Check my work-Chime in please
They made all this work in 1967. Was it because the fuel was better quality than it is today? This build is not that complicated and not that far from the original 235 HP original commando release so I am having a hard time understanding all the concern. Not criticising, just want to learn a little something here!
Hey DR, this was in response to your previous post of just sticking a bigger cam in it.
Yes they used to have higher octane gas available at the pump. But our concern at this time in history, is to be sure the effective Dynamic Compression Ratio (Dcr) does not get too high for todays gasoline. Part of this Dcr is determined by the closing point of the intake valve. By empirical data it has been determined that at sea level the Dcr needs to remain below a certain value to prevent detonation. This value is not written in stone and varies with many factors. But generally needs to remain below about 8.2 +/-.2. Further if the Dcr gets to be to low the giddy-up factor goes soft. With a small displacement engine, therefore,the Dcr needs to be particularly carefully chosen to have both a strong off-the-line-performance yet to stay out of detonation.
Now, I'm pretty sure you know most or all of this. But what you may not know is that just throwing a longer duration cam into it, does not automatically preclude a later opening intake valve.
Here are some examples of imaginary cams that all have the exact same ICA of 56*.
Cam #1 is 252*, on a 114LDA, installed at 110, ICA of 56*
Cam #2 is 258*, on a 110LDA, installed at 107, ICA of 56*
Cam #3 is 264*, on a 106LDA, installed at 104, ICA of 56*
All the cams are fictitious, and are for illustration only. Notice each cam is about one size bigger on the intake duration. Notice also that the LDAs are decreasing, as are the installed centerlines. YET all have the same 56* ICA .
Point being; your statement "Looks like I could buy a thicker head gasket or a cam with a little more duration" sounds good, but it's not quite right.
What you really might need is; to buy a thicker headgasket or a cam with a little LATER CLOSING INTAKE.
So that is where I came in with "be vewey, vewey, kewful.
I hope that clears it up. My wife tells me all the time how senseless my humor is, so I apologize for my senseless humor, and once again, I'll try to keep it in check.