V-Tec and DOHC

[civickiller]

your the one who told me to go choke myself, and to learn reading comprehension when you could so just said opps thats not what i meant, and could of just changed it easy. but you had to go off on it.

[unusualcivic]

civickiller, shut the fuck up dude, you're arguing an utterly moot point. it's dead, move on.

at any rate the question was answered long ago, VTEC does NOT have any problem with boost.

[duplox]

Originally Posted by Privatebigandrew

OK...let me put an end to this. Forced induction does not like valve overlap. Look at it this way. Compressed air is being forced into the cylinder with the intake valve open. All of a sudden the exaust valve opens while the intake vale is open too. A lot of that compressed air is going to go aout the exhaust valves due to the low pressure on the exhust side from the turbo sucking out the air. Also that air that is in the cylinder is going to want to go out the exhaust chamber even more due to the pressure from boost on the intake side. Now, contrary, a little bit of overlap (such as with VTEC) isn't going to hurt anything. it actually helps spool up the turbo faster by forcing the air out into the exhaust manifold, therby spooling up the turbo. But if you have too much overlap, too much air goes out the exhaust and boost is wasted. The ideal turbo cams would have high lift and short duration.

You are mistaken. The turbo does not "suck" air out of the exhaust. If it did, it'd be a mythical perpetual motion machine, since it is both performing work by creating vacuum and creating pressure with no outside power. If it did suck exhaust out, no one would ever buy a supercharger, because they would be FAR inferior to a turbo. Quite the opposite is the case - the turbine wheel on a turbo is a restriction in the exhaust, so there is pressure - not vacuum - in the exhaust pipes. This pressure is normally higher than the boost pressure the turbo creates, unless you have a very large exhaust turbine on your turbo, in which case you have a lot of lag! This is the reason why turbos like small overlap - the exhaust pressure is higher than the intake pressure, so if both valves are open, the exhaust is going to push into the cylinder and prevent the intake from coming in. Obviously this means less area for the intake charge to take up after the exhaust valve closes. The earlier the exhaust valve closes, the less exhaust is going to enter the chamber.
The concept of VTEC itself is not a bad thing for turbos. Just like any other stock n/a motor, its simply not cammed for best turbo power. A turbo will work fine on a vtec motor, but it'd make more power with new cams. I bet you could get better turbo performance if you increase your LSA. LSA(lobe seperation angle) is the distance(in degrees) between the peak lift of the exhaust valve and peak lift of the intake. If the LSA is increased, that means the exhaust closes earlier and intake opens later, effectively reducing overlap. Unless you know what you're doing and know how to return the cams to their original positions, don't attempt it.

Oh and by the way, if you put smaller lift/duration cams in the motor, your low end power will increase, high end power will go down.. but if you're turbocharged, that doesnt matter, the turbo will make up for the low lift.

[jcrx]

If the LSA is increased, that means the exhaust closes earlier and intake opens later, effectively reducing overlap.

Or you could just get adjustable cam gears.

[Privatebigandrew]

i must have got some bad info from somewhere....thanks for clearing it up. we kinda had the same concept going on. But, superchargers are inferior to turbo's when it comes to efficiency.

[duplox]

Originally Posted by jcrx

Or you could just get adjustable cam gears.

I assume adjustable cam gears let you adjust the timing of each cam, which is exactly what I was implying