I’ve gathered all the parts for my HEI conversion that are outlined on this forum. But I think I might have fouled up. I bought the NGK ZFR5N plug for my truck, which is a 1985 D100. I bought those because that is the plug used on the oscilloscope illustration in the HEI conversion article. I failed to read the last few sentences in the article where it states they are long nose plugs. Do I need to return them and buy the plug that NAPA calls for?

I have run them in both my slant vehicles with stock and near stock engines and they worked great. I would not run them in a high compression engine.

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“Buy the ticket, take the ride.”
― Hunter S. Thompson

Yes, you need NGK UR4 tapered seat spark plugs if you do not have spark plug tubes. Your '85 was not built with spark plug tubes.

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Joshua

Good call Joshua, I completely missed the year part of it. I've never had a peanut plug head.

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“Buy the ticket, take the ride.”
― Hunter S. Thompson

Ok thank you for the help. I’ll get the right plugs coming.

You have a '75-up head that won't take the ZFR5N (or any other gasket-seat spark plugs as required for '74-down "drool tube" heads). NGK 4s are too hot-running a plug; you want 5s or 6s to allow maximum spark advance without ping. Specifically, start with these.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Ok cool man, I really appreciate the help here. Friday June 21 is when I will be doing the conversion. I went to Summit here in McDonough, GA and returned the ZFR5N plugs. This site is such a help for my ol’ hay haulin Slant Six. I wish I could upload a pic of my /6 in action!

SlantSixDan, I learned a lot from the HEI conversion article and this forum itself. I’ve watched many YouTube videos and had no idea what the 225 /6 was capable of. I use mine for hauling hay back to our farm, towing and daily driving. I’d like to share with y’all the back story of the truck. It was for sale in the town square where I live and I picked it up for $1,500. It didn’t run well and the guy was tired of fooling with it. I sanded, primed and painted the stock steel wheels black and wrapped them with new raised white letter tires. I put a headlight switch in it because I had no running lights. I fixed the wiper linkage. It had no thermostat in it because he said it runs hot, which it did because I checked with my infrared gun. I installed a new radiator, water pump, fan clutch and 180° thermostat. I got all the turn signals working and had to replace the master cylinder. Then, after further research, I learned about that confounded Chrysler Lean Burn system. Someone before me ripped it all off, but did a botched job. The distributor did not have a vacuum advance, nor did the flyweights work. It would not advance its timing as rpm increased. The only thing I knew to was put a timing light on it and set it at base timing that Chrysler stated on the decal under the hood: 16°. So that led me to this forum and the HEI conversion. I’m looking forward to it. I also bought a tach and a gauge cluster with coolant temp, battery voltage and oil pressure. It’s a base model truck, so all it has is a speedo, fuel gauge and ammeter. Sorry for the novel, but this is a great forum.