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Discussion Starter · #1 ·
I have over 100 runs on nitrous (150 shot) on my street 403 olds, & only 10 of those runs have been on F&L SP1 (110 octane), but I've backfired twice & its been on the race fuel. I was wondering what you guy think it could be? It's a stock bottom end 403 w/ a cam, 350 heads, 9.5-1 compression. its a mid 11 sec car on nitrous. timing is set @ 17-18 idle 36 @ 2,000 rpm. I am running a NX Hitman

here's a cool little video my bro put together, backfire included http://www.youtube.com/watch?v=-8wNSR5yzgw
 

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Only thing I don't like is your timing. Way to high. And lock that fuggin distributor out,no timing advance. Get a retard box or a ignition box capable of pulling timing on the hit. Dunno what your car likes by mines locked out at 34degrees and my retard box pulls 4 degrees on the hit. Others will chime in.
 

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Let me put my 2 cents, Ok u say your not pulling any timing out of the motor when u hit the nitrous. Your car is tuned on 91 oct on the nitrous and it like it. It was a cold day @ fontana that day did u get the motor up to temp. Now this time u ran it 110 oct, so now u are makeing your tune richer now and what was your bottle psi. All these factors in. Iam thinking u didnt have enough heat in your cylinder to burn the fuel and the nitrous. Have u ever pulled a plug to see what going on in there if your motor has any heat in the plugs and also did u replace or check the power value when it back fired on u the first time. I would of left ever thing along with the pump gas it may have ran better do to the weather being colder.That my two cents.
 

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Discussion Starter · #4 ·
god damn it nelson you made some good points. my motor was @ 140 @ best, bottle pressure was @ 950, & it was abt 49% out there. But looking @ the plug it looked like it needed more timing, timing was a problem but i dont think it was a lack of timing. the power valve still good c&j put the good one on
 

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the good ones are the block off ones i dont think they would of put one on for a street carb like your, i would double ckeck if i would u lil buddy. That my 2 cents.
 

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Whats your flowing fuel pressure? The recommended pressure is 5# on that system. My personal experience with that system has shown that 5# was still a little rich.

All NX nitrous systems are calibrated at 1000# of bottle pressure. If you use a purge, I would have it a little higher before the run (~20#).

Also, what plugs?
 

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Discussion Starter · #10 ·
the 403s are weak but im shifting @ 5200 rpm, it's not stressing out the motor too much. i do ran the bottle pressure @ 1000 psi but i couldn't get it up there, it was too damn cold. my fuel pressure is @ 5, & i do remember it was running fat on the nitrous when i dynoed it, im guessing w/ the 110 it just made it fatter. i am running NGK-XR5
 

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engine was too cold...
 

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Why is everyone reccomending locked out timing?
Because when advance springs in a distributor come into play with nitrous it can cause havoc. When its locked out at say 36 degrees,its not gonna move,plus in almost every application the vehicle will run better with locked out timing. I doubted it as well but it changed my car. Then you get a retard box and have it pull timing on the hit....no worrys.
 

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I run my hitman plate with the 150 jets at 3psi and 1100psi bottle pressure. Timing locked out and retarded 4* from it's N/A setting. I had all sorts of weird issues launching on spray without my timing locked out...
 

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Discussion Starter · #17 ·
god damn, i didn't think i was that off my set up. the timing is lock @ 36, i got it curved when i got my carb blueprinted. ima try to hit up the dyno soon to work out the fuel pressure. i dont know shit abt spark plugs, so thats why i ran the XR5's, it's stock for 72 350 olds heads. will the B7S work good on the street or should i just run those when im going to use the nitrous? & what should the gap be? do you guys think i can pick up a little more e.t w/ these things worked out?
 

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Ill show u how to read those bad boys. ( plugs) We will be able to tell if u need hotter plugs or colder plugs, when u take a pass on them. And dont forget the BEER HAHA.

god damn, i didn't think i was that off my set up. the timing is lock @ 36, i got it curved when i got my carb blueprinted. ima try to hit up the dyno soon to work out the fuel pressure. i dont know shit abt spark plugs, so thats why i ran the XR5's, it's stock for 72 350 olds heads. will the B7S work good on the street or should i just run those when im going to use the nitrous? & what should the gap be? do you guys think i can pick up a little more e.t w/ these things worked out?
 

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XR-5 is too hot. Plug gap on XR-5 is too wide for nitrous as they come out of the box.

NGK makes colder plugs, B6S, B7S and B8S, that are not projected tip and are the same thread length and gasket type as the XR-5.
 
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