There
comes a point in your power buildup where you may consider adding nitrous oxide
injection to your supercharged car. This point typically coincides with
reaching a level of performance that means increased investment and diminishing
returns from your supercharger. For example, my car comes from the factory with
a 5th generation Eaton MP45 supercharger. This supercharger is limited to about
230hp worth of flow rating and so no matter what I do with bolt-on upgrades on nitrous
oxide engine, my peak horsepower will not exceed 230hp limit because
that is the point at which the supercharger becomes the bottle neck in my
system.
As
we've talked about in previous articles there is still the option of porting
the factory supercharger for a 10 to 15% gain in capacity (which in this case
would be another 23 to 35 horsepower). There is also the option of retrofitting
a larger supercharger such as the Eaton M62 to gain potential up to over 300hp
depending on the final choice of a supercharger.
This
modification path (porting or replacing the factory supercharger) can prove to
be complex and costly, especially if the supercharger is integrated into the
intake manifold (and possibly an air to water intercooler) as the case is with
many factory supercharged cars.
A
possible viable solution for this situation is to use nitrous oxide injection
to supplement the power delivery when racing, and being satisfied with a
reliable lower powered car when the nitrous is off and we're not racing.
The reason why nitrous oxide (N2O) becomes a great power
adder is twofold:
1- Nitrous is cheap as far as
horsepower per dollar goes, and especially in the situations where we're
already supercharged and so will only be using it on the rare occasions when we
do hit the track.
2- Nitrous oxide is a great 'chiller'
as it comes out of the bottle at a temperature of negative 127*F and is
capable of cooling the overall supercharged air charge mixture by over 100*F as
reported by enthusiasts, this is an additional temperature reduction over the
effects of whatever intercooler you have fitted. This in-fact makes nitrous a
great proposition for cars that have already maxed out their superchargers,
where the supercharger is running at peak rpms and producing very high outlet
temperatures. The nitrous oxide injection can effectively boost the thermal
efficiency of the supercharger when it is most stressed out and give us a nice,
cool, and dense mixture.
3- Nitrous oxide fuel delivery is
fairly straight forward to setup and to tune, especially on newer model cars
with return-les fuel systems, or difficult to crack computers that make it
difficult to upgrade (and properly tune) a much larger supercharger setup.
Nitrous oxide fuel delivery can be set-up totally independently from the OEM
ECU and fuel system and thus makes nitrous a possible application for German
cars with stubborn computers.
4- This is a racer technique... most
cars seem to perform better during the winter months because the air is cooler,
horsepower is elevated, and the tracks although cold, can be prepared for
traction and will heat up enough during the night to allow for traction and to
give people the ability to exploit the cold dense air to post their best times
of the year. As the weather gets warmer, traction increases because the asphalt
is warm and sticky, but horsepower is reduced due to warmer, less dense air.
Typically racers find that their cars vary in their quarter mile performance by
as much as a half a second between their summer tune and their winter tune,
especially if you're using a supercharger or turbocharger that compresses (and
further heats) the incoming air.
The
solution to on-track consistency, racers have found, is to combine the use of
nitrous oxide (which is summer friendly) with forced induction (superchargers
and turbochargers) which are winter friendly. In the summer time, the outside
temperature is high, and so the nitrous bottle pressure is maintained at a high
level above 1100 psi. This allows for a generous nitrous flow rate under the
sustained pressure (even without a bottle heater) which gives great summer
performance for nitrous assisted cars. While in the winter, the outside
temperatures drop significantly, the nitrous in the bottle contracts and the
bottle pressure drops, subsequently, the nitrous flow rate drops and nitrous
assisted cars show worse performance in the winter times.
The
complete opposite is true for supercharged cars that produce great horsepower
in the winter from compressing cool dense air, and poor horsepower in the
summer heat. When you combine these two power adders you get pretty flat and
consistent horsepower production year round because the supercharger shines
when the nitrous is weak, and the nitrous shines when the supercharger is weak,
and thus together, they give consistent power deliver year round.
Pre-cautions:
Now
we have to consider that nitrous oxide is an oxidizer and thus not only does it
increase the amount of air and fuel combusting in the cylinder, but it also
produces a faster moving flame front due to the oxidizer properties of the nitrous
oxide. This means that additional timing retard, great octane fuel, and
possibly colder spark plugs will be required to run spray on a supercharged
car.
Furthermore, because of its cooling effect, a 100hp shot on a supercharged
Camaro can very easily put down OVER 120 rear wheel horsepower of additional
power. This means that the 'out of the box' jetting of a nitrous kit may not be
adequate on a supercharged car and you'd have to make sure to monitor and
possibly increase the fuel jetting to match the final horsepower figure of your
car). Last but not least, if you're running a 500hp supercharged car with an
additional 120hp of nitrous oxide injection, then you must make sure that your
fuel delivery (fuel pump and fuel lines) are able to flow the total amount of
fuel required to deliver 620hp.
Applications scenarios:
1- You have a car like mine, a 2005
C230 kompressor that comes with a 230hp limited Eaton MP45. ECU on the car is a
Siemens ECU that very few people know how to tune, and the fuel system uses a
return-less setup with an in-tank fuel pressure regulator. With this kind of
setup all forms of dry nitrous injection are out of the question because we can
neither compensate for fuel through flashing the factory ECU, nor can we
elevate fuel pressure during the nitrous injection because the fuel pressure
regulator is in-accessible....
Recommended kit:
Injection location:
After
the supercharger, after the intercooler, and into the intake manifold of the
car.
Maximum
recommended injection:
25%
of the original total power figure which corresponds to around a 50 hp shot of
nitrous on our example.
Expected
final horsepower:
60
to 65 wheel horsepower and possible about 130 ft-lbs of additional torque!
2- You have a car that has an
accessible fuel pressure regulator, or an ECU that can be re-flashed for
nitrous oxide or a 'dual tune' setup. In this case it is recommended to use a
dry nitrous kit for two reasons:
First: Dry kits
are safer on supercharged cars (as long as the fuel delivery through the
injectors or raised fuel pressure is adequate) because they hold a reduced
chance of intake backfires because the intake manifold is dry of fuel.
Second: Dry
nitrous injection contains no fuel, and so we don't need to worry about fuel
falling out of suspension from the injected air. This means that we no longer
have to spray the nitrous right before the intake manifold and we now have the
option to move the point of injection much farther back. Spraying nitrous
BEFORE the intercooler, right after the supercharger gives the nitrous stream
more time and more contact with the compressed air coming out of the
supercharger which results in more cooling and further increased horsepower.
Recommended kit:
A
dry nitrous injection kit that injects only nitrous oxide from the injection
nozzle.
Injection location:
After
the supercharger, before or after the intercooler and not necessarily right at
the intake manifold of the car.
Maximum recommended injection:
25%
of the original total power figure which corresponds to around a 50 hp shot of
nitrous.
Expected
final horsepower:
70-75
wheel horsepower and possible about 130 ft-lbs of additional torque!
3- You have a car that has an accessible
fuel pressure regulator, or an ECU that can flashed for nitrous oxide or a
'dual tune' setup. You also want to make as much horsepower as possible from
your nitrous...
In
this case it is recommended to use a dry nitrous kit injecting before the supercharger.
As we mentioned in our articles on twin charging (combining turbochargers with
superchargers for added performance), when two 'chargers' are chained in series
where one charger feeds the next, then the two pressure ratios of the charger
combine because the second charger compresses air that is already compressed by
the first. For example two turbochargers set for a 1.5 pressure ratio (or 7 psi
of boost), running in sequential mode will result in a final pressure ratio of
2.25 bar (or 18psi of boost) which is more than the 'expected' 14psi that is
the sum of the two boost levels.
Similarly,
injecting nitrous oxide before the supercharger, delivers already compressed
air. This is true weather we are talking about nitrous being compressed because
it has twice the oxygen concentration as normal air or we're talking about the
nitrous cooling and compressing the incoming air. The final amount of
compression observed by the supercharger inlet will vary depending on the ratio
of incoming air to the size of the nitrous shot, and can result in an increase
in boost of between 0.5 to 2.5 psi!
This
boost increase is in addition to the power increase of the nitrous oxide
injection and so it can be an additional 5 to 25 hp.
Recommended kit:
A
dry nitrous injection kit that injects only nitrous oxide from the injection
nozzle.
Injection
location:
Before
the supercharger inlet.
Maximum
recommended injection:
25%
of the original total power figure which corresponds to around a 50 hp shot of
nitrous.
Expected
final horsepower:
75-100
wheel horsepower and possible about 160 ft-lbs of additional torque!
Things to avoid:
1- No matter where you setup the
nitrous injection, make sure not to spray nitrous into your MAS air flow sensor
or your intake air temperature sensor. These temperature dependent sensors,
tell the ECU to advance the timing in colder conditions. As we mentioned
earlier, nitrous is an oxidizer that increases the speed of travel of the
combustion event and thus requires maintained (if not retarded) ignition timing
compared to a supercharged only setup. Avoid spraying on these temperature
sensitive sensors to prevent accidental timing advance from occurring.
2- Avoid spraying a wet kit (fuel)
before your supercharger, as the wet fuel mist will damage the supercharger
rotors and strip their coatings.
3- Make sure you check your air fuel
ratio on the nitrous and don't stick to the 'out of the box' air to fuel
settings with the kit. For example an extra 2.5 psi in your intake may or may
not be compensated by your stock ECU and so depending on how well the ECU
reacts you will have to adjust the fuel jetting on the nitrous kit.
