tonskiguy

iTrader: (3)

Ok, I'm kind of new to nitrous; however I've read a lot about it and feel fairly comfortable using a 150 wet shot on my 96 Z28. I recently blew a head gasket at the #7 cylinder (see photo). The engine has about 2000 miles on it since it was rebuilt. It is a 383 LT1 2 bolt, forged bottom; static CR is 10.5/1. Dyno proven rear wheel horsepower was 400 before installing the nitrous, so I'm estimating in the 600 range at the crank while on the bottle. The engine has TPIS / AFR CNC heads secured with ARP bolts, and a GMPP P/N 10168457 head gasket. I have a FPSS, a steady 47 PSI fuel pressure, 3 degrees of spark retard via Mallory 685, window switch set on at 3500 and off at 6000, bottle pressure was 925 psi. The gasket blew at about 5000 - 5500 RPM, this was the 2nd use of the evening, and the fourth use overall. All uses were very brief, 1 - 2 seconds. Had a huge steam cloud out of the exhaust and an immediate miss and audible pfft-pfft-pfft noise out of the engine found to be at the back of the engine on the driver's side. I did not get a steady or flashing CEL. I shut it down and pulled it home. Pulled the engine (out the bottom which worked well), stripped the intake and heads and found what I had expected. All plugs, Autolite 103s, looked normal to rich with the exception of the #7 which was predictably steam cleaned with no indication of damage (see pics). I checked the block and the heads for warpage. I did find that the during the last plug change, I inadvertently left my cut off spark plug socket securely nested on the #7 plug. Could this have contributed to the problem, or was it just a poor choice of head gasket to use with nitrous? I'm planning on going back together with ARP studs and SCE ICS Titan head gaskets. I'd like to avoid this happening again, any comments or suggestions will be appreciated.

Robert56

iTrader: (2)

What was your running timing? The #7 usually goes due to a lean condition, and any problem else where, like timing, bad fuel, getting hot, bad or wrong plug etc will set it off.
Robert

Badass 2003 Z06

iTrader: (2)

probably due to too much timing...3* retard isn't enough for a 150shot

moehorsepower

iTrader: (3)

What he said....

rpmauto

iTrader: (14)

was #7 firing, if you left the socket on the plug?? You shouldve had a misfire on startup.

tonskiguy

iTrader: (3)

No, it is a cut off socket, only about an inch or so long, that slips over the plug. The plug sticks through the socket (if you ever changed plugs on an LT1, you would have possibly used one). Plug wire was on and engine ran great since last summer, for at least 500 miles.

I can certainly try more retard, what is suggested for a 150 shot?

tonskiguy

iTrader: (3)

I've got an Actron Scanner that hooks up to the OBDII port, I guess I can monitor tming with that, as well as O2 millivolt readings. I guess I'll do whatever is needed to prevent this from happening again. More suggestions will be appreciated.

Badass 2003 Z06

iTrader: (2)

it really all depends on what heat range plugs & what octane gas you run, but I would atleast retard it by 6*. Make a pull, shut it down..pull the plugs and check for any signs of detonation

tonskiguy

iTrader: (3)

I can do that, but did you see the photo's above of my plugs? They look normal to me, but maybe I don't know what to look for.

Noyzee

iTrader: (37)

no offence, but how do you guys know how much timming he should pull? i didnt see anyplace what he was running for timming? maybe i missed it?

if its stock timming you should be around 19* if you pull out 6* from that you will be ay 13* total timming, yea, car will run great. NOT

with a 150 shot you should be in the 20-24* of timming with that compression if your using the right fuel and spark plugs ect

also need to know what type of N2O system do you have? is it a plate, single nozzle, direct port? that can also help, if its direct port, check the jet, be sure they are the correct size. i have seen a jet labled at .xx and it wasnt right on.
maybe a piece of somthing blocked the jet, and that cylender went a touch lean, a little detination and the iffy head gaskets, and boom.

lots of things could cause that.

tonskiguy

iTrader: (3)

It is a Compucar system with their plate behind the TB, Gas jet-59 Nitrous jet-76 as they recommend. I always run name brand 93 octane with no ethanol. Plugs are Autolite 103s. I guess I really need to monitor my timing and probably AF ratio. As for the timing, I've never checked it with a timing light, nor have I ever recorded the numbers from my scanner. My computer was tuned by PCM 4 Less, I don't know if he leaves it stock or not. I do know he looked at my dyno run (motor only) and wanted to richen up the AF, but like a dumb ***, I thought I knew better and told him not to because the car always seamed to run on the rich side during normal driving, with black exhaust and plugs, and rich stinky exhaust, but it always ran strong when driven hard. I will check my lines and nozzles, and check my timing when I get it back together. Any other ideas or suggestions are always welcome.

Noyzee

iTrader: (37)

if it was tuned by them, its probably very high on the timming side. find out timming and drop it down accordingly be sure to lower the timming a touch more if your running pump gas. also your af shouldnt be on edge running on motor, if it is you will be realy on edge with spray