Expert Plug Reading Wanted

Dave-R · Post by **Dave-R** » Sun Jul 19, 09 1:41 pm

Probably one for Adam?

This is the plug colours from the little center 2bbl carb only. (Outers disabled)

Dual plane manifold so plugs are grouped for each half of manifold.

Cylinders 1,4,6 and 7 are fed by the left side of the carb.

Here they are in order.

Dave-R · Post by **Dave-R** » Sun Jul 19, 09 1:42 pm

Cylinders 2,3,5 and 8 are fed by the right side of the carb.

Here they are in order.

Dave-R · Post by **Dave-R** » Sun Jul 19, 09 1:52 pm

#s 3 and 7 look like they might be showing signs of detonation to me. Not sure though. here is the other side of 3 and 7.

The plus in each far corner of the engine look slightly leaner but that might be the case with just running on that little center carb.

Cannonball · Post by **Cannonball** » Sun Jul 19, 09 2:18 pm

looks hell off a gap dave, how big

Dave-R · Post by **Dave-R** » Sun Jul 19, 09 3:23 pm

55 thou. Or should be. I will check.

GTXJim · Post by **GTXJim** » Sun Jul 19, 09 3:25 pm

That looks like about 55 thou to me

Dave-R · Post by **Dave-R** » Sun Jul 19, 09 3:26 pm

Yep. They are 55 thou.

db · Post by db » Sun Jul 19, 09 3:59 pm

This looks helpful...

http://www.4secondsflat.com/Technical Information for Ignition and Carburetion.html

http://www.4secondsflat.com/plug_chart.html

Anonymous · Post by **Anonymous** » Sun Jul 19, 09 5:02 pm

What's the heat rating on those plugs? my guess is either NGK 5s or champiom 12s?

Dave , this is where individual cylinder timing would help , a jet change in metering block would help here , maybe go up 2 sizes up for #s 1.4,6,7 & see if it pulls the timing mark back towards the electrode on plug #s 1 & 7.

First off i would drop plug heat range for 1,7,2 & 3 , looks like oil contamination on #s 4 & 5 , maybe pulling oil up from valley or valve seals?

As you said Dave , there's some serious detonation goin on here , #s 1,2 & 3 especially , gotta sort that oil problem out.

If you look & the porcelane you will see how detonation has left it's mark , within a short time the porcelane will stasrt to crack & break away.

If you cut the threaded section off the plug you will be able to see the fuel ring on the shell , which will tell you how the motor is behaving @ full throttle.

Dave-R · Post by **Dave-R** » Sun Jul 19, 09 5:04 pm

Looking at http://www.4secondsflat.com/Spark_plug_reading.html seems to back up my feeling that 36 degrees may be too much total even with 97 octane fuel.

I know the yanks prefer 34 total but their fuel is usually 92 octane or a little more at best.

Anonymous · Post by **Anonymous** » Sun Jul 19, 09 5:10 pm

Dave if you drop to a lower heat range you could possibly run the motor @ 36* spark lead , with those plugs i would pull some timing out , 2* @ least , stick a set of new plugs in & gap for .040" , this will give you a good starting point to get tuning sorted , 34* seems to be where these motors perform best.

Dave-R · Post by **Dave-R** » Sun Jul 19, 09 5:11 pm

I think as far as fuel distrubution goes I will have to see what they look like with all the carbs working.

I will see if I can knock a couple of degrees of the total timing and then see what they look like after a couple of runs up the strip on all 6bbls.

Mick70RR · Post by **Mick70RR** » Sun Jul 19, 09 5:27 pm

The Americans use MON octane rating and we use RON in Europe. 93 MON is the same as 97-98 RON.

Dave-R · Post by **Dave-R** » Sun Jul 19, 09 9:51 pm

Mick70RR wrote:The Americans use MON octane rating and we use RON in Europe. 93 MON is the same as 97-98 RON.

Bugger.

Rich · Post by **Rich** » Sun Jul 19, 09 10:01 pm

I bet not many people knew that,Mick....I didnt..