Wasted Spark Vs Direct Spark

[User Name 19]

Hi Guys

Question time - I sort of under stand what both do - Wasted (fires on both compression and exhaust) , Direct (fires as its timmed to fire)

OK, im wanting to get this sorted for when i upgrade to the turbo and just seeing what ECU's can do what is there advantages to both types

i can understand why people use wasted sparks on turbos to burn the excess fuel so more exhaust gas.

does direct spark have any advantages to this besides being able to fire multiple times.

So if anyone can shed some light would be appreciated

Cheers

kym

[Guest FrantiC]

I'm sure I have explained this heaps.

Wasted spark, The cylinders are fired in pairs, which will be at opposing strokes.. So 1 at compression, the other at the exhaust stroke. The cylinder fired on the exhaust stroke reeps no benefits at all of the spark, thus it is "wasted". There is also no pressure and the spark uses minimal power to jump across the electrode of the sparkplug on the cylinder the wasted spark is firing so there isn't much power lost for the other spark..

Only benefits are:

Less wear parts, no dizzy, rotors etc.

More coils, meaning they share load and have more time to recharge for a stronger spark at higher rev's.

More adjustable timing, stock ignition will only allow so much retard/advance depending on position off the rotor vs dizzy points. Though stock is usually well enough already.

[User Name 19]

Thanks FrantiC

now does anyone have the advantages of direct spark???

[Guest FrantiC]

Advantages over what ? Wasted spark?

That there is only 1 coil, less wiring to this 1 coil, probably cheaper as you don't need so many coils etc.

Spark plugs will last longer as they are fired half as much.

[Mike 1]

Are you talking about individual coil packs or a single coil and dizzy setup?

[User Name 19]

Ok Guys

Basically what i was getting - FrantiC has explained what Wasted Spark Does, Completly understand.

but i was asking What Direct Spark is?? - i figure this is One coil per cylinder and it only fires (dependant on how you have set it up) on each cylinder

and what the advantages and dis advantages of both were.

wasted spark is easy to setup ( you still have the wasted spark on exhaust stroke), would direct spark give me off a Bang per say and would it be better for a turbo setup - due to each coil could be tunned to fire exactly when needed.

or am i on a total tangent and if i am tell me so and well leave it at that.

[Guest FrantiC]

Are you talking about Coil on plug?

Where each cylinder has it's own coil on the plug?

Edited September 9, 2009 by FrantiC

[Mike 1]

Ah, so your talking about individual coil packs or coil on plug. (Both similar, only difference is where the coils live)

Individual coils are a bit more difficult to setup because you require a camshaft position sensor (so ECU knows what stroke each cylinder is at). A number of cars wont have this.

You also need need an ECU with suffient drivers (one for each coil). This shouldnt be an issue for a 4 cyl but when you get up to 8 (or even 6cyl) cylinders or more you might find you dont have enough drivers for each of the coils. This is because wasted spark on a v8 requires 4 drivers, or 8 for individual. Likewise a 4 cyl require 4 drivers for individual or 2 for wasted spark. This also comes down to the ECU and how flash it is.

Biggest advantage is that each coil has twice as long to recharge, could be an issue at extremely high rev's. As mentioned before also means spark plugs only fire when they need to.

Hope that helps?

[Guest FrantiC]

Yeah, Only real benefits are coils get more time to recharge between fire's, but you would only really notice this at very high rpm were the spark can be weaker due to less recharge time.

Most guys find Wasted spark sufficient enough, Don't think I have ever seen anyone go an install the whole coil on plug type setup unless the engine already had it, like on an m50 or something.

[Boost Junky 1]

I think what BimmerBeast means is that he has a coil over top of each plug, so one coil per cylindeer? The difference hes describing is having the ECU controlling the coils via wasted spark vs. normal spark (each plug only fires on the compression stroke)

[No name user 379]

im converting my m50 turbo to use the cap on the end of the cam shaft as per the m5 motor,

done this before and even on a single coil i havent been able to put the spark out

[CamB 48]

The "wasted" spark is not a design feature it is a by-product of a design short cut.

That's a bit harsh (although true).

Wasted spark is good enough for an early Evo (amongst other performance cars) so its probably good enough. Given an M30 doesn't have provision for a camshaft position sensor, it seems like to much of a pain in the arse, not to mention the extra coils required and ensuring the ECU (as Mike says) has enough drivers.

Mitsubishi GDi is a good cheap source of wasted spark - 4 cylinder Lancers and 6 cylinder V6. You can use the Mitsi igniter too, so its very, very cheap. Holden also an option for 6 cylinder, but the Skyline boys are onto those.