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Message: <blockquote data-quote="Chris Stephens" data-source="post: 1486622" data-attributes="member: 24095">A couple weeks ago, I pulled out one of the spark plugs that the engine shop had put in before we put it on the dyno. They were NGK non-resistor plugs. Anytime you're running fuel injection, resistor-type plugs are recommended to avoid RFI issues (something the Sniper is known to be susceptible to). I called NGK to get them to cross the part number that was in the engine over to a resistor style of the same reach/heat range/threads, etc.When I told her the part number on the plug, the woman from NGK asked if I was running boost or nitrous. I said no, and she asked if this was a 14-15:1 compression NA engine...I said no. She then said that the plug I had is way too cold for even a higher dynamic (200 PSI cranking) compression naturally aspirated engine. She said they recommend a 6 heat range for most NA engines in the 10.X:1 range, and a 7 heat range for 11.x:1 to be on the safer side since I am at about 10.8:1. While I had her on the phone, I got to thinking about a drive a took the car on a previous day. I started it up and let it idle for a few minutes to warm up a bit. Then got in and took off. The car was running terribly. Chugging and breaking up just driving normal even though it showed the coolant was fully up to temp. I waited until I got on the interstate, then laid into it on the on-ramp. It came to life and ran beautifully! And continued to run beautifully the rest of the drive. I have tried it a couple of times since then, and it does this same thing pretty much every time. I had always assumed it was the cold start enrichment needing some tweaking, but then I got to thinking...I asked the woman from NGK if these two things could be related; could too cold of a heat range be causing it to try to foul plugs at lower RPM and idle, and then when I really jump on the throttle and hammer it, that gets them up to temp and lets them burn off the crap? She said absolutely and said again that I didn't need to run anything colder than a 7 NGK heat range and a resistor-style for the Sniper's sake. She recommended the BKR7E or 4644 part number. I contacted my tuning guy just to get his thoughts, and he fully agreed with NGK. I put those in and BAM! engine starts cold every single time and runs nicely. Still has a bit of a hiccup when cold, but I'm not gonna be the hot rodder that complains about a "bit of a hiccup" on a 635hp engine doing what it's not built to do.</blockquote>