How critical is the vacuum signal to a CIS-E knock box?

[zigm89]

I am putting a turbo on my CIS-E 16V GTI and need to figure out what to do with the vac. signal for the knock box.....

Leave it disconnected and open to atmosphere?

Connect it to the piping on the inlet side of the turbo?

I'd prefer to keep ignition timing, advance, and detonation retard as close to oem functionality as possible.

Thanks!

[ps2375]

I'd prefer to keep ignition timing, advance, and detonation retard as close to oem functionality as possible.

Why would you keep it OEM as you are installing a turbo? I would keep the vacuum line on the manifold and hope there is some sort of curve loaded on it to deal with atmosphere/boost and not kill your motor. The last thing you want is too much IGN advance under boost.

[WaterWheels]

I am putting a turbo on my CIS-E 16V GTI and need to figure out what to do with the vac. signal for the knock box.....

I'd prefer to keep ignition timing, advance, and detonation retard as close to oem functionality as possible.

I have to post the standard disclaimer first - I don't do boost and I am not the person to ask any important questions about issues with any form of boost. That said I don't follow the logic here. First CIS-e is one, if not the, worst system that VW used for adding any boost to. But fine, you're using that system and it's your car. I don't know if the knock sensor control box will retard the advance more if the pressure rises but I kind of doubt it will "see" any pressure greater than atmospheric. So if you used the knock sensor controlled ignition I believe it would be reading "load on engine" much of the time that it is running. That would mean that it would not be advancing the timing as it would with the original 16v. So you would not be keeping the advance but rather hampering any advance. Retarding done from the knock sensor hearing any ping would still function the same but it has nothing to do with the vacuum.

Might I suggest you spend the extra $400 or so and get you a programable ignition. A 16v with a turbo is not the factory setup and will require a different ignition curve which the original ignition can not provide.

[zigm89]

I have to post the standard disclaimer first - I don't do boost and I am not the person to ask any important questions about issues with any form of boost. That said I don't follow the logic here. First CIS-e is one, if not the, worst system that VW used for adding any boost to. But fine, you're using that system and it's your car. I don't know if the knock sensor control box will retard the advance more if the pressure rises but I kind of doubt it will "see" any pressure greater than atmospheric. So if you used the knock sensor controlled ignition I believe it would be reading "load on engine" much of the time that it is running. That would mean that it would not be advancing the timing as it would with the original 16v. So you would not be keeping the advance but rather hampering any advance. Retarding done from the knock sensor hearing any ping would still function the same but it has nothing to do with the vacuum.

Might I suggest you spend the extra $400 or so and get you a programable ignition. A 16v with a turbo is not the factory setup and will require a different ignition curve which the original ignition can not provide.

Thanks for the info..... We are running the system for a race series that has very strict budget rules, so any aftermarket fuel/ign. upgrades are generally not allowed. All the turbo components we are using have been obtained from Junked Saabs, Datsuns, Volvos, DSM, etc along with 'creative' home-built components (like our fire-extinguisher short runner intake).

The car spends 95% of it's life at WOT between 3500 and 6500rpm, so I am mostly concerned about full-load timing advance. I wonder what the vac. level on the INLET side of the turbo will be.... there is no boost there.

[ps2375]

High vacuum = low load at almost any rpm. The turbo inlet will most likely have the opposite vacuum signal that an NA motor would have in the plenum. Think about it, low to no boost means low vacuum/suction at turbo inlet means high load on NA, and medium to high boost means high vacuum/suction at inlet and low load on NA.

You might want to consider a vacuum advance dizzy from one of the earlier Saabs whose dizzy will fit the VW head. It is the one that the people going carbs use when eliminating the VW electronic IGN/knock box.

And one last thing to consider, at what CR will the motor be? And what will be max boost? A high CR and boost don't make a good combination with poor timing control. At least not on a port injected motor, DI has better results, but you are talking a very modern motor and most likely out of your budget guidelines.

[zigm89]

High vacuum = low load at almost any rpm. The turbo inlet will most likely have the opposite vacuum signal that an NA motor would have in the plenum. Think about it, low to no boost means low vacuum/suction at turbo inlet means high load on NA, and medium to high boost means high vacuum/suction at inlet and low load on NA.

You might want to consider a vacuum advance dizzy from one of the earlier Saabs whose dizzy will fit the VW head. It is the one that the people going carbs use when eliminating the VW electronic IGN/knock box.

Really great reply, and this does make sense. So it seems the best place to mimic a NA vac. signal would be tapping into the body of the short runner intake. $10,000 question is what will the knockbox do when it goes from negative psi to positive boost. Hopefully it just maxes out advance when it reaches atmospheric the same as a high-load NA motor. (?)

Setup will use double stacked headgaskets to give 9.0 to 9.5CR. Max boost will be ~7psi. We race endurance events ranging from 14-24 hours non-stop, so reliable hp is more important than all out max performance.

I think we'll try some experiments to see what happens.
1. Set timing per Bentley manual.
2. Rev engine to 4,000 rpm and hold steady.
3. Check timing with vac signal connected to intake; no load/boost on engine. (should be -xx.xpsi)
4. Check timing with vac signal disconnected. (0psi = atmospheric)
5. Blow 7psi into vac signal tube and check timing.

[ellocolindo]

i am interested to know this as well since i want to run a cis basic turbo on my 16v passat...

[zigm89]

Got the car started today and made a few runs to check things out.....
It pulls super strong at 5psi with a steady AFR of 12.0.
The enrichment adjustment knob still has plenty of room left for more fuel to increase the boost if we decide to get crazy.

We did experiment with the ignition timing. Advance stayed the same from 0psi and above. Looks like the stock knock box will work just fine connected to the short runner intake.

More pictures to come after we hack up the hood tomorrow.

[ps2375]

You have to hack the hood to keep the fire extinguisher? Doesn't seem worth it.

[zigm89]

You have to hack the hood to keep the fire extinguisher? Doesn't seem worth it.

You clearly have no appreciation for the awesomessess of our car.
Post-apocalyptic durability, performance, and budget.

[ps2375]

Your right, I had no idea.

[WaterWheels]

For some odd reason the movie "Mad Max" just jumped into my head Is this the race series where they pick a vehicle at random to crush at every race?

[zigm89]

For some odd reason the movie "Mad Max" just jumped into my head Is this the race series where they pick a vehicle at random to crush at every race?

We've raced the car in Chumpcar as well as Lemons....
You're thinking of Lemons however, where they used to crush the car if it received over 50% votes from other drivers - they do not do this any more. Typically only people driving like jerks or mega-cheaters got crushed.

[ellocolindo]

great idea. let your imagination run wild...