83SC Spark plugs

[NikosF]

I ordered Bosch plugs from Pelican - and realize now they are the WR5DC whereas Bentley has the spec at WR7DC. Everything is ready to install the plugs (a/c compressor moved, heater plumbing removed) - so would love to just go with the colder plugs on hand. Downsides?

[Richard C2S]

I'm curious about this also. I had 5's in my '81SC until a few months ago. My present tech, who worked for several years with an (now retired) older, long time Porsche tech who had tons of experience with air cooled cars, put the 7's in my car explaining that the older guy almost always used the 7's in the 3 liter motors.

I've only put a few miles on the car since the plug change so can't really comment on whether there is any diff in my seat-of-the-pants feel.

Will running 7's instead of 5's damage the engine?

[ASD]

I thought WR8 was the ticket?

[T77911S]

run the WR5's. it will be a good learning experience. don't worry, nothing bad will happen.
I ran a used set of WR3's out of a turbo in my 77s just to see.

pull the plugs after 100 miles and take a look them.
try a few different scenarios, try cutting the engine at mid or hi RPM (no idle) and check them.
let it idle for a while and check them. (darker)
check them after a long trip. (cleaner).

take not of the ground strap. you will see an heat mark on it. that is a timing line. it should be around the bend in the strap.

you wont hurt anything running either a 7 or a 5. (bosch).
running too hot a plug can make the plug become an igniter and cause pre-ignition. but with this engine a 5 or 7 is ok. you get more critical with hi compression and turbo engines.

best thing is to check the plugs. a really white plug I would try a colder plug. a black plug I would run a hotter plug and perhaps look into other issues as to why it is so black.

its best to run as cold a plug as you can.
the need for hot plugs is due to idling and starting. times when the mixture is richer and fouling is a bigger risk.
when I ran the WR3 in my 77, I took a long trip. pulled the plugs and they looked great. this was due to the leaner cruising mixture,
after driving around town, more idling, they were as black as coal. BUT, I still never fouled a plug.

[NikosF]

Thanks.

What say the plug whisperes about my old plugs. NGK 6s - 1-6, L to R

[ASD]

to me those look pretty normal.

[T77911S]

how many miles on engine
how many miles on plugs.

I get very picky when it comes to things like this as far as my car goes.
I only see 5 plugs, but I would shoot for what #1 looks like or even the porcelain on #5 as the darkest.
whats the timing set at, max.
3 looks a little lean, could just be the light.
2(wet) and 5 (blk around the base) look like maybe an oil issue or rich. or all the others could be lean.
individual differences I would look at injector Orings and sleeves. check intake bolts for air leaks.
maybe swap injectors between 5 and 3.

or leave it and enjoy it. if it runs smooth and good don't worry. like I said, I just get anal about mine.


I will usually just pull one or 2 of mine every now and then and check them. I may be just me but I would rather see them all look the same vs a wide range of how they look.