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.
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.
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.
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.
Last edited by ps2375; 06-03-2012 at 09:38 PM.
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.
Last edited by zigm89; 06-03-2012 at 10:06 PM.
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.
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.