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Sorry I did search but finding a lot of conflicting things. Im looking to go back to the VPowers, I have a big turbo and supporting mods. Probably in the 400hp range so I was looking at 1 or 2 colder range. Since 4306 seems to be stock range, what are the vpower numbers for the other two? I see lots of people still run those 4306s on higher hp srts so perhaps I dont need

Anyhow thank you
 

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Spark Plug heat range vs. modification rule of thumb is to go 1 heat range colder for every 75-100hp added. A spark plugs' heat range is its ability to remove excess heat from the combustion chamber. Running too hot of a plug is never a good idea as it will cause engine damage. If the excess heat is minor, this may take some time, but down the road you're likely to see something like a burnt piston.

So I would certainly go at least 1 heat range cooler. If you want to play it safe, best thing you could do is get your baby on a dyno for a couple of pulls so you know exactly where its at. if you're really in the low-mid 400s, you'll probably need to go 2 steps colder than stock.

NGK does not, and likely will not ever, make the standard nickel plug in a colder heat range (6 and 7). The 6 and 7 heat range iridium plugs were created solely for Dodge and Chrysler tuners (especially PT-Cruiser and SRT4 owners). As they were manufactured solely to fill a niche market, their profit margin on a standard nickel plug likely wouldn't be enough to justify its production. The only chance we have of a 6 or 7 heat range nickel plug would be if an engine was produced that required that plug in that heat range OE.

If you're looking for performance, and wanted to try something new, you have the following options:

Denso ITL20 - In the SRT4 dyno session we did a few years ago, the Denso iridium plug placed 3rd overall in performance. However, we've only had the 1 dyno session on an SRT4, and on all other vehicles we've tested, Dodge's included, Denso iridiums kick butt. ITL20 is 1 step colder than stock - 2 steps colder is not available.

Pulstar EF-1 - In the dyno session we did a few years back, the Pulstar plug produced the highest peak hp and highest avg hp. However, since that dyno session, there have been 3 changes:
1 - Pulstar has further improved their technology
2 - Pulstar has recommended we always set the gap to vehicle OE specs (at the time of the dyno, we were encouraged to leave the gap as is, which was .005" smaller than the vehicle setting. Since that time, they've found that always matching the vehicle's OE specs has consistently increased the plugs performance).
3 - Pulstar has released an iridium version of the plug. The standard nickel version, EF-1c, consistently performs well on the dyno. In every dyno session we've had, however, the iridium version, EF-1i always produces slightly more hp than its nickel sibling.

Best part about the pulstar plugs is they come with a 100% money-back guarantee. If you're not happy with the performance, or they die prematurely - just return them to us for a full refund :)
 

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i run ngk4306 at around 600, all stock ignition. E-85. gapped to around .032 - .030. i don't like iridium's or platinum plugs
 
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