Draco

HI guys,

Just came back from the dyno and I am trying to figure out why my N/A runs were so low.

I made 2 N/A runs back to back. First run gave 333 rwhp and 315rwtq. second run gave 327 rwhp and 304 rwtq.

I did these runs with the hood closed and my IATs reached 130*F prior to the runs and stayed around 150 at the end of the second pull. My AFR was a shocking 14.5-15, whereas I had measured it at 12.8 on the street in prior tuning (I guess having the car moving keeps the IATs down). BTW I have a wideband sensor in my x-pipe which is accurate to do this logging.

I did a third and fourth run on nitrous after these 2, and when looking at the results, my TQ curve before the nitrous kicked in (at 3600 rpm) was 40 rwtq higher then the previous N/A pull. The AFR was at the expected 12.8 - the only difference was that we opened the hood and the IATs dropped to about 90F. I compared the MAF measurements at certain RPM's between the nitrous runs and the N/A runs, and at ALL POINTS IN TIME, before and after nitrous activated, the N/A runs were measuring less air at a given RPM then the nitrous runs (prior to activation). The two N/A runs were pretty close in terms of air measured to each other.

My question/theory is: Could this high IAT have caused the MAF to measure less air, thereby providing less fuel and resulting in the lean condition I saw in the first 2 runs? I think this is possible since the MAF bases its reading on the temperature of the wires as air passes - hot air will naturally not lower the temp as much as cold air.... Please let me know what you think and let me know if my thinking is wrong.

Cheers,

Craig

samz28

could be your maf is crusty, but say if the car was running in speed density mode, it would weigh heavily the fact that high IAT requires alot less gas, since the speed density law weighs temps so much, higher iat naturally less air molecules.

same reason a dry kit results in a **** load more fuel.

Draco

I thought the dry kit triggered extra fuel by cooling the MAF more then normal to trick it to think that more air is entering the engine?

samz28

sure, but you dont think the IAT notices the frigidity in the lid too? you can set like -40C and colder to pull timin with edit, obviously if it got to -40c in georgia, hell would have froze over..

Draco

Agreed, but I thought the IAT sensor would only affect timing when running a MAF system...

samz28

I dunno. Why is there a PE VS TEMP fuel table in (hptuners/edit)?

I'm guessing TEMP = IAT , but it could be PE VS ECT?

i dunno haven't figured that one out yet..

It would make sense if IAT is cooler then add more fuel, since air density is higher. I could be wrong.

I was just looking at edit&hptuners and both have this table, my expertise however can't say if its ECT or IAT. One would think IAT since folks do tune cars mafless.

jimmyblue

iTrader: (11)

There are PE tables that push/pull based on ECT and IAT.
On my stock PCM tune files the IAT shows a table full of
0.000s and the ECT adds a little fuel above 212F. The
spark IAT table is a busier little actor, spark starts to be
pulled out at IATs as low as 98F (depending on CylAir
charge).