Okay ill start with the car 2000 gsr mid sleeved 9.0:1 wiseco pistons, eagle rods,acl bearings, skunk2 intake& Cam gears. Peakboost ramhorn manifold, neptune rtp 550 cc injectors and of course the wideband




problem im havin the wastegate is vent to atmosphere in the top end while tuning the afrs never seem to be consistant, once the wastegate is open,which makes sense spitting exhaust everywhere but i dont think it should change the afr unless fresh air is gettin in through the wastegate which doesnt make sense since it is a pressurized system im wondering if anyone else has had this issue and what they did. i thought about cranking the boost so the wastegate is shut at what will be my regular peak boost so i get good afrs. or buy all the piping to route back into the exhaust which brings me to the next thing if i do route it back in how far down into the downpipe. i think i remember something like 18 inchs to not disrupt the flow from the turbo any help would be awesome

 

Routing it back into the exhaust stream is your preference. Having open dumps shouldn't affect AFR readings. I think on my old setup, the return was right before the bend at the oil pan.

 

open dump gives a power gain of what would equal about 0.5" larger exhaust. meaning open dump with 2.5" exhaust would equal a similar powerband as closed dump with 3.0" exhaust.
I always prefer open dump. only time I prefer closed dump is if noise is a concern when at heavy throttle.

but to answer the question, no, open dump should not affect afr at all. if your afr's are getting jumpy in high rpms, either you're getting some ignition breakup from a weak ignition system or plug gaps too big, or ignition is a little too advanced or retarded, or your injectors are close to maxed out. or your turbo manifold is too restrictive.

 

im at 14.25 degrees for ignition i think that should be fine for 15 psi , injectors are a good possibility ill do a datalog check the duty cycle. ignition is fine msd blaster no misfires. but ill check the plug gap. what should it be on a boosted motor?

 

there really is no specific ideal number, it's different with every car. ideally though you want the biggest gap before breakup occurs.
my car at 9psi is usually at 0.027" with v-powers. I usually set customer cars to around 0.024" to start (v-power plugs) and tune from there.
iridiums you can add 0.006" or so

 

yeah i usually gap plugs on cars less than 400 hp to around .025 or so. much over that it goes down. my car at 475hp on stock ignition is at .018.

anyway, just make sure the dump tube is no where near the intake/turbo inlet. i had a friend whose dumped gas was being sucked up into the intake charge. on the dyno he gained like 40hp iirc by extending the dumptube under the oil pan

 

thats what im workin on right now just ordered the piping im hopin makin it longer will quiet to if not it might get routed back in but like he said it is a power gain i can feel it when it opens

 

solved static test on injectors they were faulty replaced with id 1000 idles better than stock injectors