clickwir

as I hear it, VTEC was originally designed for fuel economy.... one of the byproducts of it was more power also. More efficent engine = less gas and more power.

Kinda like how Teflon was discovered... by accident. They were trying to accomplish something else and ended up with more than they thought they would. A good thing.

So yes, VTEC does add more power... but it's original idea and design was just to make the engine more fuel efficent at higher RPMs.

But that's just what I heard... I have no proof. h:

Why is boost in VTEC bad? Or not as good as when not in VTEC?

ludeboom

VTEC is bad for boost because the extra valve lift affects the intake charge pressure or something, some1 explained it in detail a while back.
~boom

DelSolSIinMD

You mean "losing .1 litres." If it was 1 whole litre, we'd be talking about the H12

THATPRELUDEGUY

Bad for boost with factory cams, with custom cams you're talking a whole new world.

drift

look at the lobe specs, grasshopper.

the H23's lobes have less duration and lift than the H22's VTEC lobes... therefore the H22 is capable of breathing at higher rpm's. if it can breathe efficiently at higher rpm, then more power can be achieved purely by increased rpm while maintaining torque. hp = tq x rpm / 5252

the H23 has smaller lobes to give the H23 better low end response, less engine vibration due to no idle lope, and better fuel economy

again, VTEC is for fuel economy and low end engine response... not for high end power. if these werent valid reasons, then VTEC wouldnt have even been created as the need for a smaller lobe at low rpm wouldn't be there.

drift

if more lift is bad, then drag racers would be screwed.

VTEC systems lose a bit of oil thru the head due to insufficient sealing of the valve seals. this problem happens when VTEC engages... VTEC motors burn more oil than comparable motors.

more lift is always a good thing if you have a valvetrain that can take the abuse.

the problem is duration. VTEC increases lift AND duration... and extended duration means extended overlap. more overlap causes "boost-thru", as the boost charge is pushed into the head and blown right out the exhaust valves. proper cam timing or properly designed cams can resolve this issue, and in many cases, recovers up to 30hp in well tuned motors.

if lift were the problem, then ANY high lift cam would be bad for a boosted motor, which is not the case.

drift

no. more efficient at LOW rpms.

has anyone here ever heard a 350 with a lumpy cam in it before? it spits raw fuel out the pipe and idles like it's running a horseshoe shaped crank.

at cruising, the small lobes on a VTEC cam provide for better fuel economy... no need for a big, thick lobe to feed lots of air and fuel into the cylinder when you're cruising or putting around town under 50mph.

but with that smallish lobe, your fuel economy is great, birds are singing, the sun beans down and smiles upon the earth... until you want to get on the highway.

so, instead of increasing displacement (being fuel inefficent), why not make the motor rev higher? well, you need a cam that can breathe at high rpm... and that small cam wont cut it. so why not have a switching system? you get your low-rpm efficiency, while you get more power for the times you need it. plus, you dont have to put up with feeling like driving a GM product with a 350 and a lumpy cam.

by knowing the formula for horsepower, it's easy to see why Honda went this route, with fuel economy in mind, but having a bit more power on tap when needed.