I have a 557 with 10.5 compression and i am running leaded fuel. yesteraday when i was driving home i was going about 50 for a few miles and gave it a little more gas to clear the cylinders and clear her throat. right away i noticed something that sounded like knock or detonation. my coolant was at about 165 or 170, and just cruising i could hear this intermittent knocking like a rock or something was hitting the floor pan. so lifted my foot worried it might be pre-ignition. got out of the truck and did a walk around and nothing seemed out of order, she had a nice choppy idle, no smoke. i made it home. this morning i pulled my plugs to look at them and they all looked fine. no immediate signs of detonation or pre-ignition. they did look "lead fouled" how ever.

here's the question. i'm running autolite 3924 plugs. if i am getting that lead fouling going on should i be using a hotter plug to resist the lead fouling? lead apparently likes to collect on cooler areas like downstream exhaust components, exhaust valves on the back side near the stems, and around the colder areas of the spark plug. but if im wrong i can destroy my engine with too hot of a plug. get colder plugs and i end up with misfires soon again.

what heat range is good for a 557 just mostly street driving?
should i optimize the tuning of the engine first with the 3924's and then dial in the plug heat range?
whats is a typical timing range for idle and total timing on something like a 557?

one other thing. i ran 91 unleaded fine. this is a fairly new issue after running leaded fuel. i started to run vp 110 because i can get it at a pump for 7.35 a gallon and it helps with the run on i experienced with the 91...im getting a feeling my timing is off here.

 

Standard heat range plugs should be fine in most cases, and switching heat range kind of a last resort. Or, if you're making a summertime cross country trip for example.

If seven bucks a gallon is no sweat you should consider a wideband a/f ratio indicator. They are cheap, an oxygen sensor is installed in the exhaust and allows for precise jetting and such by measuring fuel and air ratios at idle, wide open throttle and highway cruise. Engine timing also has a big impact on how the plugs look. So, make sure the carb and ignition is squared away before changing plug values.

 

I'm guessing with a 557 that the engine is a 385-series (460) stroker?

165°-170° water temperature is too cold. It would be better on the engine to be in the 180°-195° range.

Higher compression or (power adders) tend to blow out the spark due to the denser air/fuel charges introduced into the combustion chambers. I don't know what your plug gaps are set at but, a high compression/power adder engine will do better with a smaller plug gap than a wide one. --particularly if you don't have a really high power CD ignition and large gauge plug wires.

For every 75-100 hp above what the engine was rated for (from factory stock), plugs should be reduced one heat range. Your timing may need to be backed off (retarded) as well.

 

Ok. I have access to a wideband o2 sensor logger and I can record data while I drive. I think 180*-190* is optimal as well. It will get there in the summer especially in traffic. I've actually got it up to 210* one day. That was a bit stessfull. The plugs are gapped at .046". And I think the plugs are rated 4 on the heat range. I find it weird I started to notice the sound after like 2 gallons of race fuel was ran. I was reading on a shell website that avagas 100LL at low cylinder temps will allow lead bromide to coat the plugs insulators and short to ground the electrode instead of creating a spark to the wire causing a misfire. So they run airplane engines at like 1800 rpm to raise cylinder temps to prevent the lead bromide from sticking to cooler areas like the spark plugs. With a dominator 1050, could I just be running rich at idle, coating the plugs, then at partial throttle to wot immediately running too lean and BAM a detonation condition? I feel like I should romp on it to clear the cylinders often. I'll start with fresh plugs, and back the timing a few degrees. Then ill tune the carb with the o2 sensor kit.

BTW I am running a summit MSD style box. And a billet distributor. And ford racing 9mm wires with a blaster coil.

 

I pulled the plugs and found they were completely fouled. So I changed them out, re-gapped them to .035" and put them back in, and I still had exhaust popping at about 1500-2000 rpm.

This exhaust I put on is new...
Also, I suspected that the timing might be way off. So I grabbed the distributor and tries to lightly twist it and it turned a bit! So now I am on to that problem. Hooked a light up to it and found that it's initial timing that I set at 12* is now at 0*. F me. So I fixed that. The idle got really smooth and the engine loved it. But I tried to hit the throttle and the popping was still there. Like small after fires.

I also noticed that somehow my fuel pressure went down from 6 to 3. So I started to think I was starving the engine. But I fixed that and brought it back up. The popping persisted.

I've read a few places that the distributor could be the problem. Either the points are worn, or the cap is cracked or the advance curve is too fast.

Since the pressure gauge is after the fuel filter I'll check that too. But at this point I'm thinking of running a vacuum advance distributor. If the mechanical advance is screwed up. Today I'll check the total timing and make sure I'm not way off the map. If I am I have some repairs ahead of me.

I also hope this doesn't mean I have flattened a few exhaust lobes out. Could excessive carbon build up on the valves lead to this? Could leaded fuel be the culprit? It started happening after I started to use vp110.

 

Try it without the VP110.

 

X2 on installing a wide band O2 sensor...that will take most of the guess work out of your troubleshooting. You probably need to change the carb jetting and ignition timing if you are changing from pump gas to race gas. I haven't been racing in a long time so I've forgotten what changes were made when changing to VP fuel. Just put in the O2 and watch the read out as you go down the road. If you're using a data acquisition system you will need to log lots of variables. Other wise a vacuum gauge and an O2 display are enough for me. From here without any data it sounds to me like your engine is too rich.

 

So i have more questions than answers today. But i do have an answer.

after a lot of research and you tube videos. i found a huge issue. everything was pointing at my piece of S**T procomp distributor. so i go out to the truck and pull the cap off and sure as S**T, there was the problem laying on the floor of the distributor housing. The carbon button, or brush had broken off along with the spring holding it in. Actually i think the spring broke and the button fell out. That would explain why the truck all of a sudden for no reason acted weird.

also 3 out of 8 terminals were burnt from arcing. and the rotor was black like a lightning bolt had been hitting it over and over.

which brings me to my new question. How the hell was the engine even firing up if there was no contact between the cap and the rotor? was it arcing from the broken piece of carbon in the cap still to the rotor? if so, that speaks volumes about the MSD blaster 2 coil i have in there. CRAZY!

the procomp should have never went in...getting a Mallory this week.
thanks for the replys...also i'll be taking care of that air fuel issue after she's back running again.