Hello,

Was hoping someone with some technical knowledge would be able to answer this question for me??

The story goes something like this......

While at Castle Combe.... looking through 'all the stalls and goodies...

Was drawn to some 'HT' leads.... (don't know mif this is the right term)

Told the guy I have a Legacy turbo 92 and he said ... these are the leads you need.... they are easy to fit... straight replacement...

Promptly went back to the car...... and there was NOTHING remotely that resembled the leads that he gave me....???

Traced the spark plug lead, but NO 'distributor' (as such)

Had a look at a freinds impreza, and there was a 'distributor' and sinilar leads to what I had bought....

I was later told that each spark plug has it's own 'coil'.

I later found another freind, with an impreza, had a similar set up to my Legacy....

So!!

Can anyone let me know why some have these setups and if one is better/worse than the other???

Any info MUCH appreciated...... ALL to be stored in my grey matter for later use!! he he he

Cheers

Phil

 

Phase 1 engine has coil packs.. one on each spark plug and no HT leads.

ECU sends a signal for a spark to each one individually.

Phase 2 engine has 2 coils which are on top of the inlet manifold and has HT leads, the ecu sends a signal to each coil pack in turn which sparks two cylinders at once.. one of which is a wasted spark as it is not on the compression stroke.

Just different ways of doing the same thing.. they went back to 4 coils on the newer cars I believe.

That is about my lot on the subject.

JGM

 

Many thanks!!!!!

 

I think coil packs are better as less bits under bonnet!

has to be a good thing

 

Fairly sure the early cars still run wasted spark even though they have a coil on each plug..

David

 

Is it 'good' to have these coil packs then???

Is there a 'better/prefered' option, to increase spark (or reduce resistance??

Cheers

Phil

 

Going back to your original point, the multiple coil setup is theoretically more efficient, as well as more reliable, than a single coil and a distributor.

There are no moving parts to go wrong, and no chance of distributor rotor/contact wear reducing the efficiency of the connection.

 

The single coil pack has no distributor either, that is an antiquated system that hasn't been used for years. They are still electronically controlled by the ECU in the same way as individual coils.

Contrary to what is posted above, on the Impreza the single coil pack appears to be far more reliable than individuals, very seldom does anyone mention the coil pack failing but individual coils are a common failure. It's also much cheaper to replace a coil pack than 4 individual coils.

Only real downside to single coil pack seems to be HT leads which are a potential failure point, but again on the Impreza these don't seem to be a common problem (unlike some engines such as Ford Zetecs which often need HT leads replaced IME).

 

The WRC cars run individual coilpack over each plug ignition.

I prefer the coilpack system. When driven sequentially, it means each coil has three times more recovery and charge time than the wasted spark system (twin coil unit on top of manifold and HT leads down to plugs.)

As to reliability, I believe that the individual coilpacks have a shorter life than the wasted spark units because of the heat they are subjected to in their standard location. I am planning to (eventually) mount mine away from the heads (probably on the chassis to reduce vibration too) using some very short HT leads, which should reduce the thermal pounding they get.

Moray

 

Cheers guys..........

Starting to increase my knowledge of me motor with your help!!


............. will be able to fill the 'washer bottle' soon eh!!

he he he

 

A single coil has to supply 4 sparks in the time that each individual coil has to supply one spark. The individual coil has more time therefore for the magnetic field from the primary coil to build up and collapse as it induces the high voltage in the secondary coil for the plug. The coil will then produce better sparks at the higher revs.

Les

 

It's not a single coil, it's two coils sparking two cylinders at one time (if one coil sparked all 4 then every time the fuel/air mixture was drawn into the cylinder and the piston is at the bottom of the stroke it would receive a spark which wouldn't be a good idea at all).

So yes the "central coil" system sparks twice as much as necessary (hence why it's called wasted spark) and theoretically the separate coils could be better but do we know for sure that this doesn't use wasted spark also? David wallis suggests it may. Also it's possible to use higher spec coils with the central unit and still be cheaper than individuals and avoiding the breakdown issue with the only real weakness being the requirement of HT leads.

 

But you can do the same upgrade with the four coils with bosch coils for under 100pounds..plus HT leads.. or did I just read your post wrong and this is what you were talking about?

They usually last 5years or 100000miles from my experiance so at 200pounds a set it is not too much of a hardship running standard individual coils either really.

JGM

 

Yeah what I meant was that any advantage of the individual coils can be had with higher spec "combined" coil, and probably still cost less while being more reliable. Decent HT leads these days tend to last years as well.

Basically there seems to be no major advantage to either method, personally I prefer the coil pack on top of the manifold simply because it's easier changing plugs (just pull the HT leads off by the boot) and it seems to have a much lower failure rate.

 

If there is no major advantage to either method, as you believe, then why would subaru go back to the individual coil over plug system in the new cars, being that this will be more expensive to manuacture and will be a slightly more complicated system?

I know my coilpacks are running sequentially rather than wasted spark... I suspect the new cars will be doing this too. when run sequentially, these have three times more recovery and charge time available than the wasted spark twin coil system.

 

or you can run cdi like me

 

You could also argue as to why they went to a central coil pack in the first place? I can't say with any certainty whether either method is more expensive from a manufacturer's point of view - they work with such massive volumes that something more expensive to the end user ain't necessarily to them, a lot of the time parts prices are high simply because they know people will still pay for them. Maybe they're saving by not needing HT leads?

I can't see how it has 4 times the recovery time, each coil in a wasted spark system fires twice every 4 strokes (just before TDC of the compression and exhaust strokes), the second one being the wasted spark. So by my maths that's twice the time not 4.

Besides I believe almost all cosworths running distributorless ignition still run with HT leads which AFAIK means combined coil packs, certainly I've seen several 500+ BHP engines using them so unless the Subaru engine has some kind of special igniton needs to run well at high power and high revs I still believe it's a non-issue. If you do feel the standard ignition isn't up to the job regardless of what type it is then CDI would be a sensible option (as david no doubt knows stronger spark with faster rise time compared to standard EDIS) rather than just swapping combined coil packs for individuals or vice-versa.

 

Re costs:
I shall not bother arguing about the differences in complexity and therefore likely differences in expense for the systems.

Re Recovery time:
If you read my post, you will se I say three times the recovery period, not four times. Its in the text you quoted!

Look at it this way, for one plug, let us assume its connected to coil 1... so:

Wasted spark:
Coil 1 - Fire
Coil 2 - Recover x1
Coil 1 - Fire
Coil 2 - Recover x1

Sequential coilpacks:
Coil 1 - Fire
Coil 2 - Recover x 1
Coil 3 - Recover x 2
Coil 4 - Recover x 3

Does than make sense now?

 

OK get your point now, seems I misinterpreted it first time round .

Has anyone actually had an issue with the coils in the Impreza on tuned motors? David why did you go to CDI, simply because it's easy to change and more reliable or were the limitations of conventional coils showing?

 

we were having problems with the autronics firing.. and not doing what it was supposed to be..

anyway after seeing the spark from the msd..

about 2 inches Long out of the ht lead, then it had to stay..

**** me the crack sound was

Impreza Coilpacks have been used on scoob 500/550 engines.

David

 

Most motor cycle engines run individual coils to be able to cope with very high rpm. The advantages are pretty obvious really.

Les

 

I thought most motorbikes ran CDI for that very reason (plus the fact that they can run with no power from the batt unlike conventional coils).

I've got a scooter with less power than a hairdryer in the garage that has CDI ignition!

 

Check it out then!

 

cdi still uses coils.