GT3 Cup exhaust and cat delete
08-30-2009, 04:14 PM
#16
Rennlist Member
I am very interested to see what you come up with.
08-30-2009, 08:17 PM
#17
Rennlist Member
Thread Starter
Borescope. I like the way you think. I know someone who has one too.
But look at the the stock Cup exhaust- if it was divided then a.) I don't think that the tips would be so very close together and b.) there would likely be a seam on the outside no?
Absent the borescope I guess you could just angle a coat hanger in the exhaust tip and if you don't hit something . . .
But look at the the stock Cup exhaust- if it was divided then a.) I don't think that the tips would be so very close together and b.) there would likely be a seam on the outside no?
Absent the borescope I guess you could just angle a coat hanger in the exhaust tip and if you don't hit something . . .
08-30-2009, 09:16 PM
#18
Rennlist Member
I have access to both exhausts on the 996 Cup and 997, but probably won't be able to see them myself for a week or two. I will check them both when I can.
Yes, usually there would be some sign of an internal wall or baffle inside, unless it is piped with a perforated pipe internally (unlikely but possible).
Yes, usually there would be some sign of an internal wall or baffle inside, unless it is piped with a perforated pipe internally (unlikely but possible).
08-31-2009, 07:39 PM
#20
Rennlist Member
Borescope. I like the way you think. I know someone who has one too.
But look at the the stock Cup exhaust- if it was divided then a.) I don't think that the tips would be so very close together and b.) there would likely be a seam on the outside no?
Absent the borescope I guess you could just angle a coat hanger in the exhaust tip and if you don't hit something . . .
But look at the the stock Cup exhaust- if it was divided then a.) I don't think that the tips would be so very close together and b.) there would likely be a seam on the outside no?
Absent the borescope I guess you could just angle a coat hanger in the exhaust tip and if you don't hit something . . .
Ok, so I shoved a borescope up it's tip,actually both tips, and here is what I found.
The first section in the exhaust is actually a honeycomb cat, just like a street cat although it did appear to be a better larger cell/higher flowing cat. One on each side and it can be seen/noticed in your picture. The shiny, first section of the exhaust on each side is the cat section. After that it is a pipe, one on each side, that comes straight out of the cat section and then 90 degree turns for the exit. Now the reason the middle section is rusty/discolored is that the pipes internally are perforated which appears to mix both sides slightly as well as act as a baffle to dampen the sound.
Make sense ? ? ?
I didn't have a camera to take pictures of the borescope display, not so sure how they would have turned out anyway, but I think it's pretty easy to picture from the description above and your previous picture.
After seeing this now I understand why the extreme cost of this exhaust system, it really is 2 cats and a muffler, not just a muffler.
Let me know if you have any other questions, I can check the 997 although I am guessing it will be the same.
08-31-2009, 08:09 PM
#21
Rennlist Member
Thread Starter
Hey kewl- thanks.
And from the original pic on page 1 - there are baby cats in there I just read.
So the question is then if you eliminate the cats, can the left and right sides empty into a common singular muffler or better off are they better being maintained separate- like this design for example:
And from the original pic on page 1 - there are baby cats in there I just read.
So the question is then if you eliminate the cats, can the left and right sides empty into a common singular muffler or better off are they better being maintained separate- like this design for example:
08-31-2009, 08:19 PM
#22
Rennlist Member
That is the million dollar question ! And the only way to get an answer is to build both and dyno, or find someone else that has already.
I would speculate some mixing would help although depending on when and how you mix it could also hurt performance. This gets into tuning the exhaust pulses, and also tuning them for a specific gain at a specific RPM range.
I would speculate some mixing would help although depending on when and how you mix it could also hurt performance. This gets into tuning the exhaust pulses, and also tuning them for a specific gain at a specific RPM range.
Hey kewl- thanks.
And from the original pic on page 1 - there are baby cats in there I just read.
So the question is then if you eliminate the cats, can the left and right sides empty into a common singular muffler or better off are they better being maintained separate- like this design for example:
And from the original pic on page 1 - there are baby cats in there I just read.
So the question is then if you eliminate the cats, can the left and right sides empty into a common singular muffler or better off are they better being maintained separate- like this design for example:
09-01-2009, 11:19 AM
#23
Rennlist Member
Thread Starter
We will go one route (at least) and compare to muffler delete but with stock cats.
Stay tuned (pun intended this time).
Stay tuned (pun intended this time).
09-01-2009, 11:31 AM
#24
Race Car
Hey kewl- thanks.
And from the original pic on page 1 - there are baby cats in there I just read.
So the question is then if you eliminate the cats, can the left and right sides empty into a common singular muffler or better off are they better being maintained separate- like this design for example:
And from the original pic on page 1 - there are baby cats in there I just read.
So the question is then if you eliminate the cats, can the left and right sides empty into a common singular muffler or better off are they better being maintained separate- like this design for example:
09-01-2009, 11:44 AM
#26
Race Car
Yes....probably not ideal for my street car though!
anyone know the story behind the buldge in the head pipes prior to the bend. Just slip joints or a stepped design? Lots of crazy cool stuff going on there.
anyone know the story behind the buldge in the head pipes prior to the bend. Just slip joints or a stepped design? Lots of crazy cool stuff going on there.
09-01-2009, 12:00 PM
#27
Rennlist Member
Comparing to muffler delete with stock cats really isn't fair, the cats are the greater restriction. Better to test vs pure open pipes, now if you can beat that then you are onto something. Important to watch how it moves the power curve, more power may sell more pipes but it is not always better. Be sure to dyno well and watch airfuels and hopefully you can adjust as needed to really optimize what you build. - Remember that your motor is just an airpump, more out means your needs for proper air and fuel in changes.
09-01-2009, 01:10 PM
#28
Addict
Rennlist Member
Rennlist Member
It was fun to open this up and see the underside of my old car. I miss that thing.
I didn't read all the posts so I apologize if I'm repeating what someone else said. When we put straight pipes on my 3.6L X51 we put the pre-cat o2s in the pipe and hung the post-cat sensors in clear air. It worked great but we would get CELs from time to time. Nothing a small piece of electrical tape won’t fix!
I would second the concern about fuel mixture. Whatever changes you make, make sure you put the car on a dyno to make sure you’re not too lean.
We did a ton of testing on the car and in general the less backpressure you have the more HP and torque you will get but as expected it gets higher and higher in the rpm range. With straight pipes my car had no torque under 4500 rpms but screamed from 6000 up.
I didn't read all the posts so I apologize if I'm repeating what someone else said. When we put straight pipes on my 3.6L X51 we put the pre-cat o2s in the pipe and hung the post-cat sensors in clear air. It worked great but we would get CELs from time to time. Nothing a small piece of electrical tape won’t fix!
I would second the concern about fuel mixture. Whatever changes you make, make sure you put the car on a dyno to make sure you’re not too lean.
We did a ton of testing on the car and in general the less backpressure you have the more HP and torque you will get but as expected it gets higher and higher in the rpm range. With straight pipes my car had no torque under 4500 rpms but screamed from 6000 up.
09-01-2009, 02:12 PM
#29
Rennlist Member
It was fun to open this up and see the underside of my old car. I miss that thing.
I didn't read all the posts so I apologize if I'm repeating what someone else said. When we put straight pipes on my 3.6L X51 we put the pre-cat o2s in the pipe and hung the post-cat sensors in clear air. It worked great but we would get CELs from time to time. Nothing a small piece of electrical tape won’t fix!
I would second the concern about fuel mixture. Whatever changes you make, make sure you put the car on a dyno to make sure you’re not too lean.
We did a ton of testing on the car and in general the less backpressure you have the more HP and torque you will get but as expected it gets higher and higher in the rpm range. With straight pipes my car had no torque under 4500 rpms but screamed from 6000 up.
I didn't read all the posts so I apologize if I'm repeating what someone else said. When we put straight pipes on my 3.6L X51 we put the pre-cat o2s in the pipe and hung the post-cat sensors in clear air. It worked great but we would get CELs from time to time. Nothing a small piece of electrical tape won’t fix!
I would second the concern about fuel mixture. Whatever changes you make, make sure you put the car on a dyno to make sure you’re not too lean.
We did a ton of testing on the car and in general the less backpressure you have the more HP and torque you will get but as expected it gets higher and higher in the rpm range. With straight pipes my car had no torque under 4500 rpms but screamed from 6000 up.
09-01-2009, 04:14 PM
#30
Rennlist Member
Thread Starter
It did with me- I found seconds at RA. With my 3.8 motor with track cams, headers, no cats, dual Burns race mufflers + mapping 4500 is min target rpm. Some the grunt of the 3.8 is lost but it howls north of there to 7k. Lots of compliments from GT3 owners too- which are always welcome.
We anticipate similar from the 996 project. Custom map is a given with these types of changes- for motor safety as much as power.
We anticipate similar from the 996 project. Custom map is a given with these types of changes- for motor safety as much as power.