New to nitrous

[find01]

Hi, I have a 86 monte SS running a .060 over 350 with 6in rods and forged 400 crank. Aluminum trick flow 58cc heads and forged flat tops running 12:1 comp. Trick flow pate type,100hp shot. The spark plugs are AR3935 which was recommended by the Autolite racing tech line. This weekend I went for a few runs at the 1/4 mile strip and pulled a couple of plugs after each run. [drove back to the pits] It looked to me to be running lean after each run. The porcelin was quite white, no noticable black specs, and the base of the plug was clean almost 50%. I kept adding more fuel pressure but the regulators [one on the nos solenoid and one on the carb] are so hard to read when the engine is idling that I am not sure what they are really set at. It looked like 9psi. If I set them with the engine off they slowly keep creeping to a higher pressure. Anyhow, long story short I burned the ground strap off of the #4 cylinder after the third run. Is this just too lean or also too hot of a plug? Is detonation also a factor? What is the proper way to set the regulators? Holley # 12-803. Your input is appreciated.

[71Hellride]

To set your regulator you should use a flow gauge right off your regulator with the fuel jet your running. If your gauge is mounted to the engine it's probably off from the vibration. Also if it's dead headed the pressure will rise to say 9lbs but as soon as you turn on the nitrous it could drop to anywhere. What are your jet numbers, your total timing, and how much timing do you pull for nitrous. The strap burnt off because of heat, the only time I've ever does that was from too much timing. It's hard to get a plug reading driving it back to the pits, but I have drove back and the plugs still be really clean. Your looking for the very base to get a reading. John talks about having a very faint line on the base. I've even heard some say it looks like you took a pencil and marked the bottom. Some like them totally clean. I like a really clean plug myself.

[John_Heard]

3935 is equal to a -7 which is a bit hot for spray, you should probably drop down to a NGK -8, or AR3934. If you burnt a strap off an Autolite, there is way too much timing in the engine as mentioned earlier by Hellride.. He's also right also that you need to set your fuel pressure flowing. Which means you need to unhook the fuel solenoid at the regulator, then hook up a gauge with a line with a 73 NOS jet in the end of it, then turn the pump on and set the pressure that way. You can buy these flow gauges from Nitrous companies or make your own, they are not hard to make.

Did you retard the timing any when running it on the spray? How much retarded did you set it?

[find01]

I checked my timing this AM [Mallory unilite dist. and highfire III ignition,] and the base is at 15 and at higher RPM maxes at 44. Roughly what numbers should I be looking at for NOS? This advance is what I have been running it at naturally aspirated, and have had no noticable detonation or kicking back on the starter. Can I also get more info on the flow tool you are talking about? This is the learning curve... Thanks

[find01]

I almost forgot, the carb is a proform 850 street series with a choke, the primary jets are 76 and the secondaries are 82. The NOS jet is 57 and the fuel is 41. The fuel pump is a "blue" holley 110 gph mounted by the tank with a 3/8in supply line.

[John_Heard]

First of all, 44 degrees is likely more timing than you need on motor only, and it's way too much for a hundred shot of nitrous and that's very likely while you melted the strap off a few plugs. You were lucky it didn't melt holes down the center of the pistons too.

I'd suggest doing some testing to find out what your engine likes for sure motor only, it may want 38 degrees vs 44 degrees (sounds a bit much). Once you find out for sure how much it wants motor only, then put the colder plugs in it, and take out say 5 to 6 degrees of timing to start with on that hundred shot. Make a pass and look at the fresh plugs to see where you are at on your fuel mixture and the heat mark on the ground strap and adjust from there.


Your 57/41 jetting is quite a bit of stagger (difference between nitrous and fuel jet size), with those jets you'll need to run around 14 psi which would be more than what your regulator is capable of. So you need to bump up your fuel jet size. What other jets do you have available?

Here are a couple retail flow tools for sale;
http://www.induction-solutions.com/prod ... owTool.htm
http://www.nitrousexpress.com/product-d ... php?id=242

These are not hard to make yourself, it's basically a ball valve, some hose, fittings and a setup to hold a nitrous or holley jet in the end.

[find01]

The jets that came with the kit are --- 33,41,52,57,62,66,70,73,82,88 The listed settings are--- [NOS jet first] 41&33 50hp, 57&41 100hp, 70&52 150hp, 82&57 200hp, 88&62 250hp. If I make an adapter to set the fuel pressure as it is flowing, can I use holley jets? because they will screw into a fitting. Do both NOS and hollety jets flow identical?

[John_Heard]

A Holley #70 Jet is about the same size as a NOS #73 Jet.

The modifications to a fitting to get it to accept a NOS jet are easy, here's a little write up I did on making fuel bleeds. You can do the same thing to rig up a fitting for your fuel flow tool.

http://www.dragstuff.com/techarticles/fuelbleeds.html

Just to clarify, you got those tune ups from NOS??? By any chance can you scan and post the sheet? Those are way off from what NOS used to send out and very lean.

[find01]

The nitrous kit is from Trick flow that I bought through Summit , which I have found to be built by nitrous express. This is a copy of there spec sheet and it also has the fuel pressures at the bottom. What do you think?

[John_Heard]

Well that makes sense, NX does have charts like that.

That chart in my opinion is too lean for a starting tune up which would put your N/F ratios upwards of 7.49:1 at 9 psi. I believe (and feel free to ask around on this) that you would be much safer pulling the timing out like I suggested earlier (5-6) degrees retard and running say 57/52 @ 5.5 psi through a flow tool like we've been talking which would be a N/F ratio of 5.96. Make a pass and see what kind of fuel ring you have on the plug and what kind of heat mark you have on the strap and then make adjustments to the tune up.

[find01]

Thanks for your input I will do what you have suggested. If I build my flow tool to set the fuel pressure to 5.5psi, should I just take my fuel jet that I will be running and insert it in the tool and then bleed the fuel just into a jar or something? Would this work okay? I see your bleed off tool must return it to the tank.

[John_Heard]

That http://www.dragstuff.com/techarticles/fuelbleeds.html page I was pointing to so you could see how to make a fitting to hold a nitrous jet for your flow tool. Put a fitting with that jet in it then stick it in your fuel jug when setting the regulator. You'll want the hose long enough so the fuel jug can set on the ground while you're adjusting the regulator. A jar is too small...

[find01]

Will do, thanks to both John and 71 Hellride. If it doesn't rain out I'll run it again this weekend and post how we did.

[71Hellride]

If it was me I would lock your distributor out. No need in fighting with the timing advance. Do you have a timing retard that is activated with the nitrous on? I built my own flow tool and got a gauge from nitrous supply. The gauge cost me $90 but i'm sure you can find a cheaper one.

[find01]

No I don't have a timing retard, but it sounds as if I should research that more. Yesterday I built a flow tool like John suggested with a couple pieces of hose, a 3AN fitting, and a fuel pressure gauge that we use for fuel injected cars in my shop. It works well and I could set the pressure at 5.5psi without it fluctuating. I set the base timing at 6 and at higher RPM it tops about 35. Do you think this will still be too much when I hit the juice? Right now I am just playing with a 100 shot so I hopefully don't trash the engine while I'm learning.