Billy W

The jet that came with the Auto Authority chips I have say 180 on it.

And Yes the car is other wise 100% stock. Except for the Ansa catback.

Danno

"Also, I was under the impression that once on WOT the DME looks up values in the Full Throttle maps (fuel & ign)."

Yes that's right. However, when you're not at WOT, the AFM is used and the partial-throttle maps are used.

"So, the airflow sensor runs out of range past 4000ish rpm? Wow. How does the computer determine fueling? Does it have some other input (manifold pressure)?"

"What if the air density changes, such as a cold morning, but it can't recognize this because it has no real airflow signal?"

An air-temp sensor is used for cold-start enrichments. There is a completely separate fuel-map for that which is triggered by the engine-temp sensor.

What happens when the AFM maxes out under partial-throttle conditions is the computer sees a fixed air-flow value from that point on. The air-fuel ratio gets leaner and leaner as RPMs (and air-flow) increases, yet the computer dumps out a fixed volume of fuel. The more boost you run, the earlier the flapper door gets maxed out. This creates a big transition between the partial-throttle and WOT maps.

I'm not saying that you can't make big HP with the AFM. You can and it's not efficient because you lose 2-3psi of boost. On a track car that's always at WOT, you can get away with just custom-mapping the WOT fuel maps.

However, on a street car that needs to crawl around parking lots under partial-throttle, or is run at other operating loads other than WOT, having high boost just doesn't work well and doesn't provide a whole lot more power.

RLefebvre

Wow, that's amazing. So, what does the full throttle table look like? Is it simply a 1 dimensional table? The fuel injector pulsewidth is simply a function of rpm? There is no engine load input at all?

So, if you tune the full throttle map for 14psi, and then you turn it up to 16psi, you get no extra fuel, you just run leaner?

That's scary! I guess if you lost boost control for some reason, and the boost climbed higher than normal, it's game over?

Does this happen with the car from the factory? Or is it a case where it never moved enough air to max out the mass air?

I'm really surpised that these things can even operate like that.

Now I understand why I'm always reading things like "Too rich at this rpm, and too lean at that rpm". I was sitting here scratching my head thinking "at that RPM, and what load? Why doesn't it just measure load to get the A/F right?"

I guess if I want to get one of these cars, I'd better factor in stand alone management into the cost. I've got it on my daily driver, I don't think I could have a racecar with such a crude system.

sm

Danno,

Do the GURU Chips have customized WOT maps? A friend asked about that this weekend, and before I go back to him touting the greatness of GURU Chips, I thought I'd ask.

fast951

The factory DME has 1 table for timing and 1 for fuel at:
- idle [rpm based]
- PT [Load & rpm based]
- WOT [rm based]

The signal from the AFM, MAF or MAP are used in a formula to determine DME output (fuel, timing,..)
Also, if the Air Temp Sensor is not used (open circuit), the DME will default to rich mixture.

TT

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva"> Wow, that's amazing. So, what does the full throttle table look like? Is it simply a 1 dimensional table? The fuel injector pulsewidth is simply a function of rpm? There is no engine load input at all?

So, if you tune the full throttle map for 14psi, and then you turn it up to 16psi, you get no extra fuel, you just run leaner?

That's scary! I guess if you lost boost control for some reason, and the boost climbed higher than normal, it's game over?

Does this happen with the car from the factory? Or is it a case where it never moved enough air to max out the mass air?

</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">The AFM (engine load) is still used at WOT. The WOT fuel table is just f(RPM) and the lookup value is used to modify the injector pulse width which is initially calculated from the AFM reading and RPM.

HansB

</font><blockquote><font size="1" face="Verdana,Tahoma,Arial,Helvetica,Geneva">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva"> I guess if I want to get one of these cars, I'd better factor in stand alone management into the cost. I've got it on my daily driver, I don't think I could have a racecar with such a crude system.
</font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Arial,Helvetica,Geneva">Another question: How much can be gained with stand-alone engine management in a race-car? When always on WOT, what would be the optimal control strategy? <img border="0" alt="[burnout]" title="" src="graemlins/burnout.gif" />

RLefebvre

The benefits of stand alone in this case might not be more power on a dyno. It would result in better reliability at higher than stock power levels. It's pretty amazing what a factory engine can put out with forced induction, when the management is right. A lot of times, people develop an idea of how strong an engine is, and what a stock bottom end can take, based on the results of "tuners." The problem is, if the tuners in question are not experienced, or are not using a good system, the engine dies from detonation, not from a simple overloading of the connecting rods etc...

For example, the Zetec engine in the Focus gained the reputation of being weak, because the first companies to attempt to turbo it were using very poor engine management, and they were killing engines with 6 psi of boost. But the pistons and rods were braking because of detonation, not because of loads from combustion pressures.

Now, this is engine is not as strong as the 951 engine, or another factory turbo engine like the Mistubishi.

But it can make good power.

Using good management, myself and others are making 240 crank horsepower, and these are used for lapping events, not quick drag races. That's almost double the output of the stock Ford engine.

One guy even made 280 wheel horsepower on the stock block, with a chipped stock computer and 15 lbs of boost. Pretty incredible.

I've read a lot of things in 951 FAQs saying "Don't buy a car that's been chipped, they aren't reliable, etc..." The thing is, the engine can probably take 400hp all day, with good management. But some of the chips seem to be pretty poorly tuned.

Guru seems to have done a much better job than some others. But it appears the stock computer has it's limitations.

Using a stand alone system, with enough load range that it's always using a 3D map with temperature compensation (so 4D, really), could probably make 400hp all day, maybe even 500hp.

Would you get more horsepower than the stock computer running 10psi? Probably not. But you could run more boost with a bigger turbo, than you could ever get away with using the stock computer.

Even thinking about it now, I'd bet you could squeeze 5-10hp more out of the stock turbo with 15psi than you could with a chipped computer. The more refined 4D mapping capability of a modern engine management system, would allow you to push the limits with timing and A/F ratio, but would have the refinement and processing power to keep you from going over the edge with detonation.

I don't pretend to know much about 951's or Porsche engine's. These are just general observations I've made on other vehicles.

p0wp0w

hey, kind of new to this stuff...but is this chip you guys are talking about the chip on the guru site that sells for $290 with the reliaboost, under the chip upgrade section? Or are you guys talking about a different one?

Thanks,
Matt

FityOne

Matt:
It is the one on the website, under the chip upgrade section.

Danno

"Do the GURU Chips have customized WOT maps? "

Yup, we've got 8 different chip calibrations to best fit your particular car's configuration. I've been working on a MAF-specific chip lately to allow MAF users to set their ARC2s on zero adjustments (with one or two clicks here & there).

p0wp0w

Thanks FityOne!

kasturbo

Danno, I'm just about ready for the MAF chips. How are they comming?

rcldesign

Just so you know... I used the Huntley chips... and if you don't have a boost controller they suck major *** because you're running too rich. You gotta give 'em 16# of boost. I have included my dyno charts from when the car was bone stock vs. adding a 2.5" cat bypass and an adjustable fuel pressure regulator. The next thing I did was a set of Huntley Chips and a manual boost controller. So I went from stock (185 HP + 220 TQ) to test pipe (200 HP + 240 TQ) to chips (234 HP + ~290 TQ) to where I am now with a MAF (haven't scanned the chart in - 291 HP + 340)

<img src="http://ieng9.ucsd.edu/~cswillia/dyno_stock.jpg" alt=" - " />

<img src="http://ieng9.ucsd.edu/~cswillia/dyno_chips.jpg" alt=" - " />

Redeye

You need to resize those charts! I can only see 1/4 of them at a time.