Wasted spark

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NORSK
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Wasted spark

Post by NORSK »

I am working on a 4cyl 16 valve normally aspirated fuel injected engine here that for simplicitys sake it would be easy to run wasted spark
Would there be a problem with "preignition" during overlap?
This type of engine will usually see around 6deg at idle up to 26deg timing at 8200rpm
Intake has 1mm lift allready at 22deg btdc according to the cam sheet
I have also heard that the cylinder that fire during exhaust stroke uses more energy than the other one
Walter R. Malik
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Re: Wasted spark

Post by Walter R. Malik »

NORSK wrote: Sun Mar 18, 2018 5:20 pm I am working on a 4cyl 16 valve normally aspirated fuel injected engine here that for simplicitys sake it would be easy to run wasted spark
Would there be a problem with "preignition" during overlap?
This type of engine will usually see around 6deg at idle up to 26deg timing at 8200rpm
Intake has 1mm lift allready at 22deg btdc according to the cam sheet
I have also heard that the cylinder that fire during exhaust stroke uses more energy than the other one
Should not be a problem ... several modern automotive engines today use that type ignition.
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Re: Wasted spark

Post by MadBill »

NORSK wrote: Sun Mar 18, 2018 5:20 pm...I have also heard that the cylinder that fire during exhaust stroke uses more energy than the other one
The waste spark takes very little energy, as there is no appreciable cylinder pressure. Consider the rotor gap of conventional distributors.
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Re: Wasted spark

Post by pamotorman »

it has be used on 2 stroke multi cylinder engine since they started to use electronic ignitions in the 60s. i would guess it also would help keep the plugs clean
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Re: Wasted spark

Post by peejay »

Walter R. Malik wrote: Sun Mar 18, 2018 9:00 pm
NORSK wrote: Sun Mar 18, 2018 5:20 pm I am working on a 4cyl 16 valve normally aspirated fuel injected engine here that for simplicitys sake it would be easy to run wasted spark
Would there be a problem with "preignition" during overlap?
This type of engine will usually see around 6deg at idle up to 26deg timing at 8200rpm
Intake has 1mm lift allready at 22deg btdc according to the cam sheet
I have also heard that the cylinder that fire during exhaust stroke uses more energy than the other one
Should not be a problem ... several modern automotive engines today use that type ignition.
I doubt any of them have significant IVO that early, though. A lot of 4-valve engines are zero or negative overlap.
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Re: Wasted spark

Post by Circlotron »

I imagine it would depend on the pressure gradient across the inlet valve and consequently which direction gases will flow at the beginning of IVO.
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Re: Wasted spark

Post by MadBill »

I would think the chances of igniting a fuel mixture via waste spark would be very slim. The valve would have to not only admit enough mixture well before TDC for ignition not to be quenched by exhaust residuals , but also open a wide enough gap that the valve mass did not act as a flame arrestor. :-k
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Re: Wasted spark

Post by NORSK »

Yes,i am not sure what to think
It is very tight to fit a cam position sensor there,but it is probably the best solution
Intake has 4.30mm lift at tdc and exhaust has 3.75mm so i would assume cylinder is quite "clean" from exhaust at tdc,but there is not much air available when piston is at tdc
Spark duration will also effect this,i don't know how long time the spark lasts,probably a couple ms but at 8000rpm that is several crank degrees
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Re: Wasted spark

Post by Heinz1 »

you can run wasted spark without any problems, i use Bosch or Beru 4 Cyl. Coil packs.
I build race engines with wasted spark since 1995 on all my Customers engines, BMW M3 S14, Opel C20XE, VW ABF/KR, rev them to 9000 rpm without any problems. Also i use Camshafts with up to 5.0mm lift at TDC.
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Re: Wasted spark

Post by NORSK »

Great info,thank you
This is an ALT alu block with ABF head
92.8 stroke 144 rod length 83.50 bore
Will use the coils from the 5cyl 2.5 vw Jetta engine,they are longer than the fsi coils and fit almost perfect
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Re: Wasted spark

Post by BlitzA64 »

I ran wasted spark on a Midget type engine. The actual type of ignition was a POS but when it worked it worked fine. I believe the MSD Midget Ignition set up is wasted spark if they still make that. It was used on at least some Esslinger Midget engines
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Re: Wasted spark

Post by Truckedup »

I run wasted spark on my several vintage racing motorcycle junk....Guys have discussions on the disadvantages of wasted spark dual outlet single coils....
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Re: Wasted spark

Post by NORSK »

I have used wasted spark on many turbocharged engines without any issues,but they have much smaller cams (less overlap)
That was my main concern,but it seems to work fine from others experience
I will have a closer look to see if there is an easy solution to fit a cam trigger,if not i will try wasted spark
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Re: Wasted spark

Post by mk e »

No cam sensor....how are you fueling it? SemSemi-sequentail?

I've never had any problem with waste spark other than running out of coil dwell time, but I have had a lot of trouble with semi-sequentail injection. All the errors eith glow variation and dead-time/offest are basically doubled and can be quite large at idle/low power with big injectors.
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Re: Wasted spark

Post by NORSK »

mk e wrote: Mon Mar 19, 2018 3:18 pm No cam sensor....how are you fueling it? SemSemi-sequentail?

I've never had any problem with waste spark other than running out of coil dwell time, but I have had a lot of trouble with semi-sequentail injection. All the errors eith glow variation and dead-time/offest are basically doubled and can be quite large at idle/low power with big injectors.
60-2 crank trigger,fire injectors in pairs,it's called bank to bank or paired
Dwell time is no problem with "coil on plugs" i believe,even when running wasted
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