Aftermarket exhaust
03-26-03, 06:07 AM
#1
Lead Lap
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Suggestions on modyfing the exhaust?
After doing some reading on this forum I decided to work on the middle part of 95 SC400 exhaust and make it a true dual exhaust. My idea was to replace the stock single pipe with the dual and the x-pipe. That would require removing the first "resonator". Unfortunately I just found out, by cutting the exhaust, the "resonator" is actually the catalytic converter.
So the question is, do you think doing the true dual exhaust and using a 2-in 2-out aftermarket catalytic converter instead of the x-pipe would be a good idea?
So the question is, do you think doing the true dual exhaust and using a 2-in 2-out aftermarket catalytic converter instead of the x-pipe would be a good idea?
Last edited by ChrisK; 03-27-03 at 05:45 AM.
03-27-03, 05:49 AM
#2
If youre worried about emissions, just run an extra cat on each side. I'd still keep the x-pipe and forgoe the 2-in 2-out cat. They are usually nothing but problems.
They sell a small hi-flow cat and a standard hi-flow; run 1 of each on either side.
Are you sure the "resonator" is a cat? I have a 92' and its definately a resonator, not a cat (manual even says so). When you remove it, it a straight through design like the mufflers. I know California models have it as a cat, and I'm not sure how other years are, but just a thought to look into.
They sell a small hi-flow cat and a standard hi-flow; run 1 of each on either side.
Are you sure the "resonator" is a cat? I have a 92' and its definately a resonator, not a cat (manual even says so). When you remove it, it a straight through design like the mufflers. I know California models have it as a cat, and I'm not sure how other years are, but just a thought to look into.
Last edited by Keith13b; 03-27-03 at 05:52 AM.
03-27-03, 07:38 AM
#3
Lead Lap
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Keith13b,
The muffler place I went to cut the pipe right after the cat/resonator, and it had the mesh going inside it, so it is the cat for sure.
I was hoping to accomplish two things with one. My idea was to use a 2-in 2-out catalytic converter that would keep the emissions intact and behave like an x-pipe or an h-pipe. Also, I'm trying to keep the cost down.
The muffler place I went to cut the pipe right after the cat/resonator, and it had the mesh going inside it, so it is the cat for sure.
I was hoping to accomplish two things with one. My idea was to use a 2-in 2-out catalytic converter that would keep the emissions intact and behave like an x-pipe or an h-pipe. Also, I'm trying to keep the cost down.
Last edited by ChrisK; 03-27-03 at 12:52 PM.
03-27-03, 12:14 PM
#4
Originally posted by ChrisK
Keith13b,
The muffler place I went to cut the pipe right after the cat/resonator, and I have the mesh going inside it, so it is the cat for sure.
I was hoping to accomplish to things with one. That is way my idea was to use a 2-in 2-out catalytic converter that would keep the emissions intact and behave like an x-pipe or an h-pipe. Also, I'm trying to keep the cost down.
Keith13b,
The muffler place I went to cut the pipe right after the cat/resonator, and I have the mesh going inside it, so it is the cat for sure.
I was hoping to accomplish to things with one. That is way my idea was to use a 2-in 2-out catalytic converter that would keep the emissions intact and behave like an x-pipe or an h-pipe. Also, I'm trying to keep the cost down.
Let us know the results.
03-28-03, 08:58 AM
#5
Lexus Champion
Chris,
It appears that you have a California certified car. These are the only ones I am aware of that have a center catalyst. I do not know if the 2 catalysts bolted to the exhaust manifolds are the same as the ones on 49 state certified cars. If they are (or you can aquire 2 of those) there should be no problem in Illinios in changing to a dual cat setup. In terms of absolute accuracy and letter of the law... I can't give you that. I don't know who could. The emissions laws are convoluted in a way that only the IRS code can exceed. I would have absolutely no reservations in going to a 2 cat layout. If your car has 2 cats and passes the sniffer test you should be absolutely legal and fine.
Now, for an actual exhaust design. You can just replace parts and HOPE or you can use an engineered design. I am mid process on a complete cat back design for the 1UZ-FE (Lexus V8). Design parameters are many including low noise at idle, light acceleration and cruise. Mellow powerful sound under aggressive acceleration. Neither of these goals are worthwile unless the system enhances the power curve. Equal or enhanced low end power with increased high RPM power is essential to a successful design. To accomplish this the system MUST maintain high velocity during low RPM operation AND allow more flow at high RPM. Using a dual-in-dual-out catalyst as you are considering would not accomplish this. It would act as a plenum and would stall the flow.
The key to an effective system is design. To this goal I have designed and computer tested a Y pipe design. The Y pipe tests better than an X pipe. I had flanges custom cut for my application (98+ engines). I can't be certain if these will fit pre 98 catalyst outlets but would consider sending one for you to test fit. Price for flanges are $60/pair in 3/8 mild steel or $80/pair in stainless. Or, you can cut off your existing flanges and re-use them but must make certain the outlet size is large enough for the piping size used. I will be using 2.25". Stock is 50mm (1.97") so using 2" would be a very slight increase. If you are not going to 2.25" I would just add a high flow Y pipe to the stock duals. The Y pipe that I am engineering is a racing style merge pipe NOT just a transition. MANY configurations have been modelled and the best performance is with dual 2.25" inlets, specific area venturi, transition to a single 3" outlet. If you wish to keep the stock 50mm pipes I would suggest a 2.5" outlet (stock is 60mm / 2.36"). Price on the racing Y pipe is $125 in mild steel, $175 in stainless.
You may have noticed that there is a definite price associated with "doing it right". You could simply replace your pipes with larger diameter ones. The system would be LOUDER but may actually make less power in the usable range. If you wish to do it right I will be glad to help you if you will tell me your goals and budget.
It appears that you have a California certified car. These are the only ones I am aware of that have a center catalyst. I do not know if the 2 catalysts bolted to the exhaust manifolds are the same as the ones on 49 state certified cars. If they are (or you can aquire 2 of those) there should be no problem in Illinios in changing to a dual cat setup. In terms of absolute accuracy and letter of the law... I can't give you that. I don't know who could. The emissions laws are convoluted in a way that only the IRS code can exceed. I would have absolutely no reservations in going to a 2 cat layout. If your car has 2 cats and passes the sniffer test you should be absolutely legal and fine.
Now, for an actual exhaust design. You can just replace parts and HOPE or you can use an engineered design. I am mid process on a complete cat back design for the 1UZ-FE (Lexus V8). Design parameters are many including low noise at idle, light acceleration and cruise. Mellow powerful sound under aggressive acceleration. Neither of these goals are worthwile unless the system enhances the power curve. Equal or enhanced low end power with increased high RPM power is essential to a successful design. To accomplish this the system MUST maintain high velocity during low RPM operation AND allow more flow at high RPM. Using a dual-in-dual-out catalyst as you are considering would not accomplish this. It would act as a plenum and would stall the flow.
The key to an effective system is design. To this goal I have designed and computer tested a Y pipe design. The Y pipe tests better than an X pipe. I had flanges custom cut for my application (98+ engines). I can't be certain if these will fit pre 98 catalyst outlets but would consider sending one for you to test fit. Price for flanges are $60/pair in 3/8 mild steel or $80/pair in stainless. Or, you can cut off your existing flanges and re-use them but must make certain the outlet size is large enough for the piping size used. I will be using 2.25". Stock is 50mm (1.97") so using 2" would be a very slight increase. If you are not going to 2.25" I would just add a high flow Y pipe to the stock duals. The Y pipe that I am engineering is a racing style merge pipe NOT just a transition. MANY configurations have been modelled and the best performance is with dual 2.25" inlets, specific area venturi, transition to a single 3" outlet. If you wish to keep the stock 50mm pipes I would suggest a 2.5" outlet (stock is 60mm / 2.36"). Price on the racing Y pipe is $125 in mild steel, $175 in stainless.
You may have noticed that there is a definite price associated with "doing it right". You could simply replace your pipes with larger diameter ones. The system would be LOUDER but may actually make less power in the usable range. If you wish to do it right I will be glad to help you if you will tell me your goals and budget.
03-28-03, 09:26 AM
#6
Lead Lap
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jbrady,
Thank you for your reply.
There is the picture of my exhaust, I'm hoping it is OK with Peter that I'm using his picture.
My goal it is to improve the exhaust flow, to make more power, without making the exhaust too loud. Also, I'm trying to accomplish this without spending an arm and a leg. Since the rear resonators and mufflers should be the straight through, I don't think I could gain much by replacing them. From my previous reading of your posts I understand that the flow problem lays in y-pipes, both of them. So my goal was to make the true dual system with an x-pipe. When I went to the muffler shop I've been told the middle "resonator" is an actual catalytic converter, after the inspection. I guess my next step will be to see if the both front catalytic converters are the same model as a "regular" system. If they are I will try to find a local shop that will take my word that it is OK to remove the third catalytic converter and get the dual exhaust going. I'm still thinking about keeping the back part of the exhaust stock for the noise and cost purposes. I'm also open to suggestions. If you think that going to a single pipe using the racing y-pipe is better, I definitely will consider it. In this case what would you suggest for the back of the exhaust?
Thank you for your reply.
There is the picture of my exhaust, I'm hoping it is OK with Peter that I'm using his picture.
My goal it is to improve the exhaust flow, to make more power, without making the exhaust too loud. Also, I'm trying to accomplish this without spending an arm and a leg. Since the rear resonators and mufflers should be the straight through, I don't think I could gain much by replacing them. From my previous reading of your posts I understand that the flow problem lays in y-pipes, both of them. So my goal was to make the true dual system with an x-pipe. When I went to the muffler shop I've been told the middle "resonator" is an actual catalytic converter, after the inspection. I guess my next step will be to see if the both front catalytic converters are the same model as a "regular" system. If they are I will try to find a local shop that will take my word that it is OK to remove the third catalytic converter and get the dual exhaust going. I'm still thinking about keeping the back part of the exhaust stock for the noise and cost purposes. I'm also open to suggestions. If you think that going to a single pipe using the racing y-pipe is better, I definitely will consider it. In this case what would you suggest for the back of the exhaust?
03-28-03, 01:34 PM
#7
Lexus Champion
Word of warning about muffler shops: VERY few have any true performance knowledge. Their goal is to build a system that fits, doesn't leak or rattle. I have seen numerous mufflers installed with the tailpipes stuck into the muffler creating a horrible flowing section. Even a good part can have its performance potential reduced or eliminated by poor installation.
That said, I think you have 2 choices. Cheap and better or expensive and optimal.
Cheap would be a Dr.Gas Y pipe, go to this link http://www.drgas.com/street-cat.html and scroll down to the Y pipes. The 2.00"x2.50" part with curved inlets should work decently for you. From it you can just run a straight 2.50" pipe back to your current cat back. Your current cat back, if straight through should flow OK, cost under $200 and improve your system noticeably. If it is too loud you can add a straight 2.50" resonator after the Y pipe. Gains??? Hard to guess but probably 10-15tq accross the range. You could also have me build a racing Y pipe in the same dimensions for $25 more (mild steel like the Dr.Gas) and pick up 5 or so more.
Expensive would be new 2.25"x3.00" piping. This would require cutting and re-using the flanges off your existing pipes or buying new flanges. New o2 sensor bungs. New mandrel bent piping. Racing Y pipe. Optional 3.00" center resonator. All parts stainless. Cost? Estimate $500. Gains? Less on a stock engine, more with intake mods and full cat back but probably around 20-30tq accross the range. This is the option I am working on. This will really shine in the higher RPMs.
That said, I think you have 2 choices. Cheap and better or expensive and optimal.
Cheap would be a Dr.Gas Y pipe, go to this link http://www.drgas.com/street-cat.html and scroll down to the Y pipes. The 2.00"x2.50" part with curved inlets should work decently for you. From it you can just run a straight 2.50" pipe back to your current cat back. Your current cat back, if straight through should flow OK, cost under $200 and improve your system noticeably. If it is too loud you can add a straight 2.50" resonator after the Y pipe. Gains??? Hard to guess but probably 10-15tq accross the range. You could also have me build a racing Y pipe in the same dimensions for $25 more (mild steel like the Dr.Gas) and pick up 5 or so more.
Expensive would be new 2.25"x3.00" piping. This would require cutting and re-using the flanges off your existing pipes or buying new flanges. New o2 sensor bungs. New mandrel bent piping. Racing Y pipe. Optional 3.00" center resonator. All parts stainless. Cost? Estimate $500. Gains? Less on a stock engine, more with intake mods and full cat back but probably around 20-30tq accross the range. This is the option I am working on. This will really shine in the higher RPMs.
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