Isky RPM 300 Adv Duration = 270, Duration @ 050 = 228, Lift = .448, Lobe sep = 112

Mummert Y270s Adv Duration = 272, Duration @ 050 = 224, Lift = .440, Lobe sep = 108

CompCam Adv Duration = 264in 268ex, Duration @ 050 = 234in 238ex., Lift = .528in .536ex, Lobe sep = 110

Whatever cam I run I would like to run it 2° advanced to keep the power curve on the lower rpm side. I already know that the CompCam will have to be run straight up because of piston/valve clearance. Opinions,

Thanks,   Dan

Do you know what the intake manifold vacuum is at idle with the car in drive? I am kind of curious. You are so right about too much cam and a Ford O Matic not playing well together. Pete

Dan.  Without knowing exactly where the camshaft is installed, the head combustion chamber cc or the distance the pistons are sitting in the hole, some assumptions must be made.  But beyond that, here are the numbers I used with the Isky 270° cam installed at 2° advanced.  Static compression ratio is 8.89:1 while dynamic compression ratio (DCR) is 7.04:1.

With the Mummert 272 cam installed at the same 2° advance, DCR increases to 7.20:1.

With the Comp Cam 264 (Int) cam installed at 2° advance, DCR increases again to 7.31:1.

In regards to piston to valve clearance, advancing the camshaft brings the intake valve closer to the piston while retarding the camshaft brings the exhaust valve closer to the piston.  Until you mock up the engine and do a physical check, you’ll not know where you stand on piston to valve clearances.  The amount the decks and heads are milled will be a player here.  But looking at the Comp Cam specs, it will tolerate a moderate amount of cam advance even with some heavy milling on decks and heads.

Thanks,  Dan

Dan.  Your valve to piston clearances don’t jive for the difference a 2° change in cam timing makes.  The general rule of thumb is 0.025” change in valve to piston clearance with each 4° change in cam timing.  Are you checking the V/P clearance with head gaskets in place and with valve lash or no head gaskets and zero lash?  Might be worth rechecking your V/P clearances.

But beyond all that, then the next choice in camshafts would be the Mummert 272 mainly for its 108° lobe centerline which works with a majority of the street driven Y exhaust systems.  And don’t limit yourself to just 2° advance as you may be happier with 4-5° advance and especially if the timing chain set is new.

Bill, what intake & carb are you running with this? How much vacuum is it pulling? Flat top pistons?

Thanks

If this is a Rollmaster timing set, then each key position on the lower gear may be labeled appropriately while the outer row of teeth are only marked with a single dot that matches up with the zero keyway slot.   If you’re using the single dot on the outer row of teeth for both cam timing checks, then you’re likely about two teeth off when you have the crank key in the 2° ADV position on the crank gear.  Each key way movement on the lower gear corresponds to at least a two tooth movement on the outer row.  Checking the intake lobe centerline each time the crank gear is repositioned will validate if you are indeed moving the camshaft as desired.  If you indeed are double checking the cam position either by the opening/closing specs or by the intake lobe centerline method, then never mind.

But back to the camshafts.  The Mummert 270 camshaft at 4° advance will have a higher DCR than the Comp Cam 264(Int) installed straight up (0° advance).  That essentially means the cranking compression on the Mummert cam will be higher than the Comp stick which translates to increased lowend torque with the Mummert cam.  Here are the numbers from the spread sheet I use.

                     Comp Cam Specs                                                                                      Mummert 270 cam specs

Bill, Im a big fan of the Ford 4100. I was going to run one on this until I ran across a "price is right" Holley 600 CFM w/ a manual choke on it. I guess if it doesnt work out I can go to the 4100. Are you running a manual or automatic?

Dan.  Are you taking degree wheel readings on each side of the max lobe lift and averaging the values?   If trying to simply center up on the top of the lobe, there will be a significant amount of error involved besides not being repeatable.  It’s normal to take readings 0.050” before and after the max lobe lift and then take the average of the two numbers for a lobe centerline measurement.