I recently had to go in for smog testing after the latest round of mods....and the hydrocarbons were way too high! Crap!
But the guys there are really cool and pretest. They suggested decreasing the timing to help decrease the HC as it was probably the combustion chamber running too hot.
I've backed the timing way back for high load and wot already (arap) but haven't seen any tuning methods for the low load/rpm timing so I've left it alone except where it's hit a little knock retard.
Anyway-it worked! And it passed!
For example-it was at 23deg. at idle and I took it down to 15deg. No noticable change in power etc./ no bogs.
Has anyone used hc testing for tuning timing in this area? How else can you tune it there?
Thanks for all info!

 

If you really want to tune by gases, you need a min of a 4 gas analyser.

You probably maked one problem, with another.

That's why you need to ACCURATELY look at all the INFO available to you. ie being able to really read spark plugs.

Things like even plug gap differences show up when you really get into 4 gas analysers.

 

whats the compresion ratio on the engine. yes you can tune with gas readouts but its better to shoot for brake TQ. thats alot harder to qantify.also having optimal timing can actually drive up NOX2 output by creating a hotter combustion event. this is all very touchy and iffy ground. there is no prefect formula for achieving optimal tune that realy striaght forward. bascially it take alot of good info and some very smart educated geuss's sometimes. also look for a trend. IE one particualr parameter that reall affect HC. the engine might have been lean?? what was the BLM and INT ?? you gave some prety vague info and i think with more detialed info further discusion could prove to be more effective.

 

Tuning for emissions by tuning for best brake TQ.
Oh, OK.
Just out of curiousity, have you ever used a multi gas analyser?.

BTW, if attempting anything like you propose the NOX would be well out of any emission parameter.

 

Compression ratio is 10:1 and blms 128+/-4; and I realize that combustion chamber shape etc etc all play a part in what timing the engine wants.
I've tuned for cruise by the least throttle needed for that rpm/load/mph by using hwy mode spark, and also tuned at wot (f/a and spark-wide band and best perf-no knock and plugs look good.) and I'm satisfied with the results.
Looks like I'll be buying a 4 gas analyzer!
Are there any good resources on using/interpreting 4 gas; web sites or books?
Gm has to tune for emissions....and I have to pass smog testing...but now the "big" question-by tuning the low load/rpm timing using a 4 gas for best emissions- could that be considered "optimal timing"? Or at least a close enough compromise? Isn't that what GM does?
Thanks ya'll!

 

hmmm well if you have a dyno to work with and say a 5gas meter it not to bad. as for bringing down the NOX2 use the egr thats what its there for. getting the best overall TQ production is just the start. if the fuel is off it will affect optimum timing as well. but then agian so will piston shape, quench, combustion chamber size and shape,head gasket fire ring design and thickness, as well as overal size. in some cases dependning on chamber design the spark plug location can effect flame propogation and burn time. this seems only to be an issue with larger engines like bigblocks and hemi's. but even small block chevys can enjoy good lug location. its not the easiest thing in the world to say that a specific pattern of tunnign will net the best results but i like to work first from what i think the spark curve should be then bring in fuel. the go back to spark and go back to fuel rinse repeat numerous times. once this is done i use the egr to bring the nox2 back under control. then after all thats done if you did the job right the engine should sniff clean.

also is this particular vehicle say having a PCV system issue or maybe even and oil cunsumption problem form worn rings ? to many variables to even begin to say whats the best pattern. but if after the fuel is right hc and co are in check and the engien is making the best possiable power then worrying about nox2 is simple.just use egr to control it. also making the AF a bit rich will help drop the combustion temperature enough to bring it down as well.

yeah if you can meet emisions at say 50% throttle and under then you should be fine. does your state WOT test engies ??