Hi there


So a friend also has a sorted 911 like my own and managed to get hold of a catless X-Pipe, I believe its a fabspeed unit without cats.

His car is a 997.1 C2S with following mods:-
1. BMC Panel filter
2. Fabspeed Silicone tube and cap.
3. Resonator removed from airbox.
4. X51 Headers
5. Softronic map
6. PSE

Car made 376BHP with the above at flywheel.

Stock cats and pipes were then removed, battery was disconnected during this and it took just over a couple of hours to remove stock pipes and cats, fitting of X-pipe was fiddly, hardest part feeding the lambda sensors through but some metal wire helped with this.

Battery was re-connected and car was driven for a good 50 miles or so to ensure the ECU had fully adapted to the changes.

I've driven the car previously and we both took the car down a well known stretch of road and noticed the following things including one issue:-
1. Hesitation/jerk when applying throttle to heavy sub 1800rpm, you have to accelerate very very gently to avoid it otherwise you got was could amost be described as a hesitation/misfire, this was not present until fitting the x-pipe, so is definetely caused by this modification, its either the xpipe design or the lack of back pressure from having no cats.
2. Car feels sluggish between 2500-4000rpm, very noticable.
3. Car feels and pulls way way harder beyond 4200rpm and seems to accelerate far harder once beyond 5000rpm, very noticably.
4. The noise, easily twice as loud, if not even more so, noise at idle is far nicer, but at high-revs it just seems plain loud, almost CUP car loud.
5. No apparant change to MPG and no bad smells.


Here is the result:-




The results seem to co-incide with what was felt during driving, the dyno operator also looked at the hesitation down low and said its probably the softronic map needing more custom mapping to dial it out or its just an issue with lack of back pressure, but my friend has since put a further 200 miles on the car today and it is still doing it.

Look at the graph in detail and you will see a major torque loss in the 2500-4000rpm region, infact the loss is as high as 40lb/ft and 30BHP, no wonder we could feel it.

However from 4200rpm things change for the better, torque is 20lb/ft better in the 4500-5000rpm region, but between 5500-6500rpm there is nearly 40lb/ft more. Peak power is up by approx 12BHP, but this does not paint the entire picture as 5500-6500rpm power is up by nearly 35BHP. This we were definetely feeling on our drives.


So in short a de-catted X-pipe does loose you considerable torque and power sub 4000rpm, which contradicts what the manufacturers of X-pipes say, as Fabspeed for instance claim no loss of torque down low for their catless X-pipe, this is clearly untrue as proven here. However there are some great gains to be had in the upper part of the RPM bands which is also very noticable.

In summary this is a great mod if you do a lot of DE events or circuit/track work, you will be faster for sure as long as you keep RPM's beyond 4000rpm and don't get sent home for breaking any noise limits.

On a road car though, well both me and my mate were not impressed, though we liked the top-end power, we were both missing the low-down power we had lost and the hesitation we were and still getting spoiled things further, then add the volume of noise and the fact it seems less exotic I think I shall soon be helping my mate to remove this mod.

However this does make me wonder, would some 200 cel cats be the perfect resolution to this? Those who have fitted 200 cel cats, did or do you think you lost any low down power/torque? Any hesitation issues with 200 cel cats? If a vendor wants to do us a deal or loan us any 200 cel cats we'd happily put the car on the dyno again and add the results to the comparison. Would be great to avoid that loss of power/torque down load, reduce the noise and hold onto the power gains, could 200 cel cats do this?

 

Hi there

Here is the gains/losses in detail on the chart:-

 

Very interesting and thorough examination - much appreciated. I was considering buying these, though was looking the X-pipe with cats on the Fabspeed website. Perhaps there is enough back pressure to make a difference.

Interestingly, I have the same setup on my car - Softronic, x-51 headers, AWE cans, (for now) intake mods...

 

Fitting 200 cel X-Pipe will no doubt limit the low-down losses, but I do believe there will still be some.

I'd suspect 200 cel X-Pipe is somewhere between catless x-pipe and stock pipes, as such expect to loose around 15lb/ft & 10BHP low-down and gain around 15-20lb/ft & 15BHP around the top-end.

The fact this mod looses low down torque and power which is what street cars make use off I see it a poor mod for any street driven car.

 

Reviving this thread hoping someone from Fabspeed will chime in as their site says "Fabspeed X-pipe catbypass will improve low-end torque and mid-range power dramatically"

 

Thanks for the deal on the 200 cel highflow cats straight pipes m8, I shall dyno the car with them fitted and see how they compare with the above.

Am hoping the straight pipe design as it's same as stock will mean no low down hesitation and that the 200 cel cats will still give enough back pressure to prevent low down torque loss.

I personally feel the issue was more the x-pipe design rather than lack of cats. As after speaking to people who know a bit about exhaust they said an x-pipe design is all about top end power and will definitely loose low down power.

It's just a shame companies like Fabspeed have to lie about certain products with marketing BS to try and get more sales.

 

Definitely looking forward to your findings! Have you considered going to a bigger plenum and tb?

Ya I'm hoping someone from fabspeed will chime in. I've been talking with John from Speedtech who has a similar catless system design, though his is more of an "x" design compared to Fabspeeds "H" design (unifying two "U" bends), and he uses oem size piping compared to Fabspeeds which I believe is a bit bigger, but he said none of his customers who are running his catless x pipe have complained about a loss of torque down low. That being said he doesn't have any dyno sheets yet

 

It isn't uncommon for a freer flowing exhaust to have worse power in low rpms. Iirc this is due to reduced exhaust velocity preventing scavenging from happening.

 

Well that's bad news. I have the x-pipe from Fabspeed in a box waiting to be put on my 997c2s. There is a chance it could be the software. You do have to tell it the car has more exhaust flow just like before, when you put the intake on.

 

No chance at all, the car was using softronic and was properly reset and allowed to adapt before going on the dyno.

Just a fact decat will loose you low down torque and power.

 

Is the check engine light on? And are you running stock mufflers, did you get extension bungs with the x pipe? Also the ecu will reset but you do have to tell it that the car has no cats if you don't have those bungs. Running no cats the car will losse power down low but not that much. You shouldn't even feel the difference.

 

No check light as the softronic tune was tuned for no cats, hence no CEL. Everything was done correct, the numbers don't lie. Catless X-pipe looses you a tonne of low down power.

After this dyno the car did a further 500 miles, with no improvement on loss of low down torque, fact is you loose power down low and gain up top.

 

So your better off getting hi flo cats rather then going catless to keep the torque range low mid and hi still there. Upgraded mufflers hi flo catt and x51 headers does that sound good?

 

Is there still hesitation ? Have you talked to FabSpeed about this?

 

It never went away, spoke to softronic who said they'd seen such issues before and said it was due to x-pipe catless design and as such not possible to resolve.

As such they were removed and factory cats put back on, got all the low-down power back and hesitation gone.

Though got 200 cel high flow cats on the way, shall see how they go and post up the dyno results in a months time.