2nd Generation Specific 1986-1992 Discussion

Just experienced a nitrous backfire..... not good

Old 10-01-2006, 11:04 AM
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Ok here it is. I'm asking for help by those with personnal experience with running nitrous oxide on a rotary. Last weekend I installed a wet nitrous kit on my 89 N/A. It was a used kit so I went ahead and verified every solenoid, lines, fittings etc before starting anything. So I know that the system is in good condition. I did also wire my 5th and 6th port open just to be sure that they wouldn't stuck in the closed position. So friday night I went with my buddy to try it out and we jetted it for a 35hp shot, start slowly then move your way up right ? Ok, so we went and hit the switch... first thru 3rd gear no problem, I made sure not to floor it before 4k rpm and it worked perfectly. Very fun I must say The thing is that yesterday, I was feeling more confident about it so we jetted it for 60hp. Went for a test ride but this time, I sprayed in 3rd gear on the hiway around 5.5k. It fluttered a bit so I let go of the throttle and BANG ! Big nitrous backfire, blew up the AFM from the inlet duct, my cone filter is all smahed up and a couple of vac. lines blew up.



My question is, why the hell did that happen ???

I have a cold air, custom exhaust (straigth pipe, no headers tho), 5th and 6th ports were wired open and I installed an FD pump for enough fuel flow. The fogger is about 7 inches before the throttles plates, on the soft plastic inlet duct.



Is the fogger dispositon by itself could cause this ? Cause I'm running out of ideas since I pretty much ruled out everything else.

Ohh, and I did not change the timing but verified it before and it was right on.



Any pointers would be appreciated.

Thanks
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Old 10-01-2006, 08:45 PM
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The N/A manifold is a scary place to be running fuel and nitrous through. Especially 89-91 with the VDI.



Convert over to direct port, try to avoid dead spots where fuel could puddle. Get a window switch and stop worrying about rpm.



Check your timing, jetting, and fuel pressure again. Did I mention to check your jetting?





Oh, and dont use teflon tape, use paste.
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Old 10-02-2006, 06:22 PM
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Ok, thanks for the reply RONIN FC.



I do agree about the manifold, but I just taught that with the air velocity and the engine bay being quite hot in our cars that fuel shouldn't puddle in there. No more money available for now so I'll pass on the direct port upgrade. For the time being, I'll put more thought in the location of the nozzle and reduce the shot back to 35 hp.



Ohh and sh*t I used Teflon tape…… omw to the store.



Will check timing, fuel pressure, spark plugs etc. again anyway cause right now the car runs like crap. I will also send my injectors for cleaning and verify compression and re-check all solenoids.



Quite sad if the engine got damaged… I just overhauled it (good compression, leaking oil seals).



Ohh and could the exhaust be too restrictive and too much backpressure be part of the cause ?



More feedback in a couple of days.
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Old 10-02-2006, 08:54 PM
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1mm of manifold gasket hanging into the runners can take fuel droplets out of suspention. Not to mention the moving mechanisms in the manifold.



Its a shame you wont convert your n2o system to direct port. The engine can run 60 hp without breaking a sweat.



If you used teflon tape, check your n2o solenoid filter for pieces of it. Thats the only concern, the tape wont burst into flames or anything.



If the exhaust is restricted, like a plugged cat convertor, theoreticaly the reversion can ignite the mixture in the manifold during overlap.
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Old 10-04-2006, 06:25 PM
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Ok..

Verified compression yesterday.

110 all around, so the engine is fine.

Need to test the AFM, ACV etc to get it to run good again.

I don't have much time to play around with the rex right now, best friend getting married this week end and it is quite crazy at work at the moment so its gonna wait.
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Old 10-04-2006, 11:34 PM
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Just my 2 cents but at work when we dyno our race motors they like the air a little on the warm side. When the air temp was about 70 deg it lost HP cosiderably. Then we bumped it up to 90 deg and it pulled up. weird how it works but i would recommend losing the cold air intake. Hope i could help even though im a neb here i do have to work on these little probs everyday at work haha. Good luck!
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Old 10-05-2006, 04:36 AM
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My guess is that the fuel simply pooled up until an explosion. Its pretty common if you have edges (or like ronin said, a gasket edge).
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