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Good description, Jim. I used Weber DGV32/36 downdraft carbs on my old MG's....I can relate. Just need to take a very close look at the 930 throttle body relative to where the ports are to fully understand.
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Break through!
Mark, Welcome. Very nice car. I find your post very exciting! Your timing numbers are much more ideal than the US numbers we have been working with. We see about 10 deg with vac or boost retard and 18 deg mechanical. You see more like -14 with vac or boost and 12 mechanical. This gives you a greater jump in advance off idle, allows you to run more advance at cruse for greater efficiency, and still pull back a significant amount on boost . A better set up for sure. To me this info is HUGE! Several times I have stated I think a way to improve our systems is to increase the range of Retard available to us. I believe this can be done by modifying the stop behind the pot that limits the total retard we can get. Mechanical Advance can then adjusted to fit the ideal on boost goal. If you car is doing so, it is proof it is achievable. Here is how the combinations might compare-- Using stock US values adjusting idle to TDC. TDC at idle, -10 on first accel -18 on boost -28 cruse Your Euro car w idle set at TDC: TDC at idle, -14 with first acceleration, -12 on boost -26 on cruse. Using US mechanical w euro advance/retard: TDC at idle, -15 on first accel -18 on boost -33 on cruse Of course you can move all these values up or down by where the timing is set at idle. If we do this with the Euro to get the on boot to -18 it would look like this: -6 at idle -20 with first accel -18 on boost -32 in cruse. This might give a lot better off idle pull, safe on boost, and better fuel economy on cruse. Ya! I love it! The best!!! ;) |
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Crazy people like me put in 10:1 mahle pistons, 300 degree duration BMW motorsport or Shrick cams, Stahl tuned headers, and dual sidedraft Weber 45 DCOE carbs with 38mm venturi's while hogging out the intake ports to around 44mm after looking at and studying alot of pics of Jim Rowe's BMW M10/M30 engine intake porting theory in his Metric Mechanic book. |
Ignition Retard, CIS, Lean surge, resident boost?
Another light bulb might be going off. Carbs and EFI have a method to deal with the lean surge that comes with acceleration by increasing fuel flow. 3.3 930's do not. (stock 3.0 930's do.) If we run significantly retarded timing as Porsche specs at idle, the adjustment at the air bypass screw must be opened to keep the idle on target. This increase in air and fuel then lies in wait for timing to create acceleration by just quickly advancing the timing. With retarded timing exhaust temps go up as the fuel is still burning when the exhaust valve begins to open. Thus, less energy it imparted on the piston and more on the turbine. This should increase our resident boost. (I used to have about .2 bar off idle.) We have found that more advance increase pre-boost response. Could it be we want to keep our timing retard at idle and concentrate jumping advance more off idle. If so, for those going to a programmable MSD, you might try keeping idle timing close to stock spec and then get aggressive with timing advance with acceleration. |
In real life use just removing the red vacuum retard line from the distributor advances timing around 10 degrees at idle and makes these cars alot peppier at city driving speeds without boost so I don't promote the stock retarded ignition timing at idle.
There's no use for it other than the higher exhaust temps it causes at idle to help heat up the catalytic conveter and lower exhaust emissions. The 1987 930 owners manual even warns against letting these cars idle a long time while adjusting the idle CO because it overheats the intake ports from heat transfer from the exhaust ports and there is less cooling airflow from the fan. FWIW, apparently letting the cylinder head ports overheat will make it difficult to properly set the idle CO accurately. I've never heard anyone besides you talk about off this "off idle lean surge". I don't have an off idle lean surge with the modified fuel head in my car and I don't think my buddies '87 930 with a stock USA fuel head does either. We both have the Innovate LC-1 controller and analog AFR gauge to see whats happening. The 930 CIS takes a second to react to throttle changes with the low airflow going through it just off idle but from my experiences it's not a "lean surge". |
J,
If just removing the Vac-Retard connection (not removing and resetting timing) to the pot makes the car snapper then the power of more ideal advance overrides which is something I was wondering about. I do not like the idea of making any more heat than necessary. I do not know if 'lean surge" is an accurate term to describe my observation. It is not so bad the car coughs. On my 3.3 C2T with euro fuel distribution head I used a stand alone Motec wide band when setting up my controller driven Andial-Fueler frequency-valve to dial in my AFR's at all points off WOT. (WOT was done on a load dyno.) With aggressive throttle application I noticed my AFR did lean at first. If I was set in the mid 14's at idle -- I would see a jump into the 15's briefly with aggressive acceleration. I am surprised if this is not evedent to others running Wide Bands. If that is the case, I guess I could have had an issue others do not ( such as binding in the metering plate, thought I had it apart to blue print the metering pin travel and noted nothing). Another possibility might be the Motec unit was more sensitive to change. I know the O2 sensor was Mote supplied and new. Maybe there could be some level of soothing difference between the two instruments to make them more readable. I believe most of the sluggishness of CIS comes from the metering plate restriction and mass. Many CIS cars add enrichment (reduced control pressure) with loss of vac including VW, Audi, and Porsche. I was told the 3.0T did, 3.3's do not. My biggest single improvement to throttle response off idle was aggressively lowering control pressure with acceleration for a brief period. I am surprised no one else sees some leanness at first with aggressive acceleration. |
Wideband AFR gauge kits have gotten better over recent years so if anything the new ones are more accurate than the Motec you used when you had a turbo. I think you've said that was around 6 years ago?
My friends car and my car are both USA 1987 models and both have 964 cams. His car has a stock USA fuel head and both cars have a K27 7006 turbo and halfbay Garretson intercooler. Both of our cars idle alot smoother and faster with the AFR hovering around 13.8:1instead of 14.7:1 when fully warmed up and thats where we have them set. Maybe thats why we don't go lean into the 15's when first giving it the gas. My steady cruise AFR is around 14.7:1 at around 2000-2500 rpm and then it hovers around 14.5:1 at 3000rpm in 4th gear or 80mph on flat Florida roads. |
I don't see the leaness, Keith. If it's there at all, I'm talking a scant 1/10's or 2/10's AFR for a half-second while the metering plate moves, but not noticeable from a seat of the pants performance standpoint.
If we really wanted to test it, and since I still have my old Andial fuel enrichment gizzmo plumbed in, I could trigger it at will from the cockpit...say within the first second of touching the throttle, and force a rich condition. Or as I threatened to do before, put a window switch in to activate the Andial at 1200 rpms and turn it off at 2500 or some arbitrary point like that. The problem with all that is too many gizzmos hanging around the engine bay, doing what a nice programmable controller could do (such as you once did, and as Thierry has done, with the AIC). |
JF,
I have suspected setting the CO at 3% was to improve off idle TQ. Do the LC's have a sensitivity setting? Anyway, when I got done with my set up I idled at about 14.5 and with accel would jump to about 12.5. Again, I lowered CP to under 1.9 bar for a brief time with acceleration and did not know about 13.2 was a more powerfull setting. Same thing on cruse. About 14.5 and instantly to 12.5 then to 12.2 on boost per the advice of my tuner at the time (he was an import turbo guy). I told him I wanted to be in the 11's on boost but he talked me out of it. I think I ended up at just under 13/1 at read line at .92 bar (K27-7200) where I was running out of fuel and could get no more air out of the turbo. |
I think stock CIS provides acceleration enrichment through overswing of the sensor plate as you initially jump on the gas. This momentarily takes it past the full throttle open position. This is set out in the Bosch Technical Instruction for K-Jet (probably shouldn't post the extract).
On my logging I can't find an instance where AFRs go lean as the throttle is aggressively openned in gear. AFR's seem to drop in direct relation to RPM climbing at WOT. Perhaps it's not sufficiently granular but you can't see it on the trace. David |
There is no sensitivity setting on the innovate lc-1. It's a weather sealed unit.
To fully calibrate the lc-1 the first time or if it has become corrupted you have to clear it's memory by turning it on for 20 seconds without the o2 sensor connected and then turn it off. Then you connect the o2 sensor in free air with no exhaust fumes around it and turn it on for 2 minutes to calibrate the lc-1 to the o2 sensor and it's heater element. Then turn it off for at least 30 seconds before starting the car with it installed in the exhaust pipe. They say you should do a free air sensor calibration once a month on a turbo car, and before every track session in a track car. You don't have to do the memory clearing step every time if it is working correctly only the free air calibration and a little red button and red LED come with it for free air calibration. You don't have to remove it from the exhaust to do that either, just wait overnight and do it before starting the car once a month or whatever. You can update the firmware on it with a laptop if needed but thats more involved. |
Got it, the LC's can be calibrated but there is not adjustment for, shall we call it, refresh rate or soothing.
Maybe this is not even a function of O2 monitors as they do not react to changes in AFR's fast enough to need such a feature. It seems the way CIS is designed it is much more sensitive to air flow changes off idle and cruse. This is part of how it deals with potential for lean-onset, shall we call it. Some of the WUR are vacuum sensing so when vac is reduced with acceleration the reduce control pressure some to richen the AFR for acceleration for what it is worth. Seems getting our AFR's to about 13.2/1 pre boost (max TQ setting) and the timing advance right is going to be our best goals. |
Found some old info from from a very good source on Rennlist back in 2001 when I was setting up my programmable CIS Fueler and was looking into what my AFR's should look like that might be a couple of interesting timing data points:
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;)
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He said: "I run about 14.5:1 and about 37-38 degrees of timing". and he said "...run about 26 degrees of timing under full boost - 200kpa (1bar) except where my torque is peaked and there I run 24 degrees of timing. I aim for a 12.2-12.5afr". I know that information is specific to an EFI car. Personally with CIS, I run about 38 degrees advanced at 4000 rpm's no-boost/14.2:1 AFR, and about 16 degrees/11.8-12.0 AFR on full boost. Safe with neighborhood generic 93 octane gas. Interesting to see where additional timing can be had without ill effects, though I don't think I have the balls to go with that much on boost with the relatively crude CIS. |
Some great data points from a real expet I thought would be good to referance here:
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Here is where it cam from: http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/537769-replacing-distributor-2.html
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I appreciate Richards input. If I had the money he charges for his parts I could go to EFI.
Cole |
Let the street be your dyno and let the SafeGuard adapt timing in each cylinder to the conditions on that day.
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john at J&S - is there some tuning needed to get the safegaurd working right? I thought the air cooled motors were so noisy that knock detection was difficult
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