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Featured Product:
The Crane Quick Lift Rocker Arm Kit.
Better Performance Through Geometry!
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How would
you like up to 25 more horsepower from a bolt-on modification to your
late-model Chevy Corvette, Camaro, TrailBlazer EXT, Tahoe, Suburban or
Silverado?
Like that idea?
Well, the parts pros at Tom Henry Racing sell the "Quick Lift" rocker
arm kit from Crane Cams which can do just that. |
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| Image:
Crane Cams |
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First, a short tech
briefing..
The valvetrain of
every Chevrolet V8 except the LT5 has rocker arms. The ratio of the
distances between a rocker arm's pivot and its tips causes its
translation of camshaft lobe lift into the greater lift we see at the
valves. Many
people quantify valve timing by maximum lift and duration at .050"
valve lift, however, a more useful measure is "lift area". If you graph
lift and duration, what's under that curve is lift area and it's
measured in "inch-degrees". |
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| Image:
Crane Cams |
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Cams can have equal
lift and duration at .050" but different lift areas. The cam with more area
moves the valves faster, so once you get to .200-350" lift; that cam has more
duration and, thus, more area. The engine with valve timing having more area
will produce more torque because its cylinders take in more air.
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five different curves are graphed. The first is the example
cam's lobe lift. The other four are how that profile graphs at
the valve tip with four different types of rocker arms. Clearly,
Crane's Quick Lift technology offers an advantage in lift area.
Image: Crane Cams |
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As the
rocker arms move the lengths of the two key radii change
slightly. Image: Crane Cams. |
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Lift area can, also, vary
due to the rocker arm's ratio and geometry. Crane Cams' intent with
Quick Lift rockers is to move the valves faster and increase lift area.
Crane accomplishes that by changing the radii of the arcs through which
a rocker arm's contact points move and, in the case of the Quick Lift,
1.8:1 version, a slight increase in ratio. |
How does this work in
real life? Mark Campbell, Crane Cams' Vice President for Research and
Development, told the Tom Henry Racing webmasters, "The stock, rocker starts the
valve off the seat at (a ratio of) 1.54. At about .450-in. valve lift, It gets
to 1.69, almost 1.7, but it doesn't attain 1.7 until the valve is all the way
open. Then, it puts the valve back on the seat slowly. That's great for
durability, but it isn't necessary with the (one-piece) valves they have and it
certainly doesn't help performance."
A Crane Quick Lift rocker
for a Chevy 4.8, 5.3, 5.7 or 6.0-liter, Gen 3 or Gen 4 V8 engine starts the
valve open with at least 0.1 ratio more than its advertised ratio. Then, its
ratio decreases through the first .300-in. or so of valve lift, until advertised
ratio is reached. That ratio is maintained through maximum lift until .300-in.
lift is attained, again, as the valve is closing. At that point, the ratio
begins to, once again, increase until it reaches at least 0.1 more than
advertised, just as the valve gets to the seat.
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This difference in
ratio change results from Quick Lift's key feature: a lower pushrod seat
which drops the pushrod/rocker arm contact point in the arc in which
that point moves. As the pushrod lifts the rocker, the radius of that
arc increases. That causes the rocker ratio to decrease slightly, rather
than increase greatly, as does that of a stock rocker with a higher
pushrod seat.
To summarize: the
stock rocker's rated ratio is 1.7:1 but that occurs only at maximum lift
with starting and ending ratios noticeably less and the "average" ratio
being somewhat less. |
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Side-by-side
are (left) a stock, investment-cast steel, 1.7:1 rocker arm for
a Gen 3/4 engine and a Crane Quick Lift aluminum roller rocker
arm. The difference in pushrod seat locations is marked with the
two arrows. The Crane rocker at right has a much lower pushrod
seat. Image: Tom Henry Racing. |
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The Crane Quick Lift, is
also rated 1.7, but that occurs from about .300". lift to max. lift with the
ratio for the rest curve being higher than rated. This higher ratio at the ends
of the lift curve means the valves move faster. According to Mark Campbell, this
increases performance and enhances throttle response. If you also step-up to the
1.8:1 Quick Lift you also gain the advantage of an overall, higher rocker ratio.
"If you plot a lift curve
with stock rockers," Campbell continues, "then plot our Quick Lift and measure
the durations at .200" valve lift; you're gonna find, depending on the cam, six
to eight degrees more duration with our rockers. Compared to other, aftermarket
rockers, you don't get as much, because they're a little more aggressive, but
the least we have seen, plotting Quick Lift against competitors at .200" valve
lift, is a four-and-a-half degree increase. When we've run on an engine dyno
with the 1.7s, we're seein' 15 hp over stock. With the 1.8s we're seeing about
20."
Do real-world results
with Quick-Lift rockers match Crane's claims? To find out, we tested a set on a
2004 Corvette Z06. First, we headed for the chassis dyno and laid-down two
passes. SAE-corrected horsepower at the rear wheels averaged 348@5987-rpm and
torque was 335-lbs/ft.@4926-rpm. We installed a Vericom VC2000 Performance
Computer, our on-board vehicle dynamics tester, and headed for the test track.
Our quarter-mile performance averaged 13.20-sec.@113.17-mph and that's with
street tires, traction which was mediocre at best and no burnout.
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installed a set of Crane Quick Lift 1.8s on an 2004 LS6 engine.
Image: Tom Henry Racing. |
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Back at Tom Henry
Racing, we unboxed Crane's Quick Lift Rocker Arm Kit (PN 144759-16)
which includes rockers, rocker nuts, pushrods and pushrod guide plates.
Following Crane's instructions we installed all the parts and adjusted
the rocker nuts. Finally, we headed back to the chassis dyno. Bottom
line with Quick Lift rockers? |
An increase of
Seventeen and a half more horsepower at the wheels. Figuring 15% powertrain
loss, that's 20.5-hp. SAE net at the flywheel, a significant improvement for
just a rocker arm change. At the track, with the VC2000 in the car we averaged
13.10@114.96, about a tenth quicker and two miles an hour faster. In addition,
with some engines, such as our LS6 test unit, about 300 rpm is gained on the top
end with peak power coming at about 6300 rpm rather than 6000.
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Crane's Mark Campbell
was on the mark. The Quick Lift Rocker Arm kit for Chevy V8s works
exceedingly well and is one of the better bolt-ons available for those
engines. Crane Quick Lift rocker arm kits for Corvettes, Camaros,
TrailBlazer EXTs, Tahoes, Suburbans and Silverados are available from
the Tom Henry Racing's Parts Department. |
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On the
chassis dyno, the addition of the Crane Quick Lift kit increased
this Corvettes SAE-corrected, rear wheel horsepower by 17.5.
Image: Tom Henry Racing. |
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Call us at
( 877) 866-7278 or e-mail us at parts@tomhenryracing.com |
