New plugs, test hit on them, afr gauge read 13.4. Stroked 350 with twin turbos. Looks to me like a little tooo much timing. Also looks like 7, 5, 6 & 8 may be a little fat. So I’m thinking take 2 degrees of timing out & dropping some jet in the secondaries. What do you plug readers think?
Ideally, you should should have ignition timing referenced to boost. Do you have any kind of ignition retard? My MSD Digital 6 has a single stage of adjustable retard. I can reference it to RPM. It's awful hard to read plugs with unleaded fuel.
Hey Larry, I’m running an msd 6 btm, it is boost referenced. Once it starts making boost it retards the timing. Initial timing is 14, total is 35, all in at 2400. I’m pulling 1 1/2 degrees per 1 lb of boost.
Yeah, that sounds optimal. As long as there are no signs of detonation on the plugs, you should be good. My plugs looked a lot like yours when I replaced them last week. One or two of them color a little dark on one side of the plug. The timing indicator (color change) should be on the curved portion of the ground electrode. That's about as far as I go with reading plugs. Like I said, it's harder with unleaded fuel and ethanol.
https://fboignition.com/articles/sparkplugreading.html Looks like your color change is closer to the threads, so maybe too much timing.
Yes, that’s a whole different ballgame with the laptop tuning. It’s easy to tune a boosted carbed v8 without all the hassles of the computers and a million sensors. 13.4 is way way way to lean IF it’s accurate. Easy to have a bad sensor.
Trying to read plugs can be tricky as a driven car wrecks the signature you are trying to read. Put in a few or all new plugs. Make a hard run like at the track and shut off the car immediately, this will preserve your plugs. Take one out on each side pop in new ones and get back to the pits or garage. A lot easier at the track or chassis dyno. I haven't had to read gas plugs in quite a few years. We generally round the corners on the ground strap and put about a 90% Crescent around the first thread. We use gas to start our engine This is a good source of reading info https://www.dragstuff.com/techarticles/reading-spark-plugs.html
I would shoot for 10.5-11:00 Max AFR under boost. It’s different than NA. I added an exhaust temp probe (EGT) at each of the 8 cylinders to help find lean cylinders. Reading plugs is not very reliable. Some people cut off the threaded section and read the porcelain section to get an idea.
Idle time after a hard pull to read the plugs can mask the viewable results. The article in the link probably explains it clearer. I always run on the rich side/safer. Last thing I do when tuning is to incrementally lean out keeping a slightly rich condition under full boost
I use the non projected tip since I run nitrous. I think they are Yr5 NGK you are probably ok at 13.5 for cruise I would say 11-11.5 is good on the floor. The "J" strap will tell you if they are too hot depending on where the line is on it. My Mustang buddy runs his with the line at the curve or over a little. Mostly it is at the top in the middle. Here is a plug site www.dragstuff.com/techarticles/how-to-read-plugs.html mine looks like this
totally missed you put that one there good site Also want to add that John is correct the real way to check the plugs is to make a pass and shut off the engine and pull the plug
I’m going to open up the pvcr in the rear & see what the wideband says. Should make a difference in the afr & fatten it up for sure
You can still read plugs for timing, and for jetting if your using race fuel.. but pump gas has so much crap in it now, it's really hard to get an accurate read on A/F with the plugs, I have found that when I take motors off the dyno, even a pump gas compression engine, which I use a mix of 50/50 110 and 91 octane to test with, the plug coloring is inconclusive. Not that nice light grey or tan you get with race fuel, much darker than that. The "fuel ring" down inside the plug on the porcelain is often times not there at all. It's just all black or dark brown. I definitely recommend that in this day and age, get a wide band O2 gauge to do your jetting. JW
Is there a chassis dyno in your area? I would use that or test MPH at the top of the quarter mile. Using a single plane TA Intake?
I asked Mark Burton and he says he stays between 11.5 and 11.8 for his air fuel ratio. And he has hundreds of hours under boost on various turbo 350s he’s done.
