yup, and a lot of that has to do with tuning the exhaust to maximise exhaust gas scouring at lower rpm, improving low rpm flow efficiency while maintaining backpressure, etc., all of which supports locating the cats further downstream and improving the headers.

ps, the quote about both cats being 400 cell was made by JD in a thread from about a year ago, so caveat emptor to all.

http://986forum.com/forums/showthread.php?t=25644&highlight=600+400+cats

Since that thread, further research and discussion on the topic lead me to discover that the secondary cats were 600 cell . I've always been someone who strives to enhance his knowledge about things. Particularly, when there seems to be a lack of reliable information . And, by doing so, I am able to better understand what it is that I am dealing with (in this case my vehicle), and hopefully be able to pass on what I have leaned to others .

I've got the Top Speed Pro-1 test pipes and they improve the sound at idle, making it a bit deeper. The car also sounds better as you rev it, but I don't have any recordings.

As to power increase, it's been so hot that I can't fairly judge but maybe some due to the improved flow and saving 7 pounds per side.
When the weather gets cooler in October I should notice a difference.

A worthwhile mod based on my experience.

I'll post before & after vids this weekend.

I found a very helpful link to an explanation that helps understand the difference between the OEM 986 exhaust and a modified performance exhaust system (in this care, the Fabspeed Maxflo system):

http://www.fabspeed.com/videos/Boxster%20986%20Maxflo%20Muffler%20Explanation%20V ideo.wmv

This may be pretty basic for those of you who have a lot of experience with these mods, but it really helped me understand the differences between the OEM system and a performance system. Thought I'd share the link for anyone who is researching an exhaust mod for the first time.

Thanks, M96!

shot some video w/ OEM cat pipes vs. fabspeed bypass pipes. will post today.

some clips comparing OEM vs. bypass.

engine is a 3.4L with a custom intake, headers & a stebro race muffler. the OEM cat pipes are from the 2.5L. the bypass pipes are 2" fabspeed.

http://vimeo.com/28638915

After posting that video, I got a call from these guys .

never exceeded 5 over..... :rolleyes:

Does current information suggest that installing secondary cat delete pipes and a Pedro style/pse style bypass exhaust muffler (modified stock s) will reduce back pressure (and therefore alter exhaust scavenging) to such a degree that there are losses in torque and power? Can one simply look at what the computer has done to ignition timing to see if it has detuned the engine via ignition retardation, to get an idea whether an exhaust system is working well? What are the stock ignition parameters and what variance would be bad as seen via the OBD port?

Yes I know dynos are the tool I am dancing around!

you have to consider the whole system and the REASON backpressure is a concern (it's not).

most people talk about backpressure like it provides something to the equation. well, again, we have to consider the SYSTEM. scavenging depends upon VELOCITY in the exhaust gas. the velocity is what creates vacuum at the valve outlet. if the pipes get too big early in the system, velocity stalls and pressure increases. this means no scavenging. we also have to consider that as the exhaust gasses cool, they condense a bit, leading to further loss of velocity (this is why people try to keep the heat in headers).

ideally, you'll have a properly designed header. the length & diameter of the primaries will be tuned to the engine's parameters (valve timing, duration, diameter, angle) and to the desired performance charictaristics of the user (high-band power, low-band torque). they will join into a merge collector that is a venturi. it will neck down slightly & then open up a bit (like a megaphone). the header itself will accelerate the air past the venturi (secondary flange). once this happens, you want LARGE pipes; back pressure is not a concern.

if you're using non-venturi style headers or the OEM manifold, it's not the loss of cats & backpressure that causes the problem. it's velocity loss due to the DIAMETER of the tube. the bypass pipes are all 2", but the OEM pipes are SMALL. this means that you'll lose velocity & scavenging lower in the RPM range. there may be some improvement at the high end. all else equal, removing the cats will greatly improve velocity & in turn, scavenging.

with OEM exhaust manifolds, 2" bypass pipes and the pedro muffler, you will probably lose power overall w/ the 2.5L and 2.7L motors. there MAY be some high end power gains. the 3.2L and 3.4L would probably make power.

if you go w/ decent headers on the 2.5L / 2.7L, the bypass pipes & pedro muffler will make power up high, but lose some torque. i found the 2.5L to be gutless w/ torque anyway, so i always opted for high RPM power & revved the crap out of it. much more fun for me!

Don't worry .... I told them to give you a break away ! :)

i was SUPPOSED to be at the track today, but tropical storm Lee had other plans. date has been revised to 9/15.

i will take some video so you all can get an idea of exactly what a well tuned, stripped out boxster w/ a 3.4L can do when i REALLY get into the go pedal....

Hey insite, are you still using the wheels shown in your sig? With as performance-minded as you are, I'm surprised you don't have something like an Alleggerita.

believe it or not, the BBS forged 2-piece are already fairly light. at some point, i will probably go lighter, but i have a lot of other things to do first....

Thanks for your thoughts......yes of course scavenge velocity is king! Can't wait to see the video. I have just had my butt kicked by 996 4/996 T

I have the same wheels from Porsche but they were three piece...BBS is actually the manufacturer. In my view it will be tough to find anything much better in 18"

My wheels are the Porsche version (sport classic II). I will try to deliver some payback to the 996 TT's; 1 or 2 going w/ us next week.....I think they will find it hard to keep up. :D

if anyone is interested, i have some photos showing the differences between OEM, fabspeed & deluboz pipes here:

http://986forum.com/forums/showthread.php?t=30237

the deluboz prototypes (brand new) are for sale. gorgeous parts.

I installed cat delete pipes with an all stock exhaust system. My secondaries we starting to break down, but i definitely do not feel a power loss. I believe they are downstam enough where back pressure is more trivial