torque spikes post vtec, problems tuning
 

hi there, first post, made my own turbo kit a few weeks back, found it to be lacking performance in the higher rpm, road mapped by myself then went to a respectible tuner to see what they could do

on the dyno graphs of torque you can see sharp drops in torque and only seems to be post vtec, the engine can be heard popping, and it isn`t detonation, and the tuner says the graph doesnt look like a missfire, instead he thought it was popping back through the inlet manifold, which lead us to believe a possible exhaust restriction causing the valves to be pushed open,

i have tested for exhaust pressure at the downpipe and there is none, before the turbo there is approx 15psi, i`m only running 7psi of boost at the moment

i have new ir plugs gapped at .30, never had problems in vtec before turbo, the turbo is fairly small, a generic t3/t4 ebay turbo, exhaust ar .63

built on a budget just to prove it can be done but looking at the possibility of a larger turbo, going to do leak down and comp tests and check valve clearances tommorrow

any ideas greatly appreciated

engine?
EMS?
injectors?
Fuel system?
Oct?
Ignition? Spark plug type ect...

can't read minds...

stock f20
aem fic
560cc, 255 pump
95 oct
ir plugs one step colder

AEM FIC is junk! That's your first problem. Also sounds like your using a log manifold and have vtec set too low. With a log manifold vtec usually has to be set above 6k rpm. That popping sound is most definitely the exhaust gasses being pushed back into the head causeing detonation because the exhaust system doesn't have enough flow due to the restrictive manifold and small turbo.

thankyou for your input, the manifold isnt quite log but it is short, i was near convinced it was turbo size but the exhaust pressure does not seem excessive which makes me question it, i was hoping for stupidly high pressure to confirm