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Old 09-25-2010, 02:35 PM   #1
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Exclamation VX exhaust manifold unique

I've seen the original VX exhaust manifold and it's unique among Honda manifolds; all the exhausts come straight out (90 degrees) to a central chamber where the O2 sensor is put in the centre, at the top. Then it goes down into a cat. That leads me to think that Honda wanted to put their 5 wire O2 sensor in the highest heat location. As the original VX manifold is hard to find, I'm going to try and modify a regular 4 into 1, locating the sensor in that 4 into 1 hotspot, at the top, then heat wrapping it to keep it hot. Has anybody done that?
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Old 09-25-2010, 06:03 PM   #2
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Re: VX exhaust manifold unique

Yes a hot O2 sensor works better. I've also found that keeping the O2 sensor closer to the exhaust port give quicker response to changes in AF ratio, except you can't put a solo wideband in an individual runner so it has to be placed in the collector, preferably in a spot that doesn't hinder exhaust flow.
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Old 09-27-2010, 10:05 AM   #3
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Re: VX exhaust manifold unique

Actually OP, if you makes you feel any better, most newer civics (1996+) have this EXACT exhaust design and the reason for this is by putting the catalytic converter closer and or using the catalytic converter like an exhaust manifold, it allows for quicker warm up temps.. My '98 Civic LX has this exact setup and considering the D-series engine hasn't substantially changed in design (save for increased deck height for more displacement, same bore size) since 88-05, I'd say you could just pick yourself up one of these OBD-II exhaust manifold catalytic converters (yes there actually is a distinction between OBD-I cats and OBD-II cats). OBD-I cats have a lower efficiency requirement compared to OBD-II cats, so OBD-II are always cleaner.

The civics that don't have this setup are the EX civics from when ever to at least 2000 model year.. Possibly in 2001 model year, they transitioned the EX to having the same catalytic converter setup as all of the other civics. Older Civic EXs have a separate exhaust manifold which bends and then connected to a catalytic converter further down stream, which allows for aftermarket upgrades, something the "newer design" doesn't allow for since the cat IS the manifold.
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Old 09-27-2010, 10:23 AM   #4
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Re: VX exhaust manifold unique

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Originally Posted by ************* View Post
Actually OP, if you makes you feel any better, most newer civics (1996+) have this EXACT exhaust design and the reason for this is by putting the catalytic converter closer and or using the catalytic converter like an exhaust manifold, it allows for quicker warm up temps.. My '98 Civic LX has this exact setup and considering the D-series engine hasn't substantially changed in design (save for increased deck height for more displacement, same bore size) since 88-05, I'd say you could just pick yourself up one of these OBD-II exhaust manifold catalytic converters (yes there actually is a distinction between OBD-I cats and OBD-II cats). OBD-I cats have a lower efficiency requirement compared to OBD-II cats, so OBD-II are always cleaner.

The civics that don't have this setup are the EX civics from when ever to at least 2000 model year.. Possibly in 2001 model year, they transitioned the EX to having the same catalytic converter setup as all of the other civics. Older Civic EXs have a separate exhaust manifold which bends and then connected to a catalytic converter further down stream, which allows for aftermarket upgrades, something the "newer design" doesn't allow for since the cat IS the manifold.
This is correct. The VX engines from 1992-1995 and the DX/HX/LX engines from 1996-2000 all use that style of exhaust manifold, which raised the temperature of the catalyst more quickly than by placing it under the car. This allowed the VX to pass emissions (and the other engines to achieve a better emissions rating) during the cold startup test. I believe that the EX models did not have this style of exhaust manifold. I had a '99 Si, so I can say with certainty that the '99-'00 Si did not have it, either.

As far as buying/modifying an exhaust manifold, I would still try to buy a VX one rather than modify a 4-1. The VX manifold will give slightly higher backpressure. I know that the full-throttle performance will suffer slightly, but the mileage will be better. Some people on this site and others with a modified header in their VX suffered mileage drops when they swapped out, even when they kept the 5-wire O2 and OBDI cat.

Have you tried the WTB forum on this site? You may have better luck than you think.
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Old 03-03-2011, 01:24 PM   #5
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Re: VX exhaust manifold unique

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This is correct. The VX engines from 1992-1995 and the DX/HX/LX engines from 1996-2000 all use that style of exhaust manifold, which raised the temperature of the catalyst more quickly than by placing it under the car. This allowed the VX to pass emissions (and the other engines to achieve a better emissions rating) during the cold startup test. I believe that the EX models did not have this style of exhaust manifold. I had a '99 Si, so I can say with certainty that the '99-'00 Si did not have it, either.

As far as buying/modifying an exhaust manifold, I would still try to buy a VX one rather than modify a 4-1. The VX manifold will give slightly higher backpressure. I know that the full-throttle performance will suffer slightly, but the mileage will be better. Some people on this site and others with a modified header in their VX suffered mileage drops when they swapped out, even when they kept the 5-wire O2 and OBDI cat.

Have you tried the WTB forum on this site? You may have better luck than you think.
I just am trying to confirm if you both are saying that using the 96 cat/manifold will yield the same results as the original stock Vx cat/manifold to a t.

I purchased a new exhaust manifold and heat shields from Honda and a new cat from Bosal. Unfortunately the bolt patterns don't line up with my Vx manifold and they claim that it did so I have to return the parts with a company that sucks on returns. Partsgeek.com. I've had lots of good parts come from them but I'm worried about the return process based on consumer reports. Worse case is I send it back and they don't refund I'll dispute it I guess. My experience so far has been good though so hopefully it will be a smooth return, even though I have to cover shipping both ways, and they may try to hit me with a restocking fee :me:

Anyways back to topic. Will the 96 Lx/hx cat perform the exact same as a stock 92-95 Vx/Cx setup?
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Old 03-03-2011, 02:45 PM   #6
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Re: VX exhaust manifold unique

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Originally Posted by Midcoasted View Post
I just am trying to confirm if you both are saying that using the 96 cat/manifold will yield the same results as the original stock Vx cat/manifold to a t.

I purchased a new exhaust manifold and heat shields from Honda and a new cat from Bosal. Unfortunately the bolt patterns don't line up with my Vx manifold and they claim that it did so I have to return the parts with a company that sucks on returns. Partsgeek.com. I've had lots of good parts come from them but I'm worried about the return process based on consumer reports. Worse case is I send it back and they don't refund I'll dispute it I guess. My experience so far has been good though so hopefully it will be a smooth return, even though I have to cover shipping both ways, and they may try to hit me with a restocking fee :me:

Anyways back to topic. Will the 96 Lx/hx cat perform the exact same as a stock 92-95 Vx/Cx setup?
If you're concerned about things not bolting up properly, going with a '96+ catalytic/maniverter from a DX civic will in fact bolt on and should output lower emissions. I plan to call the BAR (Bureau of Automotive Repair for California) and ask them if using a newer catalytic converter/exhaust manifold would pass smog or not. Considering that the design of the maniverter shouldn't have changed and identifying the difference between the '92-95 and '96+ would be difficult, even if it isn't a legal change, they won't detect it visually and will definitely not detect it at the tailpipe. Why are you replacing yours anyway?
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Old 03-03-2011, 02:46 PM   #7
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Re: VX exhaust manifold unique

my 97 LX has the same set-up, and i believe you're correct that the EX does not.

the crack in my manifold has been patched, but it's still leaking. my thought was to buy an aftermarket one at some point, and sell my old one because the cat has value.
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Old 03-04-2011, 12:25 PM   #8
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Re: VX exhaust manifold unique

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If you're concerned about things not bolting up properly, going with a '96+ catalytic/maniverter from a DX civic will in fact bolt on and should output lower emissions. I plan to call the BAR (Bureau of Automotive Repair for California) and ask them if using a newer catalytic converter/exhaust manifold would pass smog or not. Considering that the design of the maniverter shouldn't have changed and identifying the difference between the '92-95 and '96+ would be difficult, even if it isn't a legal change, they won't detect it visually and will definitely not detect it at the tailpipe. Why are you replacing yours anyway?
The car sat for two years and rusted alot. I had the cat and manifold off the car for those two years but the car is still 19 years old with 220,000 on her. I just bought a brand new stock style exhaust system for her and I'm worried about the cat flaking off in the system and ruining the resonator and muffler. Looks like I may have to wait a few more months though.

I just am wondering if the 96 cat will yield the exact same results as m 92 VX. I know they blot right up, but I'm more converned with backpressure, o2 readings and MPG. I know they are very very similiar, but will they yield the exact same results?
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Old 03-04-2011, 12:28 PM   #9
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Re: VX exhaust manifold unique

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The car sat for two years and rusted alot. I had the cat and manifold off the car for those two years but the car is still 19 years old with 220,000 on her. I just bought a brand new stock style exhaust system for her and I'm worried about the cat flaking off in the system and ruining the resonator and muffler. Looks like I may have to wait a few more months though.

I just am wondering if the 96 cat will yield the exact same results as m 92 VX. I know they blot right up, but I'm more converned with backpressure, o2 readings and MPG. I know they are very very similiar, but will they yield the exact same results?
I wouldn't worry about that too much. Considering the age of the vehicle, I'd say you have other issues to worry about. If your car is rusted a lot, then you need to make sure you get rid of the rust on the manifold because the o2 sensor uses the manifold as a ground and a rusted manifold = weak or no signal.
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Old 03-04-2011, 06:55 PM   #10
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Re: VX exhaust manifold unique

This got me thinking imz, I'll probably need to pull the shield away to access the manifold, but I remembered seeing rust around where it's exposed at the LAF on my vehicle.
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