Prince Valiant
08-07-2004, 10:49 PM
Okay, okay...I know the title looks like a lark. And to some extent it is, as I am not actually installing VTEC (R) but I am using the same principles as VTEC.
Now, one may be thinking how does one do this? It's not hard really, and doesn't center on installing a multi-lobe camshaft either. Just replace a part that you've already got with a re-engineered part and there you go.
The key is the lifter...more accurately, the hydraulic lifter.
So how does a hydrualic lifter, that's main purpose is to constantly adjust the lash of the valvetrain work as VTEC?
It's simple really...hydraulic lifters can "bleed" down of course, and in the case of the Rhoads varible lifters, they just are designed to bleed down faster than other hydraulic lifters.
Since the bleed down rate is a function of TIME mostly, and oil pressure secondarily, this works well on big cammed cars, why? As the RPM's goes up, oil pressure goes up (again, this only has a small effect on the bleed down rate) and the time that the lifter has to bleed down also goes down significantly.
See, the only time a lifter really has to bleed down is while it's on the base circle, and for a short while as the initial lifting event occurs...once the lifter moves into the lifter bore, the oil has no place to bleed out into so the lifter plunger (that holds the pushrods and pushes it upward) no longer continues to depress, and therefore becomes like a solid lifter with zero lash in the valvetrain.
Once the lifter slides out of the bore again, the plunger is moving up, oil is drawn in and then as the lifter again gets pushed up, the bleed down process starts anew.
The reason these lifters are different than others is that they are designed with groves within the lifter to accelerate the bleed down process...other lifters are designed to ressist.
How big an effect does this have? Well, one test showed the following with Rhoads variable lifters, the crane version that is made only by using a smaller inner plunger, and a standard lifter: Brand (Rhoads, Crane, Standard) followed by (Duration/Lift)
At Idle R(260/.425") C(268/.445") S(270/.450")
At 2000 rpm R(265/.435") C(269/.447") S(270/.450")
At 3500 rpm R(270/.450") C(270/.450") S(270/.450")
Vacuum with a slight load
at 1000 rpm R:11.0" hg C:9.0" hg S:8.5" hg
So once the rpms reach 3500rpm the lifter doesn't have the time to bleed down and one doesn't lose any power potential vs the standard lifter.
This of course will result in better low rpm idle characteristics and better low rpm power...not only from the better low rpm air flow characteristics, but from increased cylinder pressures afforded by the "smaller" cam.
Of course, the process is similar to any lifter installation and is quite easy....but my car will welcome the cam that is 10 degrees smaller at idle with less lift...so VTEC in a 28 year old motor. That's how it's done (cont'd)
Now, one may be thinking how does one do this? It's not hard really, and doesn't center on installing a multi-lobe camshaft either. Just replace a part that you've already got with a re-engineered part and there you go.
The key is the lifter...more accurately, the hydraulic lifter.
So how does a hydrualic lifter, that's main purpose is to constantly adjust the lash of the valvetrain work as VTEC?
It's simple really...hydraulic lifters can "bleed" down of course, and in the case of the Rhoads varible lifters, they just are designed to bleed down faster than other hydraulic lifters.
Since the bleed down rate is a function of TIME mostly, and oil pressure secondarily, this works well on big cammed cars, why? As the RPM's goes up, oil pressure goes up (again, this only has a small effect on the bleed down rate) and the time that the lifter has to bleed down also goes down significantly.
See, the only time a lifter really has to bleed down is while it's on the base circle, and for a short while as the initial lifting event occurs...once the lifter moves into the lifter bore, the oil has no place to bleed out into so the lifter plunger (that holds the pushrods and pushes it upward) no longer continues to depress, and therefore becomes like a solid lifter with zero lash in the valvetrain.
Once the lifter slides out of the bore again, the plunger is moving up, oil is drawn in and then as the lifter again gets pushed up, the bleed down process starts anew.
The reason these lifters are different than others is that they are designed with groves within the lifter to accelerate the bleed down process...other lifters are designed to ressist.
How big an effect does this have? Well, one test showed the following with Rhoads variable lifters, the crane version that is made only by using a smaller inner plunger, and a standard lifter: Brand (Rhoads, Crane, Standard) followed by (Duration/Lift)
At Idle R(260/.425") C(268/.445") S(270/.450")
At 2000 rpm R(265/.435") C(269/.447") S(270/.450")
At 3500 rpm R(270/.450") C(270/.450") S(270/.450")
Vacuum with a slight load
at 1000 rpm R:11.0" hg C:9.0" hg S:8.5" hg
So once the rpms reach 3500rpm the lifter doesn't have the time to bleed down and one doesn't lose any power potential vs the standard lifter.
This of course will result in better low rpm idle characteristics and better low rpm power...not only from the better low rpm air flow characteristics, but from increased cylinder pressures afforded by the "smaller" cam.
Of course, the process is similar to any lifter installation and is quite easy....but my car will welcome the cam that is 10 degrees smaller at idle with less lift...so VTEC in a 28 year old motor. That's how it's done (cont'd)