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Spark Plug Recommendations

September 27, 2010 | Troubleshooting & Repair

By Vince Cappelletti, Tom Farnam, Geoff Fleming, and Dan Schaefer

Bosch Plug Old / New Part Number Equivalents (provided by Al Zim)
Type OLD # NEW# Comment
Platinum WR7BP 4232 Normal plug for 356
Copper W8BC 7503 W145T1 Hot plug use in VW
Copper W7BC 7597 W175T1 Normal plug for VW
Copper W6BC 7593 W200T35 356/912 leaded gas plug
Copper W5BC
W225T1 Racing plug
Editor: The question of what plugs to use in our now 40-plus year-old cars is a frequent one. Fortunately, there are several good choices. Bosch WR7BP platinum (Bosch plug 4232) and NGK BP6HS or BPR6HIX are often used in the 356. Below are specific comments from several experienced 356ers. But if you buy your plugs from well known Registry advertisers they know what should be used in your car! There is no need to guess or listen to someone at an auto parts store who has never seen a 356 and is too young to know what a carburetor is. Additional information, unverified: Bosch/NGK equivalents, Bosch numbering system explanation.

: I have a 65/C Cab with a set of NPRs and I have run the Bosch WR7BP platinum (Bosch plug number 4232). I purchase them locally from my NAPA store for $1.99 each + Sales tax. I've been using them for about 9 years and like them. They work nicely when the plugs are gapped @ .040". My engine is fitted with Solex carbs and currently has over 100,000 miles on it since I rebuilt it with the big bore kit.

Geoff Fleming: The best sparkplug for the 356 is one designed for Saabs and Volvos! This is the Bosch WR7BP, platinum plug. Once installed, you will probably never have a fouling problem, despite oil burning, etc. Most people in our local group have used these for years. Once you convert you will never go back to anything else. I know that Al Zim sells them, and they should also be available through any good Bosch distributor. DO NOT ask for Porsche plugs though! You will be given plugs for the 911 series, which are too long and will cause the pistons to hit the electrodes...just ask for the WR7BP plugs and all will be wonderful. Here in the Northeast, we have a wide temperature varience and no other plug operates as effectively as the WR7BP. ( My own driving of the 356 was in -5deg to a bit over 100 deg.)

Tom Farnam suggests that if you want to run NGK plugs in an S90 engine, use Standard BP6HS or Iridium IX BPR6HIX (.028 gap for both). If you want the resistor (mainly an RF suppression device) use the NGK BPR6HS, which is equivalent to the Bosch WR7BP. Don't want resistor, use the NGK BP6HS, equivalent to the Bosch W7BP. For an explanation of the "Resistor" plug question, see the Bosch Spark Plug web site.

Dan Schaefer :When I bought my coupe in Sept '64, it was delivered (from the dealer) with Bosch plugs. I don't remember the part number but the head wrench, Willie, told me that I would probably need to put in new ones about every 4 - 5K miles so I needed to carry a spare set in the car. Sure as death and taxes, at about 4000 miles after that, the car started running rough, making bad noises and losing power. This happened twice more, each time at—sure enough—about 4500 miles on new plugs. In every case, the Bosch plugs that came out were badly fouled - some were oily, some were stuffed with carbon and some were shorted with lead.

I was bitchin' about it to another 356 owner and he suggested trying NGK BP6HS plugs. Getting tired of having to swap a set of plugs at the side of a LA freeway, I bought the NGK's (plus a spare set) and stuck them in. At about 6000 miles I started to get nervous that they were likely getting ready to fail, ala the Bosch plugs, so I pulled them to check. They were in perfect shape! Light tan on the center insulator, slight gap growth, no soot or oil.

Long story short, I reinstalled them and checked them again after another 6000 miles and found nearly the same condition. At another 6000 miles (now at ~18,000 miles on the set) I put in the back-up set though the original set were still working OK.

I've put about 250,000 miles on my C (it's on it's third engine rebuild) and all but those first several thousand miles were done with the NGK plugs.

Related information:

Changing Spark Plugs, by Dave Merz

Ignition Tuning Procedure, by Ron LaDow

1 Comment

Aa493c9f9299cdb0d51a6d201e2b655c 227
Mark Sabbann
January 26, 2016 at 8:23 PM
Jan. 26,2016 It appears that the recommended Bosch spark plug, WR7BP is no longer manufactured and no platinum tipped plug is available for the 356. The new number is WR7BC or Bosch #7997. It has a copper tip. Here's a list of updated part numbers for plugs: Here is a nice chart for the numbering of the Bosch plugs: