Struggling at high rpm above 6000

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Disconnect/disable the rev limiter. Loose timing chain &/or harmonics transmitted to the cam & then the dist can 'fool' the ign into thinking the rpm is higher than it actually is.
 
I agree with PRH, try removing the nitrous plate and see if the problem goes away. It is possible you introduced a vacuum leak with the plate, or maybe one of your solenoids is leaking.
 
AJ/FormS said:
127@6000?
Or is it 7200.
Or did you change it/swap rear gears? if not;
What's that convertor doing?
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It was an error... I am crossing the line @ 6300.... is where the miss firing is starting
 
Rat Bastid said:
What is your compression ratio? Seems weird to runs 12 heat range plug and then mix C12 in there. If your compression is so low you can run a 12 you don’t need the C12.
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My compression is 10.5:1.... What is your suggestion?
 
flyfish said:
I agree with PRH, try removing the nitrous plate and see if the problem goes away. It is possible you introduced a vacuum leak with the plate, or maybe one of your solenoids is leaking.
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Yep, will remove everything, including the electrical section...
 
Bewy said:
Disconnect/disable the rev limiter. Loose timing chain &/or harmonics transmitted to the cam & then the dist can 'fool' the ign into thinking the rpm is higher than it actually is.
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Could you please elaborate? Didn't really get your point...
 
JBurch said:
Here's a couple of wild guess's.........you are running out of gas, need more volume to the carb or valve springs are weak
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My first thought was valve float.
And the OP needs a 383. :poke:
Edit:
Now is a great time to switch to a solid flat tappet cam, conical springs tool steel retainers, light weight edm lifters, light weight pushrods and ductile iron rockers. Lighten up the entire valvetrain and reduce the number of moving parts. Solid vs hydraulic, flat tappet vs roller, ductile iron vs roller tip.
 
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Jax said:
My compression is 10.5:1.... What is your suggestion?
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My first suggestion is you shouldn’t need race fuel at that compression ratio. I know it sounds cool, but it isn’t needed. Did you measure the compression ratio or did you use the numbers provided on the piston box? Did you actually measure the chambers? If not, your compression ratio may not be what you think it is. I’m not saying this is your issue but it jumped out at me. As for plug heat range that 12 may be hot. You can try a 10 or even a 9 heat range and see what it looks like.
 
Rat Bastid said:
Also can you post all the cam numbers?
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Jax said:
Ok guys, thanks for all the feedback. Let me share some more details of how everything started...

Engine: Procomp heads with PAC SPRINGS ( Double springs with damper )
Solid cam .600 lift
Eagle forged crank, rods and pistons. ( Balanced )
Fuel system: Magnaflow pump, Pro systems 850 CFM carb
Ignition: MSD 6 AL Digital with MSD Blaster HVC 2 Coil, and MSD wires.
Champion RC12YC plugs.
I am running C12 mixed with pump gas.

Everything was running fine.

1 month ago, we installed a nitrous kit and a higher carb spacer....... ( the nitrous hasn't been activated or used )...... Here is where the problems started.

This weekend we tried:

Change from Champions spark plugs to NGK-7. We thought it was just fouled plugs.
Increase Carb jetting:
Front: from 76 to 80
Rear: from 86 to 88.
This helped a little bit....and struggling when almost away, but still there...
We changed the gap from 0.045 to 0.030, and the car felt on his nose passed 6000 rpm, It was literally like the car switched off...then came back to life......
We changed the gap from 0.030 to 0.045 and the misfire was there again, but didn't felt on his nose...
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BTW As additional info......

Besides adding the nitrous plate, we removed the distributor and intake to fix an oil leak we had..... Any suggestions that may arise from this process???
 
I had the same issue in my 65 A-990 Hemi car back in the day. It took some trial and error with many things that have been mentioned in this thread. Nothing worked. 5500 rpm and it started misfiring. I spoke with Warren Barnett at Barnett Race Cars and he told me to upgrade the wiring to the MSD box and replace the battery with a fresh one. The MSD needs approximately 1 amp per 1000 rpm. The battery/wiring couldn't run the electronics on the car and supply the needed amperage for the MSD at higher rpm. I made that simple change and I have never looked back.
 
Jax said:
410 stroker, with Magnaflow fuel system, Pro systems 850CFM car, MSD Digital 6 plus ignition with billet distributor.....

The car is running clean up to 6000 rpm, after that the engine starts to struggle " kind of misfire".
We have changed fuel jets, spark plug gaps, changed plugs. But nothing seems to help.
Even when we close the gap from 0.045" to 0.030" it when worst. The car starts bugging completely down after 6000 rpm... I have the feeling it is somewhere in the ignition....

Any help will be appreciated
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What brand distributor ???
 
My brother chased that same issue for a couple months. I gave him an extra coil I had laying around and that solved the issue. Can't hurt to try
 
roccodart440 said:
WHat is your fuel pressure at WOT?

What is the AFR at 6,000?

What is your top end limiter set to?

What ignition are you running?

WHat is the LSA?

What is the timing at 6k rpm?
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Could total timing be a playing a roll here?
 
Hi Guys, thanks for the feedback. Yes we got it resolved, it was a vacuum leak created by the NOS plate. The flange size of the NOS plate was smaller than the flange on the carb and wasn't sealing properly.....

We swapped the plate and it was resolved...
 
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