I am experiencing flatspots when under low load and accelerating.

Generally this occurs when opening up from about 1300-1800rpm in traffic.

I have installed AWE cats into my 997s (currently running with standard mufflers)

I did not have this hesitation / flat spots before changing the exhaust.

The local Porsche dealer has said that it is due to the AWE cats, and the difference in size / flow rate of cats and change of location of the o2 sensors.

Is this possible from the exhaust? Could something else be causing this?

I am thinking that it could be a dirty / contaminated fuel filter.

Anyone got any ideas?

 

A software update/ecu tune will fix this. How long has it been that you installed the cats? sometime your ecu will adapt to the changes on its own after driving for a while but its always good to tune it properly.

 

I had no issues on my 08 997S after installing AWE cats on stock ECU.

 

Not too keen on doing an ECU tune. Do not really want to modify the car much. Was going for a bit better sound, but not too happy with having flat spots.

 

When you change the piping on an exhaust system, you are essentially changing the flow rate of a portion of the system. This will either move your power curve more towards the right, thus giving the sensation of a flat spot, as now the power comes on at a higher spot in the RPM range, or the flow of the exhaust has slowed down in that range due to piping diameter differences. I had a similar problem in a 350Z back in the days when I went with headers + Cats. Low rpm was rather flat, until 3500 and above.

 

Check out the fifth paragraph that starts with "Graph A"...

http://www.carcraft.com/techarticles...s/viewall.html

 

Most go for full system or work in reverse order ie: exhaust, cats, headers. As I recall AWE had graphs for all combinations showing gains and different power curves after installation. Motor may indeed feel different. Stock exhaust is restrictive after all. You can reinstall stock cats to rule out a problem. I tried Ebay headers first and ended up w no bottom end. System matching is the best way to go. I would go w cans and headers before a flash. If you don't want to mod much and like stock characteristics you might just go back to stock. Don't be shy about calling them. They're top notch.

 

The symptoms that i am experiencing are not a shift of the power or torque curve, as suggested above. It is an actual hesitating sensation when getting on the power gently in 3rd or 4th gear with not enough rpm. This is not normal, and did not do it before i did any exhaust work. I started with cats and mufflers, but found the sound not to my liking, so have recently reinstalled the OEM mufflers. I am now enjoying the sound, but not the flat spots.

 

Re: "not enough rpm". What rpm is that?

 

Somewhere between 1000 and 2000rpm

 

Using those rpms in upper gears= lugging. Not a Good Thing for your motor no matter whose cats you are using. Keep the revs up and see how she feels. Good luck

 

As Gpjili noted, that's lugging the engine. The reason why you did not noticed the flat spot before is most likely due to piping differences with the stock cats and AWE ones, as well as the less restrictive flow of the AWE cats. Again, you're most likely losing TQ due to piping diameter differences, thus affecting exhaust flow in that range.

 

Hi there

Our engines like back pressure, putting in high-flow cats (200 cel) will loose you torque at below 4000rpm, but you gain power and torque beyond 5000rpm.

Its a catch 22 situation.

You could try an ECU reset, disconnect the negative terminal on the battery and re-connect it a few hours later. Then take the car for a 40 minute drive to allow it to re-learn.

I tried de-catting my car, gained huge amounts of power and torque beyond 5500rpm, but lost 40lb/ft below 4000rpm and this loss was very noticable. I also ran the car on the dyno which proved the same, big losses of both power and torque sub 4000rpm with big gains 5000rpm upwards.

My car drives better with the stock cats in as for the street low-end power and drivability is more important than chasing peak HP numbers.

 

First, I would agree with the earlier comment that the AWE folks are service focused and very good. This thread caught my eye because I have the exact same issue. I just though it was a 911 thing but I often bog down with no low end torque which I thought was odd for such a power engine. I have the full AWE system, headers, cats and muffler with no ecu or intake mods.

Any advice on how to remedy this is welcome.

 

[QUOTE=David4315;3599787]First, I would agree with the earlier comment that the AWE folks are service focused and very good. This thread caught my eye because I have the exact same issue. I just though it was a 911 thing but I often bog down with no low end torque which I thought was odd for such a power engine. I have the full AWE system, headers, cats and muffler with no ecu or intake mods.

Any advice on how to remedy this is welcome.[/QUOTE

I have the full AWE system, IPD plenum and REVO flash on a gen1 (06) The difference between stock and this motor is huge. What has happened is that the torque curve has been moved down with the engine very strong from 2500 on up. Between 3-4500 rpm it feels like a different motor. My son who has an 09 was blown away. I cannot tell you what part will best address your issue but I will say that the plenum and flash are significant here. Re low end: the motor may bog off the line but that is a function of driving technique and massive traction rather than lack of low end. It is after all a 240 ci motor and needs a bit of rpm's and clutch work to get the best start. Without some cluch slip from say 3000+ rpm you will bog it unless you brutalize the drive train. Best is to use full throttle from 3000 rpm and leave the burnouts to the V8's. Hope this helps.