there's a good write-up on this overlap thingy, cam duration and also cam lift.
EK9.org: VTEC Camshafts Specs / Comparison for Honda B series Engines
this site talks bout the b-series specs, with overlap value but no valve centre no
Specs for B series Honda Engines
and lastly this site also bout the same info on cam, no overlap info but with degrees of cam open and close
B-Series Motor Specs
shiroitenshi, do update on us from all that i can get on the net.
from my observation, b16b have extra overlap on the intake due to earlier valve open angle before TDC.... does that play much part for its power?
besides, how if a person with b18cr to use b16b intake cam, will that make the b18cr generate more power??
Hey, finally someone into the tech aspect as well.
I think if you read through all that, you have understand it roughly like me.
The thing about cams are that they can help control the static compression ratio.
Remember the intake valve closing at XX degrees ATDC?
Our static compression test gives us compression values that are larger, because they consider the intake and exhaust valves are closed during the compression stroke.
In real life, this is not the case, and as you notice, like 20 degrees ATDC the intake valve closes, your 11:1 compression has been reduced by 20degs/180deg = 11.1%, which means the 11comp - 11.1% = (11 - 1.221) = 9.779.
However, the actual volume of air going in the engine is dependent on the flow rate/speed which at the moment, is anyone's guess. Futhermore, as one of your link noted, the speed which the valves open (the lobe ramp angle) determines this also. So in other words, would 9.779 comp ratio cause knocking? it's probably dependent on engine speed, and of course the ignition timing I think, but well... that's anyone's guess, as most people don't keep track of why their engine makes power, or why it doesn't.
So if you ask whether plonking in B16B cams in a B18CR would give different performance, I think it may or may not, and there's no definite answer because you can play with the actual opening and closing timing (within tolerances, before vavle meets valve on overlap, which is why the cam spec specifices the lobe seperation angle or sometimes the mid lobe angle, at the point where there is maximum clearance).
You can tweak it a little by 2-4 degs, I think, depending on how aggressive the cams are.
A high ramp rate usually gives better performance for high comp engines, I'm sure you noticed it when you look at toda, spoon, etc, performance cams where the cam lobes are nowhere teardrop shaped like stock cams. It gives higher rocker arm wear (at the cam follower part), so that's why they don't make it too aggressive, just slightly more than stock, and which is also why they want valvesprings that are hard so that the valves won't float.
One set of cams I saw get around this by making the lift higher. like really high.. either 13.9 or 14mm of lift.
But still, much to learn about cams.
The summary of what I've learned so far comes to the following. (this is my opinion, they could be wrong, so consider that I'm just sharing what I'm thinking.
1) high rpm power need high compression,
2)high compression needs high duration cams to manage the compression at low and mid rpm.
As to exactly why.. hmm.. that one I'm not sure at all.
I need to study the how the air is going in the engine at low/mid/rpm and see how they differ to find out.
Currently, I know how to go about it, by using the Auxbox, but I need to take out the IAT and measure it at 3 different temps for calibration purposes,
The Map sensor too, and therein the problem lies. I don't have time at the moment to do so.
