Okay, here's my problem. Last year I built a 355 in my '95 C4. I took it to a local dyno tuning company in Lake Norman, NC. They tuned it and it was never right... it was waaaay too rich.

A little background on the motor first.

355cu. in.
58mm throttle body
30 lb injectors
shorty headers
.535 lift cam
low 300 duration
2800 converter
355 gears
Gutted cats
Borla mufflers

Okay, since we have emissions in NC, I decided to take it to get a Hydrocarbon reading. Legal passing is 220 ppm. Mine was at 4900.

I took the car to More's Performance and they retuned the computer on the dyno. It was better, it was at 1700 but still waaaay too much. The car would load up and bog, if you started the car with the ac on, it may fall flat on it's face.... not good at all.

I took the car back and they retuned it again, it's down to 1100ppm... again, much better but they also turned the idle up to 1200 rpm's in neutral. (Waaaay too much) The Hydrocarbons probably dropped in part just because of the increase in the idle.

I'm told that without installing cats again, I won't be able to pass emissions.

My question is, with all the people on here that have gutted cats and built motors, are they not passing emissions? Is there something I'm missing? How is everyone else doing it?

Do cats make that much difference?

Thanks,

Mark

 

You will need cats, no way to get around it in your situation. I run without cats because AZ uses the OBD-II emissions test. Which means all 96+ cars emissions tests only consists of hooking up the computer to make sure there are no codes...no sniffer test. I had my computer reprogrammed so that the rear O2 sensors, which no longer exist, always read good...so no codes. If you really want to run with no cats, have 2 sets of extension pipes made, one with cats and bolt them in when you need to pass emissions, and one set without cats...bolt those in when you pass emissions. That is what I was going to do until AZ changed their testing.

 

Based on what you quoted for advertised duration, I'd say it's because of the cam. What's the duration at .050"? What's your idle speed? If it's near stock, reprogramming it to 900rpm will help a little.

 

In NC, we too will be switching to the OBDII setup. Since my car is a '95, it will be a safety inspection only. (starting in 2006) The car right now does not through out any codes. I don't need the cats for inspection right now.

The computer is programmed to idle in neutral with the ac on at around 1100-1200 rpms... (waaay too high, IMO)

If the car is going to be OBDII inspected, I guess it doesn't matter what the hydrocarbons are but the thing runs so damn rich, it'll water your eyes.

Mark

 

BTW, I'll post the lift and duration exact specs tomorrow.

 

I think putting cats back on it will probably help quite a bit!

 

'95 is OBD I, it simply has the OBD II style connector. 1996 was the first year for OBD II.

 

No way to pass a sniffer test without cats.

 

Many DO pass without cats. I'm thinking you have too much cam for that, with your car. One problem with just slapping on cats, is they likely won't last long, running that rich. A rich mixture povides a high CO reading. HC is unburned fuel. How does the CO look? This is an idle test? Do you have a 2500 rpm or higher speed test, also? What do those numbers look like?

RACE ON!!!

 

If you have an adjustable fuel pressure regulator, you can turn down the pressure and that should help lean it out some.

 

I don't have the numbers in front of me but everything is out of whack. CO, CO2, HC's... They're all tooo much.

I've got the fuel pressure set in the 30's. Off the top of my head, I can't remember exact numbers but I guess it could be set a little less but it is where it's suppose to be.

I guess my question to everyone is simple. Surely everyone that is running a larger cam, heads, injectors, etc, etc. can't be running so rich it bogs or makes your eyes water. Even if I put the cats back on, it doesn't lean out the system, does it just absorb the extra fuel???

Thanks again,

Mark

 

No, it should not be running so rich that it burns your eyes. If you put cats on there and it's running that rich you'll probably still fail emissions and ruin the cats in no time.

What you need to do is get the tune very close to right so that it's not burning your eyes so badly, then get some cats and then finish tuning it. Any halfway decent emissions test is not going to pass with no cats. Sure there are people who claim to do it but believe me these are not strict tests by any sense of the imagination.

 

Nathan,

I may have exagerated a little, it doesn't burn your eyes but you can DEFINITELY tell it's too rich.

As far as "getting the tune to very close to right", I have been leaving that in the hands of the dyno tuners. I'm assuming that they're tuning it based on the air/fuel mixture numbers they're getting. Supposedly, it's correct.

Thanks,

Mark

 

Do you have a copy of the dyno chart? Usually they will have the AFR on there with it if they are tuning it using a Wideband O2 setup. If not, it might be worth it to find a dyno shop that has a wideband O2 setup and pay the $75 to have a dyno done on it and find out what the AFR is. If you can smell it like you say, it's probably < 10:1 I would think.