Thought I'd post up my tuning experience... as I had some good results and I know some of you are a little hesitant to try emissions testing with a larger cammed car.

Car specs:
383 Stroked
AFR 210 Heads
Cam - 226/234 @ .050 (Lloyd Elliot Custom Grind)
2 Bullet cats

Car is somewhat lumpy but not too crazy (between a cc305 and cc306). I wasn't sure if it would pass.

I filled up with 91 Octane gas with no other additives and took a nice little drive before getting to the testing station.

4 simple things in the tune:
- increase idle to 50rpm below the maximum allowed
- dropped idle timing 6-7 degrees
- lowered the overall timing tables 4 degrees (it was easier than doing one by one)
- increased fan temp back to stock values

My results were as good as a stock Camaro, and far off what I was expecting.

Here are the results:

.......Idle...........2500rpm drive
.......Limit/Result...Limit/Result
HC......300/22.........242/12
CO%...1.50/0.06......1.92/0.41
NO........N/A...........2520/89

 

Wow thats impressive
What's the cam LSA?

 

226/234 .565/.565 111 lsa

 

Did lowering the timing make the engine run smoother or hotter?

 

It will run cooler. But there is a balance of course. For emissions... less Spark, the better.

 

I'm guessing for low rpm, igniting the mixture closer to TDC (when it's more compressed and volatile) the more complete the burn, as opposed to alot of idle spark advance.

I had my car hooked to an emissions machine at school once and also noticed Much better idle emissions at like 5 degrees spark advance when compared to 15-20 or whatever stock is.

 

Could you please provide a bit more details on your setup. I have a smaller LE cam and all the emission connected and not getting anywhere your numbers.

What injectors?
Compression?
Type of cats? metal or ceramic substrate?
What "is" your timing at idle to pass emissions?

Thanks!!

 

Injectors: Injectors have nothing to do with it. You just need to tune for the size you have.

Compression: 11.5/1

Cats: Bullet style... pretty sure they are ceramic. But if they are working, either would do. If your numbers are crazy high and the car is running right... may be something to look in to.

Idle Timing: 17-19 degress on the computer. A few higher on the scanner (the computer adds a few degrees)