DI TECH
WISECO PISTONS
hanksgiving dinner at the Power
Adder family table is always awkward.
No matter how much the three kids have
accomplished over the past year, the con-
versation always turns to how Blower is a bit of
a parasite, and Turbo keeps putting too much
pressure on everyone. But the real black sheep is
always Nitrous – too cheap, and always wrecking
things when he gets a little greedy.
Nitrous gets a bad rep not because of its inher-
ent flaws, but because it’s such an “easy” path to
power – or at least it seems. You’d never dream
of throwing an 8-71 or a pair of 88mm turbos on
an engine with stock internals, and yet the ease
of slipping a little bit bigger jets into a nitrous kit
often tempts even the most level-headed racer or
performance enthusiast who should know better.
With the right parts and the right attitude,
though, an engine built for spray can live a long,
healthy and happy life, and the recipe starts with
the part that sees the most abuse on the bottle –
the piston. To find out the specifics of what a slug
designed especially for use with nitrous oxide are,
we sat down with Nick DiBlasi at Wiseco Pistons.
“A nitrous engine is a very volatile animal. There
are extreme loads within an instant, and every
part of the piston is designed with that in mind,”
he begins. One important aspect of piston selec-
tion depends on whether it’s destined for a street/
strip engine that will spend most of its life run-
ning naturally aspirated, or if it’s slated for a race
build that will see nitrous oxide applied more or
less all the time.
Defining the Problem
“It all starts with completely understanding
the customer’s needs,” DiBlasi continues. “While
we have off-the-shelf pistons that are designed
for nitrous, there are many customers who are
Because of the additional heat and pressure
generated by nitrous oxide, a typical piston designed
for that application will move the ring package
downward, away from the crown, to protect the top
ring while still providing good sealing.
68 | D r a g
I l l u s t r a t e d | DragIllustrated.com
going above and beyond what we call standard.
For those customers, we build something custom,
exactly to their needs.” That crossover point de-
pends not only on horsepower, but the intended
application as well.
“If the customer is requesting to put nitrous on
a part that was never intended for nitrous, then
we will have to custom make it,” DiBlasi says.
“Most of the off-the-shelf parts are intended for
naturally aspirated use, so we will have to convert
them to a custom piston as it’s a unique situation.
Also, if we have a shelf part designed for nitrous
where the majority of the market uses a 200-
300 shot, but someone wants to use 600 shot,
then we will most likely move them to something
custom. There is no exact formula, as every ap-
plication and duty cycle is different. We have seen
drift cars use nitrous a lot lately and will want to
move those to custom pistons, as the duty cycle
is much longer than of a drag racing engine of
the same specs.”
Step one in laying out the specifications for a
custom nitrous piston is ensuring that the cus-
tomer isn’t in the market for the proverbial one-
ended stick. “Based on the application, duty cycle,
and other engine components, we will design
our pistons to survive the conditions presented,
but there are many cases where the customer is
asking for something that simply defies physics,”
DiBlasi adds. “One of them that comes to mind
is putting a 4-inch stroke in a small-block Chevy
with a 6-inch rod. This makes a compression
height of 1.000” and simply does not give enough
room for the ring lands to live.”
Nitrous Piston Design Considerations
Once the impossible is discarded, what remains
is to optimize the piston design for durability and
power. Nitrous oxide applies cylinder pressures
and temperatures very differently from a naturally
aspirated or boosted engine, requiring a matching
approach to things like where the ring package
is located relative to the crown, the thickness of
the crown material, and even the construction of
the skirt and pin boss.
“In the design process, we will adjust the ring
thicknesses, materials, and lands to match the
loads required,” says DiBlasi. “The crown thick-
ness and taper angle of the top land will also be
For durability, the design of the pin bores and
supporting piston structure is critical. Higher
cylinder pressures require additional reinforcement,
and the entire piston needs higher rigidity to keep it
cylindrical and help the rings maintain a good seal.
Issue 134
T
DESIGNING A PISTON FOR NITROUS USE