car is a 95 Z28 355 built for spray. i run a 2 stage 300 shot. (125/175) the car goes 12.8 all motor, but all i can manage out of the 300 shot is a measly 11.7 the car is breaking up realy bad up top while on nitrous. ive changed the timing on my mallory hyfire a ton, the best timing it runs at is 7.5 degrees but it still breaks up. when i go to the track i only run 110 because the the 300 will not even ignite on pump gas. the wierd thing about the whole situation is it even breaks up while spraying the 125 shot. this happening to anyone else? id like to figure this out because i realy think the car has a high 10 second pass in it!.

 

Ive been told and by several people you gotta retard timing 2 degress every 50 hp, on my 150 shot which im running now ive retarded timing 7 just to play it safe if i retard 5 it will miss big time and go no were. So 300 would have to be retarded alot and if pull that much timing out and wanna run it stock meaning no nitrous you will not have much top end at all. But obviously safer to retard with nitrous. Also check your plugs im sure your using colder plugs for nitrous but your plugs can easily foul, with 7.5 timing takin out with 125 should not break up and when you say break up do you mean its missing. Also have you check your A/F lately make sure you running consistant fuel pressure that may have changed. It could be several things as im typing i could think of several other things to check but i dont know what yo mean by it breaking up.

 

oh i should add i have a racetronix fuel system, stock heads with stainless manley valves, comp 918 springs with comp 1.6RR. everytime i retard the timing more than 7.5 the nitrous screws up even more

 

I would put a fuel pressure gauge on it and at least confirm good fuel pressure during WOT and nitrous engagement.

 

i have a dynotune digital fuel pressure guage in my car, it never dips below 42.

 

how does it respond with just the 1st stage? like in the other post , what plugs are you running? also at what gap? are you also sure you matched the jets up for the stated hp per stage numbers?

 

Too rich? Not a strong enough spark? Plug gap too large?

Rich

 

Best advice i can give you is get it dynoed with A/F. You can figure out from there if your rich or lean and in my case first time i went i found out i had a ignition problem wasnt able to pin point the exact cause but it guided me in the right direction and figured out that it was my plugs.

 

Agreed

I had a problem on my car when I was spraying that not all the fuel was igniting. Do to the increased cylinder pressures. The car ran fine N/A but under a heavy load I had a miss. The problem in my case was the plug wires arcing.

 

im running NGK TR6 plugs gapped at .035, i also run a mallory hyfire digital ignition. enen on 1 stage it is breaking up. im going to replace my plug wires as they are looking a little on the ratty side, hopefully this cures it!

 

TR6s are a fairly hot plug for that much nitrous.

How do the plugs look after a run? Any signs of detonation?

I would highly recommend you stop running a full 300 shot and figure the car out on a 100 shot. Go up from there once it is running right.

EDIT: How are you spraying a 300 shot? All through the TB? Dual Nozzle kit? DP?

 

You have fuel pressure, start pinpointing ignition problems?

My first thoughts were that it was gapped too big and blowing the spark out ?

 

try .025-.030 gap.