1% CO Setting... Blazing Fast!

[CT911SCDriver]

Hello fellow Porsche owners... There had been some confusion as to why my 81 SC goes from fast to slow and back again every time some other shop gets their hands on it.

Well, after a lot of input from this BBS, I had heard about a lot of 3.5% CO mixtures being set on the SC. Well, after going back to the one Porsche Technician at the Porsche dealership (a friend is the manager... I get "friend" rates! :-))who did the best and fastest engine setup... come to find out that my CO was not at 2.5% like I thought, but rather closer to 3.7% Anyhow, as I had thought, leaner is better for power, I was confused about whether or not to tell them to keep it rich at 3.5%... They came right out and said 1% is where it should be! The end result, the car is a totally different car! It is blazing fast compared to what it was set at before.

It's funny, I had it set to 2.5% and checked at 2 different shops (one said 2.5, the other 2.3)! How could they both be off by so much and Porsche comes in at 3.7%??? Someone is way off on calibration... My guess is that Porsche checks more often than the shop who uncovered their machines just for me!

Think about this:

Leaner has got to be better for performance. For example, low temp thermostats seen on a lot of performance cars from my understanding keeps the car cooler, and leaner for more power. Why wouldn't the same theory apply to the SC???

Thanks.

Cy
81 SC

[wckrause]

The ideal mixture is 14:1 air/fuel (mass). Being on the leaner side results in higher efficiency, on the rich side results in better performance. Running leaner also results in running hotter. Can't explain why it seems you're experiencing the opposite, unless you were running so rich that your plugs were fouling.

Look at figure 2. from this link from a Bosch manual. Max power is on the rich side of 14:1.

http://persweb.direct.ca/aschwenk/page3.gif

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Bill Krause
'79 911SC Euro

[This message has been edited by wckrause (edited 06-04-2001).]

[This message has been edited by wckrause (edited 06-04-2001).]

[Jdub]

Wasn't there a thread recently that detailed how, if you do not remove the Oxy sensor or something, might cause a reading like 1% where in fact it is higher, or at least different?

This setting seems low to me. I can't quite understand how all the conventional wisdom seems lost where a 1% setting would cause the Pcar to rocket. If this were true, then...

Jw

[emcon5]

I wonder if the other shops were testing it at the tailpipe, and the dealer used the test port before the cat.

Tom

[Superman]

My CAT lost its guts this weekend (for track use only, of course) and I like the sound better. It also seems to have a little more power, though that's as subjective, and suspect a conclusion as you will ever see.

Lean mixures make engines run hotter. In fact, lean mixtures can burn exhaust valves. Usually, if your mixture is too lean, the engine will POP during deceleration.

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'83 SC

[pacmyster]

So is it just a crap shoot to find the setting that works best for our individual cars?? I converted to the pre 73 header setup and I think there are more ponies to be harnessed.
Pete

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'77 Carrera3.0 www.geocities.com/pcafaro2000/carrera30.html

[CT911SCDriver]

By the way... I am running without a Cat, and without an O2 sensor. I'm worried now that I may be too lean! And may cause damage to my exhaust valves!!! What the heck does Porsche call for on these engines??? The dealer tech. says 1%

So what is the truth to all of this? Lean is better or is rich better for performance?
I hear both sides of that!!!

Mystery to me.

As far as the blazing fast thing goes... it may be a bit exaggerated. I'm saying for those who run too rich, the difference is noticeable for sure if they lean it out.

Cy

[Leland Pate]

I would steer clear of "lean".

[stlrj]

Cy,

Finally there is someone else out there that has seen the light!

The 3.2 Carrera also responds very well to lean; made mine much quicker and with more torque, feeling a lot like a 3.6 now. I know because I just tested a 90 C4 on Sunday and my 3.2 feels just as fast.

I think there was a discussion in and earlier post of someone else leaning out his air flow meter about ten turns and increasing his performance too.

Don't have to worry about burning your valves either because it just runs cooler just like you experienced. In fact, I'm even running hotter plugs because it runs so cool.

In case you're wondering, rich mixtures have a nasty habit of wearing valve guides prematurely, toasting your cat., prevents your rings from seating and overheating you engine$$$$$$ not to mention what it does for gas mileage...

Cheers,

Joe Garcia
86 Carrera

[This message has been edited by stlrj (edited 06-04-2001).]

[This message has been edited by stlrj (edited 06-04-2001).]

[wckrause]

Please look at this link, and read it.

http://persweb.direct.ca/aschwenk/page3.gif

There is no mystery, that max. performance is achieved with a mixture that is richer than 14:1

It is possible that you were running extremely rich (far left of figure 2.) and that by making the mixture less rich, it increased performance.

[stlrj]

Bill,

What you may not realize that no matter how lean you try to set you injection, it will always slam full rich at wide open throttle and ignore the 02 sensor signal keeping your mixture rich; well below 14:1 no matter what you do...OK?

I do believe that by leaning it out we are moving our mixture slightly right of Pemax in fig 2. and if eveyone else is slightly left of that point it could explain the lack of performance at that level; on throttle and WOT enrichment would move you left of Pemax and result in poor performance.

If, on the other hand, your mixture is set slightly right of Pemax then on throttle and WOT enrichment would instantly move you to to Pemax which would result in increased performance.

Joe

[This message has been edited by stlrj (edited 06-04-2001).]

[This message has been edited by stlrj (edited 06-04-2001).]

[wckrause]

Joe- I know how that is done in a CIS system, by the vacuum connection to the WUR.

What you would want to happen, is to have the mixture at full throttle be at that peak point of Figure 2. on my previously mentioned link. The net result is during idle, and light throttle the mixture is slightly lean (best economy), but at full throttle the mixture is slightly rich (best performance).

My point is, lean does not mean best performance.

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Bill Krause
'79 911SC Euro

[CT911SCDriver]

Joe - is that true? That no matter your setting, it is full rich wide open? So, basically, the setting only affects idle???

Cy

[This message has been edited by stlrj (edited 06-04-2001).][/B][/QUOTE]

[wckrause]

I don't understand the term "full rich". A CIS system get's richer at full throttle. It's a function of the Warm Up regulator.

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Bill Krause
'79 911SC Euro

[CT911SCDriver]

Joe - Ok, sorry, no such thing as "full rich"... I simply meant gets "rich" at full throttle :-)

So, it will really only affect idle. Also, I find the engine sounds a bit different (in the valve train perhaps) when leaned out... and at idle. I notice a very slight "chirping" when leaned and at idle and as soon as I begin to accelerate.

[wckrause]

Not just at idle. As you open the throttle, the WUR gets more vacuum, which causes it to enrichen the mix. It's not an ON/OFF function. I think on some CIS systems with Lambda there is a full throttle switch that will enrichen the mixture further at full throttle, but I'm not sure about that operation.

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Bill Krause
'79 911SC Euro

[pacmyster]

AAAAAAAAHHHHHHHHHHH!!!!!!!!


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'77 Carrera3.0 www.geocities.com/pcafaro2000/carrera30.html

[CT911SCDriver]

Joe - it makes sense. Thanks. By the way, no cat, no smog, no O2 sensor, or any other emissions stuff on my car. I have B&B headers and exhaust too. I do know from a different post that the lambda system under the seat does something (even without the O2 sensor in place) as temporarily disconnecting the relay there does make the car idle different.

I take it that your euro is setup like mine except for the larger intake runners and euro fuel distibutor... and no restrictive emissions crap.

Cy

[CT911SCDriver]

Here's another finding I got a lot of criticism for... throttle linkage and leverage.

OK, my car was taken in for having only 1/2 throttle when the pedal was pushed to the floor. The porsche tech pulled the pedal far back, actually leaning slightly towards the driver's seat. I know it is said that will cause the linkage to bend. But here's what I noticed; that when the pedal was pushed it was achieving full throttle midway... at the rear of the car the linkage would stop at the throttle stop but the the lower section kept going and the spring just opened up until my pedal hit the floor.

The end result: was better leverage and hence, the quicker snap I felt with the car taking off and right up until 5th gear. The better leverage translated into quicker "flooring" response and quciker response overall. I swear it will amaze you!!! Pure physics here. I would try it if you never have (take the risk of bending linkage in your own hands). Unfortunately, my linkage did end up taking up slack again, and now full throttle is on the floor. I want to adjust it again making sure the nuts are tighter on the rods.

Just my finding and thoughts.

Cy

[Superman]

AAarrrrrggghhhhh.

Okay, here's the deal. the first generation of CIS (K-basic) is a purely 'mechanical' system. Incoming air moves the sensor plate and this mechanically sends gas to the injectors to match the air volume. It does not 'richen' the mixture, it just sends more gas because there is more air. On these systems several things contribute to the mixture, only one of which is adjustable. Unless you have an adjustable WUR. As most WURs are not adjustable, this and the fuel distributor are not adjustable...they are only working or not working properly.

The mixture control screw is between the fuel distributor and the air boot, as most of you know. This should adjust the mixture throughout the entire range of operation. If you get this adjusted too far to one side or another, there will be a flat spot, or poor running spot at some RPM.

the lambda systems simply add an O2 sensor, and what this does is to reset the mixture to correct spec even if it is not adjusted properly. Turning the adjusting screw without unplugging the O2 sensor will nto work because the frequancy valve will adjust re-acjust eh mixture, at the O2 sensor's command.

Both these systems, particularly the lambda systems, cause a car to run leaner than it really should. This means hotter and is a threat to your exhaust valves. If you richen the mixture, the O2 system will still keep your mixture lean. If you do this and unplug your O2 sensor I believe you will burn your CAT because the CAT will have too mcu gas to burn. If you don't have a CAT, unplug your O2 sensor and richen the mixture a little compared to spec.

Ont he K-Lambda systems, the O2 sensor is shut off during full throttle, to protect the engine from the pinging that will kill it during open throttle maneuvers.

Oh, and they key to power and performance is not 'richness' or 'leanness.' It is just an ideal mixture.

White spark plug electrodes mean the mixture is very lean. This is how they'll run when adjusted to spec. This setting does not kill CATs. The best setting for yoru motor is when the spark plugs are a tan color, but this is too rich for your O2 sensor and CAT.

I guess I had a little technical diarrhea here. Sorry.

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'83 SC