Don't understand cams
Thanks again RRR for the links.........but as alway, reading and learning, cause desire for even more understanding.
Ok here is my question. It has to do with overlap. I had this all figured out long ago but, NO.
My 340 had a MPP cam .474/280* cam with a 60* of overlap. My new cam to match my new 408 motor has a Hyd Roller Cam that is much larger.562/.550 lift 243/247 duration @.050". Gross(@.006") duration of 294/297)
So this cam by Comp, does not have a Overlap spec but by using the cam card i see that the intake close and exhaust open spec's it can be figured out. or so i though...........
so Intake opens at 19* btdc and exh close at 13 atdc. so my math says that i only have 32* of overlap. Now these ## are a @.050"
I realise that i'm comparing apples to oranges here but, that is only half of the overlap, of my smaller cam.
Now i'm sure that they differ because of the gross and @.050" But over 30+ degrees.....less???
I don't get it.
Overlap = the two durations averaged and subtract double the LDA
You didn't give the LDA but if I assume 106*, the formula looks like this;
(294 + 297)/2 less (106 x 2)= 295.5 less 212 = 83.5
If the LDA was a 110* it would look like this;
(294 + 297)/2 less (110 x 2) = 295.5 less 220 =75.5
If the LDA was 114* it would look like this;
(294 + 297)/2 less (114 x 2) = 295.5 less 228 =67.5
These are quite different cams with very different idles, for sure.And the ICAs are 4* apart depending on install,therefore different compression requirements for street use, and probably will want different TCs and maybe gears.
To make an 8.0Dcr and about 162psi,in a 408, the Static CRs would need to be 11.5,11.1,10.7, or about .4 point change in SCR for each change in listed LDAs.
EDIT; ICA is Intake Closing Angle, LDA is Lobe Displacement Angle,Dcr is Dynamic compression ratio, Scr is Static compression ratio
