"Nitrous fixes everything." Our brain tells us that this statement is a fallacy, but rarely do car guys follow exactly what their brains tell them when searching for ultimate power and performance. But science has more than once proven that the illogical can become logical with time. And science has provided racers with the mystic elixir to ale the ills.
How do we get more power from our engine, without going to the huge trouble and expense of completely rebuilding it? Or how can we get our small-block to think and breath like it's a big-block? The answer to these and many more racing questions is nitrous oxide, because nothing can literally inject more power into your engine than a dose of squeeze. We love running nitrous and wanted to see just how much we could spray into a well-built Mouse before it bit back at us.
To accomplish our goal we had to track down a willing test subject first. For that we looked no further than the 391-cid "Stroke of Genius" small-block that Hye Tech Performance built for us in the June, July, and Aug. '01 issues. We asked the engine's owner if he'd return for another bout on the Vrbancic Brother's DTS dyno. He happily obliged with only one condition: We break it, we fix it. Agreed.
To better understand how and why nitrous oxide pumps up the power in your engine we'll explain some of the basics and do's and don'ts of nitrous tuning first. We also asked the experts at Nitrous Oxide Systems if they'd be willing to supervise our test procedures and offer some advice on the dyno. Two NOS techs, Mike Flynn and Sean Snow along with NOS co-founder Mike Thermos, showed up to prod us along.
What Is Nitrous Oxide?
We posed this question to the guys from NOS and they promptly opened a copy of their current catalog to show us the answers that lie within. To your engine, nitrous is simply a more convenient form of natural air. Since an engine is only interested in the oxygen contained in that air, nitrous provides a simple tool for manipulating how much oxygen is packed in with that air. Nitrous oxide is a mixture of two nitrogen atoms and one oxygen atom, chemically bound together to form an N2O molecule. The nitrogen is actually an inert element that won't burn by itself.
The power created with a nitrous oxide system comes from the additional fuel it sprays, along with the extra oxygen it brings. If you left the additional fuel out of the equation, the nitrous oxide would just speed up the rate at which your engine normally burns its fuel and that would lead to a catastrophic failure. Since nitrous really just allows your engine to burn a greater quantity of fuel and oxygen in the same time period, you're able to add tremendous power without making radical changes.
There's no trick to using nitrous oxide. It's really no different than if you were to install a blower or turbo, or to simply swap on a better breathing intake manifold and carburetor. In fact, your engine will run like it's on steroids, because it'll be burning an amount of fuel and air that only a much bigger engine normally could. Understand that the air we live in is made up of around 78 percent nitrogen, 21 percent oxygen, and 1 percent other gases (at sea level). Nitrous oxide is formed by combining two of the major elements of earth's natural atmosphere into an easily injectable mixture to burn the extra fuel. It's only when you don't inject the proper mixture of fuel and nitrous oxide together that you run into serious trouble. Unfortunately, as with all power adders, there's a practical limit to how much you can run into before you reach critical mass and self-destruct.
To find out just where that critical mass lies, we put a tough motor to the test. Our stroker small-block was built right from the start with forged pistons, a forged crank, H-beam rods, and all the good hardware to take tons of abuse. But, everything good has its limit, and a bit later we'll show you how we went beyond it. The important thing to remember when running nitrous oxide is that too much is not a good thing, and small amounts of the stuff can go a long way. Check out our test results and pay close attention to the details we present. We learned a lot from this dyno bash, which hopefully will keep you from sqeezing your engine to the point of destruction.
The Dyno Squeeze
We wanted to push right through the envelope and see just how much nitrous our strong Mouse could take before it cried Uncle. We hope that by doing so, you'll read what we've done and not make the same mistakes! Basically, we found that even a strong motor will not live with more than 200hp worth of nitrous when 92 octane is its only source of fuel. Racers typically run 110-plus octane and some will even inject alcohol into the mix to keep the engine out of killer detonation. While our engine had more than 10:1 compression, and a more wisely built street nitrous motor would have less, we know that car guys don't always take the wisest path.
So we didn't either, in fact we did exactly what you're NOT supposed to do just to see precisely what it would do. We gathered up several different Nitrous Oxide System kits and ran through some of the recommended fuel and jet settings to see how close our power gains would come to the claims made by NOS. In truth, we don't think anyone could have come closer to perfection. NOS really has their numbers nailed down and when they say you're going to see a 100hp increase, you can bet you're making about 100 hp more.
If, like us, you insist on running strictly pump gas with your doses of nitrous oxide then consider taking LOTS of ignition timing out of the equation. The bare minimum is 2 degrees for every 50 hp of nitrous, but you're safer with 4-degrees-per-50 hp. Keep in mind that most successful racers run as little as "0" degrees advance when their nitrous systems are at the highest power levels. It's the only way to keep the engine alive, and although higher octane helps, too much advance can still be a killer with nitrous.
To begin our tests, we choose the smallest of the small nitrous kits just to see how it would do. We modified our air cleaner base and mounted NOS's Top Shot nitrous kit above the carburetor. The Top Shot is truly the easiest nitrous kit we've ever run, and it would take only about one hour to install on your car. Don't let its diminutive size and easy installation fool you, however. The Top Shot is a legitimate power adder, capable of injecting 100-150 extra horsepower, all the while hidden inside your air cleaner. Check out the dyno test figures for the Top Shot set at 100 hp to see how you can turn your pump-gas Mouse into a pony killer without anyone being the wiser.
While the Powershot kit is truly the next step up from the Top Shot, it is not adjustable, and we only wanted to test adjustable kits. So we removed our Holley four-barrel and placed the Super Powershot plate underneath. This would be the last time we had to remove the carb for our tests since both the Powershot/Super Powershot and Cheater systems we'll run share the same nitrous plate. It was so easy to make tons of power with this kit, we thought we'd found Nirvana. The first pull on our pump gas stroker with the Super Powershot jetted for a 100hp increase netted us 587 hp and 598 lb-ft of torque. That's an instant increase of 92 hp and 115 lb-ft of torque.
Next, in went the jets for a 125hp increase and the Mouse shot back with 606 hp and 625 lb-ft of grunt. Suddenly, we had a genuine 600hp pump gas small-block with just the push of a button. Of course, we had removed 6 degrees of ignition advance by this setting, just to be safe. This was too easy. We wanted more.
All during testing we kept a close eye on exhaust gas temperatures (EGTs) and Brake Specific Fuel Consumption (BSFC) figures to see how our motor was doing. High EGTs and low BSFCs indicate dangerous ground. But, so far this Mouse could handle its cheese with the big boys. We stepped up to what some might say is the maximum safe limit for nitrous oxide injection on pump gas: 150 hp. Before making a pull at this setting, we carefully rechecked the nitrous fuel system's flowing pressure to be steady at 5.5 psi. We squeezed the button again at 3,500 rpm and got 643 hp and 690 lb-ft in return. If you've ever had the chance to drive behind this much power, than you'll appreciate how excited we were. And in typical car guy fashion, we ignored the rules of better judgment and plunged stubbornly ahead with only 92 octane in our tank.
Cheater In The Mix
Seven hundred pump-gas horsepower was our goal, and we were mere ounces of nitrous away. Having no fear, we replaced the small Super Powershot solenoids with the large Cheater counterparts and went straight to the 210-hp setting, defying the wise advice of the NOS techs to start out small. We also pulled an additional 2 degrees out, (our first mis-calculation) and left the flowing fuel pressure at 5.5 psi (our second mis-calculation).
As Mike Thermos and his techs looked wearily on, we squeezed 700 hp and 755 lb-ft of sinful torque from what we were soon to find was our battle-wounded Mouse. So infected with the horsepower bug were we by then that we dove deeper into the nitrous abyss as the NOS crew amusedly watched us approach total annihilation. It was our show, and there was no stopping us now. In typical car guy fashion, we reached into the NOS kit and pulled the biggest jets out of the Cheater kit. We figured that pulling yet another 2 degrees out (10 total) would suffice, and we were ready for another pull.
Editor's note: We'll stop right here and ask you to put yourself in our shoes at this point. If you were at the track, and the 210-hp jetting just helped you to run something like a 10.13 pass, would you have gone home without testing the big jets? And if you did test the big jets, would you have taken the time to at least pour some 110-octane race gas into your tank to up your octane quotient to a safer level? While you can all sit there now and answer "yes" to both of these questions (remember, we know how your brain works), most likely the excitement of being so close to a 9-second pass would overcome your sense of reason, and those 250hp jets would be in before your tires had a chance to cool.
So we did what we felt every car guy would do, squeezed it one last time (our final miscalculation). An engine on the dyno is typically much louder than in a car because it's running at WOT just a few feet away in a closed room with only a thin wall separating you from it. But, if you can hear the engine detonating on the dyno, it's already too late. Although dyno-operator George Vrbancic's years of experience told him something was amiss as soon as we hit the button, it was over in about two heartbeats. The engine made power from 3,500 to 5,000 rpm and even cranked out its highest peak torque of 770 lb-ft before dying. With the battle won, but the war lost, we hauled our once-proud 700-hp Mouse home to see what did it in.
After a thorough review of all the dyno pulls we made that day, it looks like the engine probably started detonating on the first 150-hp pull we made (three consecutive pulls at each power level were made for all tests). Average horsepower dropped from 581 to 572 to 567 on each 150hp pull, and we think the initial damage set in then. When we later tore down the motor, we found two things that went wrong, both a result of the continued hammering from detonation.
The No. 7 cylinder bore the brunt of the load, and its moly-coated ductile-iron top ring and forged piston suffered fatally. Also, every connecting rod bearing and most of the main bearings were about to give out, showing more copper than any street bearing should. This further proves the nitrous experts correct in that 150 additional nitrous horsepower is the max safe point for even a stout motor when running on pump gas. Any more nitrous should at least be combined with a mix of race gas to get your octane well over the 100 mark. And you should always pull out at least 4 degrees of advance for every 50 hp added, that means at least 12 degrees should come out with a 150hp setting and 16 degrees should be removed for 200 hp and so on.
Keep in mind that for this test only, we had the benefit of not worrying about hurting the motor (even our meager budget can allow us a few mistakes from time to time). You'll probably never have that benefit, and we hope you learn from our prodigious misuse of nitrous oxide. We sacrificed this engine for your benefit, so we don't want any letters from you crying how you blew your motor up making the same mistakes we did.
We first ran the motor sans nitrous to dial in the carb and get some baseline power figures. These are the engine specs used in all tests.
Short block: 391cid, 3.75-stroke4340 forged C.A.T. crank, 4.030-bore size, 5.7-inch H-beam 4340 forged C.A.T. rods,10.25:1 forged JE pistons and moly rings, Clevite H-series bearingsHeads: Holley Street Avenger, ported by Valley Head Service, 2.05/1.60 valves.1.6:1 Lunati roller rockersIntake Manifold: Holley/Keith Dorton-series Strip Dominator PN 300-110Cam: Lunati solid flat-tappet 254/268 duration @ .050, .570/.612 lift, 110 lobe separation, installed straight upCarb: Holley HP 830cfm double pumper PN 0-80785Ignition: Holley Annihilator, 36 advanceFuel: 92-octane, 76-pump gas
Peak HP 494 @ 5,700Peak TQ 482 @ 5,100
Peak Power Levels With Nos KitsTop Shot100HP settingFuel PSI 5.25Timing 34HP 583 @ 5,500TQ 590 @ 4,600