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stevie 77 930's Avatar
 
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Finally set my AFR's w/ BL WUR

Inspired by the "the slilent killer of 930 power and fuel economy" thread

Well after several weekends and some bad rainy weather here in LA, I finally had a chance to dial in my Leask WUR on my 77 930 this weekend. I was able to borrow a LM1 and CIS pressure guage from my local BMW shop owner. My tuning conditions were less than perfect, IE i used a c-clap to hold in the O2 senser in the tail pipe and I had to hold the LM 1 unit in my hand while driving. I did have a deserted street in a business park that was 1/2 mile long...not perfect but I think I got it pretty good.

Here are some of my pre-adjusted #s on a car that ran pretty well before I made any adjustments:

warm idle AFR 13.10
crusing AFR 13-13.6
WOT AFR 9.8- 10.2

I am running total stock internals and stock 3LDZ. I do have have later style exhaust with J pipe, a garrettson intercooler with 965 BOV and I am running .90 boost with 29 degrees of total advance. I am also running a 84 carrera 915 gearbox with LSD. Calif car so I am running a smog pump too.

I first set my idle AFR's to 14.50 in the garage. I then headed out to set crusiung AFR's armed with a few wrenches, allens, and a pressure gauge. Using Brian's WUR make these adjustment pretty staight forward. I increased my warm pressures to 3.85 bar and i saw my cruising AF'R's get to 14.5 so i was pretty happy with that. Next was WOT adjustments. While making runs, I notice the AFS drop quickly at around 3000 rpm, by the time I got to 5000 rpm I was making full boost and saw AFR in the low 10's or even 9.9. I first increased the threashold at with pressure would drop. Slight adjustments to 3 screws at the bottom of WUR, and I managed to delay the rich condition until 3500 rpms. Next, I needed to increase WOT presures. Again, the adjustable WUR made the relatively easy. A good wack to the bottom diaphram , I saw WOT AFRs' increase to 11. One more time and I got the AFRs to 11.60-11.80 on WOT.

Gone is the eyewatering exhaust on idle and I am hoping to get rid of the black exhaust residue on my bumper and more importanly, get my gas milage to something more than 11-12 MPG's on the fwy. To soon to tell, but the car is running absolutely prefect. So here are my #'s....
14.50 idle
14.40-14.50 cruising
11.60-11.80 at WOT at full boost.

This morning I had a tough time starting, so I check my cold pressures and they were to high @ 2.75bar. One more time with the pressure gauge and lowered the pressure to 1.90bar. I think I finnaly got it.....

I look forward to your comments. Thanks to all on this board who provide such great information.
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1974 914
2018 GTS
2017 BMW 340I M Sport Package
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1976 911S , 1973 1/2 911T, 1972 911E (long gone)

Last edited by stevie 77 930; 01-24-2010 at 10:40 PM..
Old 01-24-2010, 10:36 PM
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sounds like you've got it...

Q: did you purchase the RPM switch??
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LIVN80S - - Red '79 Porsche 930 Steel Slant Nose Conversion [in 1987] w. 46k miles 3.3L; 964 Cams; K27HF @ 1.0 BAR, with Garrettson Intercooler; Rarly Zork; CIS Flowtech Fuel Head & BL-WUR.
Old 01-25-2010, 08:10 AM
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Quote:
Originally Posted by mooney265 View Post
sounds like you've got it...

Q: did you purchase the RPM switch??
+1...The rpm switch will flatten out that over rich condition at the lower rpms'.
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Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 01-25-2010, 08:28 AM
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A mostly stock 930 should not have so much of that big over rich issue on first boost.

FYI, if it was on the cold side outside say in the 50's when you set things up. Then during the summer temps will be in the 90's, you might need to reset you CO as things will get richer with the change in air density.

Last edited by 911st; 01-25-2010 at 08:51 AM..
Old 01-25-2010, 08:45 AM
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No RPM switch. Brian Leask suggested i try it without. I suppose I can fuss with the threashold settings a bit more to keep it from getting rich too soon.

When I adjusted cold setting in the AM,it was in the low 50's. I ll throw the pressure gauge on as the temps pick up in the spring and summer.

It pretty empowering when have a bit more control over what happening accross the spectrum of conditions
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1974 914
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1976 911S , 1973 1/2 911T, 1972 911E (long gone)
Old 01-25-2010, 02:16 PM
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Once set up you should not have to mess w a pressure gauge or the WUR again unless you add more mods that change air flow capacity significantly or play with the Fuel Distributor to increase it's flow rate.

Should only have to mess with the CO setting for warm weather. A wide band should be all you need.

With higher weather temp's you will get a little richer. Not a bad thing to some degree as it will protect against detonation to a degree.

Something that is interesting is the factory WUR on the 75-77 3.0 turbos enriched with loss of manifold vacuum. Not when boost hit 5psi or so. like the 3.3 Turbos.
Old 01-25-2010, 03:06 PM
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Here is an example of a good stock AFR curve. Note that the fuel curve is most rich where TQ is peaking as that is where we are most sensitive to detonation. After that point we gain some HP by leaning up a bit.

Near perfect fit.

It is when we start gulping air faster that we blow through the AFR curve.


Quote:
Originally Posted by krasuskyp View Post
...
Stock '87 mit 40k miles, 'cept for gutted cat, GReddy Profec B Spec II MBC set to 0.8bar, and spring centered clutch. Sea level, maybe 60F, Mustang dyno.

All in all I'm giddy at the curves - AFR's were so spot on Tony didn't even want to bother tinkering with anything, let alone pulling a 3rd pull - sweet! I basically called the whp dead nuts (I predicted 250whp, and was 249 before "smoothing), while torque on the other hand was waaaaay beyond expectation (even moreso before smoothing).


Just a note, most car makers program there turbos to run in the 10's on boost to protect the motor. We seem to want to be in the mid 11's with higher boost but there is more power in the 12's if the boost plus compression thing is not to high.

Last edited by 911st; 01-25-2010 at 03:37 PM..
Old 01-25-2010, 03:27 PM
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Yep, sounds like you nailed it.

Here in GA, for those who want perfect AFR's, ambient temps will move the AFR's a bit. I had to adjust mine for warm temps vs cold to get the best tune.
Old 01-25-2010, 07:43 PM
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You are there. Stockish engines don't need the RPM switch. You should now enjoy 20mpg even with the low 915 gearing. Those tranny's are a hoot behind a mild turbo!
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Old 01-25-2010, 08:31 PM
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A footnote to 911st comment.... I am using a 054 WUR on my 77 rather than a 112WUR typically used for the '75-'77 930's. The 112 requires vacuum to lean after initial warmup. Brain Leask suggested I send him the 054 to modify rather than the 112. After installing the 054, I just plugged the vacuum hose from the throttle body and obviously still using the boost enrichment side of the WUR. The 054 vents to atmosphere. The beauty of the adjustable WUR is the ability to lean or richen certain aspects of the curve, cold and warm. There just isnt enough adjustability in the idle mixture screw.

I ll run the rest of the winter and spring as it is and will check ide c/o % when summer rolls around.

Drove to and from work today, mostly fwy. Car ran fantastic. Boost seems more linear than before. i logged more than 65 miles on less than a quarter of a tank of gas. I am thinking somewhere around 17mpg's , maybe a little better.
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1974 914
2018 GTS
2017 BMW 340I M Sport Package
1977 930 (recently sold)
1976 911S , 1973 1/2 911T, 1972 911E (long gone)

Last edited by stevie 77 930; 01-25-2010 at 09:21 PM..
Old 01-25-2010, 09:14 PM
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