As some of you guys may know, I recently did a "nitrous torture test" on my J32 here on the forum and it recently ended abruptly and pretty catastrophic (broken rod). I consider myself a pretty technical person and knowledgable when it comes to engine performance and something has been ringing my ears lately on the engines destruction...let me explain:

I took the basic approach to running nitrous and like always, ran both a few basic guidelines:
1. Monitor AF ratio while spraying.
2. Don't activate nitrous below 3500-4000RPMs
3. Run a wet system on non-programmable ECM cars
4. Strengthen the fuel system
5. If any knock (aka: detonation) is ever detected, back out!

Let's start in chronological order here and begin with número uno. Ideally, forced induction should be kept around 12:1-12.5:1 AF ratio as this is generally an optimal mixture for high pressure/high temp (big power) applications such as turbo, supercharger and nitrous applications. Rule of thumb is to richen the mixture slightly if you're not confident in your bottom end so that the additional fuel cools the combustion temps down (whole other thread). I was jetted for 10:1-10.5:1 on mine and seemed to be doing fine for most of the 54 bottles. Next was never activating the nitrous in too low of an RPM range. Simple enough to understand why this should never happen. You're filling the intake manifold with LOTS of fuel/dense oxygen without the velocity it requires to move the mixture through the motor fast enough and when it reached the combustion chambers, you hydralock the piston risking bottom end destruction/damage. Third in line was running a wet system on a vehicle that DOES NOT have a programmable ECM that can add adequate amounts of fuel to accommodate the added levels of oxygen. Sure there is room for play in most cars but nobody can accurately determine what that "safe" zone is without first slowly increasing nitrous jet sizes until you run the engine lean...by then you've already jeopardized the engines integrity/mechanical well being if you didn't burn it out the first time it was ran lean! And done get me started on those adding more fuel pressure or larger injectors to accomadate the added oxygen from nitrous...ever heard of fuel trim limits, hmm? Fourth, strengthen up that fuel system. This is simple, more air requires more fuel to make additional power, period. The fuel pump on the car was replaced with a high performance 300lph pump and then I always monitored my AF ratios as well as installed a low fuel pressure safety shutoff switch just to give that added assurance. No issues ever detected. And lastly, back off if detonation is detected IMMEDIATELY! I almost always ran connected to the ECM while monitoring the most important datastreams like fuel trims, ignition states, O2 sensors, and KNOCK. Some of you may remember back when I stated that there was never any spark knock detected and therefore ignition had never retarded to protect the engine. This led me to believe that the motor itself was capable of efficiently combusting all of the mixture WITHOUT causing any ill symptoms that indicated otherwise. Here was the mistake and thought I would explain...I learned something new.

Okay, so I'm at the shop getting ready to pull the motor and begin the engine removal process when something smacked me so hard in the face I stopped everything I was doing and went and grabbed my scanner. The failure of the motor itself was rod destruction which in nitrous is almost ALWAYS caused by detonation. But I can specifically recall NEVER seeing any...even at 330hp shots! I hooked up my scanner and began logging ONLY knock sensor output as well as voltage. With my wireless scanner in one hand, and a hammer in the other standing beneath the car with it on the lift, I smacked the block to simulate extreme detonation...nothing. After doing this with no results I gained access to the knock sensor and did a continuity check and it confirmed the sensor was okay but even when a smacked the block with a voltmeter at the terminal of the knock sensor, I got nothing. I promptly ordered another and yielded the exact same results. After doing some researching I found my answer. There are two types of knock sensors. One is a resonant and the other is called a flat response. One is effective at measuring ignition detonation made by incorrect ignition and/or improper combustion and the other one is NOT. Guess which one we have. The one that doesn't: the flat response. If only had this been known I could've swapped it out with a resonance type knock sensor and who knows, could've saved the motor for another 50+ bottles.

Conclusion? Detonation was surely happening during nitrous use...I just don't know at what level. This was supposed to be a test motor so that others could benefit at the level at which to go no further on nitrous but I believe the knock sensor factor gave me an incorrect analysis on the tests purpose.

To those who are running heavy nitrous, beware of this one small mishap and FIND A DAMN RESONANCE KNOCK SENSOR!

It was fun nevertheless!

 

Were there any signs of detonation on the spark plugs during the 54 bottles. When I was using n2o, I would check the plugs whenever the jets were changed and after every bottle just as a precaution.

 

I probably changed the plugs 20 times throughout the entire duration of running spray and each time I did, no signs of heavy detonation were ever seen. Maybe some light signs but this was probably because I was changing them do regularly to try and prevent detonation, lmao.

This next build I'll make sure and have both a performance knock sensor (probably AEM) and an EGT gauge. That way I can keep a closer eye on these things. Also, does anybody know a company that makes a EGT module capable of monitoring 6 sensors at a time? I've seen the others that make them for the AF readings so I don't see why not...