend who did the the engine (which of course was the first step so many years ago

]has since passed away and along with him went all the details. here are the numbers stamped on the cam H091 910539 (I've seen GM performance cams with similar part #'s ie H---) Any help would
be apreciated.

 

[pdq67]

Is the cam a solid or hydraulic lifter cam? GM made one stock solid for the 375hp/396 engine and when it's lashed was right at .500" lift. It was used in several bigger engines.

And they also made a couple of hydraulic grinds right at .500" lift. The '65 Chevelle Z-16, 396 hi-po engine that is as rare as hen's teeth and at least one, maybe two others, a street and a marine grind!

I think Ed Staffel's book lists a bunch of Chevy grinds but I can't lay my hands on my copy right now due to moving! I bet it's in that list!!

Anybody want to look ?? Not much help... Good luck, pdq67

 

[nate]

he measured it at .501 inch lift ,huh. the only thing you can get from a michrometer is the diameter of your base circle. you then subtract that from the total height of a lobe from heel to top and that gives you lobe lift. lobe lift can be translated into actual valve lift if you multiply it by the rocker arm ratio. so lets say for example, it is .33 inch lobe lift. times that by a 1.5 rocker arm ratio for example(they make different rocker ratios) for a total of .495 inch total valve lift. so if it is a for sure .501 lift, then if you times it by a basic 1.5 inch rocker, it is .7515 of valve lift! if the guy has done all of this math, then the cam is obviously for a big block. if he told you it is .501 inch VALVE lift, then he had already done this math and assumed that it was a 1.5 inch rocker. ask him again how he came up with the .501 inch lift.

 

[Timberwolf]

Aren't most big blocks 1.7 rocker ratio? .501 lobe would make for a HUGE valve lift... .8517!!
And if it's assumed .501 valve lift, that would make the lobes down to .2947


<BLOCKQUOTE>quote:</font><HR>Originally posted by nate:
he measured it at .501 inch lift ,huh. the only thing you can get from a michrometer is the diameter of your base circle. you then subtract that from the total height of a lobe from heel to top and that gives you lobe lift. lobe lift can be translated into actual valve lift if you multiply it by the rocker arm ratio. so lets say for example, it is .33 inch lobe lift. times that by a 1.5 rocker arm ratio for example(they make different rocker ratios) for a total of .495 inch total valve lift. so if it is a for sure .501 lift, then if you times it by a basic 1.5 inch rocker, it is .7515 of valve lift! if the guy has done all of this math, then the cam is obviously for a big block. if he told you it is .501 inch VALVE lift, then he had already done this math and assumed that it was a 1.5 inch rocker. ask him again how he came up with the .501 inch lift.<HR></BLOCKQUOTE>

 

[stingr69]

The BB ratio is ~1.7 factory.

More to the point, You will not get the actual lobe lift if you mic the lobe and subtract the base circle. The lobe has a slight taper (back to front when installed in the engine if that makes sense) that is difficult to see with the naked eye. In addition, actual lift measurement will require a crowned bottom follower as it also has an effect on net lobe lift. I have been down this road before. They mic different from what you will get when installed.

Colvin's book has identifiers for camshaft part numbers and casting numbers but I do not have it in front of me right now. Maybe I can post later if someone else has not already I.D.'d it.

-Mark.

 

[Eric68]

Yeah, I think your best bet is going to be right here if someone can look up that obsolete PN and go that route. Too many variables on measuring cam lobes.

You might also try talking to a GM dealer parts department - maybe one that is real friendly to resto cars and hot rods might be able to come up with an old price list, or even a replacement PN in the computer.

 

[stingr69]

The original castings had "OMO" and 3863144 cast into them. The part number was #3863143. You may have an aftermarket replacement for the GM piece. Maybe someone will recognize the numbers. I would probably mock it up and degree the thing to see if it has the same specs as stock. If not, replace it with the correct 396/375 one. Federal Mogul(first choice)probably sells a good copy. Crane cams sells a copy for around $90 or so from PAW.

-Mark.

 

[kamero68]

We check cams for customers all the time at my shop. It is difficult to get an acurate measurement with a mic. We use a set of V blocks and dial indicator and simply take a direct reading of the lobe lift by zeroing the indicator on the base circle and rotating the cam on the blocks. If it peeks at .350, then you have .350 lobe lift. Multiply that by the rocker ratio, then you have the actual valve lift. You can check duration with a degee wheel, but you have to mock up an engine to do it.
we check evey cam we install and have found several over the years that were not what they where supposed to be. Rare, but it happens.

 

[Caligirl]

Thanks for all the help guys! I think I'm gonna go with a Comp Cam thats specs are almost identical to that what "should" have been put in with the rebuild. At least then I'll know for sure what the specs are. once again thank you all for helping out.