Hey all. I'm looking for a good, solid description why compression affects the recommended cam profile used. For example, people say "You shouldn't run JUN III's unless you're over 11:1 compression" or something along those lines. Does anyone have a technical description of why this is true? Thanks.

 

the dynamic compression ratio is affected by how big or small a cam is for example i dont know the exact spec on jun III but i know they run lots of duration so i would assume the valve closing at bottom dead center would be 50+ meaning that as the pistion is coming back up to compress the air some of it gets bled back up into the intake and you are loosing compression so to run a bigger cam like that you need to have enough static that you dont go down too low when you take that cams profile and also begin to toy with the cam gears but again if you have lower compression the cam gears can be your friend be cause you with them you can retard the intake cam and regain some of the lost compression by the massive cam sorry for the long post hope this helped

 

holy punctuation batman . . . .

But yeah, that's the gist of it - there's a good article on the subject over at http://www.team-integra.net.

 

That is one hell of a run on sentence.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Used2beAb16 &raquo;</TD></TR><TR><TD CLASS="quote">That is one hell of a run on sentence. </TD></TR></TABLE>

Good information though

EP

 

Thanks for the post.

 

And it's possible to go too high of a compression on some cams. You not only have to look at dynamic compression but also dynamic cranking pressure.

http://www.rbracing-rsr.com/comprAdvHD.htm

Here's a link to a dynamic compression calculator. First find your stock dynamic CR and cranking pressure. Once you start changing cams and you actually lose dynamic CR or cranking pressure, you are overcamming your engine. But once you start gaining more than 25% cranking pressure you are undercamming your engine. Although undercamming your engine is better than overcamming it, you still suffer from the high end. Aim for about a 20% increase. I still have ppl disagree with all the suggestions I give them and still feel all cams need a 12.5:1 static compression ratio.

 

no problem i was tired and just wanted to help lol sorry about the run ons oo here i go doing it again... lol