power gains with cat bypass pipes

[spongebob]

Found a set of cat bypass pipes on the local ebay for a very reasonable price.
They will be a part of my project to get rid of the 3k rpm vibrations among else.
Also some weight reduction is a good excuse to by these.
But has anyone noticed any powergains with these?, exhaust sound?

In the manual Us 2,7( my2000) engines has 217 hp and Row has 220hp. From what I know the only difference between the engines is the extra set of catalysators so I guess that I will at least have 3 more hp after the mod

BTW,The seller claims 25 hp increase.......

[JAAY]

8hp but you may lose some low end torque. I have bypass pipes on my car and love them

[Topless]

Power gains from removing cats on Boxster spec race cars are minimal (2-4hp @ 6300 rpm). Weight loss-yes. More sound-yes. Make your exhaust stink- oh yes.

[JTP]

Originally Posted by spongebob

The seller claims 25 hp increase.......

They must be magic pipes. Or the seller was smoking the magic pipe...

[The Radium King]

in a tuned exhaust you use unequal length pipes and a specific back pressure to facilitate exhaust gas scouring and increase torque at low rpm.

equal length pipes and reduced back pressure (high flow mufflers, cat delete) will improve large volume air flow and increase hp at high rpm.

so, you increase high rpm hp at the sacrifice of low rpm torque. i have yet to find a dyno of an aftermarket exhuast that didn't make less torque than stock in the 2500-ish rpm range.

porsche decided that most folks drive in the low to mid rpm range and designed the exhaust accordingly. ask yourself how often you really run your car over 6000 rpm vs how often you are tooling around at 2000 to 4000 rpm. that should dictate whether the cat delete will be of any benefit.

[Johnny Danger]

I didn't experience any loss of low end torque after I by-passed the secondary cats on my vehicle. In fact, dyno results later revealed a slight blip in hp when done conjunction with an aftermarket cat-back exhaust . Although some degree of back pressure is essential, keep in mind, at 400 plus cells, the secondary cats are extremely restrictive.

JD
p.s. The weight reduction is a plus also.

[jmatta]

I have Fabspeed secondary cat bypass pipes and a "Pedro Style" sport muffler (also running the Evo Hi-Flow intake). Though I can't vouch for any increase or decrease in low/mid torque, the engine revs much much freely, without the cats. Before installing, the engine (e-gas) would always hesitate on downshift throttle blips; once the bypass pipes were removed, throttle blips are near instantaneous, which would likely be due to loss of restriction.

Oh, they sound great, as well!

[The Radium King]

i will agree that the throttle response on my '00 S feels 'disconnected'; i've always attributed that to the e-gas. further, any improvement in throttle response does not necessarily mean that you are making more hp/torque. your car sounds like it is a lot for fun to drive, however.

to jd i would ask (a) the hp increase was where in the rpm range, and (b) any hp effect that a cat bypass pipe is +/- say 5 hp on a 200 hp vehicle; can any of us say that we can 'feel' a 2.5% change? there is a larger variation between two stock engines, or two engines at two different altitudes, or a hot vs cold engine, or a driver with a fat girlfriend vs a driver with a skinny girlfriend. and what effect does the audio component have on how you feel the power response (ie, it 'sounds' more powerful; the 'sound' makes you want to rev higher)?

all i know is what i've seen, and all dynos of aftermarket exhaust show a minor torque reduction at lower rpm (if they show lower rpm at all; often the dynos start at 3000 rpm).

not being argumentative; just being conversational and trying to distill the facts given the sometimes difficult nature of electronic conversation.

trk.