Commanded versus Actual a/f ratio..sort of long

[cobramanphil]

Funny how things work out sometimes. You do your best to make sure everything is done correctly (forged everything, clearances checked, no shortcuts done, making sure there is enough fuel and the correct amount of spark) and then BOOM...no compresssion in two cylinders You forget one little item and all goes to crapola

Not me, of course, but a buddy of mine somehow grenaded his brand new 331 (I personally put the heads, cam, and rear griggs stuff on this car and sold the idea of using a tweecerRT to get his car up and running). A call this morning...."dude..can you get me a tow..I just blew my motor". I get his car towed to my house and see the carnage (flame on pistons..busted valves....headgaskets..what headgaskets..they were melted on 5 and 6 Anyway buddy goes up and down and tells me he had it tuned "rich" with not a lot of timing...looked at this tune files and I see 11.5-11.9's across the board with max initial timing somewhere around 20 degrees. My first comment was...."well that was what your commanding to try to reach, but what was actual? He says, "Actual? What do you mean actual? All I tell him was you were tuning with blinds on...how did you make sure that was your actual a/f ratio?

I've searched and I did not get any hits, but what is everyone's variations on what is commanded on your a/f ratios (tweecer) versus what registers on your wideband (assuming your wideband is accurate and calibrated correctly)? I sort of just want to make it a point to new self tuners that what is commanded in your aftermarket tuning device is not what you should really go by when looking for the optimal a/f ratio (especially important on your blown or turbo motor). Looking at my w/b readings I am about .4+(-) commanded versus actual on the fuel tables.

I would work for leaning/richening the maf transfer, but for those who are stuck on the tables this should be a really important issue.

So anyway...thoughts...opinions.....

 

[Stanger007]

There are a lot of variables to cause the AFR ratio to be off -- on a N/A car you would have to be a LONG way off to cause the damage it sounds like he had!

What do you mean by max initial - is that at the dizzy? I've found you have to watch the adders -- especially the adder that comes in when things are rich... it'll dump the spark in.

I think the biggest area most guys are off is their injector settings. The MAF transfers are normally very close -- especially when you have a flowsheet to go off of.

My AFR was about .5pt rich. After I got it all setup, my AFR varies +- about .2 at WOT. Cruise is extremely close. I didn't even have to touch the MAF transfer I had except in the WOT areas once I got the injectors dialed up properly.

Wes

 

[blksn955.o]

While in WOT you use a W/B to see were your at in relation to your commanded A/F. You then work with the maftransfer and other fuel related items to get that commanded A/F to match your Wideband.

Just because you commanded a specific A/F in the tables without running that up against a Wideband you have no clue were your at or how much to change in order to reach that commanded A/F.


Also the MAF may be the issue in itself...if he is boosted and peged the maf he will go lean no matter what he is commanding. Add a level of spark to that and yes its going to blow up.

How did he have the spark tables setup?

What was his total timing?

What was he doing about taking timing out for boost?

 

[final5-0]

Honestly

When talking about Open Loop or WOT tuning .....

With larger inj's and depending upon how the meter is setup

You could be W A Y off

Your fuel tables could be off
and
Your meters curve could be off

and since a blower is involved ... things could be Way Way off

If using a Cobra file ... you got the fuel dump starting at 90mph

Lambse don't really mean a whole lot ... some of the time

This is just one of those areas ... you gotta be careful with :Word:

Most of the other stuff is quite forgiving if you ask me

It is a real challenge for a noob to get his feet wet in self tuning
with a forced combo

I'd watch him very closely and make small changes when you guys
get it all back together

Remember ... Start off with this little mantra

Little Spark ... Big Fuel

I like to do up the Closed Loop tune first and stick with it until it
shows to be stable.

Then ... start the WOT tune process.

I work with the fuel tables and upper portion of the maf curve to
obtain best results verified by a wide band. When doing
this WOT tuning you want to have your spark dialed back
a good bit :Word:

I agree with the stuff Greg and Wes said above

Grady

 

[cobramanphil]

We swapped in his old stock motor last night (upper intakes and fuel lines/rails have to be put back on though) and I have INFORMED him that I would do a tune for him with my wideband in hand. My buddy (Rick) didn't seem to have a problem with it as the visuals of the carnage pretty much has him numb

And can you believe it he has never even taken a peek at the the eectuning.org site

I told him that he must love living dangerously and russian roulette must be one of his favorite games

I didn't have much time to pull his tune and review it, but just a quick glance and I see that he had his max timing somewhere around 19-20 at the timing tables, but his fuel (although richened) was set in the mid 12s (I don't think that would be rich enough for his amount of boost -10-13psi). I would of checked his dizzy to see if he was at stock 10, but I don't think it matters at this point I asked him about it, but all he would do was and (I am talking numb)! I would be numb too, but he is one of those ex-dot.comers so money seems to grow in his backyard (he is already sourcing a dart block and wants something similar to my car). I guess I would be numb too, but I am just pissed that all the work I did on his motor has gone to crap (I think his passenger side head can be welded and repaired though).

I told him I am not going to help him with his new motor until he gets the tuning down with his stock motor

 

[Stanger007]

I'm hitting about 13.5lb of boost, running 19 total spark (10* base) and 11.7:1. Works great, takes a beating and a WOT runs almost every day.

Wes