Starting Fresh

[5150DSM]

Please disregard my previous tuning posts, I am starting back at square-1 to regain my objectivity and hopefully engender a fresh perspective. This may end up being long so please bear with me.
For the sake of reference here are the facts: 1992 Talon TSi AWD, car is in good repair with all normal maitenence recently completed(within last 500mi). Mods: 550's, 255 pump, AFPR@37psi, 2 1/2" SS intake(removed aircan and lower honeycomb, K&N filter) 3" turbo-back exhaust(no cat), MBC set to 14psi(No creeping or spiking), SS UICP(buschur), 57mm throttle body elbow...that's all the relevant ones anyway.

Ok, some questions to start: Removing the lower honeycomb in the MAF gives a 5%(roughly) signal decrease to the ECU, is this correct? Along those same lines, upgrading to a large diameter, hard intake pipe obviously increases airflow a large percentage; thereby, also creating a larger amount of unmetered air entering the engine, is this correct? And at what percentage?(again, roughly) Progressive logic leads me to assume that the larger throttle body elbow, lack of aircan, and hi-flow filter will all also have a similar effect, is this correct? How much, if at all will the 3" exhaust affect the overall airflow signal(s)? That's it for airflow.

Fuel: A 255 pump will obviously flow more fuel at 37psi than the stock pump will, how much more? 550's flow roughly 10% more fuel than the stock injectors from the stock pump and FPR, how much more do they flow at stock pressure from the 255 pump? Are there any other fuel considerations that I should have beyond volume, pressure and octane?

Now, keeping in mind that the SAFC-II/pocketlogger combo are my only available tuning tools, can a mathematical formula be accurately generated based on the airflow and fuel numbers to provide some baseline correction factors for the SAFC. Any technical data, ideas or opinions are welcome, I need some objectivity and clarity on this tuning job and I have lost my own. Thank you in advance for your patience and any help you guys can provide.
Aloha,
Tony

 

[pneumo]

Your post has many questions. I don't want to try to answer all of them at once since you seem a bit confused already. How about we focus on one issue at a time, then go from there?

Start with the basics; What is a MAF and what does it do? The MAF is a device that measures the TOTAL ammount of air going into the engine. This is important because you can do many mods that increase the ammount of air the engine uses, but it still gets measured by the MAF. For example, adding a larger turbo inlet pipe will let more air flow into the turbo, increasing power. The AFC doesn't need to be adjusted because the extra air has to go through the MAF first. The air gets measured, the ECU knows it, and the injectors are run accordingly. The same thing applies to exhaust mods. A bigger exhaust has more flow, but every single molecule of air that goes through the engine must go through the MAF first. And the MAF knows how much air goes through it.

 

[5150DSM]

Thanks pneumo.
I think I understand how the MAF works but I was making too many assumptions about the interraction between the MAF and my airflow mods. I get it now that regardless of the amount of increased airflow the MAF signal will always be 5%(roughly) less than the actual when it is hacked.
With an AFPR set to 37 psi I am flowing 37psi of fuel regardless of the pump; however, the injectors(550's) will have roughly 10% more fuel flow than the stockers due to their size.

I found out that most of my problems were actually attributed to the plugs I was using. It seems 7's were just a little too cold for my set-up, I was unable to get an even burn at low rpm's causing an overly rich condition that in turn caused rich knock, which I mistook for detonation, so I richened up more, making things worse. Changed out the plugs for 6's, reset my SAFC to -10% across the board and proceeded to street tune my low and mid rpm settings. My LFT is now 109% and my mid and high are both at 100% I can pull to red-line in third with no knock and 20-24* of timing advance at 14psi on the 14b. I will be heading out to the track to do some power tuning on Friday, so I will report back this weekend with the results.(shooting for my fist 12 second pass) Thanks for the help from everyone in getting me to this point.

 

[pneumo]

wow, that was easy! I'm glad to hear you got the car running good. Good luck at the track.

 

[CanadianTSi]

Since you've got enough fuel and your shooting for a 12 sec slip, I think your should turn the boost up to around 18ish...car should really come alive

 

[5150DSM]

Yeah, they will have Sunoco 114 available at the track this weekend, I was planning on throwing in a couple of gallons and jacking up the boost. Hopefully I can avoid the 24psi spike I got last time out(that scared the shit outta me) and keep things even through the rpm band. Thanks again for the help.

 

[kpt4321]

Since this question was posted on two boards, I am going to post my reply here too.

Originally posted by 5150DSM:
Ok, some questions to start: Removing the lower honeycomb in the MAF gives a 5%(roughly) signal decrease to the ECU, is this correct?

Somewhat. However, the discrepancy will not be the same at all points in time. At very low airflow (idle), the difference will be greater than it is at higher airflow (under boost).

For this reason, you may find that you need to add a lot of fuel in at idle to compensate, and you don't need to add much at all at higher engine speeds and higher loads.

Along those same lines, upgrading to a large diameter, hard intake pipe obviously increases airflow a large percentage; thereby, also creating a larger amount of unmetered air entering the engine, is this correct? And at what percentage?(again, roughly) Progressive logic leads me to assume that the larger throttle body elbow, lack of aircan, and hi-flow filter will all also have a similar effect, is this correct? How much, if at all will the 3" exhaust affect the overall airflow signal(s)? That's it for airflow.

You're going off on the wrong track here.

Unmetered airflow is simply what happens where air gets into the system without being "counted" by the MAF. The reason this happens when you remove the lower honeycomb, is because that throws off the factory calibration of the MAF so that the ratios of flow between the different chambers are no longer "in spec."

A hard intake pipe increases airflow, but not unmetered airflow. All the extra air that is now entering your motor because of the better intake pipe, still has to pass through the MAF and therefore it will all still get metered.

The same is true for the larger throttle body, the better filter, etc.

On a mass-air metered car, changing the exhaust will also not change anything. If the larger exhaust increases the VE of the motor and therefore allows more air to flow through under a given set of conditions, the MAF will still see that extra air and therefore will increase the fuel level appropriately.

One thing to note: If you remove the lower honeycomb, like you suggested, you cause some air to enter the motor eithout being counted. Now, if you increase the total airflow after this point, you will indeed be increasing the amount of air that is passing through without being "counted." However, the percentage of compensation that wil be necessary still remains the same, so this does not effect tuning.

Fuel: A 255 pump will obviously flow more fuel at 37psi than the stock pump will, how much more?

Yes. You can find out how much more by looking at a flow chart of the two pumps. However, I think that you are confused, and you really don't care about this difference. Keep reading.

550's flow roughly 10% more fuel than the stock injectors from the stock pump and FPR, how much more do they flow at stock pressure from the 255 pump?

None.

If the fuel pressure ramains the same, then regardless of the flow of the fuel leaving the tank, there will be no flow difference through the same size injectors. If you open an injector for a set time period with a set fuel pressure, there is no reason flow differences in the rail would effect how much fuel leaves through the injector.

If the fuel pressure rises, as is often the case with a 255lph pump and a stock regulator, then the flow will increase, but only because of the pressure change.