KyAllroad UltimaDork
10/26/21 11:57 a.m.

So the Challenge has come and gone.  One of the things I tried and had thought would be cool but failed was my nitrous setup.  The Zoomboni came with a wet kit installed but apparently never tested.

An aside at this point:  I made 7 passes down the strip this year.  Passes 1 and 2 were my first time drag racing anything other than  my AWD automatic Passat which hardly counts.  So they were just to get familiar with the process.  First time staging I drove right past the beam and the starter dude had to tell me to back up about ten feet (oops).  It was the first time the car had ever gotten into 4th or 5th gear, whee!   I was running the Avon slicks but they are only 23" tall and T-5 gears run through a 4.3 diff meant launching in 2nd, and shifting to 5th at around 900 ft....and essentially coasting from there.  Clearly if it comes back it needs 27-28" tires in back so I can run all the way through the lights in 4th and not fall into that overdrive hole.

Pass three I try my autocross trick of launching in 3rd, nope the clutch does NOT like that.  Smells like an Evo, all burny and sad.

Then for the 4th pass I opened the bottle and purged a bit of NOS (gotta look cool, you know).......and nothing.  Oh hell I'd disconnected the wires to the solenoids a while back to diagnose an electrical failure and left them unplugged.   Pull off the hood and plug them up.   Try again...still no hit.  More diagnostics back by the trailer and learn that the "system armed" switch is upside down and down is armed.  Another pass and still no laughing gas.  I'm bracket racing here and now it's dark and I can't see out of my tinted visor.  Mike loans me his to keep going, thanks man.

Pass 6 is my best attempt: 8.254  at 85 in the 1/8th and 12.983 at 103.28 for the 1/4 and when I pull off I realize the stupid switch was UP!   I'm frustrated with myself and feeling like an idiot.  Last try, I promise little car.  Back to the line for a pass on the bottle, 11's here I come!  pop pop pop pop pow pop.....  It is clearly not happy with nitrous.  Mike thinks the extra oxidizer was blowing out my spark and I need tighter gapped plugs.  Other folks have suggested it isn't jetted properly and leaned out.   Either way I was done for the night and reasonably happy with the result.  The car launched hard and felt nicely stable on the big end.  I hope it was entertaining for the folks watching (look at that fool!).

So my plea, what do I do with it to make the nitrous system happy?  The original builder included a bunch of bits and pieces including other jets.  Do I take out what's in it and install the smallest ones to reduce the shot?  Gap down the plugs (and to what)?  Both?  Option D? 

eastsideTim PowerDork
10/26/21 2:51 p.m.

From the limited info, sounds lean to me.

Did you check what jet sizes you had ahead of time?  First thing I'd do is see what size nitrous and fuel jets you have, and find a chart online to see if they match up with each other with whatever fuel pressure you are running.

If they are correct, you may want to check the fuel solenoid - disconnect the line from the plate (or nozzle if fuel injected).  Put the line into a bottle to collect the fuel.  Make sure the nitrous bottle is closed, and hit the system, either with your fuel pump running, or the engine running if it is a mechanical pump.

If you are getting fuel, and the jets are sized correctly, then I'd start looking at timing and spark plug gap and temperature.


Edit:  One more possibility I forgot to mention is your fuel pump could be maxed out and unable to provide enough fuel.  If that's the case, going to smaller jets for a smaller hit may do the trick.

Ranger50 MegaDork
10/26/21 7:04 p.m.

Spark blow out. You didn't retard the timing, you retread.

Paul_VR6 (Forum Supporter)
Paul_VR6 (Forum Supporter) SuperDork
10/26/21 8:09 p.m.

Could be a few things. If you didn't check the jets see what they are. Usually a recommended jetting will be rich and safe if all is well. If the fuel system is efi you need tiiiny fuel jets u less you have a 2nd regulator for low pressure for nitrous fuel. Usually a small hit won't max a fuel system but it could if its already marginal. Timing is fine w added octane or small hits (50). Plug gap down to .018" is recommended esp if the ignition isnt great. 

GCrites80s HalfDork
10/26/21 8:40 p.m.

Did you install colder plugs for the nitrous? One step colder is usually the rule.

Cactus HalfDork
10/26/21 11:39 p.m.
Ranger50 said:

Spark blow out. You didn't retard the timing, you retread.

This sounds like a top culprit to me.

Also, you need to set fuel pressure at the jet to be whatever it's asking for while spraying. If it calls for 6psi, and you set the pressure to 6psi static, it will drop when you open the solenoid, and you'll be lean. Pull the nozzle out of the intake, get the pumps flowing and manually cycle the fuel solenoid while spraying into a gas jug. Adjust your fuel pressure accordingly.

Stampie GRM+ Memberand MegaDork
10/27/21 6:22 a.m.

There's several things not answered here.  How is the wiring set up?  Do you have an arming switch then a micro switch on the throttle?  First with the bottle turned off, engine off, but the nitrous system energized I would see if the two solenoids actually click when engaged.  After that I would check my jets click or no click to make sure they are set up properly. Nitrous systems aren't difficult, we installed ours between autocross and drags including wiring the system.  The problem is if something goes wrong you can cause major damage.  Do the click test then come back.

KyAllroad UltimaDork
10/30/21 4:21 p.m.

So here we have a perfectly functional nitrous system.   NO2 and fuel both come on exactly as they are supposed to.

Nitrous jet is a .040

Fuel jet is a .028

clearly I need further investigation of timing.   Time to buy a timing light I suppose.

Stampie GRM+ Memberand MegaDork
10/30/21 4:30 p.m.

What's your fuel pressure?

Edit - That's a 30 shot for 5psi carburetor systems.

Mr_Asa PowerDork
10/30/21 4:31 p.m.

Thought this thing was EFI?  Does the 5.0 EFI system not lock out timing and give control solely to the computer?

Run_Away Dork
10/30/21 4:47 p.m.

^Base timing is still adjustible by rotating the distributor.

OP, What was your bottle pressure?


Google sez a 5.0 foxbody Mustang runs 39psi of fuel pressure.

Assuming 900psi of bottle pressure, at 0.040" jet is around 75hp. Internet jetting calculators say you should run a 0.023" fuel jet to match (given 0.040 nitrous, 900psi in the bottle, and 39psi of fuel pressure). So you're jetted up pretty rich. Your 0.028" fuel jet would be better matched to a 0.049-0.050" nitrous jet, good for 110hp-ish (again, assuming 39psi fuel pressure and 900psi bottle).

bearmtnmartin (Forum Supporter)
bearmtnmartin (Forum Supporter) GRM+ Memberand UltraDork
10/30/21 5:27 p.m.

From my limited you tube experience I thought nitrous always meant woes.

Floating Doc (Forum Supporter)
Floating Doc (Forum Supporter) GRM+ Memberand PowerDork
10/30/21 6:18 p.m.
bearmtnmartin (Forum Supporter) said:

From my limited you tube experience I thought nitrous always meant woes.

It certainly has that potential. 

untchabl Reader
10/30/21 10:50 p.m.

From previous experiences decades ago, a stock 302 can easily handle a wet 100-shot from a single nozzle. Much more than that and the fuel starts to puddle in the bend of the upper intake manifold and you run the risk of a nitrous backfire. If you switch to a plate setup between the upper and lower intake manifold, a wet 150-shot will be fine. If it is a stock forged piston engine, I have seen them take a wet 250-shot with the plate setup but you need to be willing to take the chance of it blowing up. 

All the above info is assuming you have base timing set correctly, proper fuel pressure, proper jetting, etc, etc. Just giving you an idea of what the engine can take. 

KyAllroad UltimaDork
10/31/21 7:21 a.m.

In reply to Run_Away :

No idea.  This thing has no gauges for bottle pressure or fuel pressure.   

Paul_VR6 (Forum Supporter)
Paul_VR6 (Forum Supporter) SuperDork
11/1/21 9:16 a.m.
KyAllroad said:

In reply to Run_Away :

No idea.  This thing has no gauges for bottle pressure or fuel pressure.   

Where is the fuel tapped, same feed as EFI? If so you need a way bigger N20 jet, looks like a 40/28 is a 75 and 15 psi fuel pressure. I don't like tiny nitrous jets so move up to a 52 on the nitrous if you are ~50psi fuel  cool probably want to take 2-3 deg out and one colder plug.

edit: runaway pretty much said the same thing, but I skimmed.

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