Rogue_Ant

When we use a larger injector and then 'hide' (MAF) the extra air in order to get the correct A/F, how much does this throw off the ign timming?

Does the DME use the VAF for its ign timming tables or does it look more at the TPS?


Rogue

RKD in OKC

I have an aluminum flywheel without the second sensor so I can't check the timing values, but...

When I got the correct AFR with same as stock AFM/MAF voltages going to the DME I saw a 7 second decrease in 3rd gear full throttle run from 3000rpm to 6500 with 2 big dudes in the car.

The only difference in tuning was to tweak the fuel pressure and MAF voltage so I get the stock voltage range to the DME with the correct AFRs. My AFR's were the same throughout the rpm range for both runs. The only thing I know to attribute the difference in performance is that with the correct voltages the timing advancment is more accurate.

That was my experience with both Autothority and Lindsey chips.

Rogue_Ant

I'm worried that by hidding all the extra air, in order to get a decent AFR, that the ecu thinks there isn't as much load on the engine, and doesn't use an accurate timing value...


Rogue

hally

thats exactly what happens to your part throttle timing, it gets corrupted if the sensor voltage is not in sync with the on chip transfer function (which maps voltage to flow). So yeah running a MAF with AFM chips is an issue for your part throttle timing.

Idle and WOT timing is purely RPM based so these are not effected, only part throttle timing is load dependant.

Rogue_Ant

How do I get rid of this unwanted timing advance? And how pronounced is it, say with 55lbs injectors?


Rogue

toddk911

So is it likely that many MAF's are not providing the stock voltages to the DME?

So in getting readings you want to make sure you are at 4.7v at redline?

Rogue_Ant

My concern is during normal driving or heavy accel, but not WOT.
If we are telling the ECU that their is less air entering the engine then what really is, then the ECU is going to be more liberal with timing, possibly too much.


Rogue

testarossa_td

Where is fast951 when you need him....
This sounds like a good tech discussion.

fast951

This subject has been discussed many times, a search should help.

Rogue_Ant

Maybe I've searched the wrong topics.... perhaps a link?


Rogue

HIGHBOOST

Man this is interesting, I look forward to the advancements in this disc.!

Rogue_Ant

In this article (under 'caveman engine management') explains exactly what I'm asking about... Timing advancement because of 'hiding airflow'.

http://www.roadraceengineering.com/evo/scc-mrstg1.htm

There was also a very good read on SupraForums:

http://www.supraforums.com/forum/sho...light=piggy%2A


So do we suffer the same issues? Can I install 55lb injectors, a MAF & Piggyback, and not worry about unwanted timing advance? Or do I need a 'calibrated' chip to go with the injectors?


Rogue

hally

the best way to cater for larger injectors is to program the correct scaling factor into the FQS table. Four global fuel scaling settings can be programmed and selected between via the DME FQS switch.
Manipulation of the airflow signal with a piggyback then becomes purely a fine tuning exercise, rather than scaling + tuning with above mentioned part throttle timing issues.

Rogue_Ant

And this is only availible with an aftermarket chip correct?


Rogue

hally

The stock DME FQS settings are:
#0 -
#1 +3%
#2 -3%
#3 +6%
#4-7 as for#0-3 but with 2.7 degrees retard.

Aftermarket chips have more agressive timing and are typically setup for a 3 bar fpr, verses 2.5 bar on the stock chips.