- For anyone who's watched The Fast and the Furious movies,
it may seem that nitrous is some kind of silver bullet to fix all of your power
requirements.
However like any type of power adder, nitrous has its pros and its cons,
and it's got its own set of complexities that go along with setting up a reliable
system that's going to work well and deliver the kind of power that you need.
While nitrous is a popular choice to add on top of a naturally aspirated engine,
we're going to be talking about how nitrous can be used to help with a small capacity
forced induction engine.
One of the key areas that nitrous is used is when an automatic transmission
is coupled with a small capacity engine running a large turbocharger.
With the automatic transmission, at the start line it's important for the
driver to be able to get the car up onto the two step limiter and this requires
a certain amount of power to get the engine RPM up high enough in the
rev range.
Often with a small engine and a large turbocharger there's physically not
enough exhaust gas energy to spool the turbocharger at low RPM
and produce boost and hence the engine will just sit there at low RPM,
not reaching the two step limiter and not making nearly enough power
to launch.
In these circumstances a realtively small shot of nitrous can be used just for
the purposes of spooling that turbo.
In this case we may be using a 50 to 100 horsepower shot of nitrous and it's
only sprayed momentarily.
As soon as that nitrous is active, it increases the engine power,
in turn it increases the exhaust flow into the turbocharger and this helps
start producing boost from the turbocharger.
As soon as the turbo starts producing boost, it tends to continue.
So the shot of nitrous is generally only needed for a very short amount of time,
perhaps a second or so.
Alternatively the nitrous spray can be used the entire way down the drag
strip and here it's really adding to the power being supplied by the turbochargers.
Now this is where it gets a little bit tricky though.
If we've got a turbocharger system on a turbo engine and that turbocharger
system is really maxed out and working as hard as possible, you may think
that if we wanna add another 200 horsepower it's as simple as just
adding a 200 shot of nitrous to the engine.
It isn't however that easy because all of that additional oxygen that's being
supplied to the combustion chamber, via the nitrous system still needs to
make its way out through the exhaust system.
And when we've got a turbocharger system that's running at its absolute
maximum, what we tend to find is that the exhaust pressure starts to build up
between the exhaust valves and the turbine inlet for the turbo.
By adding nitrous, this simply means we get more back pressure and often if we
add a 200 horsepower shot of nitrous, ultimately we may not see anything
quite like that sort of gain in terms of engine power.
That 200 horsepower shot of nitrous, on a turbo system that's absolutely
maxed out, may for example only give us 50 to maybe 100 horsepower
of additional engine power.
So as you can see, it isn't a silver bullet to fix your power woes.
We also need to consider how the nitrous system physically works.
And there are a mutlitude of ways that nitrous can be supplied to the engine.
First of all we break these down into what's referred to as a wet system
and a dry system.
When that nitrous is sprayed into the engine, we're essentially providing
more oxygen straight into the combustion chamber.
However to achieve a safe air fuel ratio and also achieve the power that that
nitrous system can provide, we also need to deliver additional fuel.
Now this can be delivered with a wet system where the nitrous jet provides
both the fuel and the nitrous together.
Alternatively we can also have a dry system where the jet only supplies
the nitrous and in this case we need to provide additional fuel via
the fuel injectors.
This is a technique that's becoming more common with electronically fuel injected
engines as we have a lot of control through the ECU and we can very finely
tailor the fuel supply to make sure we get exactly the correct air fuel ratio.
Beyond this, the nitrous can also be delivered via a direct port system,
where we have an individual nitrous nozzle for each of the intake runners
on the engine or a simpler system where we only have a single nitrous nozzle
that's generally located in the intake system, somewhere before the throttle body.
Lastly we need to talk about nitrous purge systems.
You've probably all seen cars pull up to the start line in a drag meet and a spray
of white nitrous comes up generally at the base of the windscreen.
Now this isn't all for show.
That nitrous purge system gives two functions.
First of all it gives a visual indication to the driver that the nitrous system is active
and it's ready to go.
More importantly though it purges gaseous nitrous out of the lines so that when
the car actually leaves the line for the first time, a constant supply of liquid
nitrous is available to the engine, improving the system's performance.
So there's a quick introduction to nitrous systems, and hopefully as you can now see,
it's a little bit more complex than just fitting a 200 horsepower nitrous kit
to your vehicle and expecting that that's the last you'll ever have to worry about it.
Just like a turbocharger, or a supercharger, it requires the correct system to be fitted,
a good understanding of how that system will work and the correct tuning to make
the most of it and ensure reliable engine performance.
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