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Old 04-10-2008, 10:48 PM   #21
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Quote:
Originally Posted by bobc455 View Post
Sorry but since I don't know the Honda engine design, that means nothing to me. What about a Honda engine makes it suitable to run lean, whereas most other engines strive to run at the theoretical optimum of 14.7?
Besides emmissions as Maxxgraphix stated above, keeping a 14.7:1 A/F ratio also yields better power and responsiveness. Consumers like power in their cars, so a car that feels strong is more likely to sell. The Honda VX was responsible for coining a new term: 'lean lag'. It describes the feeling of slight power loss and less responsiveness when the ecu goes into lean burn mode.

I have a Mitsubishi motor in my car. It didn't have lean burn, nor did any similar models have lean burn. The head was designed for efficient combustion with two squish bands, aka quench zones, which makes it work well when running lean. It also came with a compression ratio of 7.9:1 which works against using very lean A/F ratios at very light load- too much room in the combustion chamber and not enough fuel for the plug to light off.

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Originally Posted by bobc455
I'm also assuming that the AFR being discussed is not during deceleration or something, this is during steady-state cruising.
Yes, for the most part. In my car I can stay in lean burn up to about 5 in/hg vacuum, which is enough to pull up a hill that is slightly steeper than a typical freeway overpass at 55mph. But like I said earlier, I've set the A/F ratio richer as the throttle opens more. During closed throttle decel the fuel is completely shut off until rpm drops to idle.

Quote:
Originally Posted by bobc455
According to the "lean burn code" as described above, in order to run more economically somehow the injector PW must be decreased (meaning that less fuel is being used overall) even though the throttle is pushed further open.
Yes. Hondas version uses a wideband O2 sensor and sets the target A/F ratio leaner under the right conditions.
Since my ecu was 'hacked' to add lean burn and it doesn't (didn't) have a wideband O2 sensor it works differently. When lean burn conditions are met (speed, throttle position, engine load) the ecu goes into open loop where it stops looking at the O2 sensor for feedback and just uses preset A/F ratio targets. Then it reads the mass of air coming in, looks at rpm, picks the A/F ratio target, then calculates how much fuel to add.

One of the charts I printed off the web, which is no longer available shows that power and fuel consumption drop off as A/F ratios get leaner, but fuel consumption decreases quicker than power up until around 16.0 to 16.5:1 A/F ratios. That chart was generated using a locked throttle and fixed ignition timing. It also shows power peaks around 12.0, cylinder head temp and knock propensity peak around 13.5, and exhaust gas temp peaks with NOx at 15.7
HTH
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Old 04-11-2008, 06:04 AM   #22
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I was wondering about closed loop mode. If I set the injector pulse width for a lean condition then the ECU based on O2 input will try to compensate?

I can disable closed loop mode. But I would need to have my maps dead on. I've also been reading that lean AFR's should have more spark to ignite. Also higher compression helps. However, melting pistons is possible since the piston tops are not as strong as a diesel. Diesel engines run as lean as 100:1 at idle.

he, he, he... how about use some diesel pistons in a gas block and make a stroked motor with high compression? Or, use a diesel block with a gasser head! That would be easy.

I know that a Crane Hi-8 CDI box can fire a plug multiple times at the compression stroke. I bet many of the performance modes would help for a lean burn motor.
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Old 04-12-2008, 09:32 PM   #23
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Quote:
Originally Posted by maxxgraphix
I was wondering about closed loop mode. If I set the injector pulse width for a lean condition then the ECU based on O2 input will try to compensate?

I can disable closed loop mode. But I would need to have my maps dead on.
That's how I do it. I dialed in the MAS so when I go into open loop I get the A/F ratio that's programmed in the ecu. The wideband shows slight fluctuations of about 0.1 - 0.3
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Old 04-13-2008, 09:47 AM   #24
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Originally Posted by maxxgraphix View Post
The VTEC-E is just a VTEC. Works the same as any other VTEC. The difference is that the pistons are dished and the head's combustion chamber is small. Also the ECU has an alternate FUEL /Timing map for LEAN Burn Mode.
I think you have some things confused here

I'm not sure which "vtec-e you were saying is the same but vtec-e is similar but, still very different from regular vtec(y8/z6)

y8,y5 heads have the same casting=same head. The difference is the rocker arm assembly.

Vtec-e is in theory a 12-16 valve operation(secondary opens only enough so gas doens't pool). vtec-e uses "pins" in the rocker arm that slide over to lock the intake arms together to keep VE in par with rpm's.

Hope that helped,
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Old 04-13-2008, 10:38 PM   #25
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Quote:
Originally Posted by bobc455 View Post
Sorry but since I don't know the Honda engine design, that means nothing to me. What about a Honda engine makes it suitable to run lean, whereas most other engines strive to run at the theoretical optimum of 14.7? rod/stroke ratio? Compression ratio? Cam design? Retarded spark timing? Perhaps you know of a website that explains what makes the Honda design so different.
VTEC-E is the answer you're looking for.

The D15Z1, D16Y5, and D15Z7 utilize VTEC-E. It is a cam lobe switching system. These engines are all four valves per cylinder, 4 cylinders. Under light throttle and load, between a particular RPM band, the motor shuts one intake valve per cylinder.

This causes two things to happen. 1) similar to pinching a hose, the air is forced into the combustion chamber faster. 2) Air is entering at one "corner" of the combustion chamber and then flowing around in a circular motion toward the closed intake valve. This is referred to as "swirl".

Swirling the mixture helps atomize the fuel and distributes it more evenly. That is how you can run it so lean w/out lean misfires.
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Old 04-13-2008, 11:00 PM   #26
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Quote:
Originally Posted by maxxgraphix View Post
The VTEC-E is just a VTEC. Works the same as any other VTEC. The difference is that the pistons are dished and the head's combustion chamber is small. Also the ECU has an alternate FUEL /Timing map for LEAN Burn Mode.
This is partially true and partially false.

You are correct that the physical switching mechanism and electrical wiring for both VTEC and VTEC-E are the same parts.

You are also correct about the VX pistons and combustion chamber. But this is not true of the HX, VTi or Vi (Japan).

You are correct about the ECU map.

Where you are incorrect is that you're suggesting that VTEC-E and VTEC are the same because in fact they are absolutely and completely different.

On a SOHC, VTEC switches both intake valves on each cylinder to a "wild" cam lobe with more lift, duration (resulting in more valve overlap with the exhaust), and it opens the intake valves earlier. This occurs approximately around 5000 RPM.

On a VTEC-E engine, one intake valve per cylinder is almost completely closed (open only enough to allow fuel to pass through) until load, throttle, and RPM conditions are met and then both valves lock together so that they open the same. The lift, duration, overlap, and timing are not changed at all on the other intake valve. This occurs between 1500-3200 depending on throttle and load.

The theory behind them are completely different. The purpose behind them are completely different. The operation behind them are completely different. The only similarity is that you can interchange a spool valve from a D15Z1 onto any 92-95 D-series SOHC VTEC motor and vice versa, or between the Y5 and Y8.

I have a feeling that you know this already but you gave the wrong impression with your wording.
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Old 04-13-2008, 11:09 PM   #27
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Quote:
Originally Posted by maxxgraphix View Post
We all know that the VX D15Z1 can do 20:1. My D15B is a close cousin.
Be careful about this assumption. The blocks are very similar but the heads are different than night and day.


The VX throttle body is very small.

The intake manifold runners are small. The ports are small. The pistons are different. The valve switching mechanism is different. The injectors are 190CC vs your 240CC. The rev limit is much lower. Torque peaks at a lower RPM. As a result, one head will have very different timing and fuel demands than the other. One head will tolerate upwards of 22:1 while the other will only tolerate 16:1. One head will have it's peculiar bottlenecks at different points than the other. One head's peak VE is at a different point than the other.

What this means is that you will not benefit by copying the P07 calibration onto your ECU and running your motor with it. You are much better off sticking to the stock calibration and modifying it from there.

Try experimenting by first identifying your cruise load and throttle and then leaning out those portions of the map while adding timing. Burn through enough gas to get a good average, and then try even more.

You can safely run this motor at 13.2 in it's max rich regions. I'm not sure what the stock calibration runs.

Don't run leaner at idle. This wont help your fuel economy because it will cause the RPMs to wander. Even the VX runs 14.7 at idle. At nearly all points of the calibration except WOT high RPMs and at cruise in fact.

I hope that I have been helpful.
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Old 04-13-2008, 11:15 PM   #28
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Quote:
Originally Posted by DRW View Post
One of the charts I printed off the web, which is no longer available shows that power and fuel consumption drop off as A/F ratios get leaner, but fuel consumption decreases quicker than power up until around 16.0 to 16.5:1 A/F ratios. That chart was generated using a locked throttle and fixed ignition timing. It also shows power peaks around 12.0, cylinder head temp and knock propensity peak around 13.5, and exhaust gas temp peaks with NOx at 15.7
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That chart is here: http://forum.aempower.com/forum/inde...ic,2762.0.html

but you can't apply those numbers to it w/out a disclaimer. Those numbers are very general and often they are correct because engineers design motors around those numbers. But engines such as the D15Z1 are exceptions and those numbers do not apply.
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Old 04-13-2008, 11:24 PM   #29
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Originally Posted by DRW View Post
Besides emmissions as Maxxgraphix stated above, keeping a 14.7:1 A/F ratio also yields better power and responsiveness.
I want to add to/clarify this slightly.

14.7 is a compromise. It's not the best power, and it's not the best economy. If I want to pull some numbers out of my behind, I'd say 13.2 will yield the best power and 15.5 will yield the best economy (on your typical modern EFI, stock N/A motor). 14.7 is right smack in between. It just so happens to be the point where under laboratory conditions, all the fuel is consumed by combustion. What seals the deal is that this is also the point at which total emissions are at their lowest. You can further reduce one particular regulated gas by richening the mixture, but this increases output of one of the other regulated gases (which decrease with leaner mixtures). Gasoline is an imperfect fuel. If it were perfect, then the air fuel ratio that gave you the most power would also give you the best economy and zero emissions. Oh, AND it would have to make somebody very rich or else it's never going to happen in a capitalist economy.

Running leaner than 14.7 ensures that there is enough oxygen present to increase the likelyhood that all the HCs are burned. But it doesn't guarantee it as a smog report will prove.

The reason you don't see race cars running 13.2 at max load and RPM is because it will blow the motor. There is always a variation between cylinders. You always have a leanest cylinder that gets more air than any other despite the best efforts of the manufacturer. This cylinder affects the afr which is a measured average of the total cylinders. A common occurrence is for a tuner on the dyno to gradually lower the afr because it keeps making more power, until they reach a point where one cylinder burns down.

There is at lest one form of drag racing that will run that lean, but it's only because the engines are built for one event or maybe even one single pass and then torn down or thrown away.

NASCAR and some other forms of racing actually tune each individual cylinder. That means individual sensors on each. Each cylinder has it's own timing and fuel correction from the main map. The AEM EMS and some other standalones are capable of individual cylinder trims, but for most people it is simply too much time and effort (which means $$$ spent).
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Old 04-13-2008, 11:33 PM   #30
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Quote:
Originally Posted by DRW View Post
I use the same tune for all of my driving. The high throttle, high load section of the fuel and timing maps are set up for max power. It's very rich (about 10:1 A/F ratio) and timing is low (9 to 18 degrees at high rpm)
Light load, light throttle is tuned for max FE. It's very lean (16.5 to 18.0:1) and timing is high (32-37 degrees around 2k rpm).
The areas between max power and max FE are blended together so the fuel and timing values transition gradually. The car seems to run smoother and more predictably when the transitions are smooth, it doesn't like on/off steps.

Edit: The A/F ratio I use is very rich because the engine is turbocharged. Believe it or not, I've leaned out the WOT settings slightly. Factory A/F ratio at WOT was 9.3!
Yeah this is the one I was speaking about in my thread. Your edit makes a big difference. High compression or force inducted motors will make more power with a richer mixture than a normal motor. Another thing is that I often assume that we are speaking about Honda motors because I've only visited Honda-specific forums for the last 6 years (before that it was a Toyota forum).

9.3 is stupid rich. All manufacturers including Honda default to a ridiculously rich mixture under extreme conditions. This is to protect them from getting murdered by warranty engine replacements.

What I like about this post is that you clarify that you don't need a separate economy map and a separate power map. One tune does it all. This was a huge revelation for me when I first started learning about standalones.

You can't oversimplify and say "I run lean" or "I run rich". All calibrations should have lean and rich portions of the map.
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