Originally Posted by 1slow370

it's not vq specific, its rail harmonics. when the injeters open and close they create pressurewaves in the rail if there isn't enough volume and the waves stack up they can cause flow issues to the injector. it happens in all fuel rails, usually on smaller engines like the subarus because when you have 2 very large injectors in one tiny rail it is easy for them to effect each other. the 370 does not have a real issue with this if you want to double check why not call your tuner and ask him if there was a lean spot at a specific rpm, Usually its between 3-5k for about 500rpm on engines that get it, that he could not tune out by adding more fuel.

Edit: somebody should call cosworth and tell them their rals are garbage cuz they don't have dampers