DYNO timing and PE

[STR8BALLN]

I have been doing a lot engine dynoing and R&D lately for a project. One thing I noticed was when we dyno tested engines with a carb, the timing was fixed. Actually on most of the motors, the distributor was locked out. So then we started testing the EFI setups(tuned with HP) and I noticed the timing maps had the timing lowered around peak torque and ramped back up for peak hp. As well, they fatten the PE around peak torque and then leaned it back out. One thing I noticed was that on some setups we saw a dip occur around 3500-4k rpm as well some lost power(could be the way the test was loaded). Then changed the timing to a set timing and PE accross the map at WOT and the dip went away. Maybe its just this test engine because it seemed to like a set timing at WOT and not a ramping in/out timing or PE.

So it go me to thinking, is the pulling of the timing around peak torque more of a function of controlling potential pinging at higher rpm? Or is it an actual technique to make more power?

Curious to see what some of you have found over the years.

[04silverado6.0]

It is more for preventing detontation. I do find on a chassis dyno that when adding advance at peak torque it quits making power earlier than the area below and above peak tq. More cylinder pressure=less advance needed to make mbt. Whatever you have for advance at peak tq try adding another degree or 2 out at the top end when torque is falling off.

[Fast4.7]

Rich PE is more to kill oxygen to the catalytic converters to prevent them from melting. The timing dip around peak torque is for detonation control with the stock cam and intake manifolds cylinder pressure in that RPM range. Most of these engines were tuned to run on 87 and sacrifices in power and efficiency were made to run the crappy octane fuel.

[04silverado6.0]

Not only have i seen more timing or equal timing at peak torque not gain on the dyno but the track times do show a difference with the dip. My truck was quite a bit faster verified by dragy and backed up by time slips with a timing dip vs setting it to 25* flat at wot. The dyno proved the street tuning as well as the dragy runs, went back over on the dyno and ended up with the same exact curve.

[Alvin]

I do what I call a sweep test on the dyno.

After the tune is fairly settled out. Add timing. If it picked up at say 4000 RPM and 6400RPM, add more there. If it didn't make a difference at 5000 put it back. Repeat. You usually will get a timing table that starts off with a healthy amount of timing, rolls back in the low 5000's and then ramps back up to even more timing at higher RPM.


I do the same thing with AFR/ Fueling.