Mike

I used the calculator you linked to and I did not come close to what you posted either the first or second time. I think your cam specs are not accurate as a cam you describe as mild should not bleed off as much compression as shown. Something ain`t right. Pete

 

It just occured to me that the calculator does not compensate for solid lifters vs hydraulic lifters. Edit

Pete, what did you come up with?  I used stroke 3.44, bore 3.86, intake closing 54, alt. 1330, static cr 9.8.  You are surely right about lash not being accounted for, but how would an adjustment be made.  Lash for the cam is .020.

Mike, located in the Siskiyou mountains, Southern, OR 292 powered 1946 Ford 1/2 ton, '62 Mercury Meteor, '55 Country Squire (parting out), '64 Falcon, '54 Ford 600 tractor.

Mike

You should ask your cam maker. He is the expert. Pete

Mike, take off 10 points at .050 ( half of your lash ) because the y-blocks are solid lifter engines and that should be closer to what your cam is. For a solid cam to be equal with a hyd cam you need to add approx 10 points at .050 or at least half of the lash anyway. Comp and crane talked about this, that why I've mentioned this in the past when selecting a cam. Example a stock engine needing a 224 at .050 hyd with a stock converter,  move up to a 233 or 234 at .050 for a solid lifter engine with the same performance.

-Gary Burnette-

Thanks Gary and Pete.  I need to call the grinder tomorrow anyway, and will discuss this.  Gary, then it sounds like this cam is a clone of the Isky E-4, using your adjustment advice.  So I do have real world experience with one of them, and according to that a static CR in the range of 9.3-9.5 would be about it.

Mike, located in the Siskiyou mountains, Southern, OR 292 powered 1946 Ford 1/2 ton, '62 Mercury Meteor, '55 Country Squire (parting out), '64 Falcon, '54 Ford 600 tractor.

Mike.  A little bit of math shows that the 58°ABDC value you state is a good intake closing value for the 260° camshaft when installed straight up (108° intake lobe centerline).  This is assuming that the cam manufacturer is using the standard 0.020” measurement for the advertised duration measurement as is typically done for solid lifter cams.  Hydraulic camshafts will typically use 0.006” as the value for calculating the advertised duration.  Using your values I do get the same 9.7:1 static compression ratio (SCR) and an 8.1 dynamic compression ratio (DCR).

 

If advancing the camshaft 4°, here’s what the DCR looks like using the same combination that targets a 9.7:1 SCR.

 

I’ll add that my calculations for DCR do not involve using an altitude value.  Because the cranking speed among other variables influences the actual cranking compression, I use the DCR value rather than the calculated cranking compression value as a more accurate determination of what octane fuel should be used.  Here’s the chart I use for octane rating versus DCR.  Keep in mind that these are for the octane ratings stated on the pump and are not MON or RON octane rating specific.  There’s a safety cushion built into the chart due to the variability found in pump gasoline.

 

Lorena, Texas (South of Waco)

Thanks a lot Ted!  I may have found a little glitch today, however.  I used a 292 block, installed the cam, a 292 crank, one head and #1 intake valve today and put on a degree wheel plus dial indicator.  Dont have a piston for TDC because they are having pins sized.  At .006 off the seat the intake duration is 258 degrees.  At .5 in. off the seat it is 267 degrees, checked with .020 lash and 1.54 rocker.  The lift at the valve was .420, which was expected due to lash.  So will this throw off the calc?

I am going to print off that graph and tack it up.  The target is 8.2-8.25 DCR, at least for now.  Have reread on the topic and quench is a biggy.  Hoping to get a zero deck for quench of .043 to help keep away unwanted explosions.

Edit:  This is worrisome.  I looked at the "mechanical cam specs"  sheet that I ordered from.  Right there it says duration at .020 260 degrees, duration at .050 225 degrees.  Tomorrow will check duration at .050 and .020 to see what is going on.  But if it is only 258 at .006, that doesnt sound right. 

Mike, located in the Siskiyou mountains, Southern, OR 292 powered 1946 Ford 1/2 ton, '62 Mercury Meteor, '55 Country Squire (parting out), '64 Falcon, '54 Ford 600 tractor.

Mike.  Did you check to insure that the camshaft is degreed in?  Be sure to also check the #6 cylinder and to be on the safe side, also check the exhaust lobe centerlines.

 

The chart I’m using is specific for measurements at the camshaft and not at the valve.  But because the chart is biased in this regard, I don’t worry about the actual lift at the valve.  If I was to actually take into account what’s happening at the valve itself and if using the 0.020” value at the ramp of the camshaft, then valve lift at the valve with 0.020” lash and 1.5:1 rockers will be 0.010” instead of 0.000”.  That means the actual intake closing event would be later by whatever number of degrees that 0.010” takes to close up.

 

But to give you something to think about, here’s a set of values from a custom Isky camshaft using various potential lash settings in which to determine the intake valve closing events at the cam lobe.

 

As far as quench goes, I don’t consider it a problem until it’s over 0.065”.  That means the piston can be as much as 0.020” in the hole with a 0.045” thick head gasket before needing serious consideration.  The distance that the top ring is down from the top of the piston should really get more consideration but typically doesn’t.  Do the math on the diameter at the top of the piston and how far down the top ring resides and see what kind of volumes start popping up.  These volumes can be a serious detriment during the actual fuel expansion process.

Lorena, Texas (South of Waco)

Thanks again for all the information.  I have more to do obviously.  I'll go in and get a piston first so I can degree the cam.  Then get some readings at the lifter and valve.  For todays figures I just put the degree wheel to zero degrees at zero valve lift zero lash, and then reset it to zero with .006 valve lift and zero lash.  Read out the duration for both trials, with multiple tests for each trial.  Didnt think I could do much more without TDC established.  

Mike, located in the Siskiyou mountains, Southern, OR 292 powered 1946 Ford 1/2 ton, '62 Mercury Meteor, '55 Country Squire (parting out), '64 Falcon, '54 Ford 600 tractor.

Ted

Thank you for more great information. Can you confirm that you octane vs dynamic compression ratio is based on a fixed amount of mechanical distributor advance timing? If so, what are you using, 38degrees or something else.

The reason I ask is my first car was a Model A Ford that had the spark advance/retard on the steering wheel. So that technology is out there as are knock sensors to automatically retard or limit spark advance. Do you think they are worth looking into? For a street driven car not a dragstrip car.

Thanks again. Pete