Ok, 2 separate questions here. N2O; 150 HP jets I went to the races and when my progressive N2O hit the 100% mark or so I got a big pop through the carb and let off immediately. I know I didn't retard the timing so total was about 34-35 degrees. It should have been less, and will be next time (long story). 92 Octane Pump Gas 10.25:1 compression carb jetted real close, but not perfect Fuel should have been rich on the N2O as I have no regulator before the fuel solenoid, also a spectator noticed black smoke when I hit the juice. Plugs(Autolite 23's) looked fine, no damage the next day. porcelein is clean outer shell has some sootiness(sp?) #2 cylinder leakdown is 11% but not enough for oil contamination I would hope. Also, the soot doesn't look "oil shiny" on the plug. [/list=1] Question #1: What made this pop through the carb? Checking plugs, Cyl #2 porcelien looked paper bag brown like I always thought they should look. But, only #2 looked this way, the rest of the plugs' porcelein looks brand new. Every time I jet for color on the plug it seems too rich. So, my second question is, do I have a distribution problem in my carb/manifold setup that is causing #2 to look so dark? When jetting, what sort of color do you generally look for on the plug?
you DEFINATELY need a regulator before the solenoid! You have no idea what your static pressure is at full throttle. How big are your fuel lines? Is your gas solenoid line T'd into your carb fuel line? Or is it on a separate pump or fuel line? Once you get to 100% you are probably leaned out. Your timing doesn't sound high. Your fuel supply to the solenoid must have volume and CONSISTANT! It's not good to have pressure that comes and goes. Most systems like 5 pounds of static pressure with the regulator near the solenoid. Wife's calling me to dinner:af: always when I'm in the middle of something!
I have a Holley red pump at the tank dedicated to feeding the solenoid via a 5/16 steel line. It is internally regulated at ~7 PSI, which is what the N2O mfg assumes I think . I know they are ususally calibrated way rich, but wanted to play it safe until everything was working flawlessly. I also have a pressure switch at the solenoid that cuts the system off in the event that pressure drops below 5 PSI if memory serves me. I made 3 passes without N2O and the carb fuel system was working fine. I'm wondering if its timing or lean-out symptom. now that you point it out, I'm starting to think lean is more likely.
Adam- I've fought the same problem for years. Whenever I run over 150HP, by about 1000ft the engine will backfire hard out of the intake. If I run 250HP, it will happen sooner than 200HP (which is why I don't run either of them right now). I have played with mixture with no decent results. I don't think it's mixture. In fact last time I blew up my motor (yes, I've done it a few times now) the computer showed I never went leaner than 11.5:1 A/F ratio (which is still on the rich side). (I have a FI kit on my 455 with a wide-band oxygen sensor that gives you exact A/F ratio). I don't think it's timing either- I run about the same as you, although I will be backing off more when I run nitrous (2 deg per 75HP) in the future. I think the key is the spark plug. After a long, long talk with my nitrous guys (Top Gun) about detonation and such (after my last blown up motor), they HIGHLY recommended the Autolite 25s. I have been running the AC Delco R43TS plugs, but what can happen if your plug is too hot of a heat range is that the electrode heats up and eventually gets so hot that as soon as the intake charge enters the cylinder, it hits the hot electrode and ignites (back through the open intake valve). I don't know which is hotter- an Autolite 23 or 25, but I recommend that you switch to the coldest plug you can find. Also, I am going to start using race fuel (mixed w/ my regular fuel) on anything over a 100HP shot. You should consider this as well, especially since your compression is higher than mine. You don't mention what your bottle pressure was at- if you don't know, then you shouldn't run. If your bottle is at 650 PSI and you get it dialed in, on the next hot day when it's 90 degrees out and your bottle pressure is at 950-1000 PSI then your engine will go BOOM. Been there, done that. If you don't have a setup already, call Nitrous Express and get their heater that controls by bottle PRESSURE- don't get a cheap kit that will control by temperature. Pressure is what you need to control. I will also be closing my gap for nitrous- I have been using 0.035" but I'm going to start using a 0.029" gap (even though I have a very strong ignition system) on 150 and higher nitrous shots. Adam, I would also NOT run your system again until you get a FP regulator. 7PSI is at maximum flow, and since you're under maximum flow the pressure will be higher (9 PSI? 12PSI?). That is NOT an internally regulated pump! Running too rich can cause backfires too (although I'm in favor of the spark plug solution). One other thing, make sure that your solenoids are designed to be used with a progressive system- the progressive controller slams the solenoids open & shut very quickly, and not all solenoids are designed to do this. (It also beats the crap out of the solenoids but that's a different issue) Last thing you want is a nitrous solenoid to get jammed open. Just some words of advice from someone who's blown up too many motors (3-4, I forget) because of nitrous. But I still run it! -Bob Cunningham bobc@gnttype.org
Thanks guys, and any more thoughts, I'm definitely listening. Bob, the 23's are 2 steps colder. I'm actually using autolites because they were the coldest plug for the 455 that I could find here in po-dunk-ville. Plugs are at .032", but I'm running an old stinger S-4, so not exactly a lightning-like spark. Interestingly, I've made a test-run on the street (3000 ft higher elevation though) with the exact same setup, except 100% at the get-go after 2 sec delay, and no problems. You have a point about bottle pressure though, it was damn hot out, and the bottle may have been hot(very warm) from being filled still. I have a safety kit for the solenoids(gotta install it!). I am also wondering if the N2O provides enough extra G's to marginalize what has so far been perfectly adequate fuel system. nah, if it was, I should see a fuel press drop at the launch I think. I will have to put a gauge on N2O fuel too though maybe. I saw a real cool setup on a car this weekend (actually the car I should have beat). he has a ~1 qt cannister that looks like it is from a dry-sump oil system or something mounted on the core support where the battery would normally be. it feeds a holley blue pump with a return style regulator on it. They fill it with the good race gas. He says a quart lasts over a month. now if I can figure out where to get a cannister like that.... I know a guy that has tries some pretty wierd stuff with N2O and I once watching him get a lot of popping when he tried a home-made plate with poor distribution. Are you runing a "dry" system, fogger, or plate? I wonder if distribution is a factor?
Adam, It could be ignition,fuel mixture or distribution. If using a TA intake the nitrous plate should be run sideways. KB or edelbrock work fine in standard front and back entry. NGK are the plugs to use when running nitrous (opinion), wide range of heat ranges available. Find the best heat range for your motor, drop one heat range upto 150HP, one more range for the next 100HP. 32-34 deg total should be best for motor alone, drop aprox. 2 deg for every 75HP. Run better fuel when you spray, at 10.5-1 + nitrous is very marginal on 92 octane. Definately get a regulator for the nitrous, invaluable tuning tool. Read the plugs, you need a clean shutoff to get a proper reading. Shutoff at the earliest safe point and read the plug. A return to the pits will change the read on the plug. EGT gauges are very handy in tuning with or without nitrous. Upgrade the ignition. I would bet that your problem came from a combination of the fuel and timing you were using.
Actually I've been looking at 2-gal fuel cells lately, with that same purpose in mind. Keep 117 race fuel in there, and use it for nitrous enrichment. I have the plans in my brain, just no $$ to follow through (still reeling from the engine repairs). If your regulator is at the front of the car, then the extra Gs won't be a concern, the Red pump can keep up with a 150HP shot no problem. Find out what your system manufacturer recommends for pressure (probably 5-5.5?) and do it right. I used to run a plate (bars front-to-back), but now I have my spraybars drilled into the manifold directly (side-to-side) and that hasn't fixed the problem. But in theory the distribution is better. If the plugs aren't the problem, I think you might be too rich. -Bob Cunningham bobc@gnttype.org
OK guys, this is good stuff. Bob, FYI, Jegs lists a new 1 gallon fuel cell for $120. 6x6x12 inches. Should I drill my plate to bolt side to side (I have a TA intake)?Then what to do when I put the Q-jet back on? Drill the manifold I guess, eh? Dennis, I like NGK too. Just try to find a UR6 anyplace in MT or east ID :af: . I was thinking 29 deg advance w/ the N2O, guess that's pretty close based on your advice. Fuel and timing may be it. It almost has to be something simple as I have had OK luck before with the 150 jets. combination of the heat, my not backing off the timing might nhave been enough to let the fule problem rear its ugly head. More distributor work, this weekend, then some testing. I may just have access to a pyrometer :TU:
Adam Back when I ran the sneaky stuff I had a Top Gun Stage 5 kit with NGK's and all MSD stuff except for the wires which were Taylors. When I first started out I ran a Holley blue pump. I found that the blue and red pumps surged alot! Think about this. While you staging, the pump is building pressure and it's surging. Once you open the progressive solenoid it relieves the pressure slowly, but the pump is still surging until the solenoid is open continuously. No more surging, but now the pump has "lost it's wad" so to speak until it catches up, by this time you're about 3/4 track. You're starting the run out with enough pressure, but the pump can't keep up with the change in demand at mid track. Do your self a favor. If you already have a bullet proof ignition system, your next sound investment should be a good pump at least 120gph or better with a return line and a good regulator. I know it sounds like a stretch but it beats blowing the motor. You may be too fat at launch and to lean at 660'-1000'. Remember you need consistent fuel pressure AND volume. Also that 5/16 line's got to go. I have a marsh buggy with a Shovey 153" 4 cylinder with a 5/16 fuel line and it's barely enough. No volume. Hope this helps.
Backfire? A backfire through the intake can be either: Too lean, engaging the nitrous at too low of a rpm with a big cam, or your rotor phsing is off. I personally don't like the progressive systems. They're hard on solenoids and I've seen alot of guys have problems with them. I recommend a multi-funtion MSD box that works with a MSD 6 box or a Digital 7 Programmable. They both function the same. You can run a launch curve that takes out "x" amount timing for "x" amount of time. I used mine when I was "blowing off " my tires coming out of the hole. I run a NOS plate system and my plate is jetted "square" for example-63/63 running 5 1/2 lbs of fuel pressure. Nitrous is very sensitive with fuel pressure. 7 lbs vs. 5 1/2 lbs is alot. Running too much timing will put holes in your pistons. If you had any detenation there should be black speckles on your spark plugs. I run NGK plugs since there tips are soft and suppose to melt off easy if you are on the edge of being too lean. To check rotor phasing, line up your balancer with #1 and the timing it is running at WOT with Nitrous. If your running 29 degrees, put it at 29 degrees and pull off your distributor cap and make sure the rotor is lined up with #1 on the cap. If your running too rich it will "feel" like you have an ignition miss, breaking up going down the track or the raw fuel will ignite in you exhaust throwing those "cool" flaming back-fires out your tale pipes. Your plugs should all be white and clean with no signs of detonation or bluish/purple heat dicoloration. ARE YOU RUNNING A POWER VALVE IN YOUR CARBERATOR! With a Plate system, they tend to pull vacuum under the carb and WILL pull a power valve shut causing a very lean condition. You can run a plug and jet your carb up 8 jet sizes. Plus you know how Buicks like big carbs and like to pull vacuum under the carb as is on motor. Nitrous will just amplify it. If that fixes your pop you'll need a bigger carb or stiffer power valve. I ran a true 10.0 comp. ,508 hyd.,and a 175 shot on pump gas with no problems but I'm sure I was playing with fire. I have a sideways nitrous plate if you want to try it to see if it works better for you. FLYIN' oN tHE JUICE!!!:stmad: :stmad: :stmad:
Rick, thanks for the offer, I may take you up on it. So far I have ordered the 1-gallon fuel cell and will install a regulator with return line to stabilize the fuel pressure. Race gas will go in that tank. I'll start at the recommended pressure and work my way down when I am comfortable with everything else. Guys I know locally have had great results with the progressive, but I also know one of them scattered a motor when the fuel solenoid stuck shut. I'll get the safety solenoid installed when I do the rest of the re-plumbing. Timing will be retarded next time to 28 degrees total. Corroborating well with Bob's experience, I read today where too much advance can overheat a sparkplug easily, and also sometimes leads to tuners over-richening an engine inadvertantantly when jetting the engine for best performance with an overheating plug. In my case that may very well have fired the charge before the intake valve was closed? I have a 1000cfm BG carb and 4.5 power valves. boy, if I'm pulling that much vacuum, I've got one kickass unit! I'll put a vacuum gauge on it too. I'm probably due for an ignition upgrade but that'll have to wait for now. Also I will find some NGK's: UR6's ? My carb fuel pump should be fine, it is a 255lph walbro supposedly good for like 600 HP on a GN at 50 PSI. My line pressure is about 20 PSI to the regulator. I'll stick with the holley red since it will only have to pump from the nitrous fuel tank at the wheelwell to the plate regulator and back. Anybody see anything I'm missing?
Power Valve I will better explain about the power valve closing since there isn't going to be vacuum in the intake. If you have the nitrous plate in the front to rear configuration the power valve vacuum port is directly above the spray bar. When the nitrous is sraying out of the bar it crates a vacuum directly above it but it doesnt mean there will be manifold vacuum. There is just enough negative pressure above that bar to pull that valve shut or partly shut. I was working on a 351w Mustang that had a hot set up with a 850 Holley and a 275 hp shot plate system. When we stepped up from the 125 to the 175 we started running lean even though there was no fuel pressure drop and the fuel pressure safety switch was not turning the system off. Long story short, the power valve was starting to close. Once we blocked off the power valves and jetted the carb accordingly everything was fine. If you run a sideways spray bar its not a problem since the nitrous bar is no longer under the vacuum port. I'm not saying this is a problem on your set up but it is definitely something to be aware of. :Smarty: Be careful not to run your system too rich or it will start to break up and feel like an ignition problem. You don't want to chase ghosts. Just start where the nitrous system kit tells you. Most nitrous are jetted rich as a safety factor. NOS kits are jetted real rich. Go luck! Spray it hard, it will like it!:stmad: :stmad: :stmad:
OK, on the power valve thing. I'll have to look at that when I have the carb off. I may be going back to a Q-jet soon, so it might be taken care of that way. Also will get the fuel pressure set at mfr. recommendation. Thanks guys for some great advice. I don't want to scatter this thing, but I do want to make it work.
