Paul N

I just installed a K&N airfilter (part 33-2125) in my 98.5 2.8. Installing wasn't difficult, you just have to move some plastic covers, intake, and a unplug a few wires to get the box open. The K&N filter is not as deep as the paper filter. It is also a tad smaller, about 1/16 of an inch. However, K&N assures me it is a correct fit; I went to technical support at K&N in Riverside and had them take a look. I recommend you install the filter to the top portion of the cover first, and it seals just fine.<p>Now for performance observations. (Of course its purely subjective with no scientific measurements! So please don't send me any flames!) Throttle response seems a little quicker. This would reasonable because, because less restriction allows quciker intake of air. The most significant thing I noticed is the change above 4000 RPMs. I have observed the 2.8 (30v) has a sluggish zone from about 4300-5000 RPMs. (The graph on Wett homepage confirms my observations.) With the new filter, performance in the slugish zone appears to be improved with better acceleration. Is this because it can get more air? Someone told me there is a butterfly valve that opens up at 5000 RPMs that allows more air in and that is why the jump in performance, after the slugish zone If this is true, then the less restritive filter may be providing better airflow in the sluggish zone. <p> The other thing is the engine sounds better at the higher RPMs. I have nothing to back this up, so it may be my wishfull thinking.<p>If you want a filter, call J&M Speed Center in Riverside, CA. The number is 909-688-7110 and ask to speak to Lisa. They are local to K&N (Riverside) and can get the filter the same day. Since this is a new part number (33-2125), other places may take longer. Now for the great part, the price from them is $38.95! Other places I called wanted $48. <p>Enjoy,<p>Paul<p>98.5 Catus Green 2.8 QMS, now with K&N!<p>

Steve S.

Paul, it was my understanding that the 30V had a one-stage throttle body valve. The 12V has two stages...a primary and secondary butterfly valve. So the comment about the boost in power over 5,000 rpm may actually apply to the older 12V 2.8 engine instead. But, then again, I could be wrong. :-)<p>Steve S.<br>97 2.8QM<p>P.S. A pic of the 12V throttle body is attached...the stock one is on the right...and has the nut pointing to it. The left one has the top (or primary stage) bored out. This is the one I have on my car now.

randall

i wonder if i could save some cost, and just have a local machine shop bore it out.<p>1996 a4 2.8 qm<br>

Paul N

If the 30V doesn't have a seconday intake, then what causes that noticable slushish zone between 4300-5000 RPMs? Hmmm.....<p>Paul

Keith J

Does the modification work? The extra material is there to smooth the transition to the butterfly and reduce the turbulence around the plate. I can see the increased bore would only increase the WOT pressure drop at the butterfly, a really dirty airflow section. The pressure drop is manifested as an increase in velocity(rho * V^2 acceleration) and increasing the velocity over a dirty region INCREASES pressure drop. The secondary plate would kick in at higher mass flow rates associated with WOT completely killing all improvement. Partial throttle conditions would have the pressure drop at the butterfly.

stevebrown

Could be talking about two-stage intake manifold runner length change...?

Steve S.

I fully understand that boring it out as it has will create (more?) turbulence. But, how will this increase or decrease performance from a theoretical engineering standpoint? All I know is with less accelerator pedal travel I get more acceleration at the low end. If you have ever driven in a stock 96 or 97 2.8 12V car you will experience an uncomfortable dead spot in the power curve near the bottom. This throttle body modification seems to get rid of that dead spot. In addition, theoretically, at full throttle...with both valves totally open, wouldn't more air mass be able to pass through the modified throttle body? Again, I am not mechanically minded...so please bear with me on this stuff. My comment still stands...this is the single most significant modification that I have done to my 12V car. And, it only cost $275 plus installation. The 1.8T guys can put in their chips and get power...I cannot...I have to do other stuff to squeeze out every bhp I can.<p>Steve S.<br>97 2.8QM

Keith J

The modification might help during lower mass flow rates (MAP*RPM*%Volumetric efficiency) but it will rob the engine at higher RPM before the secondary opens. What is needed is a different program to open the secondary earlier. I can understand the increase in torque at lower RPM. I cannot see this modification helping at the critical transition. A dyno would see the difference.<p>

Kevin S

...experience redoing throttle bodies. Doing this kind of machine work is very common to many cars. The guys I know have successfully done this mod on many, many cars for their customers.<p>A point of concern is precision. The new and enlarged primary butterfly will have to be fabricated and installed precisely (no gaps/a perfect fit) otherwise you could have idle troubles.<p>If you want I can dig up the number for the "Fat Boys" and e-mail it to you... They also make exhausts/downpipes and do some pretty crazy turbo work. Last Xmas they were doing a 427ci turbo motor fo a '67 Chevy 4dr. I saw the compressor housing which had a diameter about the size of a small pizza.<p>Kevin<br>1990 Jetta GTX w/95 VR6 swap<br>1.8TQMS due in March

randall

thankx<br>pls forward by email.<p> I thought the mod was only machining out the restriction, that the butterfly valve remains the same. If it isn't then I see why it costs so much.<p><p>1996 a4 2.8 qm<p>PS why weren't u at the TO meet?