ARRGgghh !! damn hemi !! damn plate !!!

[63 Vette]

Ok, so we go to the track for the 3rd time with the my buddies 572 hemi with a simple 150 shot.

Basic combo
572 hemi
Stage 5 heads
12.5 to 1
880-900 hp on motor

Big Shot plate with 63 nitrous 71 fuel jets.

I ran over 500 lbs of nitrous through my race car last year up to a 36 jet in my 454 with no big issues. Point being, I have a pretty good understanding of nitrous systems so this problem is very frustrating:smt100

1st trip to the track we flowed the fuel to 6, 5.5 and 5lbs with the same results every time; car launches with seeminly no additional power (no pick up in 60' or 330) goes about 400 feet...pop...pop....pop. We find the plate is up side down (did I say I knew about nitrous systems)....we swap the plate over and the car does the same thing...pop....pop....pop

2nd trip to the track we flow the system with the plate right side up and it does the same thing. My buddy went by himself; he made a couple of passes and brought it home. I went over to his house and we took the carb off.....activated the system and flowed the plate into a bucket, fuel distribution looked good. I know nitrous is coming out also, we checked that. When we start the car and activate the system at 3000 rpms (burping it) the motor gains rpms very quickly and sounds good......everything sounds fine.

After the 2nd trip we replaced his plugs with non projected NGK-9's and replaced the c-12 with c-16 fuel.

We went out last night, flowed the system to 6 lbs, pulled 6 degrees of timing (34 to 28 and the car did the same thing left ok, went about 4-500 feet .....pop...pop. Looking at the incrementals the car gianed nothing in 60' or 330....maybe even a little slower. I was very suprised to see black specs on the porcelien of the plugs......with c-16 and -6 timing with a 12.5 to 1 motor ??? on only a 150 hit.

Possible issues.

The Fuel pump is an Aeromotive 1000...is it up to the task?? If it were the pump wouldn't the car leave good and then crap out?? Why does it seem to be slower at every incremental?

When we time the car at 3000 rpms the timing is jumping a round a little 1-2.5 degrees. If it is off by this much at 3000 what is it off at 7000 ?? if it is 5-6 degrees that could explain the appearant detonation......all plugs had black specs and a few had silver.....timing mark mark was all the way down to almost the first thread on the body of the plug....ground strap was almost white the entire length of it. Does the hemi head hate nitrous ??

Plugs are gapped at .030
MSD 7al2

Is it possible the Big Shot does not like jetting this low?

It seems like the system is doing nothing upon activation, and then starts to pop......we pull the plugs and see detonation. It does not respond to fuel pressure changes.

I took a new flow tool to the track last night and tested it against mine.....ckecked out ok.

Ok, I am stumped:smt102

[fasteach]

DUUMMMB question...are you SURE you have "good" nitrous from a reputable source? I had a situation similar to yours that was solved by switching bottles.
Otherwise i can only offer the basics: check all the filters and orifii, check that the timing is doing what it's told...the works.
The Bigshot plate doesn't mind being jetted low, it just still kinda hits harder than you'd expect a 150shot to run. That's where i started mine at... jets are cheaper than pistons :)
Duke

[63 Vette]

I am getting my nitrous from the same place I have always gotten it......they are friends of mine..........I will ask them if they have had other problems........

Thanks,
John

[8TREEZ]

What retard box are you using???

[63 Vette]

We are doing it at the distributor

[QIKLUV]

Ok, so we go to the track for the 3rd time with the my buddies 572 hemi with a simple 150 shot.

Basic combo
572 hemi
Stage 5 heads
12.5 to 1
880-900 hp on motor

Big Shot plate with 63 nitrous 71 fuel jets.

I ran over 500 lbs of nitrous through my race car last year up to a 36 jet in my 454 with no big issues. Point being, I have a pretty good understanding of nitrous systems so this problem is very frustrating:smt100

1st trip to the track we flowed the fuel to 6, 5.5 and 5lbs with the same results every time; car launches with seeminly no additional power (no pick up in 60' or 330) goes about 400 feet...pop...pop....pop. We find the plate is up side down (did I say I knew about nitrous systems)....we swap the plate over and the car does the same thing...pop....pop....pop

2nd trip to the track we flow the system with the plate right side up and it does the same thing. My buddy went by himself; he made a couple of passes and brought it home. I went over to his house and we took the carb off.....activated the system and flowed the plate into a bucket, fuel distribution looked good. I know nitrous is coming out also, we checked that. When we start the car and activate the system at 3000 rpms (burping it) the motor gains rpms very quickly and sounds good......everything sounds fine.

After the 2nd trip we replaced his plugs with non projected NGK-9's and replaced the c-12 with c-16 fuel.

We went out last night, flowed the system to 6 lbs, pulled 6 degrees of timing (34 to 28 and the car did the same thing left ok, went about 4-500 feet .....pop...pop. Looking at the incrementals the car gianed nothing in 60' or 330....maybe even a little slower. I was very suprised to see black specs on the porcelien of the plugs......with c-16 and -6 timing with a 12.5 to 1 motor ??? on only a 150 hit.

Possible issues.

The Fuel pump is an Aeromotive 1000...is it up to the task?? If it were the pump wouldn't the car leave good and then crap out?? Why does it seem to be slower at every incremental?

When we time the car at 3000 rpms the timing is jumping a round a little 1-2.5 degrees. If it is off by this much at 3000 what is it off at 7000 ?? if it is 5-6 degrees that could explain the appearant detonation......all plugs had black specs and a few had silver.....timing mark mark was all the way down to almost the first thread on the body of the plug....ground strap was almost white the entire length of it. Does the hemi head hate nitrous ??

Plugs are gapped at .030
MSD 7al2

Is it possible the Big Shot does not like jetting this low?

It seems like the system is doing nothing upon activation, and then starts to pop......we pull the plugs and see detonation. It does not respond to fuel pressure changes.

I took a new flow tool to the track last night and tested it against mine.....ckecked out ok.

Ok, I am stumped:smt102


big shot plates are not made to run that low...i could go into all the mumbo jumbo but simply no it will not work correctly...i have run it as low as 200hp thats it...all along i assumed it was a cheater plate. there is just to many holes in the big shot plate to flow corectly at that low of jetting....

[63 Vette]

I have been told that by NS.....they thought it would work but cautioned me it might not. It might be a good idea to put a cheater plate on it and see what happens

[94guy]

i ran a 2 stage big shot. came out on 125 and turned on 275. i ran the 125 plenty of times with no problems.

[mikeyfrombc]

my buddy has been running 175hp setting with his bigshot on a 560 bbc nad has had no issues that i know of

[xdamxincx]

i had some issues with my msd distributor . timing would jump around like you describe. the motor would pop all the time . i replaced the pickup.. it definatly helped. but the engine makes a lil pop every so often still ...i am going to put a brand new distributer in soon.

[Dave Bandt]

Hook a timing light up to a wire, rev it up, and watch what happens. If you get a stable flash your problem is not ignition related. Repeat for all the wires if necessary. I had a pickup go bad and had a similar problem. The timing was fine but would jump all over the place around 3500.....then come back again afterwards. MSD replaced the pickup and i never had a problem again. I found it like i described above.

[63 Vette]

I will try that...........thanks

[1bad442]

ohm your spark plug wires, especially your coil wire. i had the same problem the motor would rev fine on the nitrous in park, but when i would try 2 spray it on the track it would pop like crazy. turned out my coil wire had way 2 much resistance so i changed it and the problem was gone.

[63 Vette]

One more thing to check........thanks.

[68Bird]

Thats kinda what it sounds like to me...weak ignition. The increased cyl pressure from the spray is maxing out the ignition and it's not wanting to light.

Put a crank trigger on the thing too and that jumping around on the timing will go completely away.


Craig

[Mike Thompson]

Sounds very rich to me. My buddys big shot plate was on the rich side and sputtered and popped the whole way down. He was not nearly as rich as you.

[IMAKEHP]

Have you checked the flow of nitrous out of the solenoid? Just wondering if the seal is ballooned in the solenoid and it is not getting enough nitrous flow.

[Rick Crawford]

Is there a power valve in the carb.?????......It is possible that the power valve is pulling closed from the spray bar. If you run a light power valve in the front of the carb, the vacuum port for the valve, which is directly above the spray bar, could be pulling closed ...............

[Imlow78]

Plugs are gapped at .030? Try tighten up the gap to like .024 - .026. We had the same problem with an old 350 that we was using a Top Gun system back in the day. found out that the plug gap was to wide. once we tightened up the gap that thing ran like a raped ape!

also "dumb question" is the dist. locked down?

Shannon "RSP"

[old school]

How much bottle preasure?