I have a Crane Hi-6 CD ignition, billet small cap distributor, NGK TR6 plugs, 10.0:1 static compression, CC 503 cam, 113 heads ported with bigger valves, HSR intake, Zex 125 shot, tune by pcmforless accomodating a 125 shot of nitrous. Running stock lifters, shifting at 6200 rpms. I can list other mods if needed, plus see my sig. Here are my questions.

1. What should I run for a spark plug gap? I'm running .042, is that good, too big, or too small?

2. What viscosity oil should I run? I currently run 10W40, is that good, too thick, or too thin? The car isn't driven in cold weather.

3. What air fuel ratio is optimal? Is it the same at idle, part throttle, and WOT or should I see different ratios for each? I have an extra 02 bung in my exhaust system. A friend of mine has a FAST system he is going to loan me that lets me put his wideband 02 sensor in my extra 02 bung, then it checks my air fuel ratio. I know if it is rich or lean overall I can adjust a little with fuel pressure, or I can have the tune redone if necessary. The car seems fine but I want to check it. What air fuel ratio would be the best for performance but still be safe. I don't want to run lean or on the edge to get 5 extra hp, but I want to get all I can out of it. The nitrous is a wet kit so I can change the fuel jet size if necessary to change the air fuel ratio when spraying once I get it spot on when not spraying.

My tuner likes small gaps. I run stock ignition except for an MSD coil and wires. He recommends .030" but I compromise and run .035". I think your gap's fine or you could tighten it up a bit if you want. In reality, I doubt you'd notice any discernible change anywhere in that neighborhood.
10-40 should be fine, another area where IMO minor changes in preference are no big deal.
I won't even get into the discussion of optimum AFR debate.

Thanks. You gave me 2 of the 3 answers I was looking for. I've been told that opening the gap is good if you have a powerful ignition to jump the extra gap. I don't know that for a fact tho, that's why I only opened it a little bit and am asking about it. Like you said, probably no noticeable difference. For the oil I thought 10W30 Mobil 1 synthetic would be fine too. For the air fuel ratio, I've been told 14:1 is the way to go, but again I have no idea other than what I've been told. Thought maybe someone here could steer me in the right direction on that. That is the one I am concerned with most since I know I'll be checking it and don't know what I should be checking for.

Do they even make 10w40 any more?

I'd run something with a 30 weight, and a good low restriction filter. Purolator and ACDelco aren't one of em. I just put a M1-302 (mobil1) filter on my truck, damn thing holds almost a quart of oil, about twice as big as the Delco filter. You won't have ground clearance to run an oil cooler on it though unless you mount it remotely.

Thicker oil may give you a higher reading on the guage, but that doesn't mean it's lubricating any better.

They do still make 10W40 here. I used to run that in the summer in a truck I had, then 10W30 in the winter. I have a stock oil cooler, but it isn't much of an oil cooler in my opinion. It is above the filter, just an antifreeze lines in and out. I really don't want to change or move it though. I have always ran Fram filters, but am willing to change brands. You suggest a Mobil 1 filter? Are they a low restriction? I like Mobil 1 oil but have no experience with their filters.

Nitrous tends to blow out the spark from the cylinder pressure. I have always run .030 in my 87. I have been spraying it since 1995 with good results.

Many people recommend the Wix filters as being very good as well. I started using them about a year ago and have been happy.

14:1 sounds pretty lean to me, but I don't know anything about Nitrous motors.

I think you want to be more in the 13 range. I remember reading that 13.2 was optimal, but don't bank on that as I can't remember the source.

Yeah, I can't get anything concrete on the a/f ratio. My nitrous kit is a wet kit so I'm not overly worried about that, they are calibrated pretty good with enrichment fuel. I am more worried about the N/A air fuel ratio. I'm going to check it but don't know what it should be. If I can't find out anything else then I think low to mid 13's would be a good a/f ratio to run and be safe.

As a good rule of thumb, you're always better to run your engine a little too rich than a little too lean. 14:1 is too lean; you'll have no wiggle room running that lean. 12.9 to 13.1 would be my recommendation. I believe you need to strike a balance between best power and keeping the engine alive. A few seconds at high RPM, WOT and lean and BANG! you're done.

Power adders add to the necessity of keeping the A/F ratio from going lean.

I run 0-40 Mobil 1 for everyday use, although I did follow Golen's (and others) recommendation for break-in by using - Valvoline VR1 Racing 20-50.

Just my thoughts.

Jake

Thanks for the advice! I think I will run about 13.1 or 13.2 on the a/f ratio. I'll then run it on nitrous and see if it runs richer or leaner. I can adjust the nitrous ratio by changing the fuel jet size. I do need to be careful as with all that is done to the top end and nitrous and all I'm still running stock pistons and rings.

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I would dial it back to .030, or even into the high 20's. You might also look into a cooler plug range, or cutting back the electrode on the stock heat range plugs. I don't have a ton of time right now to go into it, but cutting back the electrode on the proper heat range is a better solution than running a cooler plug.

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With normal oil, I think I would go back to a 5W30, assuming you have stock bearing clearance. This will free up a bit of power, not much, but every little bit helps. If you run a high quality synthetic, you can go even thinner, maybe 0W10. That's for max power production, if you're more concerned about engine life, the thicker oil is probably a better bet. Valvoline Max Life has a great reputation and is well respected on other sites I visit that deal specifically with oil. I might even consider a 20W50 in a really warm climate.

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Optimal means different things to different people. The leaner the engine, most of the time the more power it will make, but controlling the burn temperature and detonation becomes more difficult. For most street cars on the bottle, I shoot for about 12.5:1 on the bottle at WOT. I'm a bit more of a risk taker than most people so I run my car at ~13.2 or so on the spray, but for a customers car I probably wouldn't go that lean. Since you are measuring at the header, which will provide a bit more accurate result than a tail pipe sniffer, I would aim for 12.5:1. If you dyno the car and use a tail pipe sniffer that will probably read about 13.0:1, so don't freak out if you see a leaner number from a tail pipe sniffer at some point down the road.

Cruise AFR can vary a lot, but 13-14 is about what I look for when I'm trying for max drive ability. You can go leaner to pass an emissions test or get better mileage, but it gets harder to keep the engine from bucking under light throttle/high load conditions. If you are familiar with chip tuning, you can spend weeks dialing in the drive ability; it always seems like there is something that can be better.

Out of all the nitrous cars I've tuned/dyno'd, none of them have been real close to proper AFR with the recommended jets. Don't get too hung up on manufacturer recommendations when tuning it on the spray, just watch the AFR, run conservative timing, and dial it in. Once you get the AFR dialed in, add timing back into it slowly. On a 125 shot, you should be able to run just fine on the stock timing table, but double check with your tuner to see what he's done with the timing table.

On my 91, stock WOT timing was 31 degrees. I added 6 degrees to the stock tune for a total of 37. I pull 3 degrees when I spray the 100 shot on my car, so 34 total. I have no detonation/knock.pre-igniton issues. Even after pulling the 3 degrees for the sauce, I'm still running more timing than the stock tune. That's why I say you should be fine with the stock timing table. However, double check with your tuner before doing anything crazy.

Wow, Thanks!

I am running 1 step colder than stock plugs, I can't remember if the NGK TR6 are stock and I'm running the TR55's or vice versa, but I am running 1 step colder than stock. I have been told that the better than stock ignition systems could use a bigger plug gap and make better power, but it sounds like I should cut back. I'm at .042 right now.

I ended up running 10W40 Valvoline Max Life, synthetic blend. Went with a K+N oil filter, it is bigger than my old Fram and the oil pressure is a little higher now.

My 02 bung I'll be using for a/f ratio testing is in the exhaust pipe just a few inches behind the header collector. It isn't in the header, but it is way closer to the header than the tailpipe. I do believe I'll look for high 12's or low 13's (at the leanest) when n/a for air fuel ratio. I was originally going to go with 14:1, then it seemed that low 13's would be best, but I think 13.0 would be a good target for me. I think on the bottle I'll set the jetting up to have me in the mid or maybe high 12's, or 13.0 at the absolute leanest. That should keep me safe n/a and even a little safer on the bottle since I'm still running stock cast pistons. (all this is at WOT)

pcmforless did my tune. I told Alvin to set it up figuring on me running a 100 shot. He told me to run 6 degrees initial timing with his tune. I decided to go with a 125 shot, so I set the initial timing at 5 degrees. This should keep me safe n/a from ever having any detonation, although it leaves a little power on the table. It should be pretty safe from detonation on the bottle as well. I may someday add a timing retard box to the Crane Hi-6 ignition but for now this is how I'm running.

I haven't had the chance to spray yet but the car runs like a raped ape without spray. It pulls hard right to the rev limiter at 6500, although I'm going to be shifting it at about 6200 or 6300, and it is set up to shift automatically at about 6000. I'll have to wait till good weather to dial in the air fuel ratio. All seems fine so I'm hoping it is close enough that I can just adjust it a hair with fuel pressure, but getting the tune done again isn't out of the question if it needs it. I have lots of fuel jets and I know I can open one up just a hair with a drill bit if none net me the exact air fuel ratio I'm looking for when spraying.