glie Cali to Fed spec Exhaust conversion
06-23-2001, 07:36 PM
#1
Ooglie Cali to Fed spec Exhaust conversion
What's up guys...
Just got a Stillen y-pipe, and still concerned about the potential long term effects of taking only one precat off, I decided to try to convert my Cali 2K1 to fed spec. I didn't want to try take the radiator off in order to remove the front exhaust manifold so I decided to gut the front pre-cat (It came off the manifold pretty easily). But after seeing a post from Dave Burnett (I think) about how gutting the main cat may actually decrease exhaust velocity and evacuation I decided to try something different on the pre-cat. I drilled about a 1 1/2" diameter hole right down the honeycomb material from the top through to the opposite end of the pre-cat. I reasoned that this would be a good compromise between eliminating backpressure but still not creating a large hollow area as would have been the case if I'd gutted it entirely.
Of course, before doing all this I located the two rear O2 sensors behind the main cat - the toughest part was finding the right size nuts to weld to the b-pipe for the sensors! I went to a local muffler shop and they did this in about 15 minutes for $30.
I just finished this today and have taken a couple of test drives. Like Desert Pearl, I didn't get any check engine lights. There is a slight difference in power and acceleration - but slight. Also the car seems to be running a bit rougher but I'm hoping this will take care of it-self as the ECU adjusts (same thing happened when I installed the Y-pipe two weeks ago). It's also a little louder but not by much.
Had a couple of questions on this for those who have tried anything like this or have experience/knowledge of this subject. Will the honeycomb material in the pre-cat either deteriorate more rapidly since there's now a small hole right in the middle of it or is there anything else that may occur (will exaust flow be more harmed than helped with this mod)? Would I be better off gutting it all entirely (or on the other hand just having left it alone
)?
I'm thinking if it doesn't smooth out in a few days I may just buy a front manifold with precat - or get the pre-cat separately if possible, and go back to having only one precat removed. A rougher running motor bothers me more than the backpressure difference!
Thoughts or comments on this would be really appreciated!
I'll have pictures of this in a couple of days if anybody is interested.
Just got a Stillen y-pipe, and still concerned about the potential long term effects of taking only one precat off, I decided to try to convert my Cali 2K1 to fed spec. I didn't want to try take the radiator off in order to remove the front exhaust manifold so I decided to gut the front pre-cat (It came off the manifold pretty easily). But after seeing a post from Dave Burnett (I think) about how gutting the main cat may actually decrease exhaust velocity and evacuation I decided to try something different on the pre-cat. I drilled about a 1 1/2" diameter hole right down the honeycomb material from the top through to the opposite end of the pre-cat. I reasoned that this would be a good compromise between eliminating backpressure but still not creating a large hollow area as would have been the case if I'd gutted it entirely.
Of course, before doing all this I located the two rear O2 sensors behind the main cat - the toughest part was finding the right size nuts to weld to the b-pipe for the sensors! I went to a local muffler shop and they did this in about 15 minutes for $30.
I just finished this today and have taken a couple of test drives. Like Desert Pearl, I didn't get any check engine lights. There is a slight difference in power and acceleration - but slight. Also the car seems to be running a bit rougher but I'm hoping this will take care of it-self as the ECU adjusts (same thing happened when I installed the Y-pipe two weeks ago). It's also a little louder but not by much.
Had a couple of questions on this for those who have tried anything like this or have experience/knowledge of this subject. Will the honeycomb material in the pre-cat either deteriorate more rapidly since there's now a small hole right in the middle of it or is there anything else that may occur (will exaust flow be more harmed than helped with this mod)? Would I be better off gutting it all entirely (or on the other hand just having left it alone
)?I'm thinking if it doesn't smooth out in a few days I may just buy a front manifold with precat - or get the pre-cat separately if possible, and go back to having only one precat removed. A rougher running motor bothers me more than the backpressure difference!
Thoughts or comments on this would be really appreciated!
I'll have pictures of this in a couple of days if anybody is interested.
06-24-2001, 11:11 AM
#2
From the earlier discussions on this topic, I think it was decided that there would be no negative effects of leaving the front pre-cat in and installing a y-pipe. As you have probably found out, there is not a huge difference between leaving the front pre-cat and removing it. I guess the front pre-cat is not very restrictive. Anyhow, I would not gut the pre-cat. That may create an exhaust path that is rougher and may actually hinder the exhaust movement out of the manifold. The hole you have drilled may not be as bad since it is even all the way through. Post pics of the front pre-cat. I would be interested in that. I am going to be installing my y-pipe next weekend also 
06-25-2001, 12:16 AM
#3
I've got to get them developed and buy a new scanner - I'll put them up on a Cardomain.com page. Should take a couple of days.
The engine does seem to be smoothing out a bit. I've also noticed a slight loss in low end torque but once I get past 30 mph or so I can feel a slight improvement in acceleration and it doesn't seem to have to downshift as much as before when pushed to accelerate quickly. Took it up to 110 mph today and it didn't have to downshift although I pressed the pedal almost all the way down.
I'll give it a week and then decide if I'm happy with it or not. It's a fair amount of work for just an additional 3 horsepower (according to Desert Pearls dyno graph), but I just had to try it for myself. Taking of the pre-cat and drilling a hole is very easy but relocating the rear sensors turned out to be a pain.
It occurred to me after I drilled the hole in the middle it would probably have been better as far as smoother exhaust flow to drill several smaller holes, maybe a half inch in diameter perhaps in an X pattern or something like this. I may try this in a week or so, maybe drill three or four smaller holes around the larger hole. Of course, I have to keep in mind that this may be compromising the integrity of the honeycomb material more than I'd want to.
You'll like the y-pipe!
The engine does seem to be smoothing out a bit. I've also noticed a slight loss in low end torque but once I get past 30 mph or so I can feel a slight improvement in acceleration and it doesn't seem to have to downshift as much as before when pushed to accelerate quickly. Took it up to 110 mph today and it didn't have to downshift although I pressed the pedal almost all the way down.
I'll give it a week and then decide if I'm happy with it or not. It's a fair amount of work for just an additional 3 horsepower (according to Desert Pearls dyno graph), but I just had to try it for myself. Taking of the pre-cat and drilling a hole is very easy but relocating the rear sensors turned out to be a pain.
It occurred to me after I drilled the hole in the middle it would probably have been better as far as smoother exhaust flow to drill several smaller holes, maybe a half inch in diameter perhaps in an X pattern or something like this. I may try this in a week or so, maybe drill three or four smaller holes around the larger hole. Of course, I have to keep in mind that this may be compromising the integrity of the honeycomb material more than I'd want to.
You'll like the y-pipe!
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