CAMSHAFT SHOOTOUT I

CAMSHAFT
SHOOTOUT
Part4 I
Our story-ending grand
finale on the top
camshafts of all time
Text by Martin Musial
Photos by AMS Performance
t’s time to wrap up my big round of cam testing. Finally,
my motor will be able to rest after the numerous dyno
beatings and cam swaps. Although it was an exhausting test, it really produced some great results. It’s pretty
amazing to look at the difference in power from the stock
camshafts to one of the aggressive drag-oriented camshafts.
The Tomei 280 hydraulic lifter cams put down over 50-peak
wheel horsepower more than the stock pieces, and an amazing
65 whp at redline (8,500 rpm). That could give a boost of 6 to 8
mph through the traps at the dragstrip. For well under $1,000
you can pick up 70-crank horsepower; it’s like having a 75-shot
of nitrous that never runs out.
So what did we learn? By studying the lift profiles of all the
camshafts and comparing them to the dyno data, I drew a
few conclusions. The big power cams had a couple things in
common: poor low-rpm performance and idle. They also close
the intake later to allow for higher cylinder pressure at high
rpm, which hurts the spool-up and low-rpm running. Another
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TURBO & HIGH-TECH PERFORMANCE
Camshaft Shootout
one cam has much higher
acceleration forces than the
other. Guess which cam will be
easier on the valvetrain?
This parameter is very
important because if the valve
is closed too fast, premature
valve seat and valve wear will
occur. We can actually go
further and derive acceleration
into jerk, which is the rate of
change of acceleration. The
car in my previous example
that was accelerating at 2
mph per second isn’t going to
keep accelerating like that, it
will eventually start to slow its
acceleration as aerodynamic
drag takes its toll. Jerk is also
critical in calculating valvetrain loads and harmonics. I’ll
stop there as it can go even
further than that. Cam lobe
design is complex and many
things need to be taken into
consideration. Ideally, we want
the valve open for as long as
possible but to do so we need
to open and close the valve
quickly. It’s a big game where
actually something few people design keeps peak accelerathe designer optimizes the
outside cam design circles talk tion down. This is critical as
about.
acceleration imparts loads and lift profile to maximize gains
The cams that performed
stresses to valvetrain parts.
well had good opening and
Imagine getting rear-ended by
closing ramps on the valves,
a big semitruck going 60 mph,
meaning they properly started you’re going to have huge
to open and close the valve.
acceleration, but the stress is
Analyzing the lift curves in
also huge. Now imagine being
depth really shows the inner
rear-ended by a 10-ton marshworkings of the cam lobes.
mallow going 60 mph, strange
The lift curve shows valve po- perhaps, but you’re accelerasition versus crank degrees, or tion will be much lower and
how far it’s open/closed com- much less stressful. Plotting
pared to rotation of the crank. acceleration on the lift versus
The first derivative of position crank angle graph, we can see
is velocity, which is simply
the peak positive and negative
how quickly your position is
accelerations as the valve is
changing. If it isn’t changopening and closing.
ing, then guess what? Zero
As you can see from the acvelocity. If you travel 20 miles
celeration graph on the right,
while ensuring the valvetrain
holds together. If the engine is
designed for only drag racing,
we can push the limit further
as the operating time is much
less than a road race engine
for example. A purpose-built
drag race engine might only
see 30 trips down the dragstrip before a tear down, while
an endurance engine might
have to last the 24 hours of
Daytona.
It’s difficult to compare all
of these camshafts and pick
a winner. If I were drag racing
the winner would be either
Tomei 280’s or the Crane’s. If
my car took me to work everyday and I did a few track days
throughout the year I’d go
with something more mild like
the Forced Performance 4R’s
or the Kelford 272’s. The very
mild cams like the GReddy
Easy Cams and HKS 272 would
be more suited to the stock
Evo turbo rather than the
GT35R that I used.
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53
Our story-ending grand finale on the top camshafts of all time
in one hour, obviously
you’re going 20 mph. A
valve isn’t moving at a
constant speed, so it’s
constantly speeding up
and slowing down. The
Performance Trends
Cam Analyzer software
does the math for you
and you can plot velocity on the same graph
as position. Now you
can see how fast the
valve is moving at each
position of the crank.
It’s clear now by looking at the graph that
velocity is constantly
changing. From here
we can calculate acceleration, which is the
derivative of velocity, or how
velocity is changing. If you’re
traveling at 60 mph and floor
it, you’re going to accelerate.
Let’s say you’re gaining 2 mph
per second, so every second
you’re adding 2 mph to your
speed. Why am I going over
this? Here comes the important part. A good cam lobe
TECH
interesting thing to notice is
early exhaust valve opening.
Compared to a naturally aspirated engine, a turbocharged
engine keeps a higher average
cylinder pressure longer on
the piston during the combustion cycle, so opening the
exhaust valve early bleeds the
pressure and can kill the power stroke. An exhaust note will
actually be louder and have a
more pronounced pop when
the exhaust valve opens earlier. At higher power levels the
earlier exhaust valve opening
gets rid of more exhaust gases
and reduces pumping losses.
So the typical trade-offs of
early exhaust opening and late
intake valve closing make big
power and hurt the bottom
end grunt. Normally, correct
valve overlap works well in a
naturally aspirated application
but from what I’ve seen here,
it’s not as critical in a turbo
application. More overlap
didn’t correlate to an increase
in power in most cases, but it
did hurt idle quality. The real
behind-the-scenes secret is
SCORING
Peak Power:
of boost.
The maximum power the camshafts produced at 30 psi
Power Curve: Rated on a scale of one to 10, with one being the
broadest/widest power curve and 10 being the most narrow. Quick spool-up and
clean power curve get a one here. Late spool-up with peaky high rpm power get
a 10. Drag racers can live with a 10; autocrossers might prefer a one.
Idle/driveability: Rated on a scale of one to 10, with one being
the best of the bunch and 10 being the choppiest idle. Stock-like idle and street
manners get a one; rough and rowdy cams that hiccup at part throttle get a 10.
Cam: Stock
PEAK POWER: 506 whp
Power Curve: 3
Idle: 1
Price: Free!
Notes: Good spool and great idle of course, but
low power across the rpm range when compared with
all the other cams.
Cam: HKS 272
Peak Power: 522 whp
Power Curve: 2
Idle: 3
Price: $700
Notes: One of the first performance camshafts available
for the 4G63, although outgunned by some of the newcomers, it offers a good balance of power and great driveability.
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TURBO & HIGH-TECH PERFORMANCE
Cam: Brian Crower Stage 3
Peak Power: 528 whp
Power Curve: 6
Idle: 6
Price: $354.57
Notes: One of the few cams that needed adjustment on the
cam gears to be degreed properly. It had middle-of-the-road
performance in both power and idle. These are the least
expensive of the bunch!
Cam: GReddy Easy Cam
Peak Power: 534 whp
Power Curve: 4
Idle: 2
Price: $700
Notes: Silky smooth idle
with great street manners.
Decent power gains from
this mild street cam.
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Cam: GSC S2
Peak Power: 536 whp
Power Curve: 2
Idle: 5
Price: $599.95
Notes: Good power
curve and decent street/idle
qualities. If you want good
power without sacrificing
your daily driver then this
is a great choice.
Cam: FP 4R
Peak Power: 537 whp
Power Curve: 3
Idle: 5
Cam: Kelford 272
Peak Power: 544 whp
Power Curve: 4
Idle: 5
Price: $624
Notes: Average idle of the bunch with
manageable street behavior. Great midrange
to top-end power with a slight sacrifice at
spool-up and low-rpm performance. About the
best-performing cam for
street/strip daily driver.
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TURBO & HIGH-TECH PERFORMANCE
Price: $445
Notes: Another good camshaft with respectable power delivery and idle. Trades off slightly lumpier idle than GSC S2’s with a
bit more power up top.
Cam: Crane 272 intake/264 exhaust
Peak Power: 559 whp
Power Curve: 10
Idle: 10
Price: $803
Notes: The bark matches the bite. Rough idle comes with
degraded low-rpm street running, but she zings up top!
Peak power checks in roughly the same as the Tomei 280’s
but makes more power at redline with a slight sacrifice of
midrange power. Great camshafts for drag racing.
Cam: Tomei 280
Peak Power: 560 whp
Power Curve: 9
Idle: 9
Price: $870
Notes: Race car–like idle with rough low-rpm running. Idle
quality is a little better than the Crane cams due to less
overlap. Another peak power cam that pulls great in the midrange and up top. Just like the Cranes, the spool-up and lowrpm power suffers. Another great set of drag race camshafts.
AEM
HKS USA
AMS Performance
Kelford Cams
BC Brian Crower
Oliver Rods
Crane Cams
Ross Pistons
Forced Performance
Supertech
GReddy
TiAL Sport
GSC Power-Division
Tomei Powered USA
www.aempower.com
www.amsperformance.com
www.briancrower.com
www.cranecams.com
www.forcedperformance.com
www.greddy.com
www.power-division.com
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TURBO & HIGH-TECH PERFORMANCE
www.hksusa.com
www.kelford.co.nz
www.oliver-rods.com
www.rosspistons.com
www.supertechperformance.com
www.tialsport.com
www.tomeiusa.com