ALFAGTV6.COM

[MALDI]

Was there ever a twin spark version of the transaxle V6? And if not, why not?

Just curious...

[sh0rtlife]

is there even room in the heads?

[MALDI]

I don't think so in the heads as they were made. But if the combustion chamber in the V6 is similar (identical?) to the Nord I4 2L, and the twin spark 4 is so celebrated, then why no twin spark V6 from Alfa?

[Giuliettaevo2]

The v6 engine is older then the TS ( the productioncar engine that is..) so converting it would be costly i guess.

there probably is not enough room in the heads to place two spark plugs per cilinder. remember there are some pushrods and rockerarms and stuff in there also. the Nord engine has two camshafts so there is some room between the sparkplugs but in the v6 engine this room is taken up by the push rods.

Maybe on the 24v you would have the room between the sparkplugs (because of the double camshafts) but then you have the 4 valve/cylinder problem, you can place one sparkplug between the 4 valves but where can you place the other without having to use smaller valves?

The sparkplugs for the 16v modern engines are also the long-lasting-expensive-as-hell-type so i don't know if it is such a bad thing that Alfa didn't make these engines TS...

[kterkkila]

Only in DTM.

[slyalfa]

One other thing. the dome in the 4cyl is very tall and makes for some badness that a TS will help with. On the V6 there is not much dome so I think there would be a lot less benefit from a TS?.

Then they went to 4 valves and no dome at all. and I think 4valves is worth more then TS with 2 valves.

[killaz]

Twin spark engines had some sense in their early phase (8v engines) since second spark was 10 degree later than first (if I remember). 16v Twin Spark fires both spark plugs and gap between those two sparks will depend from dirt (!) - since dirt raises resistance of spark plug.

[Mats]

8v fires at the same time.
16v fires the main plug as usual and the small one 180 crank degrees later.

[MALDI]

16v fires the main plug as usual and the small one 180 crank degrees later.

Why? (Perhaps for emissions?)

Also, Mats, are the Nord and the V6 combustion chambers quite different in shape? The V6 is flatter?

(I hate the term 'hemispherical' which is truly half of a sphere. The proper term should be 'segment of a sphere' and characterized by the ratio of the height to the sphere radius, h/a. A hemisphere has h/a=1 but looking at the Alfa V6 h/a is closer to 0.5. Hemi, I think not!)

[Mats]

I'm guessing emissions.

V6 is much flatter, more like the TS actually.

[killaz]

8v fires at the same time.
16v fires the main plug as usual and the small one 180 crank degrees later.

Wiring scheme says:



If you check under coil cover you will find (in early 16v engines) wiring like you see on second example. If you want, you can rewire to latest wiring diagram and engine will work as usual. One coil fires two spark plugs at the same time, there's no option for 180 degree later spark between two plugs attached on same coil.

Take a look at official patent:
Assignee: Fiat Auto S.p.A. (Turin, IT)

[MALDI]

Thanks killaz. I'll check it out.

Here is a more direct link to the patent:

http://www.google.com/patents?vid=USPAT4958616

[slyalfa]

The 2nd is called wasted spark.

As far as I know you want both to fire at the same time.

A single fires from the center out.
A TS fires from the edges to the center.
So if one side fired late it would have a very strange burn. now if one side burned slower then the other side I guess you could fire the slow side first. but I would think it would only be a degree or so

now the wasted works the same for a TS or a single it sparks 2 plugs with one coil (cost cutting)
as the one that is 180 out is on the exhaust stroke so the chamber PSI is very low so the voltage to jump the gap is low so not much of the voltage is wasted. the rest of the voltage is then used on the compression side( the other plug) where it needs more volts due to increased PSI.
that is why on the TS they did not have one coil feed both plugs on the same cylinder.


There is some talk where the extra spark on the exhaust stroke might give a tad better emissions. But I do not think it would unless there was a misfire. and if you have a misfire you have other problems.


now on 3 that seems like a bad idea. but you do get more time to charge the coil. but it is not like we are running at 20,000 RPM

[killaz]

No. 3 was last solution on TS engine. From year 1996 - 2002. (aprox). After all I'm not sure what TS was meant to improve? To have reliable spark or what?

Interesting thing is that we have few SP and ST Alfas here (147 and 156), which came from italian championship and all of them use single spark per cyl.

[slyalfa]

With the High dome the flame has a hard time burning even. and is also slower.

Think if you cut a slow burning fireworks fuse to lay over the dome of the piston.
Now cut it in the center and light it in the center it will burn from the center to the out side
lets say it takes 1 sec to burn all the way out.
now do this again cut the fuse in the center and then cut each half again now you have 4 parts.
now lite the the center of each half at the same time. now you will see the fuse will burn to the ends at 1/2 seconds.

There is a bit more to this but you should kinda get the idea.
The squish also plays into this too. and has a much bigger role on the V6 then the 4CYl.
the squish is the ring around the piston and it almost touches so it is like making the cylinder smaller or the fuse shorter. so if you went to the first test with the fuse cut in 2 but the length of the fuse only went to where the squish ring starts the length will be a lot shorter so it will also burn faster.