Pretty sure it's the opposite... The inside port does vacuum retard. Outside port is vacuum advance and boost retard, at least on my 88 930...

The valve is the boost side, outside port.

When you blow into the boost trigger line, when cold, no air flows past this valve. When warm, it does...

Yep, sorry. I was thinking of something else. Here is the whole horrible story of how everything works, if you can stand it.

http://forums.pelicanparts.com/uploa...1462167520.jpg


Figure 1 – Throttle body port connections

Referring to Figure 1:

I - This is ported vacuum. The port is about 2mm BELOW the throttle plate when the throttle is closed. It has vacuum from closed throttle (idle) to about 1/3 open throttle, and it has pressure under boost. A hose goes from this port goes to a solenoid valve that, when not powered, vents the back side of the distributor capsule to atmosphere. It comes from the factory with a Blue hose.

II - This is the same port as I. A hose goes from this port to a solenoid valve that, when not powered, connects port II to the air injection control valve. Another hose connects port II directly to the catalyst air injection valve.

III - This is straight manifold vacuum. It is not ported. This port is connected to the vacuum limiter valve. It also has pressure under boost.

IV - This is the same port as III. This port is connected to the warm-up regulator.

V - This is ported vacuum, but a different port. The port is about 2mm ABOVE the throttle plate when the throttle is closed. It has no vacuum at idle. When the throttle is opened a small amount, it has vacuum from that point to about 1/3 throttle, and it has pressure under boost. This port is connected to the thermo switch (non-electrical), and from there to the front side of the distributor. It comes from the factory with a Red hose.





Here is how it works:

Idle (cold start) - There is no vacuum to the front side of the distributor from port V because the throttle is closed. The solenoid valve for port I is turned OFF, so there is no vacuum to the back side of the distributor capsule from port I. The solenoid valve remains OFF until a temperature switch in the oil flow reaches 35C. With no vacuum on the back of the distributor capsule, timing is advanced and the idle speed is elevated. The solenoid valve for port II is also turned OFF, so the air injection control valve is turned on. There is vacuum from port II to the catalyst air injection control valve, causing it to inject air. Ports III and IV see manifold vacuum. The vacuum limiter limits the manifold pressure to about 22 kPa to stabilize airflow. This helps the O2 sensor/frequency valve maintain air/fuel ratio at 14.7. Port IV operates the warm-up regulator.

Idle (warm) - There is no vacuum to the front side of the distributor from port V because the throttle is closed. The solenoid valve for port I is turned ON once the oil temperature reaches 35C, so there is vacuum to the back side of the distributor from port I. This retards the timing at idle to reduce NOx emissions, and the idle speed is lowered to the warm idle speed (~950 RPM). The solenoid valve for port II is also turned ON, so there is no vacuum from port II to the air injection control valve, causing it to stop injecting air into the exhaust ports. There is vacuum from port II to the catalyst air injection control valve, causing it to inject air. Ports III and IV see manifold vacuum. The vacuum limiter limits the manifold pressure to about 22 kPa to stabilize airflow. This helps the O2 sensor/frequency valve maintain air/fuel ratio at 14.7. Port IV operates the warm-up regulator.

Part throttle (no boost) - There is vacuum to the front side of the distributor from port V, after the thermo switch has opened. It advances the timing. The solenoid valve for port I is turned OFF so there is no vacuum to the back side of the distributor from port I. The solenoid valve for port II is also turned OFF, so there is vacuum from port II to the air injection control valve, causing it to inject air into the exhaust ports. There is vacuum from port II to the catalyst air injection control valve, causing it to inject air. Ports III and IV still see manifold vacuum, but it is reduced due to the open throttle. This makes the vacuum limiter valve close, and the warm-up regulator may use the sensed manifold vacuum to enrich the mixture for accelerations, for instance.

Part throttle (boost) – Past about 1/3 throttle, there is pressure to the front side of the distributor from port V, after the thermo switch has opened. This retards the timing. The solenoid valve for port I is turned OFF so there is no pressure to the back side of the distributor from port I. The solenoid valve for port II is also turned OFF, but now there is pressure from port II to the air injection control valve, causing it to stop injecting air into the exhaust ports. There is also pressure from port II to the catalyst air injection control valve, causing it to stop injecting air. Ports III and IV see manifold pressure. This makes the vacuum limiter valve close tightly, and the warm-up regulator uses the boost pressure to enrich the mixture.

Full throttle - The whole system is under pressure. Port V sees pressure and applies it to the front of the distributor capsule, so the timing is retarded. The solenoid valve for port I is turned OFF, so no pressure is applied to the back of the distributor capsule. The solenoid valve for port II is also turned OFF, but now there is pressure from port II to the air injection control valve. The pressure from port II holds it closed so no exhaust pressure back-feeds into the air pump. Pressure from port II also keeps the catalyst air injection control valve closed, so no air is injected under boost. Full manifold pressure from port III holds the vacuum limiter valve closed, so no boost pressure can leak out of the intake manifold. Port IV is pressurizing the warm-up regulator, causing it to enrich the air/fuel ratio.

Decel - There is no vacuum to the front side of the distributor from port V. The electrical on/off switch is turned ON so there is vacuum to the back side of the distributor from port I. This retards the timing at idle. The solenoid valve for port I is turned ON, so there is no vacuum from port II to the air injection control valve, and no air is injected into the exhaust ports. There is vacuum from port II to the catalyst air injection control valve, causing it to inject air. Ports III and IV see manifold vacuum. The vacuum limiter limits the manifold pressure to about 22 kPa. This helps the fuel from the continuous injection to burn in the cylinder, and thus prevents the popping noise in the exhaust. Port IV operates the warm-up regulator in a way that minimizes the amount of fuel injected.

http://forums.pelicanparts.com/uploa...1462167564.jpg


http://forums.pelicanparts.com/uploa...1462167712.jpg

This is awesome Speedy...thank you

The bottom line is that, without the thermo valve. You get the advance from the high idle, and the advance from the throttle on tip in. That much advance on a cold car, with stock timing otherwise, usually causes a stumble when you tip in. Once the 35C switch activates though, it goes away.

Thanks guys, decided to leave the switch in...

It is interesting though, as the same switch allows boost pressure retard... And until it open, you have NO boost retard...

So, with a cold motor, if you get it on boost, you have 26 degrees of advance and full boost...

Why aren't motor grenading left and right?

Because you can run 26 degrees of advance on boost, just like every 930 with a Euro dizzy does. If it grenades it is because you boosted a cold engine ...

The USA timing is pretty belt and suspenders conservative. Plus, the thermovalve opens pretty fast, especially under load. I think you would be hard pressed to catch it closed with full boost.

I am now officially confused... I thought everyone posted in this thread that under boost you are at 16 degrees... Euro or not...

Are you saying it's possible to run a 930 with no boost retard?

Yep, common even. The Euro engine is the same basic engine, but it uses a single vacuum canister on the distributor. It runs 31 degrees at WOT on 89 RON Euro fuel, which is roughly like our 93 R+M/2 fuel.

The Euro dizzy has no retard on boost. It has one pot and that is for idle. I plug that one, set the idle manually, and set the timing at a conservative 26° for 89 octane fuel in the Alabama heat. I've talked about this before but it gets lost in all the talk of the more complex (and crappy) USA distributor function.

I really don't want to go through 27 pages of this, but you're saying Porsche used 31 degrees at 0.7-0.8 bar of boost with 93 octane?

Just looking for a safe timing data point.

The workshop manual lists 29° @ 4000rpm for the Euro 930, however I use 26° so I can run 89 octane gas in the Alabama summer.

The USA model 1987 911 turbo has a small mechanical thermal valve in the vacuum advance hose. It's an emission device.
It blocks the vacuum advance line from reaching the distributer's vacuum advance pot until engine heat soaks into it and opens it allowing vacuum advance to work.

Exhaust temperature is hotter when ignition timing is retarded because the very last of the gas mixture in the combustion chambers is still burning or just finished burning when the exhaust valve opens.

This thermovalve's purpose is to keep ignition timing in the USA cars slightly retarded after a cold start so the catalytic converter heats up faster.
Getting the CAT up to operating temp faster lowered exhaust emissions so they could sell these cars in the USA again starting in 1986.

And just to be clear, there's no boost retard from 29?

There is no boost retard on the Euro dizzy. That and the more aggressive timing curve are why I like to use the Euro ignition distributor, it helps the Euro engines achieve a rating of 300HP. I ran one on the Red Rocket for 15 years with the idle vac pot blocked off and timing set at 26°. The stock USA distributor was tossed along with the other 100lb of emission garbage.

No boost retard on 29 +or- 2 actually.

Thanks Speedy and Brian!

I'm bumping this thread in the hopes that someone might be able to comment on the potential usefulness of the new programmable CDI boxes that are offered. I am having some trouble with the tach feed of my CDI box since I've connected it to a MSD RPM window switch for the boost delay. I was going to go ahead and get my box and original distributor rebuilt. However, if there are advantages to the programmable unit, then I'm happy to go in that direction instead.

https://www.************.com/p-2059-cdi-programmable-six-pin.aspx

A few questions for those that understand these things:

1. In order to use the programmable box and software defined ignition curve, are the normal advance and retard functions of the stock distributor disabled?

2. Would there be an 'optimum' ignition curve that could optimize power and boost response?

3. Does it look to y'all like there is a way for the box to sense boost?

Thanks very much for any input that you might have. I'm planning to call Kurt at PK but would appreciate other opinions (wishfully including Cole's).

Thanks!

If that's anything like the quality of their distributor rebuilds (or "the electronic WUR they're peddling)... :eek:

We have an alternative for you Turbo guys. Gaining quite a following in the UK amongst engine builders.

CDI+ is Plug and play, multispark to 10000 RM, soft and hard limiters, fully mapable.

Bosch CDI replacement and classic car fuse panels

Available on Pelican, search '911-CDI'