Dynamic comp calculation help

[lc-gtr-1969]

Hi everyone,

I am just looking for some clarification around how I should calculate dynamic comp for my new cylinder head, as well as dynamic comps that people have successfully run on 93 MON/ 98 RON pump fuel...

Im running a cam with 305 degree advertised duration- the cam grinder for this cam measures advertised duration at .006. This gives me an intake valve closing at 74 degrees at .006 valve (closing) lift.

Using this valve closing measurement, I am coming up with give or take 8.8 dynamic comp.

So two questions...

1) Is it acceptable to use the relative 6 thou lift IV closing angle to calculate dynamic comp? I understand many cam grinders use varying ways to measure advertised duration, hence my question... my cam has a fairly steep ramp rate so it may not matter that much but nonetheless, I am interested to know... I imagine compression cannot technically start until the IV is on the seat, which makes me think the .006 measurement is not ideal..

2) What dynamic comp should I be aiming for with Aluminium head, closed/small kidney chambers with good quench area.. quench clearance about 40 thou... ? Engine will be run on race fuel (about 96/97 MON / 102 RON) when stressed (drag racing etc) but aiming for pump on street.

Any help much appreciated!!!

[Newold1]

Move this post over to Advanced Engine Tech section and you will get some good information and answers to your questions from some experts.

[lc-gtr-1969]

Ok thanks for that... Is it best that I re-post or can the moderators move it for me?

I dont know how to do it myself except for re-posting the question!

Cheers!