i know FI car people need low c.r. because the turbo/supercharger provides the compression or whatever.

but why do some people prefer high c.r.?

do you need high c.r. when you go all motor?

whats the highest c.r. for street gas (91)?

do you need high c.r. to run skunk2 camshafts stage 2?

 

If you have cams with long duration and more valve overlap you'll lose a little bit of compression in the cylinders, so to make up for that you usually need to bump up the CR a bit.

 

it's not so much of a preference as it is a...well, not so much of a requirement either. basically its recommended if you plan on really going all motor. bigger cams + higher compression to help compliment the cams

not necessarily, but if you get some nice sized cams, it's best to bump the compression as in7egrity explained above. this is where internal work comes to play.

god damn california sucks now. i wouldnt go past 11.5:1. 11:1 if you want to really play it safe.

in7egrity already explained this

 

Some more explanations

https://honda-tech.com/zerothread?id=184356

 

I'm kinda not seeing this being a viable theory for why high-profile cams like high compression.

Compression ratio's should only affect your late-compression and the first half of the combustion strokes...when the valves are completely closed. When the valves are closed, then the cams have nothing to do with what goes on in the combustion chamber. So, tell me again how cams and compression are related?

Also a high compression piston doesn't have anything to do with the CC filling process. It just sits at the bottom of the stroke, disturbing proper turbulence/swirl and taking up intake charge space (relative to a flat-top or dished piston).

Somebody give me something useful to read.

 

Good job

1. Drop the smart *** routine

2. Are you saying that cams and compression are in no way related?

3. Instead of criticizing in7egrity, post what this guy wants to know if you know so much.

4. I don't recall anyone stating that a higher compression aides in filling CCs.

5. Somebody give you something useful to read? When did you feel this statement was appropriate, much less needed? Baffling...

 

1.) I shoulda saw this coming. It's just my frustrations with people going with the general concensus rather than considering the alternatives which might or might not be true.

2.) Not in that part of the engine cycle. Prove it otherwise.

3.) I was in no way criticizing or attacking him. I was just calling into question the assumption that was made and providing a possibility of disproval. That's it. I wasn't sitting there typing thinking what a moron he was. You're making it into more than it is.

4.) I don't either.

5.) And, yes...that was my mistake.

 

 

cams have longer durations so when both valves are opened some compression is going to bleed off... u know........ duh!!!!!

 

But cams and compression are related, to some extent. With long duration the intake valve could still be open by the time the piston begins to rise up on the compression stroke and some air will escape back out, thus losing some compression in the cylinders when the valves are finally closed.

i'd like to say that is the theory i believe based on what i've learned about engine operation so far. If anybody else has something more useful i can read please post, i like to learn something new everyday too

 

I think what IN VTEC was trying to say was that valve overlap happens at the exhaust/intake stroke, not the compression stroke, which is what we're talking about right now.