Page 2 - Along the Way December 2020
P. 2
FORMANCE PUSHROD TECHNOLOGY
BY MIKE MAVRIGIAN
When extreme spring pressure, high lift and
high RPM are parts of the equation, larger
diameter pushrods with tapered ends provide
added strength and clearance at rockers and
lifters. A group of individual-location length
of intake and exhaust tapered pushrods from
Manton are shown here.
diameter while accommodating these system design incorporates a smaller valvetrain stability (as demonstrated
clearance issues. If a pushrod features top section that slides 2” deep inside a by the prevalence of 7/16”, ½” and
a single taper, the tapered end mates to larger bottom section with one or two even 9/16” OD, thick wall pushrods in
the rocker, where the heavier-mass end shims captured in between the sections professional racing).
is directed to the lifter, where impact to accurately set lash or preload. This
and dynamic loads are higher. In certain opens up a simple way to accurately set In LS applications the 7/16” OD
applications, a beefy pushrod in the 1/2” lash or preload while using far more bottom section and 5/16 x 0.105” wall
– 9/16” diameter range may feature a durable and lower mass non-adjustable bottom section create an assembly that
“clearance notch,” (as noted by Trend), style rocker arm assemblies. The adjuster has 90% greater stiffness than a standard
reducing body diameter about halfway and nut on shaft-mounted rockers 5/16” single piece design, while the
down the body to reduce rub where the weigh approximately 20 grams. Once 7/16” bottom section fits easily though
pushrod runs through the cylinder head, you add the extra material for threads the 12mm pushrod clearance holes in
leaving maximum thickness in the area and support, the system mass may grow factory cylinder heads. The bottom
that doesn’t run through the head. Flex- to about grams. This is basically the section length is sized to remain under
reducing thickness becomes more critical difference in mass of a Ti vs Steel valve the cylinder head and gasket at any lift
as pushrod length increases, as in Top hanging off the back side of the rocker during operation, resulting in the same
Fuel, where pushrods tend to be in the 11 arm, and all of this added mass does running clearance as any 5/16” design.
to 12” range. nothing to improve the rocker stiffness.
In contrast, the mass added when moving The XD-A Pushrod system has been
A fairly recent innovation is the the adjustment into COMP Cams’ proven in solid roller LS applications
adjustable pushrod, which allows precise new XD-A pushrod almost doubles its though Spintron test to 9000+ RPM
length tuning for non-adjustable rocker stiffness in bending by shortening and and aggressive dyno testing. Lash setting
arm systems. COMP Cams’ XD-A Shim supporting the smaller OD top section. stayed extremely consistent throughout
Adjustable pushrods are an example of This is a major improvement as pushrod testing and pushrod lengths remained the
this approach. As explained by Comp: bending can be the weakest factor in same before versus after operation. With
The Patent Pending new pushrod fresh cylinder heads, you may consider
setting the lash about 0.001” to 0.002”
70 JULY-SEPT 2018 engine professional
BY MIKE MAVRIGIAN
When extreme spring pressure, high lift and
high RPM are parts of the equation, larger
diameter pushrods with tapered ends provide
added strength and clearance at rockers and
lifters. A group of individual-location length
of intake and exhaust tapered pushrods from
Manton are shown here.
diameter while accommodating these system design incorporates a smaller valvetrain stability (as demonstrated
clearance issues. If a pushrod features top section that slides 2” deep inside a by the prevalence of 7/16”, ½” and
a single taper, the tapered end mates to larger bottom section with one or two even 9/16” OD, thick wall pushrods in
the rocker, where the heavier-mass end shims captured in between the sections professional racing).
is directed to the lifter, where impact to accurately set lash or preload. This
and dynamic loads are higher. In certain opens up a simple way to accurately set In LS applications the 7/16” OD
applications, a beefy pushrod in the 1/2” lash or preload while using far more bottom section and 5/16 x 0.105” wall
– 9/16” diameter range may feature a durable and lower mass non-adjustable bottom section create an assembly that
“clearance notch,” (as noted by Trend), style rocker arm assemblies. The adjuster has 90% greater stiffness than a standard
reducing body diameter about halfway and nut on shaft-mounted rockers 5/16” single piece design, while the
down the body to reduce rub where the weigh approximately 20 grams. Once 7/16” bottom section fits easily though
pushrod runs through the cylinder head, you add the extra material for threads the 12mm pushrod clearance holes in
leaving maximum thickness in the area and support, the system mass may grow factory cylinder heads. The bottom
that doesn’t run through the head. Flex- to about grams. This is basically the section length is sized to remain under
reducing thickness becomes more critical difference in mass of a Ti vs Steel valve the cylinder head and gasket at any lift
as pushrod length increases, as in Top hanging off the back side of the rocker during operation, resulting in the same
Fuel, where pushrods tend to be in the 11 arm, and all of this added mass does running clearance as any 5/16” design.
to 12” range. nothing to improve the rocker stiffness.
In contrast, the mass added when moving The XD-A Pushrod system has been
A fairly recent innovation is the the adjustment into COMP Cams’ proven in solid roller LS applications
adjustable pushrod, which allows precise new XD-A pushrod almost doubles its though Spintron test to 9000+ RPM
length tuning for non-adjustable rocker stiffness in bending by shortening and and aggressive dyno testing. Lash setting
arm systems. COMP Cams’ XD-A Shim supporting the smaller OD top section. stayed extremely consistent throughout
Adjustable pushrods are an example of This is a major improvement as pushrod testing and pushrod lengths remained the
this approach. As explained by Comp: bending can be the weakest factor in same before versus after operation. With
The Patent Pending new pushrod fresh cylinder heads, you may consider
setting the lash about 0.001” to 0.002”
70 JULY-SEPT 2018 engine professional
