Once you have your two push-rod length measurements, you are ready for
determining your necessary correct length, for YOUR VALVE Lift. The odds of you
having a NET valve lift of either the .700" or .500" is rather small, but if you
did, then you could literally have used the tool directly for those lifts and
skipped the second side measurement. But the G-TooL is a formula creator. The
DIFFERENCE between your two measurements has given you a formula that is
specific to your engine's DECK HEIGHT, VALVE LENGTH, BASE CIRCLE HEIGHT, TAPPET
LENGTH and HEAD SPECS. All these things are unique to all custom built racing
engines, so valve trains need to have pushrod lengths that bridge all these
dimension, be unique too. This is what the MEI G-TooL™
accomplishes.
Whatever the DIFFERENCE between
your two measurements is, establishes a formula that is a PERCENTAGE of PUSHROD
CHANGE for any SPECIFIC VALVE LIFT on YOUR engine. The formula will be different
for another engine, because of these "stacked" measurements mentioned above. On
the small block Chevrolet, you should have a difference between .140" and .180".
Don't be concerned if you are somewhere on either side of this range; the
formula still fits. But for our example, lets choose .160". REMEMBER that you
have just taken measurements that were PRESET for valve lifts of .500" and
.700", respectively. That is a SPREAD of .200", and this is the CONSTANT that
our formula is based on.
The formula requires your
push-rod spread to be divided by the .200". In our example that will be .160",
and would look like this: .160" ÷ .200" = 0.8 on the
calculator window. This answer represents a PERCENTAGE, not inches. This means
that .160" is 0.8 (8/10ths) of the distance that is .200", or 80%. That means
that whatever valve lift you have, to adjust for it you need to lengthen or
shorten your push-rod by 80% of that VALVE LIFT. To do this though, you need a
STARTING (or reference) POINT. Your reference point is going to be one side or
the other of the
MEI G-TooL™. You will
decide based on the side of the G-TooL that is closest to your calculated net
valve lift. To do this, multiply your CAM LIFT by the ROCKER RATIO. Your PVS (or
ME) rockers will be this figure, at ZERO LASH. If your engine has mechanical
tappets, you will need to subtract the valve lash from your theoretical NET
Valve Lift, before you divide this in half to calculate your MID-LIFT figure.
An easy example would be if you
had a theoretical valve lift of .600". This is exactly in the middle of the two
G-TooL settings. So you would simply split the difference of your two
measurements, and this would be your required push-rod length. But in reality,
you will have something oddball, that needs the math applied. Lets say you have
.720". This is OUTSIDE the spread. Gee...what to do?... Simple: you are .020"
OVER the .700" measurement, so you need to apply 80% of this .020" (which is
.016") change to the push-rod length you measured at .700". You will notice that
the MORE VALVE LIFT YOU HAVE, the SHORTER THE PUSHROD. Whatever
your push-rod length was when you measured at .the 700" side of the G-TooL™,
means you need to SUBTRACT .016" from this length. Accordingly, if your NET
VALVE LIFT is .680" (.020" UNDER your .700" VL measurement), then you need to
ADD .016" to your push-rod measurement. If your NET VALVE LIFT is closer to the
.500" side that you measured, then make this the REFERENCE point that you add or
subtract your 80% from.
Many engines will be less, like
.140" for the SPREAD. So this will make your "percentage" less than 80%. If it
were .140", that would be 70% change in pushrod length, for whatever
valve lift change you made from our reference measurements of .500" or .700" on
the G-TooL™.
When you have figured out what
your necessary final pushrod length is, it is time to go to the THIRD STEP and
CONFIRM your rocker arm MOUNTING STUD is ACCURATE. If it isn't, then the
measurements you just took, aren't accurate either. Set your push-rod to the
prescribed length your formula needs for your valve lift. Then with a dial
indicator on the valve spring retainer, rotate the engine over to MID-LIFT (1/2
of your theoretical NET valve lift). Set the G-TooL atop it as shown above.