My question may be out there a little bit, but I did want to ask to see what, if anything, can one do by playing around with push rod length? Obviously this would change the overall valve lift at the end of the parts train.

Most of the time when I see any info about push rod length, I always read something about the fact that push rod length should match the heads you are using. I understand about the 56-57 lengths being shorter, and that all of the others (54-55, 58-64) were longer. Obviously, in 56 adn 57, all Y blocks came with the ECG 6564 1.54 ratio rocker arms, hence the shorter length. Theoretically, what would happen if one were to use the longer length rod with the hi ratio rockers?

I have early heads on my 292, and one bank has a set of 6564 and the other has (had) a set of 1.43 rockers. I can only assume that one should use push rod length in accordance to rocker arm ratio as mentioned above...correct? Knowing that I am going to put a blower on the motor and I want to get those exhaust gases scavenged at a pretty good rate.....how about using the shorter push rod on the intake rocker and the longer push rod on the exhaust rocker? Would this create a dynamic balance problem with the valve train?

Does all of this sound too whacky to even deal with??? Deos anyone else ever have these crazy thoughts?

The obvious advantage to having ‘perfect’ rocker arm geometry at the valve tip would be minimized valve guide wear.  Changing the pushrod length on the Y simply changes the rocker arm ratio with only minor changes to the actual valvetrain geometry.  But talking ratios, going from a 1.4 ratio to a 1.5 ratio at the rockers for a cam that has a lobe lift of 0.287” will get you a net gain of 0.029” at the valve.  I did test two different pushrod lengths on the dyno mule going from the shortest to the longest and picked up a clean 3 HP by simply going from short to long.  That's pretty cheap horsepower.

But I’ll add this little tidbit to get you thinking.  By raising the rocker arm stands so that the valvetrain geometry is higher than ‘perfect’, the low lift flow at the valve can be increased due to the rocker now working at a faster rate when the valve first starts to open.  Camshaft design plays into this but most cams respond nicely to this on both the intake and exhaust valves.  Even though the net or overall valve lift decreases by doing this, an increase in performance typically takes place due to the valve actually opening at a quicker rate.  Remember that the valve still starts opening at its original starting point and this is not to be confused with the rate at which the valve opens.  The higher the shaft is placed above that ‘perfect’ or optimum position, the greater the acceleration rate is for the initial valve opening but this is at the expense of increased guide wear and overall reduced valve lift.  At this point the roller tipped rocker arms have a definite advantage.  On a race car this increase in wear is a moot point but for a vehicle that’s going to be used for 100K miles, it’s a point worth considering.

As Charlie brings up, the geometry should be adjusted first and then the pushrod length appropriately selected.  If the pushrod length is selected first, then rocker arm geometry adjustments are limited if trying to stay with the original pushrod length choice.

TED, as usual your years of expierence and wisdom explain all questions very well, and as you point out, generalities more than exact rocket science lay with the reassembly of used parts due to the variables of the parts used. Thanks again, i enjoy your pearls of wisedom. regards bill.