Adding more engines to your Saturn isn't hard but you will need to make
a few minor adjustments. One of ours has 5 engines. You'll need 1 stuffer
tube per additional engine. You can use the engine mount that comes with
it, just cut the additional holes carefully. Beef it up some. I used balsa
strips, installed in a grid.

If you cluster, you'll want to move the engine mount as far back
as you can, to just above the cut, next to the engine bell fairings. That's
about 1/2" from the bottom of the rocket. Don't install the engine mount
until after you've made the cut. Then you'll need to add a little weight
to the capsule, to move the c/g back to where it should be, at about 15.5"
from the rear of the rocket. There is plenty of room in the capsule for
the weight. With 1 D center and 4 C outboards, loaded and prepped, mine
weighed in at 17 ozs. with 3.8 oz. of it, in the nose. With the extra weight
and thrust, you'll also want to use nylon chutes. Other than that, build
it per instructions.

You're going to need to upgrade the launch system from the standard
Estes version. A larger pad and a 12 volt power source for the control
box. That means gel packs or a car battery, to insure enough power for
several ignitors at once. You will have to decide which way you want to
get power to the ignitors. I prefer a separate set of leads to each one.

If you use more than one engine, use ejections on all of them and not
just boosters, with only one ejection. When the boosters burn through,
they will have enough pressure to cause early separation, ending the flight
too soon and possibly damaging the rocket. I use 1 D12-5 and 4 C6-5 engines.
It goes about 225' at a good clip but still slow and low enough, that you
see everything.

I think you'll enjoy doing it as a cluster. As you build, post any questions
you may have to RMR. You'll get lots of good advice. - Randy

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With a cluster of 5 Cs located where the 5 motors should be, you risk the
destruction of the model if you get partial ignition. if only the center
motor ejects the chute, you risk everything if it doesn't ignite. I've
seen S-Vs at NARAM flown this way, and they probably had a 50% or higher
failure rate. IIRC one pretty much burned on the pad, roasting the back
end of the model.

My advice on clusters is to do them for effect only. For a S-V that
would mean a central motor with enough thrust to carry the model thorough
its entire flight safely, and extra effect motors that if ignited will
do nothing. For example an E15 and 4 1/4A3-3T. They become not much more
(or less) than FX motors. But even in competition, you get as many points
for E15+4FX as for 5 C6, with MUCH LESS risk to the model or to the people
around it. - Bob Kaplow