99PHardtop

I was wondering if anyone could shed some light on eliminating the maf and using a 2bar pressure sensor in place of the 1bar. The ignition map looks like it needs the maf to look up the timing numbers.. am I missing something here?

Thanks

QuickSilver2002

Intresting Idea. So do you plan to use the Fuel/Air muliplier table and consider 100kpa=2bar (you would need to calibrate the two different map sensors and graph out an equation for each.)

All the timing tables seem to use gm/sec, but I'm assuming that this ends up being calculated from map in speed density mode. I would try logging some data in speed density mode and trying to figure out what cells it is picking. This should allow you to eventually derived some equations.

Has anyone tried this before?

y2khawk

iTrader: (5)

Why? Stock MAF'd cars a plenty capable of hitting over 600RWHP.

Trying to convert to a 2 BAR isn't worth it IMO.

99PHardtop

Don't take this the wrong way, but my supra makes 800RWHP, and if I am going through the trouble to add turbo's to my vette, it better hit 1000rwhp without to much trouble, or what's the point. With twin T66's on your firehawk, I can't believe you would be satisfied with 600hp.

I don't want to use the maf, I want to just use a pressure sensor and do the scaling seperately. The main question here is what will happen to the timing tables when the maf isn't hooked up?

Thanks

y2khawk

iTrader: (5)

I'm not settling for 600, just making a statement about what the PCM can handle. And FWIW, I'm already over 800 RWHP with mine on a real chassis dyno, and running 2 stock MAF's and a little box of my creation.

Good luck getting to 1000 RWHP, there's more to it than just swapping in a 2 BAR MAP. (consider a 3 BAR if your serious)

If you're really dead set on ditching the MAF, go with a FAST or DFI.

But simple answer, you pull the MAF and it will go to back up speed density. From there, the air load for the spark tables is the same.

ChrisB

There is a calculated gm/sec PID that the computer will use in speed density mode - so the table will still be scaled the same way, the value will just be derived from the map sensor as opposed to being measured directly. I know you can view this pid w/ efi live.




Good luck, though I fail to see what any of that has to do with MAF vs. Speed Density. If you honestly want to hit that goal you are going to have some work to do. If you want to run a 2 bar map you might start disassembling the pcm so you can make the appropriate changes to it to allow for that. I think some of the australian variants included multi-bar provisions.

Or you could just run a larger maf setup, or switched to aftermarket DFI - which will allow you to run your map sensor?

Also, if you intend on hitting 1000rwhp you probably will need a bit more than a 2 bar map sensor.

99PHardtop

The 2 bar is for the interum until my spare engine is finished being built. I haven't used LS1 edit much, so I am just playing with it right now (that's why I am starting with a 2 bar). I don't want to put an aftermarket computer in the car at this point, I want to see what the limits of the factory computer will be.

If the scaling is converted to SPeed density for the load, can I assume the lightest load is equivelent to the lightest load in the fuel map (15kpa) and the heaviest load is equivelent to the heaviest load in the fuel map (105kpa)?

Y2kHawk, I didn't figure you would settle for 600. I just wanted to point out where I was heading. Your car sounds awesome, have you run it at the track at all?

Thanks again for the input.

Pro Stock John

iTrader: (34)

1000 rwhp = FAST or other aftermarket computer system + 3 bar map (my setup fwiw) for about five big reasons

99PHardtop

So is it not possible to run anything other than the stock map sensor with LS1 edit? I am not looking for alternatives, I am intersted in the limits of LS1 Edit. Is there going to be a problem with internal baro sensors or anything like that if I run a different map sensor?

Thanks again

y2khawk

iTrader: (5)

For a starting point, you're basically picking the worst possible option.

You're limited by the PCM to an airflow reading of 512 g/s. That's MAF or speed density, don't matter. Hard limit of the box.

I'm still not quite sure why you're dead set on trying to change the MAP sensor. The fueling is done straight off the MAF, as is the spark. The MAP sensor comes into play for BARO, and fuel injector flow calc's due to the non-vacuum referenced FP regulator. If you're even remotely serious about boost, you'll put a referenced regulator and full returning system on the car anyway. Moot point then.

Once you hit the limits of air measurement, you'll have to play tricks.

XLR8NSS

iTrader: (4)

Hmmm....So with your sum/averager box Harlan, two stock truck MAFs with the stock 453g/s calibration should be good for ~1200flyhp?

Is LS1edit all that's needed with your box to run two MAFs?

S_J_H

A few boost staged mechanical injectors could easily add another 200+hp of fuel to a flatlined maf.
Cheap, easy and just as effective for us mere mortals who ONLY want around 700 RWHP.
fuel and spark and air. Try not to over complicate it.

99PHardtop

Near as I can tell, you can't take off the maf sensor all together. I have been able to make the car run and drive perfectly on the 2bar pressure sensor until about 3500rpm, then it goes into power limiting mode. It seems that if the maf is in fail mode then it uses the pressure sensor as a "limp mode" input only, not letting you rev the motor.

THanks

69firebird

iTrader: (14)

harlan,
what kind of tricks are you speaking of? I think that this may be a problem for me as well. I have the fuel, just need the tricks now



thanks
ed
firebird455@onebox.com

ChrisB

There is a max frequency limit that the pcm will sample at as well as a max variable size that the pcm will use to store the airflow value.

The max variable size can be fixed by scaling the IFR and MAF tables by the same factor - e.g. if you scale the MAF table by 1/2, scale the IFR table by 1/2 also - this way you will end up spraying in twice the amount of fuel for half the air - so it works out.

To get around the frequency limit requires a bit more work - you need some sort of electronic device that will map your airflow to the frequency range the pcm expect. If you have a twin setup a dual MAF idea lends itself well to the application - you just need a box that will perform a lookup on the frequency, average the two airflow values, than output a frequency (can be to whatever calibration you want, as you just need to enter it into the pcm). If you have a different packaging you can go with a calibrated maf (pro-m, etc.) - you just need to convert the output to a frequency. I posted an analog circuit to do this previously, but per Harlan's suggestion I checked it for temp dependance and it varied too much for my tastes with temperature, so I am finishing up reworking it to run off an AVR. I think pro-m offers a conversion box to, though harlan mentioned his died on him.

y2khawk

iTrader: (5)

Exaclty, what Chris said.

QuickSilver2002

Does anyone have any info on that piggyback (I think it was called TCI) PSJ was going to run. That sounded like a decent budget minded solution.

Here is another basic question that I have been wondering about. Stock '02 MAF hits max frequency (1200hz) at 428 g/sec. How are people getting accurate readings of 512 g/sec. Are they using a different MAF? I’ve been getting by with PE vs RPM, but I sure would like a little more adaptive behavior.

Also, about what HP would you guess 512 g/sec at 6500 is.

y2khawk

iTrader: (5)

The curve on the plastic MAF's is slightly shallower, IE hits the max frequency at a lower flow. The metal MAF's will get to the 512 limit before 12kHz.

a decent guesstimate using the coversion from g/s to lb/min and the 10 HP/lb/min generalization at peak power

100 g/s = 130 FLYWHEEL HP

That's assuming an unmolested MAF, it's been VERY accurate for me.

So in theory, you should be able to accurately fuel up to 660 or so FWHP.

Pro Stock John

iTrader: (34)

I sold the TCI to Stealth since I decided to run leaded gas all the time at the track. It is a neat solution but he has not posted much info about it. Mac @ Fastrack can get them.

Reckless

iTrader: (9)

Matt...a friend was wondering if you are going to market the twin maf box thingy? He is thinking of going to a similar setup as you.