The flat spot.
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Teching In
Joined: Nov 2008
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From: Coolville, OH
The flat spot. Guys, I've noticed a flat spot in my RPM band during hard acceleration right between 2500-3000 RPM. The car is stock except for !EGR, !CAGS, and a catback (third cat eliminated). When I got the car it had the exhaust cut off from the front cats back. When the exhaust shop put on the new exhaust, they fabricated the y pipe. The downpipes (stock manifolds) are 2.15 inch OD if memory serves correctly. Well the Y pipe is two 2.15 OD (or whatever the downpipes are) pipes that combine into one 2.15 inch pipe before entering the 3 inch catback. The intersection is also at a fairly steep angle, but I don't know if that matters. Could the fact that both the downpipes combine into one pipe without the diameter increasing be causing a restriction? If so, could this be the cause of my flat spot in the power band? Thanks.
If it was caused by a restriction in the exhaust at 2500-3000 RPM, it would only get worse higher in the RPM band when your engine is trying to flow more air. I'm inclined to believe it isn't the exhaust.
Last edited by MjMaro; Jan 20, 2010 at 12:01 PM.
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Thread Starter
Teching In
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From: Coolville, OH
Hate to dig up one of my own old threads, but in the off chance someone is troubleshooting and comes across this, I wanted to post my solution.
I eventually had the car dyno'd. It was immediately apparent that the car was low on power, and running very lean. Unplugging the MAF net a 25 HP increase and it was now running quite rich. We removed and cleaned the MAF, and the car ran even stronger, likely due to not being so rich. Didn't get a chance to dyno it again though. The 'flat spot' was forever gone.
The PO had used a K&N Filter, and had over-oiled it. The excess oil got pulled off into the intake stream and coated the MAF, leading to incorrect readings and hence incorrect A/F ratio.
I eventually had the car dyno'd. It was immediately apparent that the car was low on power, and running very lean. Unplugging the MAF net a 25 HP increase and it was now running quite rich. We removed and cleaned the MAF, and the car ran even stronger, likely due to not being so rich. Didn't get a chance to dyno it again though. The 'flat spot' was forever gone.
The PO had used a K&N Filter, and had over-oiled it. The excess oil got pulled off into the intake stream and coated the MAF, leading to incorrect readings and hence incorrect A/F ratio.
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Good catch. In my experience, even a new(and therefore theoretically properly oiled) K&N will eventually foul your MAF anyway. I just clean mine every 5000 miles anyway...60 seconds for piece of mind.
On The Tree
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I eventually had the car dyno'd. It was immediately apparent that the car was low on power, and running very lean. Unplugging the MAF net a 25 HP increase and it was now running quite rich. We removed and cleaned the MAF, and the car ran even stronger, likely due to not being so rich. Didn't get a chance to dyno it again though. The 'flat spot' was forever gone.
The PO had used a K&N Filter, and had over-oiled it. The excess oil got pulled off into the intake stream and coated the MAF, leading to incorrect readings and hence incorrect A/F ratio.
The PO had used a K&N Filter, and had over-oiled it. The excess oil got pulled off into the intake stream and coated the MAF, leading to incorrect readings and hence incorrect A/F ratio.
My 2000 ws6 was the exact same way
Thread Starter
Teching In
Joined: Nov 2008
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From: Coolville, OH
Hahaha. Yea a standard paper filter was all that was used since. Funny, never an issue with those... Many recommend against K&N in the diesel world as well. Being that they allow more dust through, some people operating in dustier environments have noticed damage to the turbo's compressor wheel.
I don't quite get how they can advertise what they do if they don't even filter down to the same level of a paper filter. I have experienced the MAF fouling for years and just dealt with it..but also assumed that I was getting better filtration!
Joined: Aug 2007
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From: Turnin' Wrenches Infractions: 005
They won't filter the same dry. They filter the same or better I bet when wet. But, that comes at the expense of more maintenance, including learning to properly oil. I really don't get the haters of K+N, its just a simple trade off. The same haters will swap exhaust for the trade off of flow for more noise/lower ground clearance/higher maintenance....or a bigger MAF to trade flow for more difficult tuning/more expensive+less abundant replacement parts etc. The only reason a paper filter is better is because you can throw it in and go. At what point does an engine actually suffer HP loss because of the paper filter...well I'm not sure. But with all the money I spent on my car, for another $50 I'm not gonna find out.
That's been my stance..I follow the directions for cleaning/oiling and clean the MAF often. Just cost of doing business. I figured that K&N did just fine when maintained properly but there are the detractors stating they don't filter as well. Dry for sure they would not. It's fricken cotton!
