my motor looks to be making 9.9:1 static comp and aprox 8:1 dynamic comp. i dont know **** about dynamic comp and i hear this is even more important. who can fulfil me on if this is good or not? to me im depressed lol

 

The dynamic compression ratio is different from the static due to valve overlap. This is because some of the charge is pushed out of the cylinder on the compression stroke because the valves remain open during the beginning of the compression stroke. You will naturally have more overlap in a 305 deg. advertised cam then a 280, so the valves will stay open longer and more charge will be lost. This is the primary reason why low-end torque is greatly diminished when going to a longer cam, and why a higher CR is needed to compensate for it.

So, although your CR is about 10:1, you are losing a good amount of compression to valve overlap (which is perfectly normal in a performance naturally aspirated motor), but your dynamic CR is good for a street motor. The reason why dynamic CR is so important is because that is what effects what fuel octane is required and how much low-end torque you have, not the static CR. Sorry, but I don't what fuel octane you should use, but I hope I helped to explain it to you.

 

thanks i now see how it comes into play, but now the question still resides.. is 8:1 dynamic comp good for my street/strip engine? i know the static is higher then stock but because of overlap of a bigger cam i dunno if dynamic comp is higher or lower then stock.. maybe someone else will read this with a bit more info. thanks though!

 

What I would do is call the manufacturer of the cam you have, and ask them what static CR is recommended for your cam.

 

http://members.uia.net/pkelley2/DynamicCR.html

There's also one somewhere on the Keith Black site (KB-Silvolite.com I think it is)