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A/F ratio tuning
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2224
Location: MI

PostPosted: Fri Feb 26, 2021 9:40 am    Post subject: Reply with quote

I’d try setting cold and warm pressures to spec and then lean out your boost with the gold one on the bottom..

Or just try it with the vac line disconnected and plugged.. see what that gets you..
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2194
Location: Somerset, UK

PostPosted: Sat Feb 27, 2021 6:07 am    Post subject: Reply with quote

And this is why 930 owners were happy to pay for Brian Leask adjustable WURs. Its incredibly hard to juggle all the pressures. Every action has a reaction.......
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MikeDanger  



Joined: 21 Nov 2002
Posts: 636
Location: Denver

PostPosted: Sat Feb 27, 2021 3:52 pm    Post subject: Reply with quote

Carrera RSR wrote:
And this is why 930 owners were happy to pay for Brian Leask adjustable WURs. Its incredibly hard to juggle all the pressures. Every action has a reaction.......

Well when you have a 100K car vs a 1K car, thats alot easier to do!
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MikeDanger  



Joined: 21 Nov 2002
Posts: 636
Location: Denver

PostPosted: Sat Feb 27, 2021 4:13 pm    Post subject: Reply with quote

OK SO....

I hooked up the gauge and had 85psi system pressure; So far so good,
Closed the valve and 80psi Control pressure!!

So I adjusted the pin down, until it got down to about 35psi (Cold Control, 55-60F in the garage) according the the Factory chart.

Pulled it down more than I expected.

So I guess that explains some of it (didn't drive it yet)

Then I started the car, at first it started then died, I had to keep richening the CIS meter over 1 turn. (which is probably why it was so lean off throttle)

So now Im in the ball park at least.

I gave it some throttle and the A/F stayed fairly steady around 14-15.

Now while running after warm up, the Control pressure got up to 65, I leaned it out to 55 (as the manual stated) but it eventually climbed back to 60. So I was debating if this is because its heating up more, and I should leave it, OR I should turn it back down to 55?

Im wondering if I should have the A/F slightly leaner here at 5000ft going up to 8000ft
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MikeDanger  



Joined: 21 Nov 2002
Posts: 636
Location: Denver

PostPosted: Sat Feb 27, 2021 4:40 pm    Post subject: Reply with quote

One thing I can't quite figure out is, if it was so lean, then why did it run so rich on part throttle??
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Carrera RSR  



Joined: 08 Jan 2010
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Location: Somerset, UK

PostPosted: Sat Feb 27, 2021 5:29 pm    Post subject: Reply with quote

MikeDanger wrote:
Carrera RSR wrote:
And this is why 930 owners were happy to pay for Brian Leask adjustable WURs. Its incredibly hard to juggle all the pressures. Every action has a reaction.......

Well when you have a 100K car vs a 1K car, thats alot easier to do!


No. The point was many folks used to piss in the wind to get their fueling correct via the wur. It’s incredibly difficult as you are finding out. So Leask came up with a modified wur to make adjustments easier. If you give him the spec of your car he will set it up before shipping so it’s in the County and the car will run OK on installing. The owner then needs to get the car on a dyno so it can be dialled into the correct zip code.

I feel your pain. But it’s going to be a tough number of hours getting this dialed in on your car.
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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924RACR  



Joined: 29 Jul 2001
Posts: 8422
Location: Royal Oak, MI, USA

PostPosted: Sat Feb 27, 2021 9:42 pm    Post subject: Reply with quote

Of course, back then, it was not exactly common to be able to swap in a WBO2 and run it on your car for street tuning! So that was the other half of needing a dyno to set it up, simply needing the instrumentation to set it right, measure the results, and know you weren't overdoing it and going lean...

We are so lucky these days to be able to run far more complex systems on our street cars, and at obscenely cheap prices all told! The complexity of data and sensors that I now have on my 931 approaches what I run on my prototype (racecar), and the analysis capabilities aren't too far behind what I use in the day job (at Bosch)...
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2224
Location: MI

PostPosted: Sun Feb 28, 2021 12:30 am    Post subject: Reply with quote

A microsquirt box and free frankencis firmware can directly control your frequency valve and give you great tuning capability..

You could completely get rid of the WURs cold and boost changes and just tune all that yourself in tuner studio..

Works great and you get great logging capabilities too..
Also control your rad fans, boost, ignition if you want or not, all sorts..
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MikeDanger  



Joined: 21 Nov 2002
Posts: 636
Location: Denver

PostPosted: Mon Mar 01, 2021 6:52 am    Post subject: Reply with quote

Ok can someone 100% clarify which way the Bi-metallic plate moves when warm??

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MikeDanger  



Joined: 21 Nov 2002
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Location: Denver

PostPosted: Mon Mar 01, 2021 10:33 am    Post subject: Reply with quote

Ok figured it out. Looks like it goes the OPPOSITE of what I thought:


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Mike9311  



Joined: 14 Dec 2004
Posts: 1102
Location: Chicago-ish

PostPosted: Mon Mar 01, 2021 11:34 am    Post subject: Reply with quote

Fasteddie313 wrote:
A microsquirt box and free frankencis firmware can directly control your frequency valve and give you great tuning capability..

You could completely get rid of the WURs cold and boost changes and just tune all that yourself in tuner studio..

Works great and you get great logging capabilities too..
Also control your rad fans, boost, ignition if you want or not, all sorts..


I can't wait....
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1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
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1980 924 NA (R&D lightweight)
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Fasteddie313  



Joined: 29 Sep 2013
Posts: 2224
Location: MI

PostPosted: Wed Mar 03, 2021 4:16 am    Post subject: Reply with quote

Mike9311 wrote:
Fasteddie313 wrote:
A microsquirt box and free frankencis firmware can directly control your frequency valve and give you great tuning capability..

You could completely get rid of the WURs cold and boost changes and just tune all that yourself in tuner studio..

Works great and you get great logging capabilities too..
Also control your rad fans, boost, ignition if you want or not, all sorts..


I can't wait....


Here is my fuel system being tuned in its original home, on a merc V8..
https://m.youtube.com/watch?v=XMeaEuIRNRA
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MikeDanger  



Joined: 21 Nov 2002
Posts: 636
Location: Denver

PostPosted: Thu Mar 04, 2021 7:08 am    Post subject: Reply with quote

Small TIP here. With the CIS test gauge attached. If you suspect its running too rich, you can Partially close the check valve to raise the control pressure, and see how it affects the running.
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MikeDanger  



Joined: 21 Nov 2002
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Location: Denver

PostPosted: Sun Mar 07, 2021 6:00 pm    Post subject: Reply with quote

Well Another test drive:
So its driveable now. Started around 12A/F then then as it warmed up got to around 15 +/- as I started to drive, it would go up to 16-16.5 when at part throttle, and seemed to get leaner as boost began to build, until I went WOT then it dropped to 11.
I was getting a little worried. I got out and looked at the Pressure gauge it was showing 60psi. I slightly enriched the WUR (with the Bimetallic plate) and the CIS about a 1/4 turn. which enriched the idle, but the Odd thing was that it got LEANER as boost started to build until WOT again (I also gave the "boost enrichment under brass cap 1 full turn) and I got 12 at full boost.

I tried to enrich the CIS some more, but it didn't seem to enrich the Part throttle, that seems to stay in the 15-16 range.

Its a little tough to tune, when you have to jump out, open the hood, get back in..... and repeat several times.

Any suggestions from this point?

How much does the Warm Fuel pressure matter? Is the A/F more important than the pressure?

What is a normal Cold start A/F?


SO after I got back and parked it for 10 min, I started again and Initial start was 9.8 a/f(and a little shaky) but then quickly started to rise toward 14.
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2194
Location: Somerset, UK

PostPosted: Sun Mar 07, 2021 6:40 pm    Post subject: Reply with quote

MikeDanger wrote:
Its a little tough to tune, when you have to jump out, open the hood, get back in..... and repeat several times.

Any suggestions from this point?


Put it on a dynometer with a tuner who knows his onions and can adjust with clear view of performance gains/losses with each adjustment. Can also keep an eye on AFR and adjust at the same time with load on the engine. Yes it costs money, but will have a quicker outcome and limit the change of grenading the motor
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