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tirwin tirwin is offline
Hey, nice marmot.
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Join Date: Feb 2011
Location: Marietta, GA
Posts: 5,297
Originally Posted by AndrewCologne View Post
Hello everybody
and especially all Porsche lambda, raspberry loving and ... coding cracks. :-)

These days I was thinking of enhancing the lambda control by using a "wideband" AFR gauges "0-5v" output possibilities.

All I would need is a unit to tell via 12v PWM output the Frequency valve to operate at specific PWM rates, means duty cycles.
This unit would get the input via the 15c temp switch, the 35c temp switch, the micro- and the throttle angle switches at the throttle body and ... the 0-5v voltage signal of the AFR gauge system.

And so .. the closest way would be to set up a Raspberry Pi for this, as it comes with GPIOs (including PWM pin!).

What do you mean?
Any thoughts, infos, cents on this? :-)

PS: I already checked this thread but seems to handle WUR as subject only:
Let's discuss digital WURs and replacing K-Jet Lambda

EDIT: Its getting hot:
English sources are very welcome as well :-)

I've been busy lately and have been meaning to reply.

Here are my thoughts. This is a subject I've been thinking quite a bit about.

First, the K-Jet w/ Lambda box. Yes, it's 1980's tech. But the thing is you really don't hear much about these boxes failing. Not that it doesn't happen, of course, but you really don't hear much about them being a common problem source.

What you're talking about could certainly be done. I think there are a few issues:

1) I'm not sure the Raspberry pi/Arduino is the right platform. You might have better luck with using a Megasquirt ECU.

2) It would take some time & testing to account for the various states to reverse engineer the Bosch box. Take a look at this post by javadog. This gives a nice summary of the various states (or conditions) you'd have to account for.

3) I tend to agree with others that if you were going to go this route, it would be better to go with something like Megasquirt.

If you look at engine theory, you will come across the term BMEP (Brake Mean Effective Pressure). BMEP is the equivalent average pressure acting on the piston during the entire volume change in the cylinder. It turns out BMEP is a great way to compare most internal combustion engines, regardless of displacement.

When BMEP increases for a given engine, it is either because the engine was a) able to extract more power or b) the engine was able to draw more air (VE, or volumetric efficiency increase).

So why am I saying this?

If you play with the math, you can see that -- at least on paper -- there is latent power gain potential for most of our engines. The question is how much power can be gained by extracting more power and how much can be gained by increasing VE and at what expense?

The reason that people say turbocharging an engine is the cheapest HP gains is because a turbocharger dramatically increases volumetric efficiency. Now whether a given engine can handle turbocharging without blowing the motor is another question.

Take a stock SC 3.0 motor and convert it to EFI. You can do things like change the intake, cams, flow the heads, change the exhaust, etc to help the engine breathe. Those things will affect VE. The change in ignition and fuel delivery will allow precise control of the fuel delivery and spark timing which will help extract more power. Of course, you can increase displacement and compression ratio, but that is yet another cost increase. (If you HAVE to do an engine rebuild, that's one thing... but if you don't have to...)

The problem, at least as I see it, with an EFI conversion is that it isn't a simple swap out of CIS->EFI to get real gains. You'd probably want to change cams, intake, exhaust, etc. which adds additional cost on top of the EFI conversion itself. Now maybe you can do these things as incremental steps so financially you don't have to do it all at once, but my point is these are the kinds of things you want to eventually do if you want to reap the rewards so eventually most people will care about the total cost involved. (PS, some people claim that the domes shape of CIS piston are not ideal for EFI either.) The costs begin to add up quickly and there are many variables that affect the potential for real HP gains which makes it difficult to arrive at a meaningful cost/benefit analysis.

What I've been wondering is if there is a viable intermediate step in CIS->EFI conversion -- a "partial" upgrade to CIS to get some of the easiest gains without all the expense.

In a CIS K-jet w/ Lambda system, there are a few things that affect normal operating fuel delivery:

1) warm control pressure (regulated by the WUR)
2) throttle position
3) frequency valve & narrowband O2 sensor

(I'm going to ignore the bits that affect cold start for now.)

Basically, K-Jet regulates fuel delivery based on engine load conditions. EFI does the same thing and a lot more.

I like the FrankenCIS idea because you get a wideband O2 which gives you the ability to have better data and to do data logging. You also avoid the analog nature of WUR calibration, plus you can replace the frequency valve functionality too. To get the most potential out of it though, you'd want to be able to somehow know the engine load and also control the spark. Jonny (of Classic Retrofit) mentioned that he has played around with this idea and I'd like to see the idea developed more. To me, combining the benefits of his CDI+ electronic ignition timing control, multi-spark up to 10,000 rpm and more precise fuel delivery seems like it would be possible to get enough (but certainly not all) of the gains of an EFI conversion at a much lower initial cost. It is hard for me to say.

The alternative would be to integrate the Megasquirt/FrankenCIS ECU with some other ignition system to control spark timing.

A digital replacement for the WUR (AND the AAR -- why not?) would also improve reliability and reduce some of the troubleshooting hoops we usually have to go through.

Sorry for the long-winded answer, but you asked.

These are ideas that are rumbling around in my head. I'd welcome more discussion on this.
There are those who call me... Tim
'83 911 SC 3.0 coupe (NA)

You can't buy happiness, but you can buy car parts which is kind of the same thing.

Last edited by tirwin; 07-11-2018 at 10:29 AM..
Old 07-11-2018, 09:33 AM
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