***Disclaimer: high performance cams and cam tuning is an adventure
of epic proportions. Before you go out and spend $500 or so on cams
and sprockets, you need to first decide how "in depth"
you are willing to go. Cam tuning is a great way to fine tune your
Satty's hidden power. However, it's also a great way to cause mad
problems, spend some change, and want to make you kick the neighbor's
dog. I STRONGLY RECOMEND THAT A WELL QUALIFIED MECHANIC, OR A REAL
CONFIDENT SATURN FREAK, PERFORM THE NECESSARY INSTALL AND TUNING
PROCEDURES. As I'm sure you're aware, quite a bit goes into this
project, and it won't take much for all hell to break loose***
These are serious tuning tools and should only be used by serious
enthusiasts, once you introduce shaved heads, better exhausts, higher
duration cams, and better air intakes, you tweak the optimum cam
timing set forth by the manufacturer. From the factory, cams usually
operate at a conservative setting to meet drivability and smog standards,
with that said even stock motors can be tweaked to better performance
by changing the stock overlap, overlap is the precise point when
the intake/exhaust valves open at the same time, this is very important
because performance tuning will maximize the air/fuel mixture in
and out of the combustion chamber, but keep in mind that tweaking
the cam timing tweaks the overall performance as well as the overall
drivability of the Saturn's motor, that's why I say these should
only be used for serious tuning, my setup for instance is NOT street
friendly by any means, adjusting the power curve should be done
with consideration of the car's purpose. Don't think of cam tuning
as a big power builder, the fact is I've only seen gains in the
upper RPM range of 5HP. The purposes for me are to adjust the power
curve for better acceleration. My setup is for drag racing only
so take that into consideration before you go out and mimic others.
One more thing before we start, remember that adjusting the sprockets
are not to be confused with altering the lift and duration of the
valves, that is the cam shafts job, that's where the cam profile
comes into play, when I say profile I mean the precise lift and
duration for the intake and exhaust valves (through the cam lobes),
these are detailed by the cam grinder or manufacturer.
To broaden everyone's cam vocabulary, I've added these terms and
definitions to assist the article.
TDC: top dead center These terms are used to present the
piston's position within the combustion chamber BDC: bottom
It is important to have a basic understanding of the pistons and
their relationship with the valve train. The pistons regulate the
valve's positions through the crank onto the timing chain, connected
to the cam sprockets witch turn the cams. Valves open and close
at their precise times to accommodate the piston's 4 part cycle
throughout the combustion chamber. The cycle goes like this:
1. The power stroke: is when the piston has reached TDC,
both the exhaust and intake valves are closed, as the spark plug
fires, the ignited fuel and air mixture forces the piston downward,
before the piston reaches BDC, the exhaust valve begins to open...carrying
onto the next part
2. The exhaust stroke: when the piston reaches BDC and begins
its travel upward, the exhaust valve goes fully open and begins
to close as the piston reaches TDC pushing out the unburned exhaust
gases, at the same time, the intake valves begin to open drawing
in fresh air while the exhaust valves are still partially open,
thus moving onto the
3. Intake stroke: the piston is at TDC, and both exhaust
and intake valves are part way open, as the piston makes its way
downward, the exhaust valve goes fully shut, and the intake valve
goes wide open then starts to close (during this stroke is where
adjusting the "overlap" comes into play, more on this
later) the final stroke is the
4. Compression stroke: this is simply the piston reaching
BDC and starting its way upward, the exhaust valve is still shut,
and the intake valve becomes completely shut, then the cycle starts
over and returns to the Power stroke
Centerline: for a simple explanation, The number of degrees
the crankshaft must turn from TDC until the cam reaches the peak
of the lobe will be the centerline.
Duration: is how long the valve is actually held open through
the camshaft in relation to the crankshaft's rotation. The length
of time the valve is held open is measured in degrees of crankshaft
rotation. in other words, if a given camshaft has a spec of lets
say 220 degrees duration, all this means is that the cam will hold
the valve open for 220 degrees of 1 crankshaft rotation.
Valve overlap: occurs during the Intake stroke, and is when
both intake and exhaust valves are open. Proper overlap is critical
for maximum performance, because overlap will determine the velocity
of the spent exhaust gases leaving the combustion chamber in conjunction
with the intake air being pulled into the combustion chamber. In
a nut shell, the ideal overlap position will create a vacuum and
allow the exhaust gases to be pushed out of the combustion chamber,
while fresh air is pulled in. Sounds simple, but tuning the cams
to such a balance is not easy and is very time consuming. But with
some patience and alittle luck the benefits will out weigh the costs.
Lift: not to be confused with duration is how wide the valve
will be held open, this is important because not opened enough will
restrict the air's entrance and exit from the cylinder, but at the
same time, opening to much will not allow any more air to flow then
at a conservative setting.
Now we move on to asking the question "How do I know what
needs to be adjusted?" Again, I must stress that one needs
to decided their tuning goals before they begin. With that said,
we need to point out the two types of cam adjustment: Advance and
Retard, and how they will affect the overall performance. For TSN
members new and old, we'll keep it simple and address the 2 main
scenarios; Tuning a twin cam's exhaust and intake (or just one,
but why?) and single cam tuning. Advance and Retard tuning will
obviously differ with the addition of 1 more, or 1 less cam. For
the best results, the idea for both is to maximize the valve overlap.
Again, advancing or retarding will move the power band up or down
for low end or high end gains. Normally, the driver won't feel the
difference unless there are adjustments of 4 degrees +/-. For some,
the advantages of tuning will be to accurately feel what the car
is doing, not gaining 5 or 6 HP. Also, each individual application
will carry different variables (different engine modifications)
that will call for different timing configurations. SO NO COPYING!!!
(Thank god we have electronic ignition systems or this article would
lose people quick!) Tuning cams is also the best way in my opinion
to compensate for all those bolt on parts out there, and even turbo
setups where the engine is breathing a lot more air than the norm.
For N/A engines, a more aggressive cam is recommended, as in turbo
applications, examples have shown that stock cams will do. Furthermore,
recognizing cam profiles and factory timing settings will greatly
assist in the tuning process by giving you a good place to start,
and the best place to go back to. To properly adjust the cams, you
need to recognize where the valve sits in reference to the pistons.
This is where the cam/piston relationship comes into play. If you
try to tune in mid stroke for instance, you wont get the results
you're expecting. The best results from my experiences are when
I turned the crank and begin when the valves opens at TDC
Advancing: means to rotate the cam ahead to open up the
intake or exhaust valve sooner. Saturn timing chains run clockwise
so turning the cam clockwise will advance. Keep in mind that SOHC
will open the intake sooner and open up the exhaust valve later
(because they ride on the same cam) DOHC engines can advance one
side or the other, or vise versa. That is why I cant stress enough
dyno tuning is essential.
Retarding: means to rotate the cam behind to close the intake
or exhaust valve later. Once again the Saturn crank turns clockwise,
so to retard you must rotate the cam counter clockwise.
On the Saturn's SOHC motor, the cam's lobes will be in charge of
both the intake and exhaust valves. So the only two options are
to advance or retard, but keep in mind: although cam tuning on a
SOHC will not do jack for overlap, it WILL SHIFT YOUR CURVE TO THE
UPPER RPM RANGE. This is ideal for drag racers who need all the
power at the top end. Retarding will do the opposite. Fine tuning
can max the engines power for example at 4 to 5K RPM's by retarding
the cams position. This is beneficial to autocross racers whom need
all their power at low end, in and out of the turns.
The twin cam peeps out there have a slight advantage because they
can maximize overlap throughout the entire RPM range AND shift the
power curve by properly dialing in the intake and exhaust cams simultaneously.
Twin cam tuners, typically spend more time on the dyno to get to
their desired outcome. (I know I've spent enough for all of us)
but the results are to die for. LOL
In conclusion, there are no "standard settings" out there.
Each of us have different mods that require different adjustments.
If anything I hope those unsure have a better understanding. I've
gone for a simple explanation here, so those whom have outside questions
or wish to pick my brain for the hardcore details can PM me.
With all this said, read a book, or ask around after all this doesn't
doesn't seem to be enough to help. I don't know, maybe I just got
lucky, after all, all I've done is taken the above info. And put
it to practical trials and errors, I'm no mechanical engineer, but
i managed to tune my sh!t very well.
Here is some additional information for those people that want
to further research cams. Link
forum has become one of the best resources for Saturn performance
on the net. Our members are constantly pushing their cars to new
performance levels. So, log in, share your ideas, and help push
your car’s performance to the next level.
August 2005 TSN will be holding its first ever meet
in Chardon, Ohio. Some of the fastest Saturns in the country will
be attending. Activities will include drag racing, dyno, tech session,
and BBQ. Look for the latest information in the forums.
Jeff and his team Different Racing have big plans
on breaking into some really low quarter mile times this year. Last
year he posted a 12.40 on a pretty healthy nitrous shot. This year
he has a new turbo setup and some serious determination. Visit his
website for the latest news and information. I expect we'll be seeing
some low 12's from him by the end of the year.