I previously had everything squared away for the most part.

Prior to this run I installed a new MSD Digital 6 Plus to use for timing retard on my carbureted LT1 that is swapped into my '87. I set full mechanical timing at 36 degrees with 3 degrees of retard on a 100 shot.

There was some minor pinging at full throttle so I let up and coasted. I’m running two steps colder than stock on the plugs which I think could be why the mark is where it is at on the ground strap based on some of the pictures I've seen of nitrous plugs.

It has an orange like color on the porcelain to it that is really hard to see in the picture but is definitely there.

Looking at the electrode as well as looking for the “blue line” on the ground strap, which is practically non-existent, I feel like I still have just a bit too much timing.

The soot around the base ring wipes off almost completely.

I’m also guessing the jetting is a bit rich given the soot but I’m currently only running at 6 psi of fuel pressure.

What is everyone's thoughts? Is 33 degrees mechanical too much advance on a small hundred shot?

 

Is that a TR6? What is the gap set at? Looks like high speed glazing but the timing mark doesnt look bad.

 

No it is actually a BR7EF plug. I had gapped it at .033 originally.

These plugs have been in the car though for the last few weeks without any issues with the spray before however a couple of things have changed recently.

1) I installed a MSD Digital 6 Plus ignition controller and moved the timing back to 36 degrees at full advance. The box has an automatic retard function that engages when 12v is active at the nitrous solenoid. I currently have the retard set to 3 degrees. So I'm running at about 33 degrees full advance with the spray which I was before as well.
2) I did just recently fill up on 93 octane fuel and didn't use any additives to bring the octane levels any higher. Last time I ran the spray a couple of weeks ago I was running 103.

The other thing I was just thinking of is that my bottle may be getting a bit low, maybe 1-2 pounds left in it. Is it possible that without enough nitrous flow, all that fuel that is being injected from the fuel solenoid could be having a hard time igniting at the right time? Interestingly enough though I did a pull in 2nd gear, mid range rpm, and had no detonation until I short shifted a bit into 3rd.

I'm going to weigh my bottle tonight and I think I'm going to put some additive in to bring my octane levels up a bit to start.

 

Sorry, forgot to quote you in my response above.

 

7 ngk should be perfect heat range for that thing. 33 deg seems fine if 36 is best na timing. I think i was 34 best timing na, and only pulled 2-4 deg on a 150 shot. However gap wise I probably would tighten up some. 100 shot isnt alot tho, .033 should fire it. .028 may be better for abit more spray

do you also have a wideband on it? What afr was it saying? Can use both to verify fueling.

when in doubt go abit less on timing and work back up​​​​​

 

Good plan Orr. Also too much fuel on nitrous can cause detonation and is often times more dangerous than lean because there is a lot of unburnt fuel in the charge air that can preignite. If the air fuel is richer than 11.0 stop and evaluate your jetting and bottle level. I usually run no less than 12.0 to 12.5 afr on spray. The BR7EF should be fine and yes I believe the gap is a little too large. Bring it down .006-.008 and try again if all else fails. Also have you been able to verify that the timing is actually being pulled? I have had many cars with these boxes on the dyno and even though it reported that the timing was being pulled, the timing light told a different story. I actually had one that would raise the timing by the set amount instead of pulling.

 

Another thought. What is the base HP at the wheels and static compression? Also what camshaft? This will give us an idea of the cylinder pressure and dynamic compression before spray is introduced. A 100 shot is a very small shot on most V8s. We normally dont see these issues until 250-300.

 

I currently do not have a wideband on it because my sensor failed on me. I need to pick up another one. Once I do I'll see if I can get an accurate reading but I do know for a fact that I was on the rich side when the sensor was working. I believe I was at 11.8 afr at WOT on spray. That combined with an almost empty bottle may be causing my issues....I think.

 

I was able to verify with a timing light that the box is pulling the correct amount of timing when enabled. My afr sensor failed on me recently so this most recent pull that I had problems with I did not have a sensor on it. Previously I was at right about 11.8 afr at WOT on spray. Clearly rich and with a close to empty bottle was likely causing some of these issues I think.

I will try bringing the plug gap down a bit and try everything again...with a full bottle.

 

Unfortunately I have really no idea what kind of base HP I'm at right now. It's a pretty mild build on an LT1. Heads are gasket ported/polished, Comp Cams Xtreme CCA-07-467-8 camshaft, headers, full exhaust, Holley Street Avenger 750 carb, MSD Streetfire dizzy, and the Digital 6 box.
Pretty sure the LT1 compression is high to begin with...something around 10.5 to 1. With spray I'm sure that goes up quite a bit.

 

What nitrous kit? I know kits sometimes tend to be way rich out the box with the recommended jetting. I had a single nozzle kit that i ended up running a 150 shot sized nitrous jet with the 75 shot fuel jet just to get it in the high 11’s afr. That doesnt seem too rich on pump gas to me.

the original jetting on mine was low 10’s and didnt feel very smooth goin down the track. Leaning it out as much as 12.0:1 and adding 2 degs from the 6 i had originally pulled out picked up 4 mph.

 

Thanks for the info on that. Given the readout on the plugs I didn't think it was TOO rich either. I cut the threads off a plug and looked over the base ring as well and it didn't seem too bad. What I really need to do is put a new plug or two in and do a full pull then shut it down and check the plugs right away. Probably get a more accurate reading since these had some idle time on them.

It is a NOS Sniper plate kit. I've just been using the stock jetting they provide with the 100 shot.

 

verify your base timing is where you think it is.... use a piston stop to nail down exact tdc.
i ran 32 base on my stock shortblock LT1 with AI 200cc stock cnc'd heads. that was the sweet spot on the dyno n/a. 236/248 comp nx cam. i pulled lots of timing to be safe, probably 4-5 with a 100 shot. i ran pump gas and some 110 in a standalone fuel cell for awhile with no probs.

 

You had full advance at 32 degrees? I've done quite a few pulls with my dragy on motor and had it pretty dialed in at 35-36 degrees on mine giving me my best trap speed.

I verified a couple of times with my timing light just to be sure I wasn't getting some crazy readings at high RPM's but pretty steady across the board at 36 degrees.

When you were running the 100 shot, did you ever run on just pump gas?

One thing that has changed since I ran into issues is I JUST used 93 octane. I didn't use any additives to bring the octane level higher like I had done in the past. I just figured 93 would be plenty for a 100 shot...
I also notice the pinging only occurs when there is significant load on the motor, for instant I did a 3500 pull in 2nd gear and short shifted into 3rd, no pinging at all in 2nd but as soon as I hit 3rd it started.
I'm just having a really hard time believing i'd need to pull more than 4-5 degrees on a 100 shot but this is my first nitrous car so you guys would likely know better than me.

 

Stock lt1 heads usually like 36 deg sometimes touch more. Modified ported heads with chamber work can make them more efficient and end up with less timing

its not a bad idea to pull 4-5 and test on that til fuel is verified.

 

yep full advance was 32 on mine, but like orr said, it had nice heads on it so it would need less timing than stockers. my car was basically a stock shortblock lt1 with heads/cam/single plane efi. was running a megasquirt on the efi, and msd digital 7 with crank trigger and msd dizzy. the dig7 was triggering the megasquirt..
i pulled an extra safe amount of timing while i was working with the a/f, but honestly never really even messed with that either. lol. i started with a cheater plate runnig 45psi, then with a standalone cell running 5-10psi, and then moved into a 2 stage edelbrock crossbar . once going to the carb pressure in the standalone i simply started to follow the jetting suggestions i found on yellowbullet for that cheater plate. i started off with pump 93 in the tank, but believe once i did the standalone i was running at least 110 in the cell or both the tank and cell. i didnt drive the car any, only trailered to the track and back so there was no need to fool with pump anymore. the first few trips i only had a 75 shot in it, and the first time i sprayed it i did so with a button in my left hand. my 60' went from a 1.55 to a 1.35 and 7.3x to a 6.4x. i didnt expect that sort of a gain and i was all over the track hahaha.

you can try putting some good fuel in there now, but i would definately work on putting together a standalone if you can swing it. makes everything much easier and you can put some good fuel in there if you still drive the car on pump. there is alot of info on most plate jetting spreads and whatnot with carb pressure which makes setup much easier and less stressful. just make sure to pull plenty of timing at first.

 

I really appreciate your feedback on everything. First nitrous car for me so it's been a bit of a learning experience and until I have the time and $$ to tear apart and rebuild the bottom end, I don't want to do any damage to what i've currently got.

Once I've tried a couple of things I'll let everyone know the outcome and what I found took care of it.