Maybe Im missing something here. I never really gave it a second thought since the common answer is "fuel puddling in the intake". But that cant be the correct reason. Fuel in liquid state will not ignite...only vapor. As a matter of fact gasoline is more flammable in a well atomozed state, such as exiting a nozzle.

What is the ignition source?

I have my own theories and will share them. But first Id like to hear some others thoughts on the matter.

<small>[ March 15, 2003, 03:11 PM: Message edited by: 383LQ4SS ]</small>

 

what if a sparkplug lit when the intake valve was open?

 

A sloppy timing belt can account for some... or timing too far advanced.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by 383LQ4SS:
<strong> Maybe Im missing something here. I never really gave it a second thought since the common answer is "fuel puddling in the intake". But that cant be the correct reason. Fuel in liquid state will not ignite...only vapor. As a matter of fact gasoline is more flammable in a well atomozed state, such as exiting a nozzle.

What is the ignition source?

I have my own theories and will share them. But first Id like to hear some others thoughts on the matter. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Finally someone gets it!. You just made my friday so much better! <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

383LQ4SS,
You are way ahead of the game my friend. Fuel puddling was proganda come up by NOS to sell dry kits. Lean conditions, rpm (lack or to much), and timing or ignition are some of the more common reasons.

 

They only way you could ignite that "fuel puddle" if you have the intake valve open during ignition like valve float or if it runs really lean with a backfire through the intake. I can see it being a real problem on high dose of nitrous and fuel. I only run a 150HP shot and have has no problems.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Tony TNT:
<strong> </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by 383LQ4SS:
<strong> Maybe Im missing something here. I never really gave it a second thought since the common answer is "fuel puddling in the intake". But that cant be the correct reason. Fuel in liquid state will not ignite...only vapor. As a matter of fact gasoline is more flammable in a well atomozed state, such as exiting a nozzle.

What is the ignition source?

I have my own theories and will share them. But first Id like to hear some others thoughts on the matter. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Finally someone gets it!. You just made my friday so much better! <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

383LQ4SS,
You are way ahead of the game my friend. Fuel puddling was proganda come up by NOS to sell dry kits. Lean conditions, rpm (lack or to much), and timing or ignition are some of the more common reasons. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Allright I am going to set you straight. TNT and NX would like everyone to believe that a wet system is the safest thing on the planet. Plain and simple EFI manifolds suck *** at flowing fuel. Ever notice how rough a dyno pull looks with a single nozzle wet system. Plain and simple the mixture in every cylinder is different. This causes each cylinder to produce different amounts of cylinder pressure. What causes a backfire on any engine? A lean cylinder causes a backfire. At this point you have all that fuel in the manifold ready for ignition. The biggest problem people have with dry systems is that they don't understand how they work. Now being as intake manifolds are designed to flow equal amounts of air to each cylinder wouldn't nitrous have a better chance of getting to each cylinder equally since it much lighter than a fuel molecule. I build dry systems for NMRA Real Street that will make 200hp more than the competitors best single nozzle system. I'm issuing the challenge. Let's see what you got.

 

Thanks for the replys guys. But lets not turn this into a "which kit is safer, wet or dry" thread.

Lets discuss wet kit nitrous backfires only.
And when giving your reason please provide a description of how its possible.

A few guidelines that seem to apply to wet kit nitrous backfires:
1) They occur usually at lower rpm.
2) They occur more frequently as the shot size increases
3) they are more prone on some intakes/cars than others.

NOS Nelson...thanks for registering <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> ..how would a lean condition cause a backfire. What would be the ignition source?

<small>[ March 14, 2003, 03:35 PM: Message edited by: 383LQ4SS ]</small>

 

Yes....it seems valve float would definately give the correct circumstances for a backfire. I havent seen many high RPM backfires though. I have only seen...with my own eyes...backfires at lower rpm. And really, Ive only seen it happen to a ton of crustangs <img border="0" alt="[jester]" title="" src="graemlins/gr_jest.gif" /> .

Anyone else see any high rpm backfires? Or mostly lower rpm backfires?

 

The heat generated by a lean mixture will ignite the fuel as soon as the intake valve opens. Carbed plate systems do the same exact thing when they are set-up to lean. Why do pistons melt when an engine is run too lean? Because of heat. Some manifolds such as the 4.6L 2V ford manifold make fuel flow much more difficult thus leading to lean cylinders. I'm not here for war..because I know i'll win. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> I am tired of reading and hearing about the nonsense being promoted in the nitrous industry. If you do not understand how a dry system works then don't try and criticize it.

 

No...no need for war. We should be able to have a level headed tech discussion. So if nyone has ANY theories...throw them out on the table without fear of being flamed.

For example. I dont entirely buy the lean theory. reason being...i have seen plenty of wet kit go severely lean with no ill effects and no backfires. Also if the cylinder is lean that would lead to a more rapid combustion of the AF mix in the cylinder. So the "fire" would be long gone by the time the intake valve opened. I suppose if severe detonation were takig place a dieseling effect could happen though.

Anyways...my theory is almost the opposite. I do believe it has to do with puddling fuel. But I dont believe it ignites in the intake. I would think if fuel did puddle...it would migrate towards the cylinder and some unatomized fuel would make its way into the cylinder. This fule would be unlikely to have a complete burn and may still be combusting as the intake valve opens causing a chain reaction back up into the intake. There are several factors that seem to corroberate this.
The lower the rpm you spray the larger the ratio of nitrous/fuel to regular intake charge, the lower the velocity to keep the fuel in suspension, the more likely the backfire.

The intakes that are not wet kit freindly are the ones that obviuosly terrible for having fuel flow down them. Which leads me to believe there is a "puddling" problem that is contibuting. If it were just a lean condition causing it...it seems the intake design would be less of a factor than it is.

Now this is a tech discussion...feel free to rip into the above. But in a constructive way. I dont want this to be ruined by big egos or general bias for one kit or another. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />


PS....I run a 200 shot dry kit and I am partial to dry kits as well but believe both have thier merits.

<small>[ March 14, 2003, 06:37 PM: Message edited by: 383LQ4SS ]</small>

 

Have somebody ever tried to drill and tap the back of the intake for a dual nozzle setup spraying from front and rear????? No flames for stupidity just a thought??????? <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />

 

going from the rear would not allow the nitrous to be metered, if its a dry system, and you would be going against the airflow, so i dont see it effecting any other than teh back cylinder, and possibly just the one side thats farther back.

 

I was speaking of a wet setup....and you could jet appropriatley,,,,Like I said just a thought... <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

 

How about going with a direct port fogger

 

The only time I've ever personally experienced a backfire was on my old direct port setup. I ran my bottle pressure up to ~1800 psi on acciednt and then tried it anyway <img border="0" title="" alt="[Roll Eyes]" src="images/icons/rolleyes.gif" /> This resulted in a nice explosion. Everything besides my bottle pressure was the same and I never had any problem with the setup before or after the ignorant bottle pressure incident.

Jeffrey

 

I think NOS Nelson and 383LQ4 both have their good points.

383LQ4, you say backfires could be caused by fuel and nitrous atomizing in the intake, but that contradicts your low RPM theory. I would think that less atomized intake charge would be less likely to burn because it's velocity is less...?

Here is another issue to think about:

Does the extra fuel from the wet kit CAUSE the fire or the nitrous?

That's all I have for right now...good thread.

 

Nitrous in itself is absolutely non flammable. If a cylinder runs lean it builds heat. Once the intake valve opens the fuel hits that heat and is ignited. There is no way possible for it to be ignited from running too rich as that would cause a pop in the exhaust and not the intake. As for floating intake valves you have the compression stroke to follow way before the spark plug fires. An engine is an engine regardeless of size or injection type and if you run them too lean they are going to backfire out the intake. This is just magnified with a nitrous system because of the extra fuel present.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by NOS Nelson:
<strong> Nitrous in itself is absolutely non flammable. If a cylinder runs lean it builds heat. Once the intake valve opens the fuel hits that heat and is ignited. There is no way possible for it to be ignited from running too rich as that would cause a pop in the exhaust and not the intake. As for floating intake valves you have the compression stroke to follow way before the spark plug fires. An engine is an engine regardeless of size or injection type and if you run them too lean they are going to backfire out the intake. This is just magnified with a nitrous system because of the extra fuel present. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Yes...good points <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
But wouldnt it be possible for actual liquid fuel to survive one complete cycle back to the intake stroke? A pop in the exhaust followed by a pop in the intake?


</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">383LQ4, you say backfires could be caused by fuel and nitrous atomizing in the intake, but that contradicts your low RPM theory. I would think that less atomized intake charge would be less likely to burn because it's velocity is less...? </font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Actually...maybe I didnt do a good job of describing it..but yes...a less atomized mixture would have a harder time igniting but I think there would be plenty of vapor/atomized fuel to make a nice little boom. Even if only 25% of the fuel dropped out of suspension..that would leave 75% to ignite.

Again...I am still unconvinced in my mind either way. In this situation I think expereiance on the matter would help greatly.

NOS Nelson can you describe some of the circumsatnces that youve seen some backfires?

Anyone else with firsthand experiance with backfires?

Fireball? What were the conditions during your mishap?

 

I have only had one backfire and it was when I had just put my MAF kit on the car. I was making a pass on the spray and the clutch wouldnt let me go into 4th. The engine tagged the limiter on spray and blew up my maf sensors and lower airbox.

I didnt really think of the technical reasons as to why it happened though.

 

Hmmm...that would seem to support the lean theory. Rev limiter cutting out atleast half the fuel momentarily.
Thanks...any more experiances guys?