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Alan L's Avatar
 
Join Date: Apr 2006
Location: New Zealand
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930 WUR adjustment

I have been tweeking my pressures and got the car to run pretty well with some good AFRs across the range. I should have left it there. But tried one more tweek to see if I could improve it. For whatever reason, I cannot get it back to where it was.
Internally there is the boost /main spring adjust - with an allen key. This seems to adjust cold pressure setting. I set mine at 24 psi. When I checked the boost dump I got 7 psi drop. So good so far.
I am now trying to set hot pressure - while leaving cold pressure at 24 psi. It is dumping far too much fuel on boost now.
I can find a small screw above the bimetallic finger. I have concluded this helps the hot pressure setting. Depending whether the screw is seated on a set of points , you seem to have two resistance ranges. It draws 2 different current rates depending whether the screw is on or off the points. On the points 0.48A, off the points 0.26 A. I figure this setting determines how much heat/bend the finger gets to set the hot pressure? Flipping between the two settings - depending where you leave the screw.
Except I can't get more than another 12 psi out of it. (36 psi hot max).
Unless I crank up the cold pressure again.
I'm trying to keep them down a bit because it leans off and hesitates too much on low throttle.
Dam this is frustrating. I had it nailed a few days ago - pulling well from 2000 rpm, holding 11.5 - 12.0 thru the boost range.
I just tried to nail the dead spot below 2000 rpm - which I could well have lived with.
Have I sorted these adjustments right?
Is there anything else I can do/tweek?
Alan
Old 07-03-2008, 03:22 AM
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Cynical Misanthrope
 
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Alan, do you have the C2T WUR? I've found my C2T WUR is a more complicated animal than the basic ones on the earlier 930s. I have a top bimetallic with your described two-resistor switch, plus a lower bimetallic and a bottom diaphram for altitude adjustment.
The top bimetal has two parallel resistors, and the switch you describe is a tiny bimetallic thermoswitch that ungrounds the second resistor on the top bimetallic at sub-freezing (approx) to warm up the WUR more slowly and provide longer enrichment during winter driving.
My lower bimetallic also had a heating resistor (it broke).
From my research the bimetallic strips should be OFF the spring seats at warm temperatures, so tweaking them should ONLY affect cold enrichment. The threaded inner concentric spring seat you mention I believe is warm adjustment, it's what I had to tweak to reach my 60psi warm CP. I have both my bimetallics completely retracted right now and accordingly I have NO cold enrichment. My car starts right off the key (credit the start-up injector) and runs great from cold with 4bar CP.
I tried lowering the threaded inner concentric spring seat and got asphyxiatingly rich CPs, but it seemed this was strictly warm CP. I could adjust this down to get <12 at WOT/redline, but it made for 12:1 cruise and <9:1 boost onset . This was a hot CP around 2bar
Sorry I could ramble on this for hours, but I was just in there A LOT and spent hours reverse-engineering the thing. I would love to tweak on the spring rates to adjust boost onset enrichment.
__________________
X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.
Old 07-03-2008, 09:33 AM
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Thanks Jon - I don't think I have the C2T WUR. The only other diaphragm I have in there is the boost one.
When I say the diaphragm springs -adjust (allen key screw) sets the cold pressure - it equally sets the hot - in that it sets the baseline pressure on the diaphragm. Which in turn affects the hot and cold ultimate pressures. Yes, I have reverse engineered them too - crude stuff for such precise requirements.
So, with the bimetallic screw off the points, (low current draw) it warms up more slowly - but ultimately gets to same pressure setting hot?
Makes sense - whichever way I went, and for however long on heat cycle, I got the same hot pressure. It would seem to only have a 12 psi range - which by the book is about half what it should be - WUR specs - cold approx 20 psi (depending on ambient temp) hot 50 psi.
So, I'm missing half the warm up range. I guess I'll just have to bump the diaphragm spring pressure up.
I wondered about playing with the single bottom spring for boost dump rates too. But it was working as per the book at 7 psi drop, and I previously had it running very sweetly with stock internals. But If I keep getting excessive dump at boost, I will harden this spring up incrementally - 10%, 20% etc.
If you know where to go, it is quite cheap to get custom springs made up - few $'s.
That will be my final tweeking option before buying a digi WUR - which may well be happening sooner than later.
The odd thing is, my cruise AFRs go too lean - flat spot on throttle. While on boost, with the low CP, it dumps too much. So I am struggling between the two ends of the spectrum. If it was rich on cruise too, it would be simple - harden the CP.
But I will give this another crack - since I had it working pretty well a week ago.
What screwed me up was I was tweeking the bimetallic screw thinking I was fiddling hot pressures - the measured response first time was precisely where I was trying to head. So, I kept at it for more tweeking. I am suspecting the response I measured was some inconsistent fluke in the WUR and threw me right off track.
Regards
Alan
Old 07-03-2008, 01:02 PM
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Cynical Misanthrope
 
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Is your car O2/closed-loop? Curious because I can screw up my CP pretty bad, so bad that it won't run with the O2 sensor unplugged, but the lambda circuit will drag it kicking and screaming into somewhere near stoich. But the higher the revs go, the richer it'll get the lower my CP is.
So yes I'd like to try a stiffer boost enrichment diaphram spring; shorter and stiffer so it may actually modulate enrichment based on pressure rather than staying up, up, up, then flopping down when you cross the 0.5b threshold.
If I was committed to staying CIS I'd go straight for the UWCIS though, and not monkey around with this contraption. I am, however committed to MSII. Parts are accumulating on the bench and I have to remind myself I'm broke every time the whileyerinthereitis starts in. So yes I'm going EFI, no it's not going to be a hero project at all.
__________________
X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.
Old 07-03-2008, 01:41 PM
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To try and answer more of your questions (rather than monologue-dribble), the tiny thermoswitch closes once it reaches a certain temperature, thus activating the second heater, thus bringing the bimetal to op temp. The purpose for this design is if the engine is started at sub temp (whetever the thermoswitch opening temp is set at) then the engine will have a longer enrichment period than the standard 120sec provided by the single element resistor heater.
As for trying to get your cold CP set, I think you'll have to carefully tap your bimetal post in and out, but being it is a VERY stiff spring it takes very slight changes to radically change the CP, and why I just ended up taking mine out of the equation. In NorCal I can get away with this, dunno where you are.
If you are compelled to get your cold CP, I'd start there, and set the bimetal post so that the bimetal end is completely lifted off the spring seat when it's at op temp (probably a pretty fine adjustment), then use the adjustable concentric spring seat to set your hot CP.
__________________
X-1, AFM744, Jon, '92 C2 Turbo
JE 8:1 pistons, 964 cams, 38mm intakes ported/polished/twinplugged, ARP hardware, B&B headers/exhaust, 355whp. Full-blown GT35R 3.2 intake EFI pending...
Where my misspent time and money is currently going.
Old 07-03-2008, 01:52 PM
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Thanks Jon. Could try shifting the pin as you suggest. Will lift the CP initially - I had it right once, maybe I'll hit it again. No not closed loop. I fitted my AFR as a remote unit - to monitor things and hopefully not blow anything up.
Regards
Alan
Old 07-03-2008, 01:57 PM
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