[NOS327]

Was out goofing around the other night, things seemed OK. Race a car with very loud exhaust, two races. Nothing too exciting. Drive home I romp on it once and it's pinging like a MO-FO! WTF!? Somehow decided to go for 40° timing. I finally got around to pulling the plugs tonight and crap.. Speckles on most, porcelain eroded off others, rainbow on a couple straps. Here's two samples. What's with the speckles? and what causes the porcelain to erode like that around the positive electrode?

I compression tested it, 145-160 all around. Thinking about borrowing a bore scope. What should I expect to see? You guys think it's hurt?

Pictures not resized smaller for better clarity. Note: I use bronze looking anti-seize, that's not rust. And my drive home was 15-20 miles of in town driving, so the mixture is/was all over the place for the rest of the discoloration.

Speckles:

Porcelain erosion:

 

[Slow 69 SS]

Too much timing, not enough fuel. Speckles are most likely aluminum from your piston.

 

[Matt Compton]

Definitley too much timing. Going to assume this is a pump gas piece. Plug is pretty hot also may explain erosion. Speckles look like oil to me getting past the ring under detonation. More info on your combinaton would be helpful.

 

[NOS327]

10.9:1 383, Probe Flat tops, plasma moly rings, .028 gaps. AFR 195 Eliminators. Lunati 241/251 @ 050, .590/.590 lift, 112LSA, 108ICL. Hooker Supercomps, Holley Stealthram EFI. Is a mild nitrous deal, but had timing bug out on me a couple weeks ago, so I pulled n2o plugs, put these 3924 plugs in for a couple weeks of timing inspection and no bottle. Pump gas NA and add 110 for spray. Car typically runs great with 37 deg of timing on pump gas, even in the heat. Air fuel is 13.0 at WOT, was a champ all night. My part throttle a/f is 13.8, but my acceleration enrichment is still a work in progress (blips 10:1) and as timing has been giving me headaches, my idle mixture seems to vary (typically richer than I'd like around 12.0:1). After this happened I put timing light on and it is at 40°. so yeah, too much timing.

I compression tested it, everything seems OK. Neighbor says speckles are piston fragments as well. poop.

If this were your motor, what would you do? I really don't want to tear it down. Hoping to take a peak with bore scope over the weekend. Pistons going to be pitted pretty badly you think?

Thanks again.

 

[Uncle Paul]

If the compression was down I would worry otherwise drive it.
Now if you go in the nitrous section I think you will find that Moly rings and nitrous is a No No.

 

[NOS327]

..been told moly ring good to 250hp spray. only spraing about 150 for now and intended to head up to 225-250 type jetting, but like I said, most say moly rings are OK at these "low" nitrous levels.

 

[Mike Beck]

I wouldn't go above 150ish with nitrous. Why the timing problems? What ECM are you using? I have EFI, have done EFI on many, many combos, only one ever gave me problems, it was just the plug wire/ non resistor plug combo...... I run non-resistor plugs all the time, no problem. Those plugs may be too hot. With EFI you can certainly run a nice cold plug and have no problems with them.

 

[slowstang]

moly rings may survive for a while at 250 but depending on where the top ring is at on your piston if its up high ,which i think your probes are then it will put alot of heat on the rings and the moly will come off

 

[NOS327]

I run the Holley commander 950. Got a few years with it, never had these timing issues. Suspecting rotor phasing or maybe dist gear coming loose on shaft. Pulling down to inspect tonight. If I don't find anything, I'm going to throw a whole new distributor assembly in to rule out pick-up and module.

slowstang, you are right, short top ring land. Most likely hang around the 225pills. My tune-ups are usually pretty close, got wideband and keep close eye on plugs. Hoping it'll get me by for a year or two.

 

[gray86hatch]

I have never ran one that lean. You are playing with fire that much timing comp and afr on pump gas. Then spraying it. If the plug looks like that the damage was being done and the car had slowed as a result. Mine slows way before you see something on the plug.

Tim

Tim

 

[NOS327]

13:1 A/F at WOT with 8.4 DCR on 91 octane N/A is playing with fire?

I've been fiddling with the car all day, things seem happy. I added some 110 to the tank to get the octane up a bit, just drove around with the wife for an hour, few hits, life seems good.. Doing some pre-emptive replacements on distributor, pick-up, module, and updating firmware on ECU this coming week....just in case.

 

[Faulty81]

no its not, that a/f is fine (motor only), but 40* is to much IMO . I get 12.6 13.1 WOT for A/F with 93 octane running 19* int and 18* advance

 

[Mike Beck]

NOS327, I have a 383 in the wifes car and with pump gas I can't go above 34 total without the possibilty of rattling it. I can do 36 in good air, but in the heat I can't keep the car below 170 and it will rattle a bit. I just leave it at 34 total all the time.

When I spray it I pull a lot to be safe since I don't put race fuel in it. Have shot it with 150hp with no problem but I pulled 8 degrees from the 34.

Are you running a wet-system or do you fool the Holley to do the fuel and timing?

On pump gas you should run it between 12.0 and 12.5 A/F. Put it on a chassis dyno and try it sometime.

 

[Faulty81]

MIKE, on a "daily street car" isnt 12.0 rich ???? i agree with the timing, 40 is way to much.

 

[Mike Beck]

I am only talking about full throttle. At part-throttle run that baby 14.5 to 15.0 A/F, as lean as you can and with as much timing as you can. If you have trouble with tip-in and can't get it right with the accel pump then run it fatter 'till you like it.

That's the beauty of EFI, we can do whatever we like with timing and fuel at any rpm and load on the engine.