Just Curious --- When installing a performance tune into a modified vette, is there a "one and only" set of readings that need to be matched up or adjusted to --- or is there a lot of subjectivity in set points?

If there is, how much of a HP variation is likely to be seen in moving from a "conservative tune" to one that is much closer to the edge (of what is acceptable w/o introducing risk to engine operation)?

 

Many variables and ranges of variables. All based on what has been done to the engine, how and where you drive it, etc. Most tune to get the most out of their particular set up. A professional tuner could better answer your questions, their are also some good books and classes on the subject.

 

If you only want to get maximum HP, its actually pretty simple. You set the fueling to achieve the target A/F ratio (about 12.7) at WOT and ignition advance timing. You use a wide band O2 sensor to monitor A/R ratio and watch for knock retard so you can decrease advance at those points.

However, to get the best idle, start up, drivability, MPG, and transient behavior under a variety of conditions, that's where a tuners earn their money.

Go to HP Tuners forum. It took me a month after I got the software before I even tried to change anything. There are so many settings and no two tuners would come up with the same settings. Lots of really fine settings for various conditions.

Let me put it to you this way, say you want to remodel your house. Take down a few walls, add some lights, plumbing, etc. Sounds easy until you actually try to do it.

 

Thanks for the info. I was just thinking back to the old days when we could dial in more advance and lean out the engine to build more HP. The trade-off was increased potential for burned pistons or valves if we went too far.

I suspect the same thing can happen here too --- I was just curious as to what the range of variation was within setting up the tune biased toward the rich side vs setting it up biased toward the lean side.

 

The LS likes to run rich. Lean is a no no.

 

The factory PCM set up on my 2005 LS2 is to command at WOT 13.0:1 below 1750, dropping to 11.9:1 at 5000 rpm then leaning out to 12.2:1 up to red line. I looked up other people's tunes on HP Tuners website and they are all over the place and depending if the car has any power adders such as turbo or supercharger. One of the reference books says the ideal a/f ratio for max power is about 13.2 but that varies by engine and mods. My car is NA so I set my car in the range of 12.5 to 12.7 to be on the safe side.

The primary reason the factory makes the a/f rich in WOT is to keep exhaust gas temps and the cats within the temperature range where they will last. If the factory tune also senses when the cats are get to hot then adds up to another 21% more fuel to cool them down. This can be adjusted or turned off.

As for ignition advance, the factory was again conservative with about 20-21 degrees advance at WOT. I increased mine to about 26 degrees but during a recent dyno test, going from 26 to 28 degrees advance only resulting in about 3 more RWHP.

However, I am currently running 30 - 45 degrees which is an increase of 8 - 12 degrees in the 1600-1800 rpm cells where I am cruising on the highway in 6th gear between 65-75 mph. This really helped increase highway fuel economy to over 28 mpg.

The ignition advance is on a big table by every 200 rpm and every .04 of cylinder air mass which similar to vacuum in the old days. This is amazing considering the power the engine can deliver. How much advance your engine can tolerate in this rpm range depends on heads, cam, and other factors.

There are actually two main spark tables...one for high octane and one for low octane. If the PCM senses knock, it look at the low octane table and depending on how often and bad the knock is, it will recalculate the ignition advance between the two tables. Pretty sophisticated.

 

Correct. I had a conservative tune safely on the rich side (11.9-12.2)and then went to a more aggresive tune biased toward the lean (12.6)and picked up .25 in ET over the conservative tune. That's quite a bit.

 

Honda question: 92 honda accord jump time 180 degrees after tune up yn what can i do 2 fix well first thing to do then is to put the crank om top.

 

 

You gotta be kidding. These cars make peak power around 13.1:1 AFR.

 

Oh hell, what do I know! Must of been thinking with the factory tune.