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Smart quod bastardus
 
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Join Date: Oct 2002
Location: Baltimore, MD, USA
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Quote:
Originally Posted by 356-930 View Post
The results you posted are the result of vacuum and absence of vacuum. The mechanical advance, whether working or frozen, has no effect at low rpm. Itís a centrifugal mechanism and dependant on rotational speed and speed change to act on timing. Donít know where it begins to move but not likely under 2,500 rpm.
Remember, the term vacuum advance is misleading. When a vacuum is pulled on the vacuum port of the distributor, it retards the spark. As vacuum decreases with rpm increase and/or engine load, timing advanced due to the loss of vacuum.
Based on your posted data, you are 7 deg advanced at idle with vacuum. Loss of vacuum moved timing to 27 deg or added 20 deg of timing which is as it should be.
Mechanical advance may vary from distributor to distributor but expect 18 deg.
Timing with full centrifugal advance in will then be 45 deg. If you hook up the boost retard (uses same line as the vacuum line) 8 deg of timing will be pulled out above 5-psi and net timing will be 37 degrees.
Based on the factory setting (29 degrees is marked on the crank pulley) 37 is a bit much.
I find it reliable on my í79 930 engine to disconnect the vacuum to the distributor, plug the vacuum line, run the engine up to 3500-4000 and advance the timing until the engine starts to stumble, back it off till itís running smooth again and lock it down. The point the timing makes the engine stumble is a nominal maximum timing level. With the vacuum hooked up again, suspect you will be close to 0 degrees.
If youíre not running boost retard, Iíd be nervous with timing in excess of 29 degrees at 4000, especially under boost with a potential of getting to 1-bar.
You should also be nervous if you donít have a handle on the engineís AFR under boost.
This is exactly what I stated in my post, except I see 22 degrees of advance without vacuum connected because it runs right up to the 29 degree timing mark, I guess this is still within tolerance of 20 degrees which you said was normal.
But what bothers me is the fact that with 18 degrees allowable in the mechanical advance, this puts me at 47 degrees BTDC at 4000rpm with my current set up.
Now if I hook up the boost retard line and get back 8 degrees that leaves 39 degrees total under boost conditions. This still is about 12 degrees too far if you target 27 degrees BTDC at 0.8-1.0 bar boost which from previous posts on the forum I see as safe limit. Is 27 degrees too conservative or can I run more safely? What is a real safe timing limit above 27 degrees I hope.
In order to get here I need to run 5 degree ATDC timing at idle.....and from my experience the driveability of the car at low rpm is absolutely horrible at this setting. I have even run around 0-1 degree BTDC before and this is the reason I am now at 7 degrees BTDC.......
I cannot see how the factory set the car to run at 5 degrees ATDC and got the car to move out of its own way at low speeds.
Last season when I was running the 0.8 bar spring at these same timing settings it ran well and I never heard pinging. I just wonder if it was still happening just not audible enuff for me to pick up on it, or if something has changed in my distributor over the past few months.
Need to try teeing the vacuum line into the boost retard fitting on the dizzy can and at least getting that amount of retard back....thanks for the tips.
__________________
1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 04-11-2008, 09:13 AM
  Pelican Parts Technical Article Directory    Reply With Quote #41 (permalink)
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Quote:
Originally Posted by fredmeister View Post
This is exactly what I stated in my post, except I see 22 degrees of advance without vacuum connected because it runs right up to the 29 degree timing mark, I guess this is still within tolerance of 20 degrees which you said was normal.
But what bothers me is the fact that with 18 degrees allowable in the mechanical advance, this puts me at 47 degrees BTDC at 4000rpm with my current set up.
Now if I hook up the boost retard line and get back 8 degrees that leaves 39 degrees total under boost conditions. This still is about 12 degrees too far if you target 27 degrees BTDC at 0.8-1.0 bar boost which from previous posts on the forum I see as safe limit. Is 27 degrees too conservative or can I run more safely? What is a real safe timing limit above 27 degrees I hope.
In order to get here I need to run 5 degree ATDC timing at idle.....and from my experience the driveability of the car at low rpm is absolutely horrible at this setting. I have even run around 0-1 degree BTDC before and this is the reason I am now at 7 degrees BTDC.......
I cannot see how the factory set the car to run at 5 degrees ATDC and got the car to move out of its own way at low speeds.
Last season when I was running the 0.8 bar spring at these same timing settings it ran well and I never heard pinging. I just wonder if it was still happening just not audible enuff for me to pick up on it, or if something has changed in my distributor over the past few months.
Need to try teeing the vacuum line into the boost retard fitting on the dizzy can and at least getting that amount of retard back....thanks for the tips.
Agree, 5 deg ATDC yields no power.
Yes, 27 deg is conservative. 29 is reasonable but you are apparently well above that.
Try setting timing at 4000 by advancing until engine stumbles/mis-fires, back it off till smooth again. You won't hurt the engine as it's not under load. Even if timing gets high, no damage. See where timing settles at idle. If still 7 deg BTDC then that's where the engine is happy.
Do hook up the boost retard. If you're not running all the control valves, just plumb the vac and boost pots is parallel. Works for me.
It's possible the crank pulley is mis marked but not probable.
If you were running same timing at .8bar and didn't burn a piston, chances are you were not detonating. With 1bar, I'm with you, be concerned. Also agree that with all the noise these engines make under boost, hearing ping is impossible.
Bosch makes a knock sensor but I don't know how it works. Probably a piezo-electric accelerometer. Might be something to play with.
J & S Electronics makes a knock sensor system that might work (I believe it uses a Bosch ping sensor) but the single coil system will be out of production for another 2-months. It reportedly has a boost retard capability as well as adjustable rev limit. Don't have any experience with the product but it's specifications look promising. http://www.jandssafeguard.com/
If you can't wait for the J & S unit or if the advance you have used in the past is needed to wake up the low end and detonation at 1bar is a real possibility, go to the MSD ignition with boost retard module. You can pull out 15 deg total with that system.
Let us know how you resolve the problem.
Chris
Old 04-11-2008, 10:07 AM
  Pelican Parts Technical Article Directory    Reply With Quote #42 (permalink)
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Wow that's a lot of reading but that's my kinda thread.

Here is what I have found, not a turbo but same 930/63 motor and a dual pot dist.

First of all the car is light and has 7.81 gears (72 911E lightened), then I added a 79 3.0 with SSI's and dual out sport, so it wants to rev quick, little load.

I was not happy with the performance, my guy had set the timing to stock 5 BTDC when I had the motor swapped, tried all sorts of mixture setting blah blah. Then I tried to recurve the dist to go quicket with lighter weights (and bent the tabs back for more advance), seems to be better but also seemed to detonate or at least run rough at top end can't tell.

Then I recurved with heavy weights and bumped the timing to ~20 BTDC which gave me ~40BTDC at 5k, it wouldn't advance much after that because of the heavy weights so the second stage of advance never came on (maybe at 7k). This produced super snappy response, now I am glad I put in a posi rear as well. I am still working of some fine tuning with the mixture because I am anal, I have always tested, re-tested, then tested again and after a while forgot what I tested so I try something new and test again. Sometimes that means breaking stuff but WTF.

I can hang with some pretty quick cars while cruising around the Bay Area, I have even surprised some bikers even a lambo or Ferrari. I can honestly say that I was ready to ditch the 3.0 until I played around with it, remenber the factory settings are for smog/heavier cars/restricted exhausts/emissions etc.

Keep up the good work guys, you can really get some decent response and power with the correct tweaking.
__________________
72 911E w/3.0, Dansk 2out, SSI's...RS look
88 M5 300hp
2004 GTI 1.8T
2011 VW Golf TDI

Last edited by Porsche Head; 04-11-2008 at 07:10 PM..
Old 04-11-2008, 07:07 PM
  Pelican Parts Technical Article Directory    Reply With Quote #43 (permalink)
Smart quod bastardus
 
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Well did some more testing and this is what I have found:
Timing at 4000rpm with vacuum line attached= 45 degrees BTDC. No engine load.
This is in line with previous findings on my 79 distributor of 22 degrees retard under vacuum and 18 degrees approx of mechanical advance.
Now the boost retard measured under 10-15psi = 10 degrees additional retard.
So all in all I have the following with 7 degrees BTDC timing at idle vacuum line attached:
at 4000rpm under 10-15psi boost = 35 degrees BTDC.
This is the best I can get with my stock (dual port canister) distributor which is in perfect working order.
I am now at a loss on how to get back to anywhere near 29 degrees BTDC at 1.0 bar boost 4000rpm without setting static initial timing to 1 degree BTDC at idle. At these settings the low rpm performance off the line is worse than my old VW beetle.
Anyone running anywhere around 34-35 degree BTDC at 4000rpm on pump premium gas?
__________________
1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 04-17-2008, 01:01 PM
  Pelican Parts Technical Article Directory    Reply With Quote #44 (permalink)
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Quote:
Originally Posted by fredmeister View Post
Anyone running anywhere around 34-35 degree BTDC at 4000rpm on pump premium gas?
I ran 48 deg at 4000 rpm, 0.8 bar, 3.3 930, sc cams, 0.8 bar, water/meth injected, no intercooler. Distributor boost retard pulled out 8 deg leaving 40 deg adv net. Drove 3000 mi and it didn't blow up. Low weight vehicle, no prolonged boost, no hill climbing under max boost and no audible ping (doesn't mean it wasn't there).
Now running 40 deg at 4000 rpm, 1.0bar, added MSD boost retard taking max timing back to 29 deg by 12 psi.
Always 91 octane CA gas.
I believe the only sure method of determining max safe advance will be a dyno and instrumenting the engine with knock sensors.
A $600 MSD unit seems like a reasonable investment compared to a $16000 engine rebuild.
Old 04-17-2008, 02:50 PM
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This thread is amazing. It seems there are some wild numbers out there being run on Pump gas. The manual for a Euro is MAX 29 degrees at 4000 rpm with boost retard coming in. And that is on much better fuel than is available here now. Scary, very scary!
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---Les Garten---85 930, Andial IC, GHL Headers, Fabspeed Dual, K-27 HF2, 3.4 JE Full Finned 7.5:1 CR, 964 CAM'd, Carerra 3.2 Manifold Cut/Flipped, Tec3r, Siemans 55#, GSF Fuel Rails, Clewett Crank Trigger, Clewett Cam Trigger,Dual Plugged, ARP Head Studs/Rod Bolts, Clewett Wires.Tial 46mm WG, Tial 50mm BOV, WEVO Shifter,934 Boost Gauge, Wideband EGO Sensor/Gauge, C2T Head Gaskets, '88 MB 300TE,BMW R100RT
Old 04-17-2008, 07:21 PM
  Pelican Parts Technical Article Directory    Reply With Quote #46 (permalink)
 
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Hereís a piece of a post about timing experiments for a 4-cylinder air cooled engine, either VW or Porsche, ďTypically a seat of the pants comparison of running advanced timing will show that the car is faster with more timing, but a stop watch will show you that it isn't- as well as a dyno pull.
The reason for this is the added advance that is given to the engine at lower RPM is very notable in the driver'ís seat, but what you can't sense is the loss of upper RPM power after peak torque. The added advance is also directly related to the MPG and head temps that you will net.Ē (Jack Raby, Air Cooled Technology)

This phenomenon may very well apply to the 930 engine.
A post in a different thread shows a 3.3 with EFI running from 30 deg at low rpm, low loads and backing off to 15 deg at high rpm, significant boost.
Neither post answers the question at hand but they do contain knowledge that points to the fact more timing is good in the low end, (we know that by our own seat of the pants experiments) and bad at the top end (detonation and burned pistons).
To push the envelope, looks like more boost retard than is available with a stock distributor, instrumentation and dyno time are a necessity.
Old 04-17-2008, 08:25 PM
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Redesigned knock controller is coming soon with new features.

Triggers from points or OEM electronic, or directly from magnetic pickup. System can be ordered with a second ignition driver for the twin plug ignitions. Provision is also made to drive the early Bosch CDI ignition box.

Features include two rev limiters (staging and top end), nitrous retard, cranking retard, boost retard with "when" and "how much" knobs, and of course individual cylinder knock retard.

Does not require a "PC" to set up. Four test points on the front panel allow you to preset the controls using a meter. For example, to set a rev limit, measure the voltage at the corresponding test point, and adjust the knob. For example, to set a 6250 RPM rev limit, adjust the knob to read 6.25 v on your meter. Other controls are set similarly.

I made a short video last week of our coil on plug version working on an F150 Lightning. These trucks were supercharged from the factory to 8 psi, with no knock control. This one is making 19 psi with different pulleys and is tuned for 91 octane.

He ran it for two weeks on 89 octane after installing the system, and performed a plug check for signs of detonation and found none. In the video he is transitioning back to 91, but has about equal amounts of 89 and 91 in the tank.

Our coil on plug system has a "knock finder" display to show which cylinders are knocking. The last frame of the video clearly shows that cylinder #5 is prone to knock. I heard from another guy with an F150 who said the wrist pin in his #5 broke. Could be this cylinder runs a little hotter than the others.

http://video.google.com/videoplay?docid=-4592990325318074993

Last edited by John at J&S; 04-23-2008 at 03:06 PM..
Old 04-23-2008, 03:02 PM
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The knock sensor for a 930 sounds like a useful and nice setup.

I've noticed the only way I can hear pinging/detonations during full throttle accelerations is with the windows up.

Removing the rotting foam rubber engine compartment sound pad helped to hear high frequency engine noises in the cabin too.
Old 04-24-2008, 10:09 AM
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Quote:
Originally Posted by JFairman View Post
The knock sensor for a 930 sounds like a useful and nice setup.

I've noticed the only way I can hear pinging/detonations during full throttle accelerations is with the windows up.

Removing the rotting foam rubber engine compartment sound pad helped to hear high frequency engine noises in the cabin too.
JF,
You may be interested in this thread also. He hasn't sold me yet on his sensor.

knock sensor
__________________
---Les Garten---85 930, Andial IC, GHL Headers, Fabspeed Dual, K-27 HF2, 3.4 JE Full Finned 7.5:1 CR, 964 CAM'd, Carerra 3.2 Manifold Cut/Flipped, Tec3r, Siemans 55#, GSF Fuel Rails, Clewett Crank Trigger, Clewett Cam Trigger,Dual Plugged, ARP Head Studs/Rod Bolts, Clewett Wires.Tial 46mm WG, Tial 50mm BOV, WEVO Shifter,934 Boost Gauge, Wideband EGO Sensor/Gauge, C2T Head Gaskets, '88 MB 300TE,BMW R100RT
Old 04-24-2008, 12:16 PM
  Pelican Parts Technical Article Directory    Reply With Quote #50 (permalink)
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