ALFAGTV6.COM

Hi guys,
I thought I'd play with the advance curve of the inductive V6 distributors (and 4cyl also). Most 2,5 engines had them, with or without vacuum advance.These distributors have the classic spring and weight controlled advance curve. To change this curve, you need different springs and you regulate their tension (among other things). The resulting curve can be checked safely and quickly on a dedicated machine. I spent the best part of last week building such a machine from scratch. A 4-legged stool, an old 12v fan motor, a Bosch ignition (coil+module), a modified top part of an oil pump shaft, a distributor inductive trigger (used for a reference signal), an aluminum graduated protractor, a fabricated rotor with pointer, a tachometer and a twin power supply (one for the ignition and a variable one for the motor).
The thing works perfectly and its a snap to make advance curve changes! I took some pictures, I hope they'll show ok. Don't laugh, the damn thing WORKS!

I could only fire off one shot at a time! Here's another one.

Jim,

WHAT Tha?

That looks great, what does it actually do?

I'm sure we could time-travel with that.

OK, only kidding, are you saying it's for checking existing spring tension or substituting differest springs to achieve different curves?

I've made some home-made tools/testing equipment but your leaves mine for dead. Keep up the great work.

David

Cool, I guess you need to hook up a timing ligt to that thing?

No, Mats,
The thing is complete as you see it. The wire pointer tip,in place of the rotor actually SPARKS to the protractor as it goes around. You can't see the pointer of course (from about 500-6000rpm) but you can very clearly see the steady spark (actually 4 or 6 sparks) and see it move with rising rpm, therefore you can measure the advance angle. Its very practical. Today I did 5 distributors for a few friends in Historics here.
Regards,
Jim K.

Aha!

Sounds like a party starter, fire it up and bring out the beer!
Maybe needs a little music to be 100%






Still think a timing light would be a safer easier solution though.

Even if I wanted to, I can't use one because all 4 (or 6) sparks are on one wire (the coil wire) and they are not separate. A timing light would have a hard time coping with this frequency (200Hz for 6krpm in 4, and 300Hz for 6cyl).
Its not bad, the sparks are only 2-3mm long.
G'night!

Jim,

How is the contour like? Is there a linear relationship between RPM and advance? I'm, assuming that it does since the advance is controlled by some sort of a spring.

Hi Z,
Here's the std gtv6 2,5 curve (in engine rpm and crank *) given by the centrifugal mechanism-springs and weights:
800rpm=0*
1200rpm=1,5*
2600rpm=9,5*
3000rpm=11*
3800rpm=12,5*
4200rpm=13*
4800rpm=12,5*
6000rpm=12*
These are the average values of advance, the limits being +-1* on either side.DON'T ask me why the curve falls at high rpm,ask AR!!! (This only happens on turbocharged motors).
Its one of the peculiarities of life, like why did Bush get elected twice,you know! Anyway, the AR part number for the above distributor is 116.46.05.011.00, or Bosch 0.237.301.008.
There is also a vacuum advance diaphragm, which at max vacuum adds 5* (low throttle opening).
The above data is given by AR in their gtv6 2,5 ''inspection specifications'' booklet.
Regards,
Jim.

SORRY!!!

The * values should be double!! (I forgot to multiply them for clarity). These are DISTRIBUTOR * shown (half of crank*), the rpm is correct -at least I got it half right!
Humble apologies!

That's very impressive Jim.

Distrubutors??????What are those??Hey Jim,nice one. Very novel way of "reading" the advance curve..Now if only we can sort out those cam profiles...........Dont hassle,Im busy with a couple but these tests cost a lot of money,so be patient

Barry

Jim that is such a cool device, has a very high WTF factor !

So the advance curve for the stock distributor is those numbers you've quoted x2 . But it will also have a degrees added for the "stock" tickover timing offset. I think the stock crank marking is 9 crank degrees ?
So at 3000 rpm the stock dizzy gives the engine 11*2 + 9 = 31 degrees of spark advance & at 6000 rpm it gives 12*2 + 9 = 33 degrees. Plus up to 5*2 = 10 degrees if "cruising".

Does that seem correct to you?

JimGreek wrote: DON'T ask me why the curve falls at high rpm,ask AR!!! (This only happens on turbocharged motors).

Because they (the AR engineers) were stupid!

Probably has something to do with back-pressure and the higher temps at higher revs. Safety thing.
The problem is that the lowered advance boosts the exhaust temperature like nothing else. Probably why all the std 75T manifolds and the exhaust housings crack...

Very easy to get the manifiold and turbine a nice bright yellow color.

Mats,

At high rpm should the advance be high as well? I curve it down a little on my car.

26 degrees at WOT 4000rpm
23 degrees at WOT 7000rpm

Not sure if this is good or bad myself.