40ZR1

My BluePoint 383 cu in engine calls for racing spark plugs. What racing spark plugs and how are they different than regular plugs? Also, the gap calls for 0.045" is this too large a gap?
Thanks
CJ

856666

Recommended Spark Plug: Champion 792

https://blueprintengines.com/product...or-bp38313ctc1

About Racing Spark Plugs
https://www.enginebuildermag.com/201...g-spark-plugs/
Phil

SWCDuke

Racing spark plugs are for racing engines that spend most of their life at high load and revs. They are sometimes called "cold plugs" because they are designed to rapidly transfer heat to the cooling jacket so the tip doesn't overheat and lead to preignition, which leads to detonation that can rapidly destroy the engine.

Road engines operate under light/low average load/revs and need relatively "hot" plugs in order to keep the tip temperature hot enough to burn off deposits, so they don't foul. A cold racing plug will rapidly foul in normal road use.

The best road plugs for vintage small blocks are AC heat range 5, like AC 45 or equivalent in another brand. The AC 45 is a conventional 3/8" reach, gasket seat plug, but modern aftermarket heads may use taper seat or longer reach plug with aluminum heads. These plugs will have suffixes/prefixes to indicate the different geometry, but the second digit should still be five. (The first digit, 4, in the AC system means "14 mm thread".)

For a racing engine AC heat range 2 or 3 (the second digit in the number) would be suitable.

Gap is a function of ignition system type. If a point type use .035". If a high-energy inductive or CD type, wider gaps are acceptable/beneficial in lighting the fire.

Duke

R66

The article on racing plugs says there is no negative side of the colder plug other than lost power. I disagree, the more unburned fuel (carbon) left in the cylinder the more oil is washed off of the walls and the faster cylinder wear along with the increased friction on the cylinder wall and rings. I believe heat range is extremely important when choosing a plug for a specific application.

SWCDuke

The article wouldn't download for me, but it sounds like it has some bad information. Heat range has nothing to do with an engine's maximum power. It's all about average power demanded by the driving conditions. For a racing engine that sees very high average power output for extended periods a "cold" plug is required to keep tip temperature below the point where an overheated tip can cause preignition that leads to destructive detonation.

A relatively light vehicle with a large displacement engine, like a Corvette is loafing most of the time. You rarely are at WOT for more than a few seconds at a time in normal road driving, so a relatively "hot" plug is required to keep the tip temperature above the point where the plug will rapidly foul.

Duke

GTOguy

As a guy with 4 decades of experience up close and personal with plugs, I agree with Duke and R66. Cold plugs on the street foul in my experience. Hot plugs in a race application tend to run hot and enhance pre-ignition. The ranges Duke recommended are not only spot on for small block Chevrolets, but they are also applicable to Pontiacs, Oldsmobiles, and Buicks of the same vintage.