Originally Posted By: NTrails
Sorry to resurrect this old thread, but I gotta chime in here due to my recent experience(s)...
I've just been through a lifter/cam replacement process on my '08 G8 GT, after it suffered what was initially thought to be a collapsed lifter, but upon tear down of the motor was found to be a broken exhaust valve spring. Long story short is, now I've got a non DoD cam with a bit more duration and lift on both intake and exhaust, new LS7 lifters, pushrods, seals, guides, oil pump, etc. When the engine builder went to tune the motor on the dyno, he re-installed my Volant CAI with its Donaldson PowerCore filter. Granted that filter has been installed in the car for approx 2 years now, Donaldson (Volant) claim a 100k mileage change interval, which it's not even 20% consumed now. After tuning out the AFM tables, etc., the numbers were significantly low, so he removed the whole thing, airbox and filter. The next set of pulls gained over 32 HP and nearly 25tq. He was astonished, sent me the printout and said he was gonna stop tuning it until I fit something else in there. We tried to find a suitable filter to fit in that airbox, but it's 6 inch flange ID and 6.25 inch airbox width are proving difficult to find anything (even a porous K&N) to fit inside. I told him to go ahead and finish the tuning with no filter, and I will deal with the air filtration after I get my car back. I've kept the factory airbox assembly as I live in California and every 2 years I must remove the Volant and install that BEAST of an airbox (with its numerous passages and chambers leading to nowhere, all for sound deadening purposes) and let the state visually inspect it. It is so large, it is in 3 pieces! We both agreed that that thing wouldn't provide sufficient flow either, based upon the tiny size of the main air passages and the numerous direction changed in the pathway the air travels.
What I take from all this is, while my Donaldson provides excellent filtration, is it at the cost of nearly 9% of my power? I really don't want to put some leaky K&N on there, stock airbox isn't an option either. I wish I could find an AEM filter to fit in there.... The only other options I can think of involve scrapping the Volant unit altogether (taking the <>$350 hit) and purchasing another airbox solution. There are a few options out there, I dunno if any are CARB approved, so I'd still be required to swap it out for bi-annual inspection. Those options are from $300 to $600 give or take.
So that's my story. I'm interested to hear of anything I might be overlooking which might bring further resolution to this air filtration issue. Today I dug out the old PowerCore filter I changed out 2 years ago. Interestingly, upon inspection the construction of that filter varies from the one installed recently, whereas there are nearly double the number of "layers" in the newer one, making the "pleats" far smaller, narrower and closer together. I dunno if that would lead to an increase or decrease in flow, but it certainly must have some effect. BTW... I installed the older one as it looked cleaner, and the larger "pleats" look like they'd flow better. I have no way to test the actual flow of either of these filters, even un-scientifically, due to the large 6" flange they have.
Have you contacted Volant? That would be my first step. Their selection might have been "just" adequate for your G8 when stock, and not so much for your now tuned and modified version.
