Severe detonation on 383 LT1???
Severe detonation on 383 LT1??? Recently installed a nitrous express 50-150 horse wet kit on my 94 LT1. The motor was designed for nitrous, and has a relatively rich nitrous tune, running plugs that are 2 steps colder than factory. The nitrous is setup to come on at WOT at about 3500 rpm. Easing into the pedal, just before it hits the floor, where the nitrous is triggered to come on, the car detonates extremely bad when the nitrous comes on(so bad that it blew the header gaskets out, on both sides). I know the jets are setup properly, and it does it on the 50, 75, and 100 jets. Never tried the 150 jets, but dont want to til I figure out what the problem is. I have about 60 pounds of fuel pressure at WOT. I noticed a couple problems. Just got the bottle filled, and it is only at about 680 psi un heated. Havent tried the bottle warmer yet. I was able to get the nitrous to work on my other bottle, which has been sitting almost empty for about 2 years, at only about 550 psi, no detonation occured at all, until the pressure got down to about 400 psi where the car shoots flames out the exhaust, probably from the extra fuel and barely any nitrous, as it is a wet kit. Could my problem be just a bad fill? I bought the kit used, and
Im sure it worked in the other car, and Im sure my wiring/plumbing is good. My air fuel guage goes slightly leaner when it detonates. Any info will help. Thanks a lot, sorry for the long story.
Nick
Im sure it worked in the other car, and Im sure my wiring/plumbing is good. My air fuel guage goes slightly leaner when it detonates. Any info will help. Thanks a lot, sorry for the long story.
Nick
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Joined: Apr 2005
Posts: 685
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From: Clarksville, IN
2 things I notice are 60 psi fuel pressure and 42lb injectors. Your fuel pressure should not be that high @ WOT. It should be around 40 psi. The injectors are a little big for that set-up. I have a similar set-up with LE heads and a slightly bigger cam and run 36lb injectors (Though if tuned right the bigger injector should not be problem). When you group these 2 things with a rich nitrous tune and low bottle pressure, its way too much fuel. This should not cause detonation though. How are you determining detonation? Sound?, computer log? Are you using a wideband O2 with the AFR gauge? If its narrowband you cannot go by that as its highly inaccurate. Like Tony said, how much timing are you pulling out and what is the plug gap?
We need plug gap. And did you detect knock with a scanner?? How lean is it going when the detonation is present. The fact that it goes lean when on the spray is not good. What jets are you using and are you posiutive that the fuel solenoid is working?? I ask this because at such a low bottle PSI if the fuel solenoid is not working it may just cause horrible knocking instead of blowing up, which would happen if the bottle was at normal PSI (1050) without the fuel being delivered. is that a wideband o2 sensor or narrowband showing lean? if its a wideband what exactly was it showing?
Have you pulled your plugs and where any melted?
I dont think ou have detonation...it sounds to me like you are just running SUPER RICH...and even more so when you spray since your bottle pressure is so low.
Detonation usually does not blow out HEADER gaskets...but normally HEAD gaskets and burns plugs...etc.
You need to take your car to a dyno with a wideband...get the AF around 12.5-13.0 and get it running right ALL MOTOR first. Then you need to get that heater hooked up, fresh bottle fill and run with the nitrous at whatever PSI the manufacturer recomends with the recomended jetting...also do this on the dyno with a wideband...or atleast with a wideband if no dyno is accessible. Then try tuning the nitrous combo using the jets from 11.5-12 to 1.
sounds like you have so much fuel its not burning in the chamber completely causing a multitude of other problems to me..
Have you pulled your plugs and where any melted?
I dont think ou have detonation...it sounds to me like you are just running SUPER RICH...and even more so when you spray since your bottle pressure is so low.
Detonation usually does not blow out HEADER gaskets...but normally HEAD gaskets and burns plugs...etc.
You need to take your car to a dyno with a wideband...get the AF around 12.5-13.0 and get it running right ALL MOTOR first. Then you need to get that heater hooked up, fresh bottle fill and run with the nitrous at whatever PSI the manufacturer recomends with the recomended jetting...also do this on the dyno with a wideband...or atleast with a wideband if no dyno is accessible. Then try tuning the nitrous combo using the jets from 11.5-12 to 1.
sounds like you have so much fuel its not burning in the chamber completely causing a multitude of other problems to me..
Im thinkin your right about the fuel situation. Ran it a few more times, with a buddy behind me, and he said it was straight flames out the exhaust. It is running at 12.7 when I hook a wideband up to it, dont know what it is at with nitrous. The slightly leaner situation was not on a wideband, just my air fuel guage on the stock O2. I noticed another thing. If I crack the valve on the bottle with it out of the car, it does not shoot white out, and the nozzle barely even gets cold. On the old bottle, with now about 400 psi, the bottle still freezes up instantly. The plug gap is whatever it is from the factory, according to the sticker on my radiator shroud, cant remember what it is. As for the timing, not sure. I need to throw the tech II on it and check that. How much advance should it have when spraying? Thanks for the info.
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Originally Posted by 94strokedz
Im thinkin your right about the fuel situation. Ran it a few more times, with a buddy behind me, and he said it was straight flames out the exhaust. It is running at 12.7 when I hook a wideband up to it, dont know what it is at with nitrous. The slightly leaner situation was not on a wideband, just my air fuel guage on the stock O2. I noticed another thing. If I crack the valve on the bottle with it out of the car, it does not shoot white out, and the nozzle barely even gets cold. On the old bottle, with now about 400 psi, the bottle still freezes up instantly. The plug gap is whatever it is from the factory, according to the sticker on my radiator shroud, cant remember what it is. As for the timing, not sure. I need to throw the tech II on it and check that. How much advance should it have when spraying? Thanks for the info.
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