z-ya Posted August 29, 2006 Share Posted August 29, 2006 Hear's a good one for ya.... I was at the track this weekend with the supercharged car, and it ran great for the first 4 sessions. Then it started running progressively worse. I checked everything, and then the plugs. Three plugs had gaps that we way off. Two the gap was almost closed, and the other the gap was probably 5 times what it should have been. The plugs do not look like any detonation happened, and the compression on all cylinders is within spec. I corrected the gaps, and it runs fine. Any ideas? A couple photos from the event: Quote Link to comment Share on other sites More sharing options...
Twizted Posted August 29, 2006 Share Posted August 29, 2006 That happened to a friend of mine once. He had dropped a small screw into the head when he was changing the valve cover gasket. It bounced around between different cylinders before being discharge out the exhaust. We didn't think that was the cause until we couldn't find that one screw, then it dawned on us. We did find the screw later in the muffler. Just a thought. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 29, 2006 Share Posted August 29, 2006 Good photos!!! Wish I had shots like that of my car! Looks like you're in need of some more rear roll stiffness or maybe just stiffer springs all around... Quote Link to comment Share on other sites More sharing options...
z-ya Posted August 29, 2006 Author Share Posted August 29, 2006 Nope, nothing in the cylinders that I know of. Unless, somthing got in through the intake. I'm not using an air cleaner now. It had just rained, so there was no dust or dirt. Maybe some rubber? Hopefully it's out of there by now. I have a Supertrapp on there, I should see if there is any debris in there. Yea, the photos came out good. I'm running 225lb front, and 250lb rear. I think I do need stiffer springs. I've got pretty heafty sway bars but it still has a fair amount of body roll. Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted August 29, 2006 Administrators Share Posted August 29, 2006 Pete, GREAT pics. Thanks. It sounds like your ground electrodes possibly got so hot they were essentially melting and depending on which way the ground electrode was facing, up or down, (plug index), dictated which way the ground electrode “fell†as it went elastic. If this is the case, you’ll need colder spark plugs. You should be running at least a 7 or an 8 heat range in NGK speak. If the ground electrodes did get so hot they were essentially melting, 2 heat ranges colder would be a good starting point. Of course, with a much colder plug, that means all the time the engine is running and you are NOT working the engine, the plugs will be carbon fouling as they won’t be in their heat range till you have been standing on it for period of time. Quote Link to comment Share on other sites More sharing options...
z-ya Posted August 30, 2006 Author Share Posted August 30, 2006 Paul, Thanks, I think you figured it out. I'm running BP6ES in there now. I'll try some BP8ES I have on hand. It makes sense that if the plug is not dissipating enough heat (because it is not cold enough), the electrode will get too hot. At this point the cylinder pressures will cause it to move because the electrode is fairly soft. Thanks, Quote Link to comment Share on other sites More sharing options...
Sam280Z Posted August 30, 2006 Share Posted August 30, 2006 My understanding is that the heat range of a plug only affects the temperature of the center electrode and insulator. It does this by varying the amount of contact area and path that the heat has to travel through to get to the grounded portion of the plug. The ground electrode and outside threaded portion of the plug are the same regardless of the heat range and should be only slightly above the temperature of the head. I wonder if it is possible to have defective metallurgy in the plug or if you are a bit too lean on the top end. Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted August 30, 2006 Administrators Share Posted August 30, 2006 My understanding is that the heat range of a plug only affects the temperature of the center electrode and insulator. Sam, I respectfully disagree. The ground strap, if the proper heat range, will indeed run hotter. Taken from Champion spark plugs.... "If you make modifications such as a turbo, supercharger, increase compression, timing changes, use of alternate racing fuels, or sustained use of nitrous oxide, these can alter the plug tip temperature and may necessitate a colder plug." Also, the way I understand choosing the right temp range is shown in the below pic... This clearly illustrates the ground strap running hotter. Twenty bucks says Braap is right Quote Link to comment Share on other sites More sharing options...
Sam280Z Posted August 30, 2006 Share Posted August 30, 2006 Learn something new every day. It sure looks like my understanding was incomplete... Now I'm curious as to why... I don't make bets unless I'm certain I will take your money. I especially don't make bets when I certain you will take mine Sam Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted August 31, 2006 Administrators Share Posted August 31, 2006 Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted September 1, 2006 Administrators Share Posted September 1, 2006 Pistons struck electrodes at high rpm. DAW How does that *open* a gap? Quote Link to comment Share on other sites More sharing options...
z-ya Posted September 1, 2006 Author Share Posted September 1, 2006 I find it hard to believe that I stretched the rods when the rev limiter is set to 6500RPM. And, one of the gaps was at least 5 times what it should have been. I'm still convinced I had the wrong heat range. Wll know for sure after next event in October. Quote Link to comment Share on other sites More sharing options...
mobythevan Posted September 1, 2006 Share Posted September 1, 2006 I saw a SBC race engine once that the pistons hit the electrode, but here was the deal. It was a huge domed piston and if the plugs were not indexed to keep the electrode up then the piston dome hit them and closed them down. Unless your running a dome piston like that engine I see no way of the piston contacting the plug. Quote Link to comment Share on other sites More sharing options...
jnjdragracing Posted September 1, 2006 Share Posted September 1, 2006 I would have to concur with Braap and Rontyler on this one. John Quote Link to comment Share on other sites More sharing options...
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