Well I've just turned about 9500 miles on the Random Technology High Flow Cats and I have just started to smell more of the NOx (emissions) coming from my car. At first I thought I might have unintentionally slipped the clutch, as the smell is similar to burnt clutch. After further inspection I realized that my h/f cats have quit functioning "optimally". I'd be interested to see what the catalytic converter core looks like at this point.

Still no bad rasp (since the plenum install) and no negatives other than the emissions and slight odor. I wonder how much worse, if any, this will get? Hopefully the sound will remain EXACTLY the same, as I'm in love with my cars exhaust tone.

 

Neff,

I've had R/T's on for 3,000 miles. I believe I do have the "raspy" sound people speak of. I was very pleased with gains though and willing to live with sound. At 3,000 miles I had headers installed. During header installation we found one of the cats collapsed. I had heard or felt no indication of this when driving. We suspect collapse was due to running real rich with S/C installed, but no real way of knowing. I do not want to have to keep replacing them so I am going to replace with crawford cats next week. I will repoert back on any changes and compare the two.

I did not notice any odors like you mention, but you have 3X as many miles on yours.

~ KZ

04 G35c DP/Willow: Vortech S/C, R/T cats, Crawford v5 plenum, Stillen headers & exhaust, JWT clutch & flywheel, Eibach sways, grounding wires, misc. smaller items...(376HP/317TQ)

 

Neff,


Judging by your mods, you are probably running noticeably leaner than stock. This has two major repercussions: First, your EGT is higher than stock, producing more NOx. (which you are smelling) Second, due to the higher EGT (exhaust gas temperature), less carbon monoxide is present as a catalyst feed gas, which in turn reduces the converter efficiency substantially (at least the reducing catalyst portion)

The higher temps are actually better for the oxidizing catalysts, which store O2 for use when the a/f ratio goes higher than stoich. When you see the a/f ratio "dithering" on either side of stoichiometric, the cats are alternating efficiencies between the oxidizing and reducing catalysts.

It's my opinion that without adjusting your a/f ratio thru tuning or a SAFC-style device your problem will continue to worsen.

Just my $.02

Wayne

'04 G35X Graphite/graphite, NAV, wood, premium

"May you lead an interesting life..." -- Old Gypsy Curse

 

But w/o a pre-cat O2 sensor, how do we know what A/F ratio I should be at "nominally"? I really wonder how much I've deviated from stock since I've never seen a stock curve for A/F ratio which has been taken pre-cat. If I knew that data, I would buy a Crawford set of cats and have Doug pre-weld in a bung to do adequate testing. For this VERY reason, I am skeptical of what TS is doing with our ECU's...

Do you have (or can you locate) a dyno chart for a stock G35 coupe, model year 2004.5 or later, that shows an A/F graph in a known gear, that has been taken before the cats, that I could use for comparison purposes?

Also if I purchased an Apexi SAFC-II, how would I "tune it" w/o knowing how far off from stock I am actually running? I also bet I'm well below 14.7 or stoichometric... How far? I have no clue.

 

what does it mean to have a "cats collapse". Is the "filter" material is no longer viable?
Do the cats then become an inefficient test pipe?
Do you have to replace the entire cat or just the "filter"

 

In closed-loop operation (and a stock ECU), you should be normally be running just on the rich side of stoich. You will see dithering (jumping back and forth between very rich and very lean) as the ECU adjusts fuel delivery to maintain close to 14.7:1. I would opine that you are probably OK here.

In open-loop mode (wide open throttle and other heavy load conditions generally) is where you are probably leaned out a wee bit much. Adding or subtracting fuel in a couple of key areas could optimize your A/F without costing you too much HP. Some of the benefits would be reduced EGT, better cat performance, increased resistance to detonation, etc. Don't go too rich, or you end up with the opposite problem, outlined in the above post.

I don't have the dyno info, but will probably do my own 2004.5 A/F ratio testing soon, as I have finally found an AWD dyno not too far away.

As far as the tuning goes, do everything on a dyno if you can. The more variables you can control the better. I would shoot for 12.5:1 to 13:1 A/F ratio on a N/A car. One full point lower for a F/I car is a good starting point as well.

As far as TS goes, I think that they are doing an admirable job tuning by mail. As a former owner of a tuning company specializing in late-model GM cars, I personally know how difficult it is to tune "over the phone." The basics are the same, whether you are tuning 4 cyl Hondas or monster V8's....timing/load/fuel........ The main differences are that our cars have a lot less "left on the table" horsepower-wise, allowing for less dramatic improvements, and the drive-by-wire systems adding complexity.

Just my $.02

Wayne


'04 G35X Graphite/graphite, NAV, wood, premium

"May you lead an interesting life..." -- Old Gypsy Curse

 

I think you're smelling unburned hydrocarbons (UHC), not NOx.

I'll check it out Friday.

2004 G35C 6MT Black. Killer.

 

NOx, HC, CO... whatever... I can still smell it. If anyone has a post of a stock G35 coupe, 6MT that is a 2004.5 (new ECU) at the pre-cat location (I'd even settle for the tail pipe at this point) I'd love to see the A/F ratio... anyone?

...and DED, there are more important threads for you to be replying to, like... are you going to be joining us for poker this Friday night? [img]/w3timages/icons/smile.gif[/img]

 

You can't smell CO.

2004 G35C 6MT Black. Killer.

 

I always thought that oxides of nitrogen (NOx) and carbon monoxide (CO) were odorless gases. One can smell hydrocarbons (HC) when excessive amounts are present, such as during a lean misfire condition as well as when an engine is running overly rich.

*'03.5 MT6 Sedan, Premium, CB*
Z-tube, Pop-Charger, Coupe Mid-Pipe, Autovation pedals

*'00 Saleen S281-SC*
Mucho mods. See it here!

 

Well, this was my reasoning for going with the Crawfords, and I would recommend switching.

At this point (as far as TS ECU goes) I notice when Im driving in gear, there is no smell. When I hop out (even after a hard run) there is no smell. However, if I rev in neutral sitting there, all I smell is gas. I've been looking into the SAFC, but is tuning every 500 rpms really precise enough?

2003 Black 6MT
JWT/Z tube, UR pulley set, Crawford Headers, Cats and v5 Plenum, Injen SES, TS ECU Crawford tuned, JDM Pedals, JDM battery cover, G-tech RR.
More mods to come....stay tuned.

 

I've had mine collapse on me before (RT Cats @ 13000 miles) You'll definitely know when they go completely bad, you can stomp on the gas and the response will be minimal at best. Also the sound will be completely muffled like a complete blockage, the material inside the cat basically collapses and clogs it up.

 

Here's a bit of info on cats: http://www.autoshop101.com/forms/h64.pdf

And some on NOx: http://collections.ic.gc.ca/abnature...r_nitrogen.htm

The really smelly stuff is the Hydrogen sulfide (H2s) that is produced...nasty rotten egg smell.

If you have a rich condition, as headpaneer said, it is a strong odor as well. When it gets very bad, the fumes even sting the eyes. It's like taking a little whiff of nitro exhaust

Good luck, keep us posted.
Wayne

'04 G35X Graphite/graphite, NAV, wood, premium

"May you lead an interesting life..." -- Old Gypsy Curse

 

So basically, if the cats collapse, air flow is drastically restricted and the car is a slow pig. With the RT's I guess this condition is inevitable... So maybe I should just gut them and be done with it. I'm almost tempted to just throw on the stock cats and leave them on for a while.

FYI, the odor that I smelled has now disappeared. I'm not sure if it was something related to my new tires running on freshly poored asphalt, or if it was really my cats. (The tires had glue on them from a slew of Toyo stickers that I removed.) I'll keep an eye on things and report back.

 

Well since this thread will not die I thought I'd post another update.

The smell is gone and has been gone for a couple of weeks. I'm not sure what I was smelling, but fortunately everything is great again. Oh yeah, the cold weather is here and the cats and plenum are really waking up. I'm happy!!!