TTinCT

to get the best spark is higher....So when you have the larger gap, the coilpack works harder than it needs to product the same level of voltage..

I have seen on other forums that the spark can get "blow out" if there is too much of a gap..which means literally that the spark is impacted by the level of pressure in the cylinder.

As some of us are running much higher boost levels (19psi on Ko3's and as much as 23-24psi on ko4's) i think that we are probably at the higher end of the coilpacks capacity.

If you research gapping of plugs and forced induction it is really important to keep that gap tighter....

As the known c/p issue seems to have been mostly resolved by the newer revisions.....if your packs have never been done, you are on borrowed time...

I definitely have one of those early cars and am on my second set of packs. I have never had a failure on the TT, but had several on my wifes 2003 A6...

I am sticking with bad gaps do not help the coilpacks...

InTTruder

set the gap tight on spec, and swap C/Ps before replacing them. There's no excuse for running higher gaps: that makes the voltage required go up as a function of a logarithmic scale.

Interestingly, empirical observations are used to quatify this and say that for a change in density, the voltage required is essentially linear. Ergo, this means that GAP is the critical determinant, even in an engine on boost. The difference in boost pressure is still on the order of only one bar to 1.5 bar. This doesn't multiply the voltage very much.

For the insanely curious, study Paschen's Law. It at least lays out the math. Not surprisingly, air has a fairly high minimum voltage to "breakdown" (ionization really) compared to helium and argon. Say welding!

FWIW- The dielectric strength of air is approximately 3 kV/mm. Its exact value varies with the shape and size of the electrodes and increases with the pressure of the air. Again, if our boost remains in the 1-1.5 bar range, that still means we require about 3kV per mm of gap.

You can see that at a constant pressure, increasing the gap from .028" (.71mm) to .035" (.89MM) makes a huge change in the voltage required. Just on air alone, the volatge changes from ~2100 volts to ~2700 volts (w/o any log in the calc). Thats a pretty big change, nearly 30%. Now throw in an air/fuel mixture, turbulence, and the need to have a consistent flame front move over the cylinder head in milliseconds, and you have a grasp of the problem.

WTH does this all mean?
- Keep your gap correct!
- At signs of trouble, regap TIGHT on spec and then swap C/P set around and see if the problem stays the same or moves w/ the offending C/P. Try to keep the offending plug in the same cylinder.
- Keep a spare C/P or two!

DAMN my head hurts!

TTinCT

;-P

I would only add, that the practice of swapping an offending coil pack when it fails is not a great practice(unless it is an emergency). This is of course with the thought that they are all well used and not recently replaced.

In the event the mileage/usage is minimal....then a single coilpack replacement is more than likely fine...

Replacing a single coilpack of a group of high mileage/usage packs furthers the problem of troubleshooting and likelyhood of legacy coilpack failure....(not to mention mixing versions of coilpacks)

While i have no proof, or testing to show this....it is experience with this motor and seeing others experiences that leads me to this conclusion...

Consider them maintenance...my current packs will be replaced in 15k with my next plug change.

InTTruder

Good advice Hans- troubleshoot for fun, but get serious (and complete) when you "fix" a problem.

I'm ordering a set. Just wish I could tell whether to order E or R-

TTinCT

i have not seen anyone running the R's yet....

oh...and me and the word "moderation" are probably a bad combo!!! ;-)

David_TT225QC

A lot of the current stars were cars that nobody paid a lot of respect to. A good examples are those 356's, MGAs, Healy's. Everyone was buying them cheap and then beating the crap out of them at the track. Today, what would that be? Miata?, Dodge SRT4? I sold my R32 and don't regret it but can't help thinking that I will someday....

Blue TTop

Interesting that the ad lists only the 180hp TT. I wonder if the "E" type is for the 225?