Which Cats clog first?

[Jeff Williams]

After a lot of thought and testing, I believe the cats on Lola are what is causing the reduced power.

I am in the process of ordering all the Magnaflow components for a complete new exhaust system, including cats, and wanted to know if I should worry about the pre cats.

Has anybody seen plugged pre cats, or is it the main cats that get plugged? I think 11 years of California gas, and heavy city traffic did it's toll on the cats.

I am going with the following:

Magnaflow part # 94005 unviersan 2.25" catsMagnaflow part # 10415 4" round resonatorsMagnaflow part # 11385 5" x 8" oval dual in/dual out mufflerMagnaflow part # 35121 7" polished SS tips

The x-pipe will either be a Magnaflow part, or one built by the muffler shop. The rest of the system will either be mandrel bent ss pipes, unless the shop I use doesn't have a mandrel bender. The mandrel bends really don't help that much, in my opinion. They just look better. The system will be completely 2.25" from the down pipes to the tips. I am not looking for a much louder system, just a lighter one with a deeper idle tone.

Even if the exhaust doesn't help the car breathe better, it should sound better, and the tips will definitely look better.

[elwesso]

The pre-cats tend to clog frist especially on the 94s...

[Jeff Williams]

Wes, Are your pre cats punched, or are you using JDM exhaust manifolds? I thought I heard that you had no cats on your car.

Living in Alabama, I think I can do without the pre cats. There are no state inspections, but no commercial business will remove the cats, and won't work on a car that has the cats removed. That is why I was going back with a little bit larger cat, and thinking about removing the pre cat.

I have punched out cats before, and they always give a raspy tone to the exhaust aftwards. You can hear the exhaust almost pinging in the empty chamber.

Hey Dennis, does T3 have any JDM manifolds laying around? Will they work on my LHD Q with the HICAS plumbing?

I do need to replace the O2 sensors. I bet it will be much easier to do it off the car.

I am not that environmentally friendly, I work for an airconditioning business. I own a gas powered lawn mower and weed eater.

[elwesso]

the JDM manifolds actually may be MORE restrictive than the US manifolds with punched precats... Theres still that same bottleneck..

Yeah I punched my pre cats..... considering how much work it is to get hte manifolds out, the precat punching is really good...... It made it kinda raspy, only thing i didnt like was the fact that it kinda makes more noise under the car, instead of behind the car.

[Jeff Williams]

I bet some header wrap would reduce the "under the car" noise some.

I guess, when I get all the parts in, and have the muffler shop selected, I will just punch out the cats before I take it to them. If you could slide a small piece of straight pipe up to fill the void in the precats, it would help with the raspyness. Or, if you could gain access, just weld a straight pipe in it's place.

[Jeff Williams]

Here's a shot of the other side:

[mattd1979]

I have weak power too on my car and was wondering if you also gain power as soon as you hit 5000rpms. Let me know as Q45 tech thinks that my cats may be plugged. Look at my thread:

zerothread?id=168553

in Infintiti online mechanic. It is titled "Q45tech-interprit these consult results" towards the top. You can also cut and paste the link I just gave in your address bar.

[Q45tech]

I never think anything without accurate measurements of systems.

Yet to see data?

[Jeff Williams]

Lola (black Q) seems to have good power over say 4,000 RPM. She runs better when cold, than after heated up too.

I have the NICO ECU, and have felt an improvement in power and acceleration.

I don't think they are completely clogged, just very restrictive, and possibly got somewhat melted when Tony got the car hot.

He had a waterpump failure on a cold morning, and the car ran hot. When I got the car, it was down on power. I had T3 replace the KS, and Byron do a once over on it. Dennis drove it and ran a consult on it. It was much better, but still not as hot as Layla (silver Q) was.

[Jeff Williams]

I never think anything without accurate measurements of systems.

Yet to see data?

You drove her last April, when I had the KS replaced. Your data showed that the temp never really got warm. I have flushed the sytem, replaced the hoses, belts, and thermostat. The advance was not as great as it could be, but was tolerable. Your comment after you drove it was, "Eh, it's a 94" I believe.

This thread may be better suited in the general forum. I was just wondering if the cats clogged up, would the pre cats be the first to go, or the main cats.

I will be making my own assumptions as to what is wrong with the car, if there is anything wrong. She will still hold her own against a Mustang, if I wanted to race, and I typically don't.

I am replacing the exhaust, and wanted to know if I should do anything about the pre cats.

I have decided to drill them out before I have the exhaust replaced. I am getting Magnaflow cats to replace the main cats, so I will be legal, if not as INFINITI originally intended .

[elwesso]

Tech was replying to Matt's question/post...

When you do the exhaust you should put flanges in there so you can take the cats out and replace with a test pipe.

[Q451990]

I have "heard" of the pre-cats melting... from what I have seen you'll know it when you look in there. Should be easy enough to gut the honeycomb stuff with a pipe or ratchet extension. The raspy noise is probably only noticeable during warm-up.

Good luck!

Heath

[mattd1979]

My precat backpressure gauge arrived this evening so I will try to see if I can get the o2 sensors out tomorrow to get some readings for you so you will have some results. I have just replaced the sparkplugs which were the hot ones and I put in the medium temp plugs. It still has pinging but the time at which it comes in now has been moved up to around 6500 instead of 6000 RPMs as before.

[elwesso]

I have "heard" of the pre-cats melting... from what I have seen you'll know it when you look in there. Should be easy enough to gut the honeycomb stuff with a pipe or ratchet extension. The raspy noise is probably only noticeable during warm-up.

Good luck!

Heath

I notice mine a lot of the time...

It was kinda fun to bust the precats to bits

[Jeff Williams]

I just got the shipment notification on my new cats, resonators, rear muffler, and SS Tips. I went with all 2.25", since I won't be forcing air in the engine via super or turbo means any time soon. It should sound rather nicely. I went with round resonators, to give a little more sound, and the rear dual in/dual out is a little smaller and an x-design that should be nice and throaty. Now I need either the x-pipe or a new H-pipe. I may clamp in an h-pipe first, to see if I get any popping on deceleration, then change to the x-pipe.

I will have to get me another Q or an M before I go too wild on Lola. The Cali Customs and adjustable rods are next.