engine is a warhawk ls7 et heads , boost is max around 22-23 (vortec ysi) supercharged. Injectors are 1000cc rci with driver , ignition is cdi . Fuel used is vp 109 , afr is around 12 -12.2 ,on full boost .At present we are able to get one clean run with a set of new plugs , on the next run the engine misfires and there fore a lower hp from 1100 drops to say 800. we have tried all different plugs like ngk ( r5724-8 , -9,-10 ) ngk v grove b7efs,b8efs, b9efs.we still cant make a consecutive run. my thoughts would be cylinder temps causing our problem. compression is about 10.1 -10.2 . something is not right , one the engine gets hot or cylinders the engine brakes down on full load even at 5600 rpm. Another issue could it be electrical interference,from some where , im using the msd leads i think 8.8.Today we done a run using champion c57 , it has a smaller side strap and i think so far they have been better for one dyno pull but then brake down for second . if any one has experienced this , your thoughts or help will put my mind to rest.

 

if the motor cools down, is it ok without changing plugs?

 

12-12.2 afr full boost=brave

 

the engine behaves better when it has cooled down like 20-30 min

 

other than being too lean...

what crank position sensor do you use?

 

Try your A/F in the 10.8 range and switch to a AR3934 spark plug 25-26 gap.
BTW, what do your plugs look like after the 1 clean pull you get with them?

EDIT: I will say that on my old setup, we had a popping issue and breaking up issue as well. I did not have enough GROUND straps on the motor to the chasis for the computer to work properly, and I also changed out the Altenator as well. The altenator wasn't charging to full potential in the higher rpm's, therefore wasn't supplying enough voltage to run everything properly. After those 2 change's, my issues were gone.

 

thanks for your concerns , im not 100% sure on afr but my tuner has it at safe levels. we had one run and all is good at cooler temps but 2nd run always seems to fail , so we changed the leads which were cool , this took about 20 mins then tried another run and it was great could there be some electrical interference say at higher engine temps that causes issues with say the leads. we have the cdi coils mounted to the body not the engine . the engine is grounded , but not the cylinder heads.

 

Check your charging system then. You may have just enough juice for one good pull, and then after that your battery is not charged back up enough and your altenator cannot keep up?

 

I was thinking the same thing. EGT's might be a good idea at this level.

 

I think it is the ls2 but that to be certain i would have to ask my engine builder

 

if all else fails, try changing out the crank sensor with a new one...

 

this is a thought that we will try in the morning . we have the battery in the boot , and have been told to fully charge the battery and disconect the alternator and that causes less interference or something, the big turbo cars making 1900rwhp are doing that, they said to try that.we have moved the computer inside the car , Im not sure if its earthed .

 

the plugs look clean , exhaust fumes not as black as martini race fuel we used in the past, the vp 109 seems better.

 

The big turbo guys are also probably running a 16volt sytem( 16 volt battery) which allow them to do this with out altenators!

 

Thanks for your support . the plug that you said to try , is it semi projected, i seem to think the non projected works better with a nine heat range from ngk we used the ngk b9efs v power it made good clean power on 1 run , also the champion c57cx on one run but which ever plug we use the second run seems to fail us .

 

You've got to figure that the crank is putting out 1600-1800hp due to the belt ect.You need a 16volt battery system,bigger plug wires.I would also back A/F to 11-1.

 

The AR3934 is a Non-projected tip with a copper core.

 

IF we use a 16 volt battery would that affect any electrical components ie pcm, electric gauges , injector driver . what affect does hp contribute to the crank sensor, or is it rpm related issues. we are using the msd 8.8, tried top gun , what larger coils do you recomend, thanks.

 

Problem resolved , various minor ajustments made 3 consecutive runs with great results thanks to all your input.

 

What exactly was it then?