Transient Fuel

[mikeyv]

I have a 2000 LS1 Camaro and I'm running OLMAF. I've finally got my ve and maf tables down. The car runs awesome. The next thing I want to accomplish is my transient fuelling issue. When I cruise along then hit the gas it goes lean for a second like up into the 16 afr range then back to stoich. When I let off the gas it goes rich then back to stoich. I've read some stickies about transient fuelling but i'm just not sure what exactly i'm supposed to change and in which direction I should change them. Fuel to wall impact factor-increase or decrease? Fuel wall boiling time-increase or decrease? Can anyone shed some light on this subject in lamens terms. I couldn't quite grasped the concept of the stickies that I read about this subject. I guessing the main ones that need to be changed are-
Fuel to wall impact factor vs. ECT vs. Map
Impact factor gain vs. airflow
Fuel boiling time vs. ECT vs Map
Thanks in advance for any help or suggestions. Mike

[EC_Tune]

Start with impact factor and only adjust the MAP line that you hit when you transition. Say going from 50 to 80 Kpa - only adjust the 80 Kpa line.

The boiling time really shouldn't be changed because you aren't affecting the boiling time of the fuel only the amount of fuel.

[WS6FirebirdTA00]

what injectors do you have?

[mikeyv]

How much do I start adjusting it by? Increase or decrease by .010? Or more?
My injectors are stock.

[WS6FirebirdTA00]

weird, never really seen issues like that with the stock injectors, mainly with larger injectors.

[EC_Tune]

^^^ I agree with Mike, not normal with stock injectors unless the heads are extensively modified or you have a significant cam change - which at that point you need larger injectors anyway.

[mikeyv]

I've got ported LS1 heads and a 226/230 .575/.595 112+4 cam and I was told that the stock injectors should be sufficient enough. I just figured that my issue had to do with transient fueling. If I let off the gas it goes lean then comes back down. I stab the gas it goes rich then comes back to stoich. Can you give me any other suggestions on what to change besides the injectors? EC Tune suggested to start with the impact factor but by how much should I change it? Increase or decrease? Thanks for any help guys. Mike

[WS6FirebirdTA00]

That is BS, all these shops try to say they do all this on stock injectors. I tuned a bolt on car the other day that was at 82% DC and it was hot as hell out. I also did an F13 cam only car with stock injectors that was running over 100%. Post a log of this and your tune.

[mikeyv]

I'll post a log and tune as soon as I get back in town. What should be a decent DC%?

[WS6FirebirdTA00]

less than 80%

[EC_Tune]

Yeah I just tuned a 224/228 cam that was in the 90% DC area. I think Mike is definitely correct, you need some red top 30's at a minimum. Maybe jump up to the green top 42's or lucas 42's.

[WS6FirebirdTA00]

Also, as you get closer to the 100% DC you will lose control of the injector. This is the reason to keep the duty cycles under 80% so you do not approach this range. I will have to find the article on this and post it, it was quite interesting.

[mikeyv]

I've got a newb question. I was going to try and log for duty cycle but I could not find it under the pids, could you point out where I can find it. I thought it would be under the fuel system pids but to no avail. Thanks. Mike

[WS6FirebirdTA00]

under user defined I think