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What are the AFR ratio's you want for a 931 ?
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Dutch924-racer  



Joined: 23 Jul 2007
Posts: 1005
Location: The Netherlands

PostPosted: Sat Apr 22, 2017 5:10 pm    Post subject: What are the AFR ratio's you want for a 931 ? Reply with quote

My 931 (series 2) engine rebuild is finished I am now adjusting the mixture.

I have a Innovate wideband sensor/ gauge.

What are the AFR ratio's I want to aim for at:

idle
cruise
full throttle/boost
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CÚdric  



Joined: 27 Aug 2004
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Location: Sweden

PostPosted: Sat Apr 22, 2017 6:25 pm    Post subject: Reply with quote

I would start out with 14.7 at cruise and 11 at wot, should be a good start, thats how my cis is setup.
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ideola  



Joined: 01 Oct 2004
Posts: 15502
Location: Woodstock IL

PostPosted: Sat Apr 22, 2017 11:34 pm    Post subject: Reply with quote

I have two 931s with wideband AFR. One is with S1 CIS/ignition, and one is with Euro S2 CIS/ignition.

Get the car fully warmed up, to the point that your OIL TEMP is at operating range. Then go through the full regimen to set mixture and idle speed. Use the wideband gauge to get the mixture at 14.7:1 at proper idle speed on a fully warmed up engine.

On both of my cars, I get very steady idle + 14.7:1 AFR, and this results in proper cruise AFR, somewhere between 14:1 - 15:1, with WOT / full boost AFR in the 10:1 range. In my case, the WOT AFR may end up being richer than Cedric's because both cars are running higher-than-stock boost levels.
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morghen  



Joined: 21 Jan 2005
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PostPosted: Sun Apr 23, 2017 8:34 am    Post subject: Reply with quote

I keep mine at 13.5 AFR at idle, 11AFR at full pedal and boost.
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1565
Location: Somerset, UK

PostPosted: Sun Apr 23, 2017 8:33 pm    Post subject: Reply with quote

A stock WUR is extremely difficult to tune to ensure the best AFR's across the throttle and rev range. Many owners will report differing results. 14.7 is your target for idle and cruise. At wot, 10's is safest for non IC'd turbos. 11's is safe for intercooled turbos. Low 12's if you feel brave.

The one to watch with our cars is the mid range boost enrichment. Our wurs are set up for non IC. Therefore over enrichening the mixture as soon as boost kicks in regardless of throttle position. So sapping power and wasting fuel as you accelerate at semi or full wot and full boost. Hence the 'Brian Leask' type solution which many 930 guys on their modified cars.
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ideola  



Joined: 01 Oct 2004
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Location: Woodstock IL

PostPosted: Sun Apr 23, 2017 11:27 pm    Post subject: Reply with quote

Carrera RSR wrote:
At wot, 10's is safest for non IC'd turbos. 11's is safe for intercooled turbos.


Good point...

Worth mentioning that the two cars I cited are both intercooled: the 80 S1 (941) has progressive water-meth injection that starts sparying at 5PSI with progressive (linear) increase up to full boost (@ 12PSI). The 81 Euro S2 (Club Sport), of course, has many modifications, and is also running my TMCC (liquid to air intercooler).
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Dutch924-racer  



Joined: 23 Jul 2007
Posts: 1005
Location: The Netherlands

PostPosted: Mon Apr 24, 2017 4:50 am    Post subject: Reply with quote

My gauge at cruise before adjustment reads about 18-22.

I turned it richer but the car began to smoke, so turned it leaner again. After a test drive the spark plug looks very black and a bit wet. So still to rich.

I turned it leaner agian and now it reads about 13.5/14 at idle but the strang thing at cruise still around 16/17. On boost it drops to 12-14.

I don't understand it now anymore. The Innovate kit is just about 200 miles old and was recenlty calibrated.

If I go of the gass, the exhaust makes a popping noise.The exhaust is straight through sport system, so maybe it is normal.

My sparkplug (W-3-DPO Bosch platinum) looks now like this now:


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Series 2 engine
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937 DITC
Fast road camshaft
Forge recirculation valve + boost controller
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Carrera RSR  



Joined: 08 Jan 2010
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Location: Somerset, UK

PostPosted: Mon Apr 24, 2017 8:04 am    Post subject: Reply with quote

What are you turning ?
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Dutch924-racer  



Joined: 23 Jul 2007
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Location: The Netherlands

PostPosted: Mon Apr 24, 2017 4:55 pm    Post subject: Reply with quote

the mixture screw on the mass air flow meter (3mm allen key)
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937 DITC
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Forge recirculation valve + boost controller
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1565
Location: Somerset, UK

PostPosted: Mon Apr 24, 2017 6:46 pm    Post subject: Reply with quote

Dutch924-racer wrote:
the mixture screw on the mass air flow meter (3mm allen key)


That only effects the idle mixture not the AFR through the rev range. if you want to specifically adjust other areas then it's the WUR
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1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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morghen  



Joined: 21 Jan 2005
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Location: Romania

PostPosted: Mon Apr 24, 2017 9:32 pm    Post subject: Reply with quote

Carrera RSR wrote:
Dutch924-racer wrote:
the mixture screw on the mass air flow meter (3mm allen key)


That only effects the idle mixture not the AFR through the rev range. if you want to specifically adjust other areas then it's the WUR


I respectfully disagree. If you adjust for a richer mixture the CIS head/plunger will open more for the same amount of air drawn trough the plate.
WUR will increase the pressure when on boost so more fuel will flow trough the system.







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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1565
Location: Somerset, UK

PostPosted: Mon Apr 24, 2017 10:06 pm    Post subject: Reply with quote

I thought the same Ciprian. If you enrichen the idle mixture then this would enrichen the whole sytem in a linear way, therefore enrichen cruise and WOT as the same time. On my car it did nothing for the cruise or WOT AFR's, only the idle. But I did not over adjust to prove the theory.

I have read that there are two seperate adjustments on the WUR to change the AFR elsewhere in the rev range/WOT. I think I linked a Rennlist page in the thread I did when messing around with the boost enrichment/delay.

But I may be completely wrong
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1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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Dutch924-racer  



Joined: 23 Jul 2007
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Location: The Netherlands

PostPosted: Wed Apr 26, 2017 3:26 am    Post subject: Reply with quote

I forgot to tell, I run 98 ocatane fuel and car is now still on stock boost level.
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Series 2 engine
951S turbo and intercooler
937 DITC
Fast road camshaft
Forge recirculation valve + boost controller
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canyonblaster  



Joined: 20 Aug 2012
Posts: 386
Location: Denver, CO, USA

PostPosted: Fri May 05, 2017 9:43 am    Post subject: Reply with quote

Carrera (& others!),

Would my IC car benefit form this mod?

Hence the 'Brian Leask' type solution which many 930 guys on their modified cars.

(EDIT: I just sent an email to Brian Leask)

Thx

Carrera RSR wrote:
A stock WUR is extremely difficult to tune to ensure the
best AFR's across the throttle and rev range. Many owners will report differing results. 14.7 is your target for idle and cruise. At wot, 10's is safest for non IC'd turbos. 11's is safe for intercooled turbos. Low 12's if you feel brave.

The one to watch with our cars is the mid range boost enrichment. Our wurs are set up for non IC. Therefore over enrichening the mixture as soon as boost kicks in regardless of throttle position. So sapping power and wasting fuel as you accelerate at semi or full wot and full boost. Hence the 'Brian Leask' type solution which many 930 guys on their modified cars.

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Carrera RSR  



Joined: 08 Jan 2010
Posts: 1565
Location: Somerset, UK

PostPosted: Sat May 06, 2017 4:33 am    Post subject: Reply with quote

if boost is significantly increased and the dizzy advance and retard has been recurved and the timing advanced.
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1980 931 - forged pistons, Piper cam, CGT turbo, 951 ducted FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife LSD
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