Nitrous blowing intake manifolds

Aaron · Post by **Aaron** » Mon Oct 10, 2005 6:51 pm

I'm sure we have all seen the videos, a Cobra blowing its intake/throttlebody across the room, the Vette blowing its intake manifold through the hood, etc.

My question is, why does the nitrous cause intake manifolds to blow off (Most commonly in the plastic composite manifolds found on the new LSX motors)? I can see a forced induction (Turbo/Supercharged) blowing them because the manifolds are physically under pressure, but to my knowledge the nitrous doesn't pressurize the manifold at all, right?

The only thing I could thing of is the motor somehow backfiring, but that is pretty rare with fuel injected cars, especially ones with ECU's as accurate as today's OBDII systems.

The Corvette Z06 I referred to:

S8n · Post by **S8n** » Mon Oct 10, 2005 6:58 pm

Fuel puddles in the manifold and then ignites. Usually with a wet kit that is before the throtle body. The LSx manifold has a nice flat bottom for fuel to sit on.

Mach10 · Post by **Mach10** » Mon Oct 10, 2005 7:22 pm

Fuel + air + spark = Explosion :scratch:

Aaron · Post by **Aaron** » Mon Oct 10, 2005 9:00 pm

Mach10 wrote:Fuel + air + spark = Explosion :scratch:

No shit?

Just traditionally the fuel is sprayed almost directly into the cylinder, so doesn't have a chance to ignite really, and there isn't normally a source of spark in the intake manifold.

And for reference, fire needs air, fuel, ignition source, and a chemical chain reaction, not just spark air and fuel.

Thanks S8n, I think I understand now, but you'd still need some sort of spark, I'm guessing it either gets that hot, though I'd think the intake would melt first, or a backfire sends a flame up the intake tract.

S8n · Post by **S8n** » Mon Oct 10, 2005 9:08 pm

aaron wrote: Thanks S8n, I think I understand now, but you'd still need some sort of spark, I'm guessing it either gets that hot, though I'd think the intake would melt first, or a backfire sends a flame up the intake tract.

Exactly. Hence the term "nitrous BACKFIRE". Combination of poor air/fuel ratio, too aggresive cam profile, or just one really lean burn can put fire into the intake. Basically a poorly setup nitrous sytem (biggest is probably not using a window switch or WOT switch not adjusted properly), or a malfunctioning system (plugged nozzle)

Aaron · Post by **Aaron** » Mon Oct 10, 2005 9:35 pm

S8n wrote:
aaron wrote: Thanks S8n, I think I understand now, but you'd still need some sort of spark, I'm guessing it either gets that hot, though I'd think the intake would melt first, or a backfire sends a flame up the intake tract.
Exactly. Hence the term "nitrous BACKFIRE". Combination of poor air/fuel ratio, too aggresive cam profile, or just one really lean burn can put fire into the intake. Basically a poorly setup nitrous sytem (biggest is probably not using a window switch or WOT switch not adjusted properly), or a malfunctioning system (plugged nozzle)

Ahh I see, thanks for the help.

Was just curious, I don't have any nitrous plans anytime soon, or anytime at all. Though I would like to see what it could do for our 1986 Accord, 12 valves of carbureted fury :love10:

Blue Shift · Post by **Blue Shift** » Tue Oct 11, 2005 3:33 am

Nitrous is obviously an oxidizer. An intake manifold charged full of fuel and nitrous probably makes a pretty nice bomb if ignited. As said above, I bet the wet shot really does wonders in that department since you have a shot of fuel and nitrous already premixed.

In those little hobby torches, they use a cartridge of nitrous and a cartridge of butane to make a flame over 4500 degrees. A well mixed butane/air mixture burns somewhere around 2500 degrees. A mix of fuel and nitrous isn't really something you want to mix together and light off in an enclosed container...

The Dark Side of Will · Tue Oct 11, 2005 10:56 am

aaron wrote:
Mach10 wrote:Fuel + air + spark = Explosion :scratch:
Just traditionally the fuel is sprayed almost directly into the cylinder, so doesn't have a chance to ignite really, and there isn't normally a source of spark in the intake manifold.

And for reference, fire needs air, fuel, ignition source, and a chemical chain reaction, not just spark air and fuel.

ignition source = spark and fire IS a chemical reaction
fire doesn't need air... just oxidizer.
The less you open your mouth the more time you have to listen and learn.

You're thinking of direct port N2O, while most of these backfires come from "wet" N2O sprayed at the TB. Since port fuel injection is de rigeur on modern engines, modern manifolds are no longer designed to be "wet", and thus may have puddle points or various other characteristics that are not desirable for a "wet" manifold.

Aaron · Post by **Aaron** » Tue Oct 11, 2005 2:38 pm

The Dark Side of Will wrote:ignition source = spark and fire IS a chemical reaction
fire doesn't need air... just oxidizer.

But in order to have the flame the fuel source needs to go through a chemical chain reaction, normally initiated by the presence of heat/spark/air.

You're correct on the second point, I just normally say air out of habit.

Kohburn · Post by **Kohburn** » Tue Oct 11, 2005 2:42 pm

the flame IS the reaction - its just rapid oxidation

to say that you need a chemical reaction to get a flame is redundant

Aaron · Post by **Aaron** » Tue Oct 11, 2005 3:02 pm

Kohburn wrote:the flame IS the reaction - its just rapid oxidation

to say that you need a chemical reaction to get a flame is redundant

WRONG. The flame causes the chain reaction. But in order to get the initial flame, the fuel source must go through the reaction. THis reaction can be caused by a flame, but if its the initial ignition, then it is most of the time caused by high heat, spark, and air.

Remember the degree I'm 60% of the way through is Fire Protection and Safety Tech. I've had more classes on fire ignition, detection, and suppression than most firefighters.

Kohburn · Post by **Kohburn** » Tue Oct 11, 2005 3:25 pm

aaron wrote:
Kohburn wrote:the flame IS the reaction - its just rapid oxidation

to say that you need a chemical reaction to get a flame is redundant
WRONG. The flame causes the chain reaction. But in order to get the initial flame, the fuel source must go through the reaction. THis reaction can be caused by a flame, but if its the initial ignition, then it is most of the time caused by high heat, spark, and air.

Remember the degree I'm 60% of the way through is Fire Protection and Safety Tech. I've had more classes on fire ignition, detection, and suppression than most firefighters.

OMFG - the spark triggers the chemical reaction between the fuel and oxygen - the flame you see is one of the forms of energy released during the chemical reaction

i thought you were in college? :scratch: its just basic chemistry..

the flame/explosion is on the other side of the equation.. (and yes there are other triggers than just a spark - but we are talking about a gasoline engine here (diesel is heat/pressure) -- chapter 5 - balancing chemical equations.

Mach10 · Post by **Mach10** » Tue Oct 11, 2005 3:31 pm

Dude, you're going to fail that course. Oxidation isn't a chain reaction.

A Chain reaction is a series of reactions where the product of one stage is the required element for the next stage.

The flame or spark is the input energy for a combustion energy. But it can also be replaced with heat and/or a catalyst (such as platinum for hydrocarbon/hydrogen based reactions).

The flame is the RESULT of the reaction, jackass. Heat, sound, and light are the energy by-products of any number of hydrocarbons reacting with oxygen. (or the released oxygen supplied by nitrous oxide). If the flame occurs in the presence of any unoxidized reagents, it provides the initial reaction energy for any other reactions. Energy input can't be described as the chain element.

Again, all Aaarronn wants is for us to get on our knees and pray to his mighty leet skills. If he knows more about heat and fire than most fire-fighters, god save anyone who calls 9-1-1. :knob:

I took Physics and Chemistry in University for 2 years, but you don't see me ragging on your 9 month Community College cert.

whipped · Post by **whipped** » Tue Oct 11, 2005 3:36 pm

I saw a fire once.

Aaron · Post by **Aaron** » Tue Oct 11, 2005 3:42 pm

Mach10 wrote:A Chain reaction is a series of reactions where the product of one stage is the required element for the next stage.

The flame or spark is the input energy for a combustion energy. But it can also be replaced with heat and/or a catalyst (such as platinum for hydrocarbon/hydrogen based reactions).

That is exactly what I'm trying to say.

But the flame itself can cuase nearby fuels to undergo the chain reaction and thus ignite, as it produces heat. This is how spot fires ignite.

Oh, thanks for letting me know that the 4 year Bachelor's of Science degree I'm working on is actually a 9 month certification...

Mach10 · Post by **Mach10** » Tue Oct 11, 2005 4:20 pm

aaron wrote: Oh, thanks for letting me know that the 4 year Bachelor's of Science degree I'm working on is actually a 9 month certification...

How the hell did you manage to get through 2.5 years without knowing how an exothermic reaction works? "Flame" isn't a reagent, unless you were born in the 1300s. It's not a material, and it's not part of a chain reaction.

BURNING FUEL IS NOT A CHAIN REACTION.

Fissioning Uranium is a chain reaction.
CFCs reacing with O3 is a chain reaction.
maltose-maltase enzyme reactions are chain reactions.

I fully support anyone who wants to get an education... But I'm disturbed that it can be so badly lost on some people :p

Explain how an Anthropology major/Psych minor (yes, I switched degrees) can know more about chemistry than a BaSC with more classtime experience. Were you sleeping or something? :scratch:

Aaron · Post by **Aaron** » Tue Oct 11, 2005 7:51 pm

Mach10 wrote:BURNING FUEL IS NOT A CHAIN REACTION.

I didn't say it was. The burning of fuels causes nearby fuels to undergo the chemical chain reaction necesary for them to ignite.

I said this, "The flame causes the chain reaction." This was wrong of me, I should have phrased it "The flame CAN cause the chain reaction on nearby fuels."

Mach10 · Post by **Mach10** » Tue Oct 11, 2005 7:54 pm

I'm just repeating myself. There is no chain reaction.

chain reaction
n.
Physics. A multistage nuclear reaction, especially a self-sustaining series of fissions in which the release of neutrons from the splitting of one atom leads to the splitting of others.
Chemistry. A series of reactions in which one product of a reacting set is a reactant in the following set.

Did you take chemistry in Hindu or something?

Aaron · Post by **Aaron** » Tue Oct 11, 2005 8:10 pm

The Fire Tetrahedron, taken from http://www.matchrockets.com/fire/firemain.html

Taken from http://www.ci.phoenix.az.us/FIRE/homefire.html, "Fire occurs any time four elements are present - fuel, heat, oxygen and the chemical chain reaction. When these four elements are together, fire occurs. If any one element is removed, fire is prevented. These elements are collectively known as the "Fire Tetrahedron" or the "four faces" of fire."

Do you need more, or is that enough?

Aaron · Post by **Aaron** » Tue Oct 11, 2005 8:16 pm

I somehow got confused in one of my earlier posts, saying that the 4 ingredients were "air, fuel, ignition source, and a chemical chain reaction."

So what can I say, but oops.