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Big Block Chevy Spark Plugs

MIG Gas Delivery and the Small Block Chevy Evolved in a Similar Way and Time!

 Both had Advances and Setbacks Before

They Were Optimized!


Click for a PDF Report on the Similarities

Chevy's 502/502 comes with AC Brand Rapid Fire #4 spark plugs.  A unique problem created when building the Pro Street Rod required the  use of another  plug.  If your having heat range problems with a street/strip ride the solution developed may be of interest.

Stuffing a Big Block Chevy in a '34 Ford requires some careful planning.  During construction, some old plugs were put in the engine so debris did not get into the cylinders.  When the steering column was being installed it was put very close to the engine to have the steering wheel placed as far right as possible.

The above picture shows how close the left rear plug is to the steering shaft universal.  All would have been fine if that old set of spark plugs had been standard length!  But they were not!  They were Bosch platinum from an old Jaguar!  See the photo at left of the AC plug supplied and the 1/4 inch shorter Bosch!  A 1/4 inch isn't much but it might as well be a mile when you don't have room!!  What to do?  Started the engine with 7 AC's and one old Bosch!  After examining the plugs, even the AC's looked like they were too "cold."  They were probably fine on the Dyno at full throttle, but that's not how one drives on the street.  But when you put your foot to the floor you don't want to preignite, blow off the plug tip or worse!

The solution.  Find out which Bosch Plug would work!  That's not as easy as it sounds.  All the info on plug types and fitments ask for car, engine etc.  Not much help for a 502/502.  Found a fellow who sells Bosch Racing Plugs in NY but he wanted to sell only in lots of 100! Finally found a Bosch Tech Line 1-800-521-5462.  They were very helpful in defining the heat range, size etc. 
For example, the FR7DPX  finally selected means:
  1. F = 14mm plug with 5/8 hex head.
  2. R = resistor plug
  3. 7 is the heat range. For Bosch 1 is the coldest and 11 the hottest.  Some racing plugs can be less than 1.
  4. D = reach which for what is needed for the 502/502 is 0 .708 tapered seat extended tip
  5. P = platinum
  6. X = gap = 0.044 inches
Getting to the correct heat range required trial and error.  In fact at one point it was thought one plug would be needed for the summer and another for the winter!
Tried a few Bosch standard copper core plugs; # FR6DCX which ran OK in the summer but was too cold in the winter (black at the bottoms.)  They also fouled a few times and required removal and cleaning.  Switched to FR8DCX which are two heat ranges hotter but when examined, a few appeared to be excessively hot.

Thought the Platinum would have a larger heat range.  The Bosch technician agreed and with his help the FR7DPX was selected.  They have worked very well for several years.  No fouling (as long as one does not push your foot more than about 1/4 throttle when starting a old engine.)  The plug porcelain is a nice tan color on most plugs with a few slightly black, cylinders # 4 and  # 2 that are running a bit richer.

Thought spark plug selection was resolved!  However although the FR7DPX's were performing well for about 3000 miles, at the last Street Rod Show of 2005 (that ended at 9 PM), the temperature was cold.   The accelerator was mistakenly given a full pump- -big mistake!  The car missed the 16 miles home.  Next day checked and # 5 plug was fouled.  Cleaned it and all was fine.  Getting ready for the 2006 season the car was started after a several months layoff.  It missed for the short trip so it was back in the garage.

This time the front two plugs on the right side, #'s 2 & 4 were very dark gray to black.  These were the culprits.  Plug # 3 also showed a lot of dark gray.  Decided to put a set of Bosch FR8DCX  in all cylinders.  These are a heat range hotter and copper center core construction.  The NGK's used for several Corviairs were one of the first to use this approach.  It does extend the heat range.

Since there is a good deal of Internet Traffic on this page - - keep you posted on results.   First 10 mile run was perfect, started very quickly with only enough accelerator peddle movement to have the electric choke set!  Subsequent starts were also fine.

Two years have passed and had a plug fouling episode again.  Probably my fault but found a new  Bosch Plug.  Similar to what I have been using it is called Super Plus and they add Yttrium!!  It appears Yttrium in very small quantities improves the ductility of copper.   Perhaps it helps in production with the copper / nickel alloy center electrode joint.  Perhaps it's always been there and some marketing type just labeled it different!    Since it was time to at least check the  plugs and I found a deal on Amazon for $1.37 each-decided rather than just check the plugs would install new ones!  (They list for $4.90 each!)  The Bosch part number is 7957.  The old plugs actually looked OK.  Six of the old plugs were a nice tan color and two were gray with some black.-cylinders 4 and 6.   Keep you posted on results.


Note: We're "hitchhiking" on our commercial web site to bring you this information on Big Block Spark Plugs.  Many "Car Buffs" have purchased our 6 foot prefitted Shielding Gas Saver for their MIG welders.  We also added  3 and 4 foot systems for smaller MIG welders, Part Numbers WAT-FB3 & FB4

This Ad Helps Bring You  Free Information on Welding Race Cars & Street Rods

Have a Welder?   Improve Weld Starts and Have Shielding Gas Cylinder Last at Least Twice as Long! 

Note: Our Patented GSS is Not Available in "Stores"

A home shop fabricator in Georgia with a Miller TM 175 amp welder purchased a 50 foot Gas Saver System ( GSSTM ) so he could use a larger cylinder and mount it on the wall of his shop.  He wrote:

"The system works great.  Thanks for the professional service and a great product."   Click To See His Home Shop


A Professional Street Rod Builder Had This to Say:

With their standard MIG welder gas delivery hose the peak shielding flow at weld start was measured at 150 CFH. That caused air to be sucked into the gas stream causing poor weld starts.  With the GSS replacing their existing hose, the peak flow surge at the weld start was about 50 CFH.  Total gas use was cut in half.

Kyle Bond, President, quickly saw the improvement achieved in weld start quality as a significant advantage!   Kyle, an excellent automotive painter, was well aware of the effects of gas surge caused by pressure buildup in the delivery hose when stopped.  He has to deal with the visible effects in the air hose lines on the spray gun in his paint booth!  The paint surge is visible and creates defects unless the gun is triggered off the part being painted!  We can’t do that with our MIG gun!




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