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carrpet

930.66 Ignition timing for Classic Retrofit CDI+ installation

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Hi there

I am about to fit one of the Classic Retro CDI units so first step is to check the ignition timing.

The Porsche Technical Specifications booklet tells me I should be at 2 degrees + or - 2 BTDC at 900+or- 50 rpm with vacuum connected

So I warmed up the engine then connected up the strobe to No.1 Cylinder at 900rpm (the strobe includes an rpm readout which is useful) and pointed the strobe at the c/s pully, bearing in mind I have A/C so there is another between myself and the alternator pully so you can't read any description of the markings on the fan pully.

Sure enough the timing mark appeared at about 5mm left of the mark on the fan housing. How do I know the fan housing is in the correct position I ask myself ? I could see no other timing marks although I am sure there is one at 29 degrees for the 4000 rpm check.

The strobe allows me to dial in advance and retard degrees so I was able to bring the timing mark back to the fan housing line by artificially dialling in 5 degrees (not yet sure if it is advance or retard !).

So that's what I have got. Decided not to do the 4000 rpm bit yet.

Questions

  1. Before I make any adjustments how do I check the fan housing is in the correct reference position ?
  2. What is the timing mark I can see - is that TDC or is it 2 degrees BTDC ?
  3. If I am 5mm (5 degrees) to the left with the timing mark I can see, is that advanced or retarded v TDC ?
  4. I believe my distributor in a 930.66 rotor runs anti-clockwise. Do I rotate the distributor clockwise or anti-clockwise to advance or retard ?
  5. Is there only one lock nut on the distributor body - I hope the answer is yes !!??
  6. Can I adjust the basic ignition timing using the laptop app that comes with the CR CDI unit ?
  7. Should I be concerned about the current timing setting
  8. What is the correct order of doing things
  9. Is there anything else I should be considering ?

I look forward to your thoughts and advice

Regards

Peter

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Hi All

Since posting I have consulted with esteemed neighbour, Oberstleutnant Comerford who advised me that the timing mark that I can see would be the tick-over specification of 2 degrees BTDC and that I should stop pi**ing about and get on with adjusting the timing to bring the timing back to the pully mark, which I have now done. The tick-over dropped 100rpm and I have adjusted that back to 900 rpm. Timing is now spot on at 2 degrees BTDC at 900 rpm which now allows me to install the CDI module tomorrow !

Regards

Peter

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Now having read the instructions in detail the CDI comes with an in-built 7.5 degree of retarded timing so I now have to advance the distributor back to where it was and slightly beyond by 7.5 degrees ! I hope there is enough scope for adjustment as the original distributor position seemed to be at the limit of travel ! We'll see tomorrow !

 

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Hi Peter, 

It’s very difficult to find accurate timing data for the 930 as most of the information out there (Pelican etc) is for the early motors and the 68 US model. My specified timing is 29 BTDC @ 4000rpm and 0 +\- 2 at 1000 +/- 50rpm, which is the same as your spec above. 

I think the mark on the pulley is Z1 TDC and not 2 degrees BTDC. The spec is between 2 ATDC and 2 BTDC. If using the distributor to advance the timing turn the important spec is 29 BTDC at 4000rpm, not idle. 

The 930/66 distributor has vacuum retard at idle, vacuum advance and boost retard. I’m not sure if the Retrofit CDI is fully programmable? If so you need to incorporate or if using your distributors advance/retard then you need to ensure timing is to spec at max centrifugal advance. 

Cheers 

David 

 

 

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The dizzy still runs the curve in a standard install, so the CDI+ should deliver the same timing curve when fitted to the car as the old CDI - that is why you check and document the timing before following the install instructions and then check the new box when fitted. It should be easy to install - let us know how you get on 👍🏻

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Posted (edited)
4 hours ago, carrpet said:

Now having read the instructions in detail the CDI comes with an in-built 7.5 degree of retarded timing so I now have to advance the distributor back to where it was and slightly beyond by 7.5 degrees ! I hope there is enough scope for adjustment as the original distributor position seemed to be at the limit of travel ! We'll see tomorrow !

 

The 7.5 degree thing is only true if the dizzy is locked and you are doing timing using CDI+.  

As default, our units now come shipped In a mode that does not require the distributor to be moved (unless your timing is out anyway).  In this mode the distributor controls the timing curve. 

Edited by Jonny Hart

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7 hours ago, Jonny Hart said:

The 7.5 degree thing is only true if the dizzy is locked and you are doing timing using CDI+.  

As default, our units now come shipped In a mode that does not require the distributor to be moved (unless your timing is out anyway).  In this mode the distributor controls the timing curve. 

Thanks for clarifying that Jonny. It might be worth revisiting the installation booklet to make that point clear.

Stage 1 of my installation is going to be a straight swap. I will lock the centrifugal weights and go to the digital timing curve as a second stage - not today

Regards

Peter

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8 hours ago, johndglynn said:

The dizzy still runs the curve in a standard install, so the CDI+ should deliver the same timing curve when fitted to the car as the old CDI - that is why you check and document the timing before following the install instructions and then check the new box when fitted. It should be easy to install - let us know how you get on 👍🏻

Will do.  I removed the old CDI unit last night so just 3 M6 hex bolts and inserting the 6 wire plug away from success - in theory !

Regards

Peter

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10 hours ago, flatsix777 said:

Hi Peter, 

It’s very difficult to find accurate timing data for the 930 as most of the information out there (Pelican etc) is for the early motors and the 68 US model. My specified timing is 29 BTDC @ 4000rpm and 0 +\- 2 at 1000 +/- 50rpm, which is the same as your spec above. 

I think the mark on the pulley is Z1 TDC and not 2 degrees BTDC. The spec is between 2 ATDC and 2 BTDC. If using the distributor to advance the timing turn the important spec is 29 BTDC at 4000rpm, not idle. 

The 930/66 distributor has vacuum retard at idle, vacuum advance and boost retard. I’m not sure if the Retrofit CDI is fully programmable? If so you need to incorporate or if using your distributors advance/retard then you need to ensure timing is to spec at max centrifugal advance. 

Cheers 

David 

 

 

Hi David

The ignition timing settings are quite clear for the 930.66 in the Tech Specification Booklet art 4000rpm is 29 degrees + or - 1 degree, with vacuum disconnected as you indicate. 

I get your point about the importance of the 4000 rpm set point. I need another person available for that one !

Thanks for the input

Peter

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3 hours ago, carrpet said:

 

Stage 1 of my installation is going to be a straight swap. I will lock the centrifugal weights and go to the digital timing curve as a second stage - not today

 

Hi Peter, 

I’ve gone this path with a programmable MSD unit some while ago.

Although installed and configured, I’ve never actually shifted to my own curve and still use distributor timing. I’m using it as replacement for the OEM CDI box much as you will with Jonny’s kit. I was modifying for track days but don’t do very many now so it became less important to me. 

My start point was to construct the timing curves for my distributor to understand how it works and what each function actually does in terms of timing; idle retard, boost retard, vac advance and centrifugal advance. I did this with a strobe and vacuum pump as I just couldn’t find any information that I could trust. You need all this to design the curves you want to programme. When you get to this stage I’m happy to share what information I have. 

Cheers

David 

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2 minutes ago, flatsix777 said:

Hi Peter, 

I’ve gone this path with a programmable MSD unit some while ago.

Although installed and configured, I’ve never actually shifted to my own curve and still use distributor timing. I’m using it as replacement for the OEM CDI box much as you will with Jonny’s kit. I was modifying for track days but don’t do very many now so it became less important to me. 

My start point was to construct the timing curves for my distributor to understand how it works and what each function actually does in terms of timing; idle retard, boost retard, vac advance and centrifugal advance. I did this with a strobe and vacuum pump as I just couldn’t find any information that I could trust. You need all this to design the curves you want to programme. When you get to this stage I’m happy to share what information I have. 

Cheers

David 

Thanks David,

I fitted the CDI+ unit this morning and the timing at tick over did move by about 4 degrees. I had a parcel delivery by UPS in the middle of doing this so had to stop !!

I haven't adjusted the timing yet and I need to check it at 4000 rpm for 29 degrees. I will subsequently develop the curves as you suggest.

Regards

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Yes, although a bit nerve wracking always check the timing at 4000 RPM or so (generally most distributors are on max advance by then).   Better to know that the max advance is correct. 

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Posted (edited)


All the Porsche published distributor curves I’ve seen are for each mechanism. Eg, the weights, the vacuum(s) have their own graph.   This means you have to sum the values and also take into account the static advance (if not zero) to get the true engine advance. 
 

[The graphs also shown distributor advance and RPM so multiply both axes by 2.]
 

Our CDI has a fully programmable curve to replace that of the distributor weights. Since the vacuum advance is a physically separate adjustment mechanism, that part will still work in the same way and is not affected by locking the weights.  
 

 

Edited by Jonny Hart

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8 hours ago, Jonny Hart said:

Yes, although a bit nerve wracking always check the timing at 4000 RPM or so (generally most distributors are on max advance by then).   Better to know that the max advance is correct. 

OK I get that !

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7 hours ago, Jonny Hart said:


All the Porsche published distributor curves I’ve seen are for each mechanism. Eg, the weights, the vacuum(s) have their own graph.   This means you have to sum the values and also take into account the static advance (if not zero) to get the true engine advance. 
 

[The graphs also shown distributor advance and RPM so multiply both axes by 2.]
 

Our CDI has a fully programmable curve to replace that of the distributor weights. Since the vacuum advance is a physically separate adjustment mechanism, that part will still work in the same way and is not affected by locking the weights.  
 

 

Hi Jonny

So in theory, if I lock out the weights, since I know I am spot on at tickover, with the inbuilt timing curve which mimics my distributor in perfect order, should deliver 29 degrees at 4000 rpm. Is that assumption correct ?

Regards

Peter

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1 hour ago, carrpet said:

Hi Jonny

So in theory, if I lock out the weights, since I know I am spot on at tickover, with the inbuilt timing curve which mimics my distributor in perfect order, should deliver 29 degrees at 4000 rpm. Is that assumption correct ?

Regards

Peter

Only if you DONT lock the weights.  In this mode, the box fires as soon as it sees the distributor trigger signal  just like the old Bosch unit  

If you lock the weights the unit needs time to do the adjustment hence you have to turn the distributor. 
 

Electronic ignitions cannot ‘go back in time’ to fire the spark before the distributor trigger point.  Hence they need to see the trigger point ahead of the max advance required by the engine.  

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20 minutes ago, Jonny Hart said:

Only if you DONT lock the weights.  In this mode, the box fires as soon as it sees the distributor trigger signal  just like the old Bosch unit  

If you lock the weights the unit needs time to do the adjustment hence you have to turn the distributor. 
 

Electronic ignitions cannot ‘go back in time’ to fire the spark before the distributor trigger point.  Hence they need to see the trigger point ahead of the max advance required by the engine.  

Hi Jonny,

If I do lock the weights then re-set the tickover timing to specification of 2 +or - 2 degrees BTDC, then using the USB interface install your stock distributor curve for a 930.66, then in theory the timing at 4000rpm should be 29 degrees. Is this correct ?

Peter

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3 minutes ago, carrpet said:

Hi Jonny,

If I do lock the weights then re-set the tickover timing to specification of 2 +or - 2 degrees BTDC, then using the USB interface install your stock distributor curve for a 930.66, then in theory the timing at 4000rpm should be 29 degrees. Is this correct ?

Peter

Assuming I also disconnect both the vacuum advance and vacuum retard connections for the 4000 rpm check !

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1 hour ago, Jonny Hart said:

^ yes. 

Thanks Jonny, I think I've got it !

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Hi Peter, 

Are you planning to go to with electronic advance in place of centrifugal because you want to change the standard curve or for some other reason?

If looking for performance benefits then I think changing the ‘centrifugal’ advance brings some potential gains in terms of mid-range driveability but misses the benefit that would come from changing the boost retard curve to keep more total advance in at WOT and full boost. Even this potential is limited as you have no way of sensing detonation or precisely controlling fuelling alongside timing so you have to stay conservative. 

My aiming point with the ‘centrifugal” curve was only to bring full advance in a little earlier at 3,000 rpm rather than 3,500rpm as with my own distributor. I think 29 BTDC is enough without knock sensing and/or EFI. My main planned change was to reduce the level of retard on boost and make the curve linear.  Big gains here if you can keep it safe. 

Just my thoughts. For street use I’m not sure it’s really worth the effort and risk. Real world I suspect you get most of the benefit by just using the box in place of the OEM CDI unit and letting your distributor do the timing.

David 

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2 minutes ago, flatsix777 said:

Hi Peter, 

Are you planning to go to with electronic advance in place of centrifugal because you want to change the standard curve or for some other reason?

If looking for performance benefits then I think changing the ‘centrifugal’ advance brings some potential gains in terms of mid-range driveability but misses the benefit that would come from changing the boost retard curve to keep more total advance in at WOT and full boost. Even this potential is limited as you have no way of sensing detonation or precisely controlling fuelling alongside timing so you have to stay conservative. 

My aiming point with the ‘centrifugal” curve was only to bring full advance in a little earlier at 3,000 rpm rather than 3,500rpm as with my own distributor. I think 29 BTDC is enough without knock sensing and/or EFI. My main planned change was to reduce the level of retard on boost and make the curve linear.  Big gains here if you can keep it safe. 

Just my thoughts. For street use I’m not sure it’s really worth the effort and risk. Real world I suspect you get most of the benefit by just using the box in place of the OEM CDI unit and letting your distributor do the timing.

David 

Hi David,

I was mainly coming at it from the pragmatic view of replacing sensitive mechanical components (centrifugal weights only) which will deteriorate with age and use with a digital curve which will not be subject to ware and therefore in theory a constant over time . I wasn't expecting to modify anything to do with ignition timing beyond standard. I was going to leave the vacuum advance and retard as standard. Is it possible to have a curve which replaces centrifugal weights plus the vacuum advance and retard mechanics ??

Regards

Peter

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24 minutes ago, carrpet said:

I was going to leave the vacuum advance and retard as standard. Is it possible to have a curve which replaces centrifugal weights plus the vacuum advance and retard mechanics ??

I think the centrifugal mechanism is pretty bullet proof as long as it’s moving freely - easy to check by rotating the rotor arm. It should move a little way (about 13 or so degrees worth) against the springs. Better still check timing with the strobe at 4000, idle and off idle and compare with the data to check in spec. You’re more likely to have a problem with the vacuum advance/retard sticking with corrosion but you’ll keep this risk. 

You can go fully electronic but I don’t think with Jonny’s box (not really familiar though). The MSD 6530 unit I have does all this - I selected for this reason and did all the work but never actually switched to my customised curves as I felt it had no real value for street use. If I did it now I’d use the Retrofit box as a straight replacement for the CDI box or go full EFI. 

David 

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13 minutes ago, flatsix777 said:

I think the centrifugal mechanism is pretty bullet proof as long as it’s moving freely - easy to check by rotating the rotor arm. It should move a little way (about 13 or so degrees worth) against the springs. Better still check timing with the strobe at 4000, idle and off idle and compare with the data to check in spec. You’re more likely to have a problem with the vacuum advance/retard sticking with corrosion but you’ll keep this risk. 

You can go fully electronic but I don’t think with Jonny’s box (not really familiar though). The MSD 6530 unit I have does all this - I selected for this reason and did all the work but never actually switched to my customised curves as I felt it had no real value for street use. If I did it now I’d use the Retrofit box as a straight replacement for the CDI box or go full EFI. 

David 

Hi David,

You can program whatever curve you like into Jonny's box from what I can see. However some of the vacuum advance stuff at starting is thermo time switch related is it not ? Please advise. So my assumption was unless you measure more parameters a simple rpm / ignition advance is not going to be sophisticated enough to cope with tempearature / time related parameters. I am learning here so I might be wrong.  I understand that my 930 has a way of changing the ignition timing for cold starting. Now you have got me thinking. There didn't appear to be much if any change in timing at start up with or without the traditional vacuum connected. I left the rear vacuum connection in place ? Perhaps you could help me checkout that my vacuum advance systems are working correctly ? Could an inoperative or partially operating vacuum advance contribute to a cold starting problem ?

Regards

Peter

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With Jonny's CDI+ box you have two options.

1 - you can program an advance overlay into the box, so that you add or subtract different amounts advance at any or all points of the ignition curve, or

2 - lock the distributor (effectively removing the centrifugal advance element) and fully program an ignition curve into the CDI+

 

I'll be locking my distributor and programming a standard ignition curve, then visiting a rolling road to have the curve optimised (once my resto is finished).

Peter

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