09-06-2011, 04:38 AM
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#1
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Location: Atlanta
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never exceeded 5 over.....
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09-06-2011, 05:54 AM
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#2
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Join Date: Sep 2009
Location: toronto
Posts: 2,668
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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!
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09-06-2011, 06:13 AM
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#3
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Location: Atlanta
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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!
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09-06-2011, 06:41 AM
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#4
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Join Date: Nov 2008
Location: Massachusetts
Posts: 4,810
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Quote:
Originally Posted by insite
never exceeded 5 over..... 
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Don't worry .... I told them to give you a break away !
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Don't worry … I've got the microfilm.
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09-06-2011, 08:18 AM
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#5
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Join Date: Sep 2004
Location: Atlanta
Posts: 1,820
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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....
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09-06-2011, 08:35 AM
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#6
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Registered User
Join Date: Jun 2007
Location: Littleton, CO
Posts: 456
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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.
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"Of all the extreme sports I've ever participated in- windsurfing, kite boarding, wake boarding, tow-in surfing and snowboarding- skiing, for me, made everything else easy."
-Chuck Patterson
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09-06-2011, 09:14 AM
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#7
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Join Date: Sep 2004
Location: Atlanta
Posts: 1,820
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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....
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09-06-2011, 09:38 AM
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#8
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Registered User
Join Date: Sep 2009
Location: toronto
Posts: 2,668
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Quote:
Originally Posted by insite
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....
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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"
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09-06-2011, 09:46 AM
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#9
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Join Date: Sep 2004
Location: Atlanta
Posts: 1,820
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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.
Quote:
Originally Posted by jaykay
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"
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09-07-2011, 01:36 PM
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#10
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Registered User
Join Date: Sep 2004
Location: Atlanta
Posts: 1,820
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if anyone is interested, i have some photos showing the differences between OEM, fabspeed & deluboz pipes here:
Cat Bypass (Test) Pipes
the deluboz prototypes (brand new) are for sale. gorgeous parts.
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09-09-2011, 09:25 AM
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#11
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Registered User
Join Date: Jan 2010
Location: NY
Posts: 130
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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
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09-19-2011, 05:24 PM
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#12
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Registered User
Join Date: Sep 2004
Location: Atlanta
Posts: 1,820
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here's some video from the track last week. i played w/ the GoPro a lot & have some great footage, but i'm still stringing it all together. this clip is a full lap at talladega gran prix with some footage reeling in & passing a TT.
this track is a bit small for the TT to really stretch its legs; it's weight penalty hits it hard here. that means this is a good opportunity for me to eat his lunch.
here's the TT vid:
i'll post more later; i got a GREAT clip of a C5 Z06 coming out of a pretty quick corner with the camera facing backward.
Quote:
Originally Posted by jaykay
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
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09-19-2011, 05:50 PM
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#13
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Registered User
Join Date: Sep 2009
Location: toronto
Posts: 2,668
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Heeeheeeeee! Nice work! Looks exactly like the guy who blew by me too!
Whats the red band/lanyard on your arm we don't have to wear those up here??
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09-19-2011, 07:10 PM
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#14
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Registered User
Join Date: Jun 2007
Location: Littleton, CO
Posts: 456
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That was beautiful, insite. It's no surprise you can drive that smoothly after reading all your posts. Thanks again.
__________________
"Of all the extreme sports I've ever participated in- windsurfing, kite boarding, wake boarding, tow-in surfing and snowboarding- skiing, for me, made everything else easy."
-Chuck Patterson
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09-20-2011, 02:56 AM
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#15
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Registered User
Join Date: Sep 2004
Location: Atlanta
Posts: 1,820
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thanks for the kind words, guys.
jaykay -
the bands are arm restraints. some tracks require them if you want to run with the top down. they connect to the shoulder harnesses at the harness cam, so un-doing the harnesses also releases the arm restraints.
they always looked like they'd interfere w/ driving, but they really don't.
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