Skele4door

iTrader: (1)

I'm finally buttoning up my LS1 powered 1993 RX7 and wanted to see if anyone had suggestions on tuning for emissions without cats. It will be tested in Texas, so it will need to pass a visual (shouldn't be a problem) and a roller sniffer. The car has a stock 98 longblock running with a 2002 harness/PCM and has no rear O2s, cats, EGR, or air injection and will be running speed density. All of my tuning is being done with HPTuners.

I've already read a lot of documentation about tuning for driveability and performance and have spent a few hours searching the forum. I just wanted to see if anyone had suggestions on passing a sniffer without a cat since I didn't see very much useful info. I believe I should make sure the car is nice and hot and I should shoot for running at exactly 14.7:1 during the test. Does anyone have any other suggestions such as gas (87, 93, E85), plug gaps, etc?

To register the car I've got to have an inspection, so I'm hoping to get it tuned well enough to pass the sniffer. After it is legal then I can spend time datalogging/tuning without having to worry about gettin pulled over for registration/inspection. Thanks in advance for any help.

danielgoforth

iTrader: (1)

I thought that Texas didn't have a sniffer test and only checked for codes. I don't see how you could possibly pass a sniffer without cats though.

Skele4door

iTrader: (1)

They would just check for codes if the chassis was an original OBDII car. Since it's a 93 it is tested with the applicable standards for the chassis.

dan@masportspeedshop

iTrader: (6)

I, too, would be surprised if the car passed a sniff test without cats. The catalytic converters burn up the unburned hydrocarbons in the exhaust. Tuning can get you close to ideal, but probably not close enough to fool an accurate 5-gas analyzer. Pray theirs is old and hasn't been calibrated/serviced in ages. Usually the test station will look for approximately 13-15% CO2 and 1-2% O2
content in the exhaust. Carbon monoxide (CO) and hydrocarbons (HC) are also typically measured and maximums vary depending on state regs. TX is clearly more relaxed than CA. If you have a nice lumpy cam installed and tuning to suit, say goodbye to the passing grade. Advanced ignition timing (needed on cammed engines) increases HC and NOx count, so with no converter, say goodnight. Best bet is to tune with a converter, then remove said piece when you're on the track.

turbolx

There are plenty of high-flow cat options out there that won't cost you any real power. I strongly suggest you get one if you want to clean up your emissions. It makes a huge difference.

Beyond that, you'll also need to make sure that the engine is running close to stoichiometric under normal conditions. This goes a long way toward minimizing the work left for the cat to do in cleaning up the engine's raw emissions. If you leave it running constantly rich or lean, you'll probably fail even with a decent catalyst.