Gutting pre-cats bad for your car ??
07-30-2009, 11:09 AM
#1
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Join Date: May 2009
Location: Louisville, Ky
Posts: 181
Gutting pre-cats bad for your car ??
I have posted earlier that i am going to change my engine due to internal issues and i have another motor that is sitting at a shop ready to be put in. It came with the manifolds and precats and was wondering if gutting them causes any issues with the cars performance or overall driveability. I know it may throw a CEL and ive read on the SIMs or spark plug things to fool the computer. I mentioned it to the mechanic and he didnt recomend doing it at all. I know several people have done it and wonder if they have had any "side effects"?
07-30-2009, 11:34 AM
#3
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07-30-2009, 06:55 PM
#4
gutted cat = FAIL or something like that. Why not buy an aftermarket y=pipe which deletes the cats? much safer.
My concern about gutting cats is they are both different sizes. So you have a 2.1/4" tube which suddenly opens up to about 4" (maybe more or less) and then about 6 inches farther along you go back to the 2.1/4" tube. This will cause turbulence, the exhaust gasses will flow much faster through the narrow pieces and slow down considerably at the wide gutted out piece. So you have 2 sides with different flow with huge areas which will have turbulent exhaust gas trying to speed on through. Not good for horsepower at all.
Assuming that a gas is flowing through a pipe of 2 inches at any speed you like. Suddenly it comes upon a chamber that is 2 to 3 times larger than the pipe it was flowing through. There will be a big drop in pressure, and a reduction of flow. Then the gas is forced back into the 2 inch pipe where suddenly it will be forced to flow at the original pressure and speed. But that area where the large chamber (gutted cat) will have much turbulence. Hope that makes sense.
My concern about gutting cats is they are both different sizes. So you have a 2.1/4" tube which suddenly opens up to about 4" (maybe more or less) and then about 6 inches farther along you go back to the 2.1/4" tube. This will cause turbulence, the exhaust gasses will flow much faster through the narrow pieces and slow down considerably at the wide gutted out piece. So you have 2 sides with different flow with huge areas which will have turbulent exhaust gas trying to speed on through. Not good for horsepower at all.
Assuming that a gas is flowing through a pipe of 2 inches at any speed you like. Suddenly it comes upon a chamber that is 2 to 3 times larger than the pipe it was flowing through. There will be a big drop in pressure, and a reduction of flow. Then the gas is forced back into the 2 inch pipe where suddenly it will be forced to flow at the original pressure and speed. But that area where the large chamber (gutted cat) will have much turbulence. Hope that makes sense.
Last edited by knight_yyz; 07-30-2009 at 07:16 PM.
07-30-2009, 09:55 PM
#5
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Join Date: Sep 2007
Posts: 9
If putting in a new engine, how about these?;
http://tinyurl.com/l5o5o6
I was going to, until I got a look at the rear cylinder manifold bolts, chickened out and ordered Warpspeed...
http://tinyurl.com/l5o5o6
I was going to, until I got a look at the rear cylinder manifold bolts, chickened out and ordered Warpspeed...
Last edited by lifesabeachnj; 07-30-2009 at 09:57 PM.
07-30-2009, 11:38 PM
#6
gutted cat = FAIL or something like that. Why not buy an aftermarket y=pipe which deletes the cats? much safer.
My concern about gutting cats is they are both different sizes. So you have a 2.1/4" tube which suddenly opens up to about 4" (maybe more or less) and then about 6 inches farther along you go back to the 2.1/4" tube. This will cause turbulence, the exhaust gasses will flow much faster through the narrow pieces and slow down considerably at the wide gutted out piece. So you have 2 sides with different flow with huge areas which will have turbulent exhaust gas trying to speed on through. Not good for horsepower at all.
Assuming that a gas is flowing through a pipe of 2 inches at any speed you like. Suddenly it comes upon a chamber that is 2 to 3 times larger than the pipe it was flowing through. There will be a big drop in pressure, and a reduction of flow. Then the gas is forced back into the 2 inch pipe where suddenly it will be forced to flow at the original pressure and speed. But that area where the large chamber (gutted cat) will have much turbulence. Hope that makes sense.
My concern about gutting cats is they are both different sizes. So you have a 2.1/4" tube which suddenly opens up to about 4" (maybe more or less) and then about 6 inches farther along you go back to the 2.1/4" tube. This will cause turbulence, the exhaust gasses will flow much faster through the narrow pieces and slow down considerably at the wide gutted out piece. So you have 2 sides with different flow with huge areas which will have turbulent exhaust gas trying to speed on through. Not good for horsepower at all.
Assuming that a gas is flowing through a pipe of 2 inches at any speed you like. Suddenly it comes upon a chamber that is 2 to 3 times larger than the pipe it was flowing through. There will be a big drop in pressure, and a reduction of flow. Then the gas is forced back into the 2 inch pipe where suddenly it will be forced to flow at the original pressure and speed. But that area where the large chamber (gutted cat) will have much turbulence. Hope that makes sense.
07-31-2009, 05:59 AM
#7
Senior Member
Thread Starter
Join Date: May 2009
Location: Louisville, Ky
Posts: 181
If putting in a new engine, how about these?;
http://tinyurl.com/l5o5o6
I was going to, until I got a look at the rear cylinder manifold bolts, chickened out and ordered Warpspeed...
http://tinyurl.com/l5o5o6
I was going to, until I got a look at the rear cylinder manifold bolts, chickened out and ordered Warpspeed...
07-31-2009, 06:32 AM
#9
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Join Date: May 2009
Location: Louisville, Ky
Posts: 181
you are correct. headers will eliminate the precats all together. I would like to see a dyno as well
07-31-2009, 06:45 AM
#10
most people that gut their pre-cats dont gut them for performance reasons, but to save their engines from consuming oil or consuming more oil than they already are.
i kinda though it was obvious that it wouldn't help peformance,the design is horrible as knight yyz stated. i got the obx headers and the only problem i have with them is the flex section(but all my mounts being solid it doesnt help that situation) and those were under 400 bucks,kinda a pita to install (being a 2 piece design) but well worth the money in the end. id say just get them and you wont regret it.
and put them on the new engine before installing the motor,it will save you so much a of a headache.
i kinda though it was obvious that it wouldn't help peformance,the design is horrible as knight yyz stated. i got the obx headers and the only problem i have with them is the flex section(but all my mounts being solid it doesnt help that situation) and those were under 400 bucks,kinda a pita to install (being a 2 piece design) but well worth the money in the end. id say just get them and you wont regret it.
and put them on the new engine before installing the motor,it will save you so much a of a headache.
07-31-2009, 06:58 AM
#11
well the closest you will get to dyno numbers will be you trying it yourself and dyno yourself, nobody here with gutted cats wants to do it, so if u do gut ur cats, i guess you can swing by a local dyno shop and clear everybody's minds on here
07-31-2009, 07:01 AM
#12
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Join Date: May 2009
Location: Louisville, Ky
Posts: 181
yeah i guess that is always an option. I think i am going to pass on that though. i am not really that worried about the performance gains of it as much as i am the overall driveability.
07-31-2009, 07:09 AM
#13
most ppl arent... but i know most ppl just have to be curious if it has some kind of gains... just afraid or ashamed if numbers were crappy.... if i knew how to gut a cat myself i would sure love to just get it over with, does it make at least 1hp or not??? i believe here in MD there was an altima with gutted cats that must have had some power gains due to track times... but idk if the same goes for maxima's
07-31-2009, 02:30 PM
#14
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Join Date: Jul 2009
Location: New Jersey
Posts: 42
Your cats hold a certain amount of pack pressure for the engine to run correctly. If you gut them, you lower the back pressure which may make the engine run bad. I would not do it either. It'll cost a fortune to get new ones to put it back to normal.
07-31-2009, 03:28 PM
#15
I'd like to see someone buy 3.0 exhaust manifolds, plug the egr and put a 5th gen y-pipe on there. It would all fit.
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