Reading Plugs New To Me

[stroker1]

Reading nitrous plugs is something I'm new to. But I have printed acticles from this site and pics also. But in some pics it says plugs where cleaned with brake cleaner. Prior to that they where covered with soot. How normal is that?

All my plugs are covered in soot every time. I have helped tune a couple n20 motors before but we didn't have the trouble with plugs being sooty and almost wet. It's so bad I can't even tell the fuel ring and the heat lines. Brake cleaner helps but they still are hard to read. N/A the engine ran pretty clean, but ever since I sprayed it the plugs load up pretty bad. And best I can tell I only have 5.25-5.5 lbs flowing thru the jet. Unless my gage is way off. It kinda seems real fat to me. I ran 3 passes on a set of plugs AR3933 and the idle went to crap and plugs look real sooty. I'm running a Cheater shot at 150 set up and pulling 6 degrees. Total timing is 32, running 5.25-5.5 lbs fuel pressure for the N2O. Motor is running 7 lbs. fuel pressure for carb.

BTW, I have a 383 sbc with 13.3:1 compression, Holley Blue for the motor, Holley Red for the Nitrous. I had the Red pump laying around. People have told me they don't think the Red pump will work for the nitrous. But unless my gage is wrong it is flowing OK thru the jet and only dead heads 6.25 lbs when not spraying. I'm not running a regulator on the Red pump. The Blue Pump on the motor has a 804 regulator I think. It is adjustable from 4-9 lbs. I think!!

You guys got any suggestions? This is a 383 sb S-10 stock suspension, PG with 4.56 gears, 28x10 slicks, Caltracs, 750 Holley DP with Proform base and main body 80 jets squared, 4.5 power valve, Cheater kit with 150 jets, 2" Fenderwell Hussler headers, MSD Mechanical Distributor locked out, Sunnoco Blue fuel. Truck runs low 6.90s in the heat on motor. A best of 6.60 so far on a 150 shot, in bad weather. This past Thursday night it went 6.66 @106, 6.66 @106, 6.69 @106. 60 ft sucks at 1.56-1.60, it will do better than that on motor. May be spinning after launch just a little. I know there is more numbers in it with the right tune up.

And it's a Gray truck if that helps. Maybe it would be faster painted another color! LOL

[mytmouz]

.3 tenths on a 150 shot with that et leads me to think something is not right. How are you flowing the fuel pressure? I recommend removing the plate and flowing it by letting it spray through the bar into a bucket while setting the pressure. This will get you close to what the actual run pressure will be. You can also spray a little NOS after setting the pressure to see if the 'noid is opening all the way. I had a similar problem when I first tried to spray my truck. I flowed it like this and found the screen in my NOS 'noid was partially clogged. With the 175 jets I went from a 10:60 to a 9:23...

[John_Heard]

Those sooty plugs were out of my car. It used to really color the cold plugs bad coming back on the return road. I sent the carb in to Pro Systems and Patrick got it fixed up so it wasn't so pig rich at idle and light throttle. You might work on cleaning up the idle mixture and maybe dropping to a lighter power valve so that it doesn't open quite as early. THat might help some.. You could also probably drop back one heat range hotter on your plugs, an AR3934 would be one step hotter and help burn those deposits off better - The AR3934 would be approx equal to a NGK - 8 plug.

The colder plugs you're running will foul out when you're driving around on them much, and that's what sounds like yours are doing. If you can try pulling the plugs right after making a pass on the return road or have someone tow you back with a 4 wheeler so you can see what they are like right after a pass. Need to do that with a fresh set of plugs in it to see where you are. The part throttle driving is what's probably coloring the plugs so much because you shouldn't be all that far off with the 80's squared@5.5 psi., maybe a bit fat but not enough to cause problems in most cases.

[stroker1]

tporter, I was flowing it thru the jet attached to the end of my braided line. I just took the jet out of the plate and made a fitting for it. I was too lazy to take the plate off, because I had all the adjustments done to the linkages and stuff.

John, I might try a warmer plug next time. I might have to get them in a Champion or Autolite. I don't have access to NGK unless I order them. Steve Ashworth Performance carries the Champion and Advance Auto Parts carries the AR Autolites. I don't know of a NGK dealer in my area that carries race plugs.

The plugs absolutely must be retracted tip, because my pistons will close up an extended tip plug. In fact I had to mill the spark plug relief on the pistons just to clear a retracted tip AR3933 plug.

I am going tonight to borrow my buddies flow gage tool. Maybe that will shed some light on things. I just don't understand why it would run OK on motor but after I started spraying it the plugs look really sooty. Unless my fuel enrichment pressure IS actually higher than the gage is showing.

Thanks Guys!

[stroker1]

I just flowed my fuel system for nitrous, the Holley Red pump. I used my buddies flow gage 0-15 psi. I'm not using a regulator. With the 73 jet it has 5.2 lbs. And with the 71 jet that I was using for the 150 shot it has 5.5 lbs.

That's kinda weird but what do I do?? It is in spec according to the NOS instructions. And I flowed it for about a minute and watched the gage. It didn't seem to fluctuate. Yet my plugs seemed really rich when I ran it last. Getting bummed out.

[John_Heard]

I forgot to ask how much timing do you have in it? Are you seeing any kind of heat mark on the plug strap?

[stroker1]

I'm running 32 deg. total locked out. That is after pulling 6 deg. out for the 150 shot. I can't really tell where the heat line is on the ground strap. Because the plugs are so sooty and when I clean them with brake cleaner or carb cleaner they still don't really get clean enuff. But I don't have an expert eye for nitrous plugs.

I think my set up is kinda at an awkward point where it is kinda hard to tell what to do next. For sure it's got to be rich, but I can't really tell about the heat just yet. I think maybe I should work to get the mixture leaner and then see where my timing is. Does that sound good to you all? And also I'll try 1 step warmer plug. I'll go to a AR 3934 providing it has the same tip as the 3933.

Another thing, at what point should I start to tune by MPH or should I forget that and just read plugs? Oh, and John I will work on the idle and low throttle and see if I can clean it up some.

[John_Heard]

If you're not seeing any heat mark on the ground strap, you might need to put another degree or two in it to get some heat in there. That will also lean it out. Don't take fuel out and add timing at the same time, one change at a time.

Sure you want to watch your MPH as you make changes, but the spark plug is the bottom line as to how good the tune up is.

[stroker1]

OK, I got her leaned down and cleaned up the idle. I went from 80 jets squared to 75F/79R in the carb. Power valve is not blocked. I also turned idle mixture screws in a half turn and actually picked up a little more vaccuum. And opened the secondaries a tiny bit more. Also, very important, I changed to a AR3934 plug. Idle looks much better. I also went to a .063"N/.063F" jetting on the cheater 150 shot.

Sad news is I still don't know what she'll do. After the burn out, I left the line and she sprayed...then stopped...then sprayed.....then stopped and was popping the whole time. So I shut if off half track and coasted in. Long story short, the snap ring that holds the reluctor in place on the distributor shaft was broken and timing was jumping around everywhere. Never seen that before. Hopefully the magnetic pickup is not screwed up. The snap ring was busted up pretty good.

[John_Heard]

OK, I got her leaned down and cleaned up the idle. I went from 80 jets squared to 75F/79R in the carb. Power valve is not blocked. I also turned idle mixture screws in a half turn and actually picked up a little more vaccuum. And opened the secondaries a tiny bit more. Also, very important, I changed to a AR3934 plug. Idle looks much better. I also went to a .063"N/.063F" jetting on the cheater 150 shot.

Sad news is I still don't know what she'll do. After the burn out, I left the line and she sprayed...then stopped...then sprayed.....then stopped and was popping the whole time. So I shut if off half track and coasted in. Long story short, the snap ring that holds the reluctor in place on the distributor shaft was broken and timing was jumping around everywhere. Never seen that before. Hopefully the magnetic pickup is not screwed up. The snap ring was busted up pretty good.

You may still be a bit off on the carb jetting, typically a power valve is worth 8 jet sizes, so 71/79 would be closer (I assume rear is blocked). Sounds like it's running cleaner.. Never have heard of one busting a snap ring off either...

[stroker1]

Thanks John. Nah the rear power valve is not blocked off. It is a 4.5 but I'm not sure if it would be any better to block it off. Seems to be doing OK, venturis not dribbling anymore since I changed from 6.5 to 4.5 PV front and back. What would be the advantage of blocking it except a little added saftey?

Reason I put the 75s in the primaries is to lean down the low speed mixture for driving around the pits and return road. Other than that what's wrong with square jetting a carb? Kinda seems like really you would want just as much fuel on the front as the back.

[John_Heard]

For drag racing typically you want to block off the rear power valve because it can become uncovered during launch and pull fuel away from the valve. You also want jet extensions to prevent the rear jets from becoming uncovered too.

Many people block off both front and rear because of problems with blowing a power valve if the car backfires or hiccups. As long as you don't have issues like that though you can run a front power valve and it'll run a bit cleaner at part throttle and idle. For that setup you would run 8 steps less on the front (with power valve) than the rear (no power valve). So say you blocked your rear one off you want something like an 87 in the rear and a 79 in the front (8 less in the front). With a front power valve, that setup is square jetted when you figure in the power valve.

And yeah, you do want to have the same front and rear (square jetted) in most situations.

[stroker1]

For drag racing typically you want to block off the rear power valve because it can become uncovered during launch and pull fuel away from the valve. You also want jet extensions to prevent the rear jets from becoming uncovered too.

I guess I never thought about the power valve becoming uncovered. I do have jet extensions, they helped my bog at the 60ft but I still have both my power valves. It don't seem to be running out of fuel any at all right now, but maybe it is getting uncovered and I just don't know it's affecting it. Looks like it would bog down though.

Thanks for pointing that out John, I never thought about the PV becoming uncovered on the launch. I just know for most purposes that I've seen the PV always made a smoother transition from part throttle to WOT without going lean.