1987 930 Ignition Timing Question

[SG930]

After help on the vacuum lines I thought it would be best to check the timing. It was set at 0 degrees on warm idle with vacuum line hooked up. Would measure 20 degrees +/- at 4000 with vacuum disconnected. My spec for my car is 26 degrees at 4000 with disconnected vacuum. I could get it to 22 degrees and the distributor slot is maxed out. Idle would be around 5 degrees then. Is this normal? I have read some people slot the hole a little more. Distributor has 80K miles. Engine rebuild has 5K. Air injection is all removed. Don't know the history of the dizzy but maybe it needs a service.

Fab speed intercooler, modified fuel head, Adj Wur, KZ27, RPM switch, B&B headers, RarlyL8 Street Muffler

[porschyard]

Move the distributor one tooth so you can get the adjustment you need.
With the mods you have I would set the timing at 29 BTDC @ 4000 with the vacuum advance hose disconnected.
Looking at where the timing is falling at this point it does not look like the vacuum retard is working. You need to check both the retard and advance to see if they are working. If you are only getting 20 degrees of advance. you are losing out on a bunch of power.
Richard

[908/930]

Yup, as porschyard said, sounds like you are out one tooth.

[porschyard]

If the distributor vacuum pods and centrifugal advance plate are working correctly and the base timing is at 29 BTDC then it should be around 31-32 BTDC at 4000 with the vacuum advance connected and around 4-6 BTDC at idle with the vacuum retard connected.

Richard

[SG930]

Well it's been a few weeks since I have had the intercooler off. The vacuum retard is connected to disconnected Air injection solenoids. It's not tied to anything so I'm not sure how to test the vac retard. The vacuum advance holds vacuum as I tested it with a mini vac.

[SG930]

Just wanted to double check before I pull and adjust the dizzy.
0 degrees at warm idle with vac plugged in.
26 degrees at 4000 rpm with vac plugged in (on mark).
22 degrees at 4000 rpm Un plugged vac advance (checked with light) .

I have one but not the other. Looks like if I get the 26 or 29 with vac disconnected, I will not get 0 at idle? That's yet to confirm.

I do have that rusted nipple of the unused vac retard side. I'll send Pic tomorrow when i can resize it. Could that effect anything? If unplugged, am I checking mechanical advance?

[SG930]

Here is the close up of the retard side. Does not look promising. Only hooked up to old plugged AI lines but saw posts of how it disintegrates both sides.

[gsxrken]

Get yourself a mityvac that does vacuum and pressure tests. That way you can start the car with no hoses attached to the distributor, set your timing to your desired 26-29*BTDC at 4,000 RPMs, and then use your mityvac to apply vacuum (and pressure) to both sides of the canister and witness the effects on your timing. Or lackthereof, if nothing changes.

Along with a CIS pressure tester and a digital ohmmeter, it's a good tool to add to your kit if you want to DIY.

https://www.amazon.com/Mityvac-MV8255-Selectline-Vacuum-Pressure/dp/B002YKGZBW/ref=asc_df_B002YKGZBW/?tag=hyprod-20&linkCode=df0&hvadid=692875362841&hvpos=&hvnetw=g&hvrand=13087190971746031167&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9004242&hvtargid=pla-2281435180778&psc=1&mcid=de968ef377643af7a669ac2e80c51a5d&hvocijid=13087190971746031167-B002YKGZBW-&hvexpln=73

[SG930]

Thank you Ken. I do have that mityvac. I'll need to attached to both after getting my 26-29 degrees to see whats going on while the car is running. The vac advance side holds vacuum cold not started.

Any suggestion on the fact that the vac retard goes to disconnected solenoids?

Appreciate all the help!

[gsxrken]

If your car is like my 1986 one, the rear-most nipple on the canister is your boost retard. This should drop about 10* or so off whatever your total mechanical timing is at 4,000 RPMs.

Take a look at Speedy Squirrel's excellent diagrams on the last few pages of this thread to figure out how to bypass the solenoids and go straight to the correct nipple on the throttle body. https://forums.pelicanparts.com/911-930-turbo-super-charging-forum/500986-ultimate-930-distributor-advance-retard-timing-turbo-lag-msd-mod-thread.html

[porschyard]

Originally Posted by gsxrken

If your car is like my 1986 one, the rear-most nipple on the canister is your boost retard. This should drop about 10* or so off whatever your total mechanical timing is at 4,000 RPMs.

Take a look at Speedy Squirrel's excellent diagrams on the last few pages of this thread to figure out how to bypass the solenoids and go straight to the correct nipple on the throttle body. https://forums.pelicanparts.com/911-930-turbo-super-charging-forum/500986-ultimate-930-distributor-advance-retard-timing-turbo-lag-msd-mod-thread.html

Ken that is not how the 86-89 vacuum pods work.
The forward facing port is vacuum retard and is only in a retard position with a closed throttle and manifold vacuum. As soon as the throttle is opened you loose manifold vacuum to that port and the timing advances. The rear facing port is a ported vacuum advance and will advance timing off boost 2-4 degrees past base timing and timing will retard back to what ever the base timing is set @ 4000 rpm on boost.
78-79 California cars had a boost retard vacuum pod setup but the 86-89 cars are different and the only boost retard is when the vacuum advance loses its ported vacuum do to boost pressure.

Richard

[SG930]

Here is what I got. I traced over the flow direction of the inside port, the side facing the fan (advance? need help). I don't know what's front or rear, just the port facing the fan (right) and the port facing the driver rear tire (left).

The inside port (Fan side) goes to a dual mounted solenoid switch. From only one of the switches, it goes to the front of the TB, port I (rear of the car.) The other switch has been plugged after I removed the plugged vacuum lines.

Per my previous posts the outside port (left, driver rear tire, retard?) goes directly to the rear of the throttle body (Port V)and by passes the vacuum thermal switch.

I'm confused on the terminology on which is retard and which is advance. I don't have blue or red hoses so it's also confusing. Based upon Speedy Squirrel's diagrams, I believe the hoses are routed correctly. I think I disconnected the wrong port (Port V) while checking timing where it should be port I for advance? This should clear it up.

I will leave the one solenoid in line as I don't know if the lamba stuff is working or not as the O2 sensor is in place and I have not looked under the driver seat to see what's all there. Thank you all again as I'm way late to the game and appreciate the resources and your patience.

Andy

[908/930]

SG930, take a look at the ultimate 930 distributer thread sitting about 25 lines below this one, on last page 29, it shows cut away of the advance pot, it is actually a small pot within a larger pot, small pot towards the fan goes to the solenoid then low side of the throttle plate.

The hose connection on the outside pot away from the fan is the important one, it does most of the movement.

[SG930]

Here are the 2 Figures I have been referencing (Thanks Speedy Squirrel). The #4 area would be the fan side port(inner) and the #5 area would be the outer port (driver rear tire side).