Chriscamaro loves playing sports, modifying cars, and playing video games.
A Binary Choice?
Forced induction is great. It's always there when you need it. It comes on fast and strong, and it adds at least 25%, usually more, to your factory power at the wheels. There are also the highly controversial new electric superchargers which, in my professional opinion are even better, as they have no parasitic losses and make more with less. Nitrous is fantastic too. Its instant on/off capabilities and canned power make it extremely versatile and fun.
However, it seems that not a lot of people have ever thought to put the two ideas together. Why is that? Maybe it's because they're afraid of blowing up their engine. This is a good fear to have! You certainly don't want to blow up your engine. We've all seen the YouTube videos of people losing thousands of dollars in the blink of an eye because their car just couldn't take what they gave it.
The problem, however, is not inherent to the mods. It's inherent to human nature. People are impatient. They want immediate results. Even the most experienced car enthusiasts sometimes cut corners because they think they know better or they are trying to take shortcuts with time or money or both. If you do your homework, spend the money and take your time, forced induction and nitrous are perfectly safe. More central to this article is that they are even better together... if you do it right!
Air Temperature Is Very Important
Boost and Juice Have Seasonal Strengths and Weaknesses
Forced induction of any kind involves compressing air to high pressures. The thermodynamics of it are very straight forward. Not only will you raise the temperature of the air charge because you're compressing it, but compressor work goes up exponentially with the desired outlet pressure, meaning your compressor has to work harder and harder to get you the pressure you want, which puts strain on the engine one way or the other (unless you have an electric supercharger). So you have 2 factors working against you. One, the resistance on the engine makes it more prone to knock and 2, the increased intake air temperature makes the engine more prone to knock. To counter this double whammy, you have to reduce engine timing to inhibit knock and decrease your AFR to get a richer mix that will act as a coolant. On top of all of that, in the summertime, the air is warmer, to begin with, so you've got to lower your timing even more! Temperature is your enemy when it comes to boost, so these mods do their very best in winter. Remember that point. Winter is good for boost.
Nitrous oxide doesn't have this sensitivity to air temperature because the nitrous decomposes at combustion temperatures, which means by the time the spark goes off it doesn't matter anymore what the timing was. The nitrous will hit after the spark, not before. The problem with nitrous is maintaining bottle pressure. Nitrous is a compressed cryogenic gas. When it comes out of liquid form, it cools everything around it, rapidly, including the bottle. This makes the bottle super cold and reduces the bottle pressure. The longer you spray, the greater the pressure will drop and the less power you'll get from it. This means nitrous works opposite to blowers with respect to temperature. Nitrous likes the hot summer weather because the bottle won't cool off as quickly and will maintain pressure longer, yielding more power.
If you haven't picked up on it yet, it seems these 2 mods pick up the slack for each other. Having both installed means you can use either one depending on the climate. With electric superchargers, this really can be an exclusive OR, but with most forced induction you can't shut off the blower so you're either using your super/turbo by itself or you're using it along with the nitrous. Let's get to that.
Supercharger and Nitrous: A Synergy of Power
In theory, using either one mod or the other, depending on the climate is a great idea, but you can't always use just one or the other so what about using them both at the same time? As mentioned already, superchargers and turbochargers both use compressors to raise the air pressure going into your engine. As mentioned, this heats the air up tremendously and requires you to protect the engine by lowering your spark, so the engine doesn't knock. I should also add that on top of this you've got to have colder spark plugs and plenty of extra fuel.
Furthermore, many forced induction mods have what's called an intercooler. An intercooler is a special radiator which helps dissipate some heat from the air leaving the compressor before it goes into the engine. That's because the air is so hot that it becomes exceedingly difficult to keep the engine from knocking on pump fuel even with your spark adjustments, if you don't cool the air off somehow. Intercoolers are often necessary and add complexity and weight to your supercharger. Enter nitrous oxide! Nitrous oxide is the perfect substitute for an intercooler. In fact, it's orders of magnitude better. Instead of passively radiating heat away from the intake air, you're shooting cryogenic mist into it, instantly dropping the temperature by 100 degrees or more. This has several benefits.
First, you don't need an intercooler, and if you've got one anyway, you're helping it along big time. Second, if the outlet of your supercharger is cold, the pressure drops. When the pressure drops, the compressor has less work to do so it spins up. When it spins up, it does more work and compresses the air more. Eventually, this recursive looping reaches a new equilibrium point with the compressor working more efficiently and yet producing greater outlet pressures at a lower temperature than before. Third, the nitrous oxide still hasn't decomposed yet so on top of the gains from its cooling effect on the air, it's still going to add yet another 100 (or whatever size shot you selected for your system) horsepower on top of everything else AND you can do all this without having to retard your spark as much as you would have before. You will still need high octane fuel, cold plugs and plenty of fuel enrichment for this to work correctly but it is the perfect modding combo if there ever was one.
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A Word of Caution
It is very very very important that you tune your car properly and have all the supporting hardware you need before you attempt to activate both your blower and nitrous together. Nitrous makes forced induction less likely to cause damage to your engine per unit horsepower added but only if you tune it properly and have the right equipment. If you have the wrong plugs, fuel pump, fuel pressure regulator, MAP sensor, fuel injectors, gas or tune, you will get bitten, and it only takes one time to blow an engine and put yourself in a whole lot of debt.
Step one, upgrade all of the equipment that's needed to support both mods. Buy new spark plugs, injectors, map sensor, etc. first and install them. Then use your tuning tool to calibrate them in the ECM. You can't change plugs, map sensors or injectors without calibrating them or you won't get what you think you're getting. All of these pieces of hardware reference their own tables that are different from one manufacturer to another, from one model to another. Make sure you dial in all of these tables first, while your car is still N/A and only then should you move on.
Once you've dialed in all your supporting hardware go into your VE table or your MAF table (do both if you don't know which table you're using) and richen up all the cells that are above 100 kPa. Don't be stingy. Add more fuel than you think you need and then go to your spark tables and lower the spark by a couple of degrees in all cells above 100 kPa. Then install your blower and conduct several road scans while under wide open throttle to see if you have any knock. Adjust your spark and fuel accordingly until you are all dialed in.
Now it's time to add the nitrous. If it's a wet kit, make damn sure you've got your fuel jet sized correctly for your nitrous shot. If it's a dry kit, make damn sure you have tricked out your ECM to add the correct % of extra fuel to go with your dry shot. You can also add fuel using your fuel pressure regulator, but I hate this method because you don't really know if what you're getting is too much or too little and it's very hard to adjust anything. No matter which method or kit type, go to your spark tables once again and drop the spark in every cell above about 90 kPa by 2 degrees per 50 HP. Then, just as a precaution, swap your jets, so you're spraying about half of what you intended to spray. You can always change a 2 dollar jet in 5 minutes rather than blow up a 10 thousand dollar engine. Conduct a test with real-time gauges on your laptop screen monitoring knock and AFR. Set the gauges to turn red and go nuts if the AFR or knock goes beyond reasonable values (like 13:1 or 2+ degrees). Also, check your fuel pressure for any abrupt drops. Abort immediately if you see anything like this. If not, complete your WOT run and adjust your settings accordingly. Increase your jetting slowly and redo your road scans until you're up to your target jetting. Do a couple more road scans on different days with hot and cold weather to establish your upper threshold. Once you're confident that your settings are safe, you're home free.
Now presumably you've been keeping your logs, so you know what settings worked for boost only. If you haven't done so already, you should transfer the difference in settings between boost only and boost with nitrous to your tables that rely on intake air temperature. There should be IAT sensor tables that adjust both spark and fuel. Leave the supercharger only settings for the main fuel and spark tables (because the super is always on) and transfer your nitrous settings (the delta in settings) to your IAT tables. Then you can use the IAT sensor trick (switching between the sensor and a resistor) to access a normally unused column of the table only when you hit the nitrous button. This way you don't don't get nitrous settings when you're only running boost.
In order to pull this combo off, you need to know how to tune your ECM. You need to be able to install a few upgraded parts and sensors or at least get a mechanic to do it. You need to be able to road scan your car and analyze the data. You need to have some basic electrical and mechanical skills. Having said that, it's really not that hard. What makes it seem hard is that you've never done it before, but once you do it, you'll realize how easy it was. Just go slow, be patient, don't cut corners with money and ask questions of forums if you don't know something. Don't guess. If you're the kind of person who's comfortable installing a supercharger, then this combo mod should really be a piece of cake since installing a blower is more complicated than adding a nitrous kit and a tune to a blown vehicle. Have fun.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
Question: Spooling a supercharger is a constant variable (jumbo shrimp). Adding cold nitrous will not change the spool, as with a turbo. Correct? At least my personal experience with turbocharging and nitrous would not appear to be the same with a belt driven compressor.
Answer: Adding nitrous will not directly change the spool of a turbo unless you want to consider the additional exhaust pressure's effects downstream. But no, not really. What it does is supply immediate power until the turbo can spool however and sometimes this is important if you're not running an S/C.
Question: I am running a modified (stock crank and rods, SpeedPro hypereutectic pistons, Comp Cams etc.) Buick Gen III Supercharged 3.8L V6. The injectors were upgraded from 38# to 44.5# and are currently operating at ~ 80%. The throttle body is from a Northstar V8, and the MAF from a vette. The ECM was professionally tuned to accomadate all the mods running 100 octane fuel. I am adding a wet nitrous kit. Will the upgraded injectors at ~ 80% be sufficient or should I go to 65#?
Answer: If it's a wet kit, it's not the injectors but the fuel pump that's limiting. That and the bottom end of the L67. I think 100HP shot is a good number to start with and in that case, your injectors can't supply that much fuel so you have to tap the fuel line and the pump needs to supply 33% more fuel (approximately) since the L67 can put down almost 300 ft-lbs.
Question: Any information on spraying a small dry-shot into the inlet of a twin-screw, and adding fuel via the ECM? I’ve found a couple references to people doing it (Terminators) And read some engineering talk about it. The consensus seems safe, and that any small shot will likely result in double the power, I.e. a 25shot making an additional 50hp.
Answer: The key is to take advantage of the heat quenching ability of cryogenics like N20. Placing the shot right after the screw, where the temps are highest will cause a change of state of the N20 and further heating of the gas. All that latent heat gets soaked up by the N20 and reduces charge temp, just like an intercooler, but better. The extra HP in this case is from increased volumetric efficiency. Basically you are changing the efficiency map of the S/C so it is more efficient at the expense of the nitrous, which is now a gas. However, the nitrous will still decompose and yield O2 so don't lose much and gain quite a bit from charge cooling. The engine will suffer less parasitic loss turning the screw.
© 2014 chriscamaro