Well we started putting together my son's 331 today. I decided to cc the swept volume of the cylinder to figure the actual compression ratio.

swept cylinder volume -5cc valve reliefs: 687cc
combustion chamber volume 61cc
valve reliefs 5cc
head gasket .045 9.3cc

deck height is zero-piston tops are flush with the deck surface at tdc

762.3/75.3=10.1-1 static compression


Then we degreed in the cam and found the actual intake valve closing point- .018 valve lash divided by 1.5 rocker ratio equals .012 of lifter rise when the valve hits the seat. The swept cylinder volume at the intake closing point was measured at 537cc.

612.3cc/75.3= 8.13-1 Dynamic compression


this is with a XS268S comp cam missing about .007 lift off the nose from wear. and also 2 degrees less duration at .050 from wear

What do you guys think? Does the math look right? Would you consider running a used solid cam missing .007lobe lift from wear or should I buy a new one? I've got new lifters. Desktop Dyno says 410HP?

hey Bob...If you think he cam is too worn..ill buy it back. Im not sure how much you lose when you break in the cam. I broke it in with EOS and single springs..im not even sure how accurate comps specs were..either way, let me know how it goes

Bob,
I come up with 679.5 for swept volume.
4.03 x 3.25 correct?
The actual compression is 9.9 if your head gasket is .045 x 4.166
This includes the area above the rings which I estimated at being down .200 & a piston crown of 4.010 which is about what it should be hot.
What head gasket are you running? Most are .039-.041 compressed & 4.100-4.166 in dia.

To the cam. If it is actually worn that much I would not even consider running it.
Are you sure it is worn that much? If so the top of the lobe will show definite wear & will be shiny across it's full surface rather than dark at one edge.
How are you measuring this wear?

Hey Mike, Thanks for the info. The head gaskets I used for measurement are the cheap ROL set that came with the gasket set. They measured at .051 so I figured about .045 compressed? I might get some felpros around .038 to put in. Yes the bore is 4.030 with a 3.25 stroke, I didn't consider the area around the piston and directly above the top ring--I had grease sealing that area when I measured it :D I never considered the crown of the piston when hot either. I checked the piston to deck clearance and it was at 0 + or - .001 when I rocked the piston. Then I brought the piston down to BDC and greased the perimeter, put plexiglass over the top of the hole and filled it. It measured 692cc's and then I subtracted the 5cc's for the two valve notches for a total swept of 687. I was wondering after Desktop dyno also showed a figure close to yours but I measured this three times with all being within 2cc's :confused:
9.9 or 10.1 both are ok with me considering this is just a 327 with flattops, I was crossing my fingers hoping for at least 9.5-1 smile.gif
The cam is shiny across the nose of the lobes and I do see pitting on two but thought overall it looked to have quite a bit of life left in it. I checked the lobe lift with a dial indicator and was alittle surprised. I guess I'll probably get another one, I was hoping to use this considering it looked to have survived its first break-in.
BigJimzlll, The cam looked fine I thought when I got it, it was just today that I took the time to measure it and give it a good eyeball. I didn't expect a warranty. smile.gif

Bob,
The volume at the rings is not a big deal as you are only talking about 2 tenths of a point in compression ;)
you are right on the ROL gaskets, they are thicker.
They will only compress a couple of thou at most so you can figure .050
I would get some FelPro 1043's.
They are 4.080 & .039 thick. Check to be sure they don't hang into your chamber, they don't work on some combustion chambers around the intake valve relief.
The 1003 is 4.166 & will fit. They are .041.
Both will give you better quench.

Looks to me like your calcualtions all show a decent match; but IMHO your cam is too wiped to put back into a new build. Should be a good cam choice for the application though. Just get a new one of the same part #.