Somebody sent this to me, power level goes flat AFTER the VDI opens, stays well below peak power level prior to opening. Cobb AP, high flow cat and rear exhaust, RB intake

Other curve is a factory stock RX-8, same day/dyno

This should be interesting (or more likely not given the usual forum parrots ) ...

 

I had one looked almost like that when my CAT was getting plugged up...but I would expect it to be lower before the APV opened as well.

Is the VDI actually opening?

Spark?...missfires? AFR?.....any indication it is running out of fuel? P2's?

 

the curves between the two cars is mirrored through the VDI operation until 7500 rpm ...

WOT dyno run, You don't think the P2s are already engaged prior to the VDI opening?

 

SHould be .......AFR's? are they "normal" stinking rich...or tuned?

 

I'm going with bad diaphragm on the SSV actuator .... it will open but will not retain the vacuum and slowly closes again

edit
Or the VDI diaphragm

 

my first question too. i hear you team , for that 250 of rpm they are the same but that could be turbulence from the barrel VDI trying to open and then not fully opening or even slamming shut again

do you have AFRs?

 

i was also thinking of just posting

 

ive always seen it as a problem with the pickup itself but the last dyno day around here Jeff did identify an ignition issue on one car that looked like that. is it possible to tell the difference on the graph here without scoping the car itself

 

Loose spark plug wire connection, either at the plug, or at the coil.

At lower rpms, the resistance in the combustion chamber is low enough for the electricity to jump the wire to plug gap, and then the actual spark plug gap, and still create a proper combustion event.

As the rpms get higher, and the mixture is richened, the resistance at the plug increases to the point where the spark goes to ground at the loose connection point, usually shooting around the spark plug instead of through it.

BC.

 

Thats the stock RX8 curve though, not the one in question. Definitely a pickup issue IMO for that gap tho' ...

 

No problem. Bend over and cough ....

 

so you just leaving us hanging or can you share more info or let us know what you think/know it is?