Need some tuning advice (boost vs. timing)

[edhead81]

I'm finally putting my car on a dyno Saturday and tuning it. However, I foresee a problem. I'm afraid my IDCs may be too high at redline. I haven't been able to do a run to redline at WOT yet (lack of suitable roads, cops) but the logger is reading 85% IDC at 5800rpm. The fuel system is total stock and I'm running at 12psi and I have DSM intercoolers, intake, and downpipe so I'm certainly flowing more than stock. I'm pretty sure I'm running a bit rich (stock tune) and leaning the mix should buy me some headroom with the IDCs. So, if my IDCs are over 90% at redline at 12psi running 11.5:1 AFR on 93 pump, would it be better to drop boost to 10psi and bump up base timing from 5 to 7 degrees assuming no knock is occuring?

[spfan]

which logger are you using? when i was on stock fuel setup and running 14psi, my mmcd palm logger, and my shiver's palm logger would both record well over 100% duty cycles. it has to do with it being an estimated duty cycle. not an actual. assumptions are made in the program, and they get the numbers close, but not exact. for example, i've seen 120% + and not hit fuel cut on both of those loggers. shiver's seemed to be a little more accurate than the mmcd for what it's worth.

[DoctorDex]

Higher IDC's can be good. IDC's of over 90% means that the ECU is pulling timing up top, which is what you want if you are running more boost.

[Bret Brinkmann]

Originally Posted by edhead81

...So, if my IDCs are over 90% at redline at 12psi running 11.5:1 AFR on 93 pump, would it be better to drop boost to 10psi and bump up base timing from 5 to 7 degrees assuming no knock is occuring?

That is a good question. There is only one way to find out. These cars like timing, but what turbos you have will make a hugh difference also. 10 psi on the 9bs is not the same as 10 psi on Evo 16gs. A better question would be how much timing advance will give me the same horsepower as a boost increase with these turbos.

I have heard of IDCs higher than 100% also with no problems. I used to worry about IDCs but if your injectors go static, screwy things will happen and you'll know it. If you go lean up top and fuel pressure drops when you try to add more fuel, then your pump is maxed or you have a restriction to fuel flow (like the lines are too small or a clogged fuel filter). If you go lean without a fuel pressure drop and can't richen it up by increasing duty cycle, then the injectors are maxed out.