MSD Spark Plug Gap

Paulporsche · 09-01-2008, 06:14 PM

Surprisingly a search did not yield the type of info I was looking for.

Those w/ SC or 3.2Carrera engines and an MSD CDI: What plug gaps are you running and w/ what heat range plugs for street cars?

I have always used 7 range plugs. W/ an MSD does a gap of .040 or .045 " sound right?

dion914-6 · 09-01-2008, 06:21 PM

MSD Install, now no power

I think your answer is in this recent discussion.

Dion

T77911S · 09-02-2008, 03:43 AM

good question paul, i am testing a set of W4cs plugs out of my brothers 930. i was going to post basically the same question/ results.
like you, i was using W7's. i am doing this to test detonation and fuel octane.
so far i have had good results. i am using 87 octane, before, i HAD to use 92+ or it would ping. it starts good, runs good with no fouled plugs. i pull 2 out every few days and check them and they even look good, despite they were used.
next i am going to bump the timing up a tad to see where it pings.
i have not run it above about 4200 because of a miss,( i have a 914 rev limiter in there and i think it is coming in too soon). i think i am going to end up using W5 plugs in the end.
i also have an MSD, i have set the gap as big as .065.
before i learned about about plugs, i thought hotter meant more power. if the plug gets too hot, it can ignite the fuel early causing detonation.

Paulporsche · 09-02-2008, 11:47 AM

T77911S,

You said you have used a gap as wide as .065. Have you settled on that, or is it some other figure?

Formerly Steve Wilkinson · 09-02-2008, 02:14 PM

Ask Steve Weiner. porsche@rennsportsystems.com. The fabulous thing about Steve is that he will answer you in detail even though he charges his real customers triple digit rates.

dshepp806 · dshepp806's Garage

Quote:

Originally Posted by Formerly Steve Wilkinson

Ask Steve Weiner. porsche@rennsportsystems.com. The fabulous thing about Steve is that he will answer you in detail even though he charges his real customers triple digit rates.

+1 on this,.....big bang for the buck, too.

Best,

Doyle

Paulporsche · 09-02-2008, 06:35 PM

Thank you. I have sent a request to Steve.

snbush67 · snbush67's Garage

Paul,

I have MSD Coil, Box and Wires, I am running NGK BP6ES with a .065" gap and running 87 octane, I tried running cooler plugs (4's) for whatever reason but my engine temperature went up, and when I opened the gap up it cooled down but seemed to lose a bit of umpth, I ended up sticking with the BP6ES and experimented with gaps between .045" to .065" the lower gap settings give higher engine temps and less power.

Edit:

NGK : Lower number = Lower heat dissipation

Shane

T77911S · 09-03-2008, 09:02 AM

Quote:

Originally Posted by snbush67

Paul,

I have MSD Coil, Box and Wires, I am running NGK BP6ES with a .065" gap and running 87 octane, I tried running cooler plugs (4's) for whatever reason but my engine temperature went up, and when I opened the gap up it cooled down but seemed to lose a bit of umpth, I ended up sticking with the BP6ES and experimented with gaps between .045" to .065" the lower gap settings give higher engine temps and less power.

Shane

interesting. i have W4's in now and my temps seem to be a little higher. i am thinking maybe the more heat the plugs are dissipating into the heads is making the temp go up, but then if they dont dissipate that heat then it is staying in the plug and could that cause spark knock?. oh what to do what to do.

i guess i need to put the W7's back in and check temps.

paul, i think i went back down to around .045, maybe a tad bigger.

dlagerstrom · 09-03-2008, 09:27 AM

T77911s, I think you need to be careful about comparing Bosch and NGK heat numbers. As I understand it, NGK hotter is lower and Bosch is the opposite. I don't think you can compare.

Shane or anybody, can you explain when you need the resistor type plugs and when you don't? I see Shane is using the BP6ES as opposed to the BPR6ES which our host has and the difference is R is a resistor plug. What gives and what should you use???

Flieger · Flieger's Garage

Resistors in the plugs help suppress radio frequency interference in the same way that resistors in the plug wires do. This is to prevent static noise on ausio systems and also protects and electronics like computers.

If you don't use the radio and run CIS,MFI,carbs (not Motronic), you can loose the resistors and the wires may last a little longer and you will have a little higher voltage at the plug. This gives a more vigorous arc that can bridge a wider gap but also will erode the electrodes on the spark plug a little faster.

The resistance values are small enough that these effects will be relatively small.

snbush67 · snbush67's Garage

Found this excellent explanation:

http://www.ngksparkplugs.com/tech_support/spark_plugs/p2.asp?mode=nml

It appears that NGK lower numbers mean higher temps as stated above I guess that explains my issues with the 4's.

snbush67 · snbush67's Garage

This one too, it explains gapping and heat:

http://www.ngksparkplugs.com/tech_support/spark_plugs/installation/index.asp?mode=nml

T77911S · 09-04-2008, 03:23 AM

Quote:

Originally Posted by dlagerstrom

T77911s, I think you need to be careful about comparing Bosch and NGK heat numbers. As I understand it, NGK hotter is lower and Bosch is the opposite. I don't think you can compare.

yes, your are correct, they are backwards. i was only refering to heat ranges I was using. shane said he used a cold "4", i assumed it was a bosch even though he referenced am NGK later.