Here are pics of my cylinder number 4 spark plug. The ground electorde was melted off and about 1/8" of the insulator is missing. However, the center electrode has no damage.

http://public.fotki.com/1max2nv/1max2nv/engine/

It looks like I have some initial preignition follow by some sustained pre-ignition.

 

I have done the same thing after only 1 run with BKR7E's as well. Even went to NGK for some advice, they recommended some racing plugs which I tried but they did not work with nitrous, ok N/A but as soon as I hit the spray it starting missing. I got back to them and they said they would call me back but never happened.

Not sure what the cure is, I was even using 114 octane for the nitrous.

Make sure you do a compression check of that cyl to see what it is, it would have caused damage.

Thats why I bought the wideband so I can properly tune on the track. Want to know for sure what the A/F is.

 

Jime,
What's the possibility that I have cause damage to that cylinder? My EGT didn't go above 1400F. What kind of damage could I have caused? Holes in the piston and melted the valves? Was your motor okay after the incident?

 

Didn't do any damage I could see on mine, compression was still ok, but it did scare me a bit. That was the last time I was at the track and only on a 35 shot so I still have to find out why.

I would watch it very closely though, scary sheit.

Not sure of the reason or solution yet.

 

This happened with 125 shot. I thought my plugs were fouled at first. I usually do a quick burst with the nitrous bottle closed to check to see if the fuel solenoid would open. I then ran with nitrous for few seconds and I got the flashing MIL, so I shut it down. I drove the car around NA and it seem fine so I didn't bother to check the plugs. The next day I started to get really bad misfire during NA WOT so I pulled the plugs. I just got a compression kit today so I hope that cylinder is still good.

 

waaaaaaaaaaaaaaaaaaaaaaaaaaaaay to lean change the plugs with new ones (what heat range are you using need to be 1-2 range colder)

 

I did a compression test on all the cylinders tonight.

205 205 205

190 180 190

180 psi is the one that I ran lean on. I don't have any previous result to compare to so I assume I lost 10 psi on cylinder #4.

Any input??

 

Jim,
What were your compression test result from that incident?

 

Mine are still in the 190-200 range. I think I am going to keep it to 100 and under from now on though. I hope to hit a very high 12 next year on a 35, this year was a 13.1. If so I will probably race in the 35-75 shot range. It gives a good advantage even bracket racing to be in the 12's, much easier to race from behind vs the front.

After 2 years of messing around I believe that anything over 100 is pushing the envelope. Oh it will take it for a while but its only a matter of time until you toast it. Its nice to try a 125-150 occasionally if you think you can set a best time but not for regular use.

3.5L can probably handle a bit larger but you are still on the edge, especially if the setup isn't 100% all the time.

 

Preignition won't cause your EGT to rise b/c it's not properly combusting. The extra heat is being absorbed by your pistons, rings, plugs...etc, and usually will not show up as a high EGT spike...