what plug to use on modified 930?
 

What plug is the right temp range (or offers the most effiecient use of the added fuel odf the euro cis) for these mods on a 1986 930 turbo

Euro CIS
1.2 bar boost
euro injectors
100 oct av gas (always)
headers

You could stick to the OEM W3DPO, but they are a pretty cold plug, so you could even move up to a W4CS plug.

I run denso iridiums, I'll have to look up the model number for you, but I have to run a cold plug to help prevent detonation. I'm one of the few around here that run 1.2 bar.

I recomend NGK B8EVX

Goran, here in the states the EVX (platinum) are discontinued. The replacement is EIX (iridium)for the suffix. I know there is still stock of the platinums scattered, I too used them but in the heat range of 9. The Platinums were also cheaper than the iridiums. If you can still get them they are great plugs. I run BKR9EIX, what I like about this plug, is that it has a 5/8 hex instead of 13/16. This makes it easier to get the socket in the tight confines of the 911. specially if you are running twin plug. Word to the wise you must NOT use those generic sparkplug gap tools on iridium plugs. The ground strap must be bent by itself and not using the electrode as a fulcrum. Rule of thumb is for every 100HP over stock, you run "1" heat range colder.

Novice question
 

What does the heat range of a spark plug refer to? How does it relate to detonation?

Thanks for the schooling:)

Didn't know that EVX are discontinued but B8EGV works equally well. I found 9's too cold. Frankly, even 8's get fouled unless you don't give it a boot now and then.

It is really cold where you are......... Well atleast to me it is. In Florida (hell) it is hot and well just flat out hot,,,,,,and humid. I have never fouled a 9 but I suspect the colder weather definetly playing a big part in it. Do you guys put your cars away in the winter? And how long are your winters?

A givin plug designed for a specific motor will run a steady temp and as long as the mixture is correct, it should last quite a long time. If you have more power being generated the the plug can become too hot and promote detonation. (meaning the plug will be so hot the temp of the plug will ignite the fuel in the cylinder before the coil sends the spark). To control temp or to change the range of the plug the amount of ceramic exposed in the end of the plug determines how hot it will be. If the ceramic is recessed alot in the end of the plug the colder it is, the more exposed the hotter it is. The more power you make the more heat you can generate. so finding the right plug to live in extreme motors is a neccessity. As Goran states you can go to cold and foul the plug. Climate, elevation, and all elements of nature definetly play a part. But if you have normal mods to your 930, only 1 or 2 heat ranges colder would be sufficient.

The temperature of the spark plug relates to how much heat it conducts out of the combustion chamber. See this page for a great explanation: http://www.ngksparkplugs.com/tech_support/spark_plugs/p2.asp

Different plug manufacturers use different heat range numbers or letters in their designations. Even more confusing, some get colder as they increase and some get hotter as they increase. The hotter they are, the less likely they are to soot up and the more likely they are to cause engine detonation. Your goal is to find a heat range that doesn't soot up in normal driving and doesn't detonate when you are driving at full performance levels.

On my engine (roughly 425 flywheel hp) I use the NGK BKR7EIX plugs which are a couple of steps cooler than the NGK BKR9EIX plugs (CORRECTION, 7s ARE A COUPLE OF STEPS HOTTER THAN 9s IN THE NGKs). I'm dual plugged and it seems to be a reasonable range for my street use with occasional spirited driving. My choice was based on the OEM range of the twin turbos minus one heat range. It wasn't based on extensive trial and error.

I got confused about NGK & Bosch numbering a lot, but I thought for NGK, 7 is hotter than 9?

Thanks for the info, mppickett and GJF.

Yupp. NGK 7's are hotter than 9's. Bosch is other way around.

Porsche started with recomending NGK 8's in turbocharged cars to be on the safe side, which went down to 7's as they noticed that owners weren't driving them hard enough to "unfoul" the plugs.

You are right. Sorry about the confusion.
Mike

Best advice I've read lately regarding modified engines.