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Underbody braces, turbos and more!

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PostPosted: Sat Jul 05, 2008 3:44 pm 
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Joined: Sun Sep 02, 2001 11:55 am
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Location: Calgary, Alberta
This will be a quick primer to another thread I’ll be making for FE on the GT.

The voltage coming from the MAF is one of the primary inputs the ECU uses to determine how much fuel to inject at a given rpm and load setting. The velocity and pressure on each side of the MAF will effect how air is going through the MAF and impact you’re air/fuel ratio (and your mileage). The size of your inlet pipes, filter type, even a cold air intake has the ability to make big changes (or little tweaks).

You can see below some reasons why I think some guys might be getting 25mpg, and others 35mpg with seemingly little differences between the cars. The graphs below are datalogs from my Swift GT with different intake setups. The top line is air/fuel ratio, middle rpm, and bottom throttle position in % (it takes about 15-20% throttle to do 100-110km/h).

Stoich where all fuel is completely burnt is theoretically 14.7 pars air to 1 part fuel. 10:1 is generally getting close to pouring fuel out the tail pipe, and 18:1 range usually has some lean misfires with 21 being the max lean this system can read.

I must emphasize that there were absolutely no electronics inline with my MAF during the tests and all changes are simply from removing a pipe here, changing size here, etc..

This first one shows how rich a small intake pipe with factory airbox and cold air is at startup. If you follow the TPS line back you can see that at 0 throttle the a/f is close to 11:1. And just lightly accelerating its 10:1 and even dips into the 9s.

Image


The below shows the warm up period with a 3” pipe and some lame-o CDN tire air filter. You can see how much leaner and closer to stoich you are just during warm up with a proper intake pipe.

Image

This is just to show that by removing air filter, and with a big pipe between MAF and the throttle body… that I can make my car impossibly lean. The only way to drive the car is either on or off, and it’s pretty much 18:1 or leaner no matter what the TPS setting is. You’ll notice the rpms not changing much as it is more about trying to keep the car running at this stage.

Image



Here’s a somewhat popular ‘power mod’. Cold Air Intake… it is a good theory, but I’ve always noticed less power and less fuel economy out of a cold air intake on the Swift because of how it changes the air flow going over the sensor. The smallest change in throttle and it wants to go rich, and it even shows it having a difficult time staying closed loop for stoich. Even WOT the CAI runs so much richer that any gains from the colder air are potentially offset by the 11:1 a/f ratio

Image


So what is your aim for fuel economy?

You want to have an intake system that:

Won’t cause the MAF to read impossibly rich during warm up period.
Won’t force feed air over the MAF like a CAI causing your car to go rich at the slightest touch of the throttle, or make it difficult to cycle the o2 (unless you have means to tune out the problems)

This is what my GT looks like with a custom 3” pipe between MAF and TB, a 52mm TB, and some cheapo heatshielded Ractive air filter from Cdn tire. You’ll notice the o2 is cycling nicely, and it’s managed to stay in closed loop despite adding even 50% throttle.

Image

More ins and outs of GT fuel mileage tuning to come (along with the numbers).

Thoughts here are also applicable to power tuning. When the MAF is happy and reading the right A/F for you, WOT performance will correspond.

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PostPosted: Sat Jul 05, 2008 4:08 pm 
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Location: Saskatchewan
good to know!

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PostPosted: Sun Jul 06, 2008 11:50 am 
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Location: Findlay,OH
Great info. How did you monitor this?

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PostPosted: Sun Jul 06, 2008 12:46 pm 
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This was done with a 5 wire wideband o2. It's made by Zeitronix and it seems fairly accurate although slower when used at the back of the car than my LM1.

Before testing, I used the wideband with a tailpipe attachment at the back and kept the factory narrowband in the front. I wanted to make sure my factory single wire o2 sensor was working and switching properly. And then I installed the wideband sensor in the factory manifold in place of the single wire sensor and it is currently simulating the factory narrowband signal to the ECU. I wanted to make sure the Zeitronix unit simulated the factory narrowband sensor accurately.

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PostPosted: Sun Jul 06, 2008 5:51 pm 
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whattheeee wrote:
This was done with a 5 wire wideband o2. It's made by Zeitronix
How did you hook in to it to get the graphs, laptop? And how much does this fancy lil feller set you back? If you don't mind me asking.

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PostPosted: Sun Jul 06, 2008 9:41 pm 
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http://www.zeitronix.com/

It has various inputs that it can accept to monitor. You then have to log with a laptop (LM1 has internal memory to log with).

If you just buy the box and don't want a gauge, it's fairly cheap... but if you start adding on the EGT, gauge, pressure sensor, etc.. it starts to add up. Check out their site.

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PostPosted: Sun Jul 06, 2008 11:57 pm 
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whattheeee wrote:
http://www.zeitronix.com/

It has various inputs that it can accept to monitor. You then have to log with a laptop (LM1 has internal memory to log with).

If you just buy the box and don't want a gauge, it's fairly cheap... but if you start adding on the EGT, gauge, pressure sensor, etc.. it starts to add up. Check out their site.

Cool thanks. And very interesting on how much a intake setup can change the AFR.

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PostPosted: Mon Jul 07, 2008 2:49 am 
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great work there bud only one thing.

The ecu is current sensing off the maf not voltage... it means a whole lotta difference if you try and fool the ecu with a different setup. Its not easy.

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Understeer is when you hit the wall with the front of the car and oversteer is when you hit the wall with the rear of the car.HP is how fast you hit the wall, torque is how much you push the wall out.


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PostPosted: Mon Jul 07, 2008 9:13 am 
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Hmmm? GT is different than the 3 cyls (whatever it is they use, I recall something like flapper on turbo3). At any rate, it's no mystery that there is a 0-5V input that the ECU sees from the MAF. This signal is what I've modified on many GTs with a piggy-back such as Split Sec, Link, SAFC2, etc.. 25mV steps are actually too large for my liking when tuning on a GT.

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