P Mack

iTrader: (6)

I know, I was responding to humpin's post, i guess I need to learn to use the quote button more often.

Black02SS

iTrader: (36)

I did the same test with my MAF and it was off about the same amount.

HumpinSS

iTrader: (1)

IMHOthe IFR table is right no matter what you do to it. Its the ve table you need to worry about.....

P Mack

iTrader: (6)

I agree. Even if the IFR table is not truly right, you "assume" it's right and change everything else to match. Why? Because it's the most likely to be right and even if it is wrong, since it is only a 1-row table it doesn't complicate the other calculations much.

For example, if you assume your ve table is right and change your ifr to match, you may get your ifr table to match over the whole MAP range at 2000 rpm, but it could be completely wrong at 5000 rpm. Well there's no rpm axis on the IFR table so you know the problem lies with the ve table.

HumpinSS

iTrader: (1)

Agreed this is why i stopped messin with the IFR table long time ago...

gojo

iTrader: (12)

HumpinSS,
"If the WB was problematic and the maf has shown to be inaccurate with changes to the intake exhaust and internals of the engine (cam) how do you propose tuning this thing?"
I may not be making my self clear. You are asking me what I'm questioning.
I agree that if you have stock injectors and want to tune SD and stay in SD it's not that hard to do. What I think is that if either the MAF or the IFR is wrong then going back to running the MAF is problematic. It would seem that knowing the correct IFR values would make the VE tuning relatively easy. In my case I am not convinced the SVO 30's flow as we think. If you have wrong IFR's then how do you get a correct VE table? I don't think we know all that are affected by the VE table and prefer that it be the priority.
To answer your question on tuning, with 0'd MAF, with what I guess and not with what I think I know.
Get the injectors flowed and input correct IFR #s. Zero the MAF and input logged VE #'s. Adjust VE's to get decent trims. Get the MAF on line and adjust it based on new trim #'s.
One more question. If the MAF and IFR's are "correct" then shouldn't we be able to calculate our own perfect AFR?

HumpinSS

iTrader: (1)

Sorry, I was drinking a little last night and didnt mean to sound so aggresive

SVO 30# injectors @ 44.1 (3 bar) is equivalent to 34.64@58.5 (4 bar). this is all at 0 vacuum. What made snese to me was to take the stock injector values and divide the 2 at 0 vac the percentage difference needs to be multiplied across the whole table. To check my theory i took the min and max ifr values, divided them to see what the difference was and compared the old and percentages and they were spot on. After this test i assumed the IFR table was in fact correct and left it alone (I am running Racetronix 32 # @ 3 bar injectors). After this scaling my trims were still in line and i didnt hve to adjust for them only difference was my ms dropped from old to new....

If you have a lid or anyhting the skews the original intake tract then the maf is most likely inaccurate. this can be tested with the WB

1. plug the maf and log afr
2. unplug the maf and log afr

And yes if the maf is accurate at measuring airflow (providing the right g/sec or air is entered at those frequencies) then the AFR should fall right into place. After all the computer main function is to measure air, calculate fuel (injecter pulse width) to aceive either stioch or the commanded AFR

NoGo

iTrader: (2)

As far as injectors and the accuracy of the IFR table, it isn't the flow table that is typically off on the injector table, it is the offset. Calculating flow can be done with a simple formula.

New Flow = Old Flow * SQRT(New Pressure / Old Pressure)

However, the offset of the injector cannot be directly calculated with any desirable accuracy.

The offset changes dramatically with different sizes in injectors. Additionally, the stock offset table is fairly vanilla for the stock injectors.

Poor offset corrections can be minimal (as with most SVO injectors) or enough to foul plugs (as is the case with 72 lb high impence)

Bottom line is there is always going to be some admissable error coming from the IFR table.

Additionally, HumpinSS is correct about the MAF. Typically, there is always somewhere along the curve that the MAF is not correct. Once the intake tract is changed the complete accuracy of the MAF can't be trusted for exact results.

With all that being said though, in the end we are just playing with fuel and air. As long as your a/f stays where it is suppose to be and the drivability is great than it doesn't really matter where the error is coming from or where you are correcting for it.

-Kevin

gojo

iTrader: (12)

"With all that being said though, in the end we are just playing with fuel and air. As long as your a/f stays where it is suppose to be and the drivability is great than it doesn't really matter where the error is coming from or where you are correcting for it."
I agree with that.
I would like to get the right IFR values so that I can caculate the PE numbers. I realize it's not a really necessary thing to do but I have the time to play with it.
As for calculating PE numbers that is easy, but I'm not sure that the 30# SVO numbers everyone is using are correct. It may be that the fuel rail pressure needed to flow 30# is 43.515 and results in 3.90 inj flow at 100kPa. When using those #'s everything seems to fall in place.

NoGo

iTrader: (2)

I do agree with that. If you work it out on paper the injector flow rate at 103.1 kpa for 30# injectors should be

New Flow = Old Flow * SQRT(New Pressure / Old Pressure)
New Flow = 30 lb/hr * SQRT(58.0 psi / 43.5 psi)
New Flow = 30 lb/hr * 1.15
New Flow = 34.63 lb/hr

Convert to g/sec....
34.63 lb/hr = 4.36 g/sec (@101.3 kpa)

However, in reality, this number often lends to a lean condition if you just punch the numbers in. Typically, I use something in the lower 4's for 30lb injectors.

Alot of this error though could be the offset. The offset simply adds or subtracts a look-up number to the derrived injector pulswidth. Without a truely accurate offset curve, we really don't know if it is the offset or the actual injector flow that is causing the error.

J-Rod

Ok, folks may have a different opionion, but in SD I look at IFR as a way to "tune" AFR across the board (I've used it to tune the AFR for a whole tune). VE tuning is where I fine tune fueling for specific values.

It is interesting to consider using the meter for feedback to determine if your IFR is off, and use it to tune IFR. That is a novel concept. I'd like to see somefeedabck on how that goes.

Tuning the MAF fail frequency to 0 is also very intriguing. I will have to check that once I get my HPT box back.

Good info, keep it up guys...

NoGo

iTrader: (2)

I use the IFR the same way as more of a 'global' change.

As stated earlier, just air and fuel.

HumpinSS

iTrader: (1)

I would think an accurate MAF would be a little more important than the IFR table. I say this becaue with the correct g/sec from the maf and any IFR value the computer can figure out what the pulsewidth should be for the desired AFR.


Hmm I think I stand corrected on my theory after sitting here thinking about it. gojo has a point with figuring out the correct IFR table.

If dynair is back calculated from the ve table and you have ifr values that are to far away from where they should this will skew the dynair calculation since the ve value is the starting point for this calculation

NicD

iTrader: (7)

I have been saying this for years. Glad to know I am not alone here.

gojo

iTrader: (12)

NoGo,
Do the calculation without correcting for 58 lbs. Also do it this way for 28.2 stock 2003 C5 injectors. The 100 kPa number comes up the same as what is programmed stock. That's how/why I ended up with 3.90.

Humpin SS,
All I have been trying to say and not well, is that all the aformentioned methods work. The new zeroed MAF method makes it so simple that I won't bother to do it any other way. Any way we use to tune will only get us close anyway, unless we have a load dyno and lots of time.

gojo

iTrader: (12)

Did anyone tell you what a great find this is?
Thanks

horist

I can't take credit for it Keith showed it to me when he was helping me out

NoGo

iTrader: (2)

This is also the way to run a hybrid MAF/MAFless tune on the vehicle (f-body's only).

NoGo

iTrader: (2)

The rating of the GM injectors are given at the rated fuel pressure of the GM cars.

Most other injectors on the planet are rated at 43.5 psi (or 3 bar). In order to correct them to our table you have to account for fuel pressure.

If you just take 30 lb injectors straight across it comes out to 3.77. That would be far to rich for that injector size.

gojo

iTrader: (12)

Makes sense. I'll try it that way and see whether I can get my trims back.