What would be the drawbacks to a 2.5 inch exaust minus cats?

[extremetoy1]

Putting together a Stainless 2.5" exaust(SP?) for a 95, are there any draw backs to omiting the cats? has anyone ran an FZJ 80 without cats and had any problems? In MO. we have no emissions tests after september-yeah I know Federal BLAH BLAH BLAH, whatever- So no need to waste your peter beaters typing to tell me how its wrong/and or illegal. Before I get flamed about how illegal it is, I dont really care (plus I am not in cali where the smog Natzis work)

 

[FJBen]

I would assume you would still run the O2 sensor? I know on the 95 and later there is one downstream O2 sensor that controls the mixture as well...maybe that could cause problems with it running correctly? maybe not...Thats the only thing I could think of.

 

[extremetoy1]

That may be an issue unless I get some feed back on methods around this or what signals it sends and how to modify or manipulate the signals.

 

[alkaline747trio]

'95 + you are pretty muched screwed. I think you are 48 state required to have cats (unless you can bend those rules), but you will definately have poor performance due to that downstream O2 sensor. I don't know if anyone has found a way around it on an LC yet, but I'm sure it's been done elsewhere. You'll be a pioneer for it, forsure.

 

[Erratic]

Are we positive the downstream 02 sensor controls mixture? I really have no idea, but i would think the first one would do that. There just would be a lot of variables for the computer to compensate for if it was trying to adjust fuel relative to what comes after the cats. Like efficiency of the cat at different temperatures etc. Just seems like it would be there for emissions purposes only. I bet with a chip there would be a way to change that. I know on some cars you can do that.

 

[extremetoy1]

I can see some benifits to an exaust without cats, Flow and heat reduction (those cats work on the premise of HEATING up to red hot inside and burning off leftovers), the second O2 sensor is where I am hung up on design right now.

I know the 1FZFE isnt a hot rod but all engines can be made to flow a bit better, along with other mods there can be some HP gained with a series of flow enhancing mods.... NO K&Ns! i am guessing after searching no one has had any of the intake or head extrude honed yet , but will be looking into these mods later after we work out an exaust.

 

[MaddBaggins]

A friend of mine with an OBDII Cherokee ran the after-cat O2 sensors farther down the line, rather than stock location. Now it still passes emissions and sends good readings back to the computer. He's a mechanic by trade and helps build and modify lots of offroad vehicles as a hobby after hours. He said by moving the sensor farther down the line it brought the reading back closer to what it should be. I believe it took some trial and error to find the sweet spot.

 

[alkaline747trio]

Madd, did he also remove the cats? I'm sure you posted because he did, but just making sure.

 

[IBCRUSN]

You could get a service manual and find out what the readings are supposed to be for the rear o2 sensor and design a dummy to install. There are dummy sensors marketed for OBDII Ford's and Chevy's, just check out Summit and Jeg's. Once you know what readings the ECU is looking for you fake it out.

 

[MaddBaggins]

Madd, did he also remove the cats? I'm sure you posted because he did, but just making sure.

Yup.
and on another note
I'm running 2.5" tube and my cats are for show only, but I don't have downstream sensors or OBDII. I pass emissions with flying colors BTW. visual and idle sniff test here in Tucson. They can't run fulltime 4wd rigs on the machine. For grins my buddy and I put my rig on the lift, gave the brakes a light pressure to simulate drag, plugged in the sniffer and ran it for a few minutes. I'm well under requirements, and far cleaner than many vehicles that pass emissions.

 

[fzj80kidpen]

From what I understand the first 02 sensor is for fuel/air ratio, timing etc and the second is only checking the sin wave or pulse of the exhaust to make sure the cat is doing is job. There are dumpy 02 sensors that can be bought that give a false feedback (as if a cat is there). I am no expert and have not done this myself but I have read about others doing it. Its been discussed here before many times.

 

[SUMOTOY]

xt:
According to my bosch catalog a 1995 doesn't have rear O2 sensors (except CA). Yes, you can delete the cats without a problem.

Install the 02's in the downpipe before the collector, so that you still have 2 bank control of the fuel system.

With the 1996 and later trucks (OBDII - 4 O2's) it can get trickier, but you can most likely still remove the cats, since long term fuel trim is +/-15%. On occasion for track only cars, I've had to put a diverter in front of the rear o2 to slow down the flow rate sample of the exhaust. I doubt you will see a performance increase deleting the cats, but you can do it. Remember heat = velocity, and dual cats (2.25L each) are going to be pretty efficient anyhow. Your gains should come from the cat back IMO, where some good high flow mufflers can give good gains.

Edit: xt, I show thru 12/94 build date as 2 O2's and 1/95> as 4 O2's. Do you have 2 or 4?


HTH

Scott Justusson

 

[DuManchu]

I could be wrong, but wouldn't increasing the exhaust diameter along with removing the cats reduce your low-end torque? True there might be more torque to be had, but I would think the factory setup is pretty darn good for making low-end torque.

At least that's how I was taught.

 

[bjowett]

The 1FZ would probably benefit everywhere in the powerband from a 2.5" system.

Manifold work...
https://forum.ih8mud.com/showthread.php?t=61295

Cylinder head, basic port job
https://forum.ih8mud.com/showthread.php?t=45593

 

[extremetoy1]

I could be wrong, but wouldn't increasing the exhaust diameter along with removing the cats reduce your low-end torque? True there might be more torque to be had, but I would think the factory setup is pretty darn good for making low-end torque.

At least that's how I was taught.

I dont beleive the 1FZFE would be hurt too much in the torque department.... more than enough when geared correctly.

I do realize that heat does make it move more quickly, I may use a heavier gauge SS to address this. I see some good coming from the CATS being gone as they generate so much heat- more that there are 2 of them.


Bjowett, are you supercharging the engine you are building?

I have followed your threads since you started, we are on the same page when it comes to fab wotk (I had an adapter made to hook up the tundra V8 and auto to a Rover LT231 for my 91 80) I realy dig your work so far and thumbs up to you for thinking outside the "bolt on" box.

I will post some pics this weekend of my 91 project and its beginings on my tundra v8 thread here.