Hitting the exact Compression Ratio Options

[malcolm2]

I am to the point on my rebuild that I need to make a decision. (IMG:style_emoticons/default/confused24.gif)

I am sure that this type of discussion can become very technical and fill volumes of books. I am not asking for that.

I am the kind of person that wants to know "why" a certain cam needs a certain CR. In order to make the best decision, I need answers. Or if it is a huge secret, that is fine too. I can go blindly along with the crowd.

Maybe it's really what. Has anyone experienced What an engine will do, or what will I see or feel if my cam mfg recommends 8.0:1 CR and my normal state (no shims) is 8.35:1 CR? To get to just about 8, I have calculated that I need about 2mm of deck height. I am currently sitting at 1.62mm average DH with a variance between cylinders of 0.15mm. So I need two 0.4mm shims and two 0.5mm shims and I will be dead nuts on 8:1. (IMG:style_emoticons/default/stirthepot.gif)

So the mfgr's value can be reached (if I can round up the shims), but I am curious to know how differently the engine will function if I go shim-less or even only get half way, maybe 8.2:1. (IMG:style_emoticons/default/WTF.gif)

[Jake Raby]

It is common to achieve different true deck heights on opposite sides of the engine. It is generally a .005-.007 differential from the 1-2 bank to the 3-4 bank with 3-4 always being tighter.

The cam that he is running was developed and tested with a maximum and minimum compression ratio. It doesn't mean that he is being forced to run this CR. It simply means that the stories about how awesome this cam has worked for others that he may have read might not be applicable to him.

(people wonder why I stopped recommending anything to anyone under any circumstance)

[malcolm2]

It is common to achieve different true deck heights on opposite sides of the engine. It is generally a .005-.007 differential from the 1-2 bank to the 3-4 bank with 3-4 always being tighter.

The cam that he is running was developed and tested with a maximum and minimum compression ratio. It doesn't mean that he is being forced to run this CR. It simply means that the stories about how awesome this cam has worked for others that he may have read might not be applicable to him.

(people wonder why I stopped recommending anything to anyone under any circumstance)

Not running yet, still building. Truthfully, I have heard no stories, you and I had a phone conversation, and I went with it. There is that expectation of greatness. Shouldn't there be? I am simply inquiring, curious and respectful of the opinions of folks that have the experience.

Thanks for the tidbit of knowledge above. Validates my findings.