I am interested in installing dual electronic ignition onto my Potez so as to replace the ageing distributor. I have read the article written in the LAA magazine by Steve Brown and I am incredibly interested in this system. The question I have however is whether or not the timing for the megajolt can be delayed by 180deg as I wish to install 2 VRSs, one mounted to the top of the crankcase and one to the bottom. This will mean that the timing will be 180deg out for the bottom sensor (270deg btdc). I cannot remove another tooth at 180deg as this would surely double the rpm readout.
Does this mean that for dual ignition with 2 VRSs, there must be 2 timing wheels?!
Megajolt Ignition
Moderators: John Dean, Moderator
Re: Megajolt Ignition
This is not an uncommon situation as far as I know.
You just set the '180 degree out' ignition to fire the opposite two cylinders to the '0 degree' one, assuming wasted spark electronic ignition. Most electronic ignitions are wasted spark as it gets around the need to halve the crank speed, which the distributor runs at.
With wasted spark the two cylinders that come up to TDC, both the compression and the non-compression strokes both get their plugs fired at the same time. In the compression stroke cylinder the spark ignites the mixture, the non-compression one does nothing, i.e. it is wasted.
It's nothing new: Ford cars from the 80's onwards and most Japanese parallel 2 and 4 cylinder bikes bikes do this.
It's also what the Leburg aircraft electronic ignition system does.
By the way, I'm assuming in a Jodel D150 we are talking about a 4 cylinder horizontally opposed (flat) four stroke engine.
If the Potez engine you are referring to is not one of these (radial? rotary?) then you may need to think again, although I wouldn't rule out something similar!
You just set the '180 degree out' ignition to fire the opposite two cylinders to the '0 degree' one, assuming wasted spark electronic ignition. Most electronic ignitions are wasted spark as it gets around the need to halve the crank speed, which the distributor runs at.
With wasted spark the two cylinders that come up to TDC, both the compression and the non-compression strokes both get their plugs fired at the same time. In the compression stroke cylinder the spark ignites the mixture, the non-compression one does nothing, i.e. it is wasted.
It's nothing new: Ford cars from the 80's onwards and most Japanese parallel 2 and 4 cylinder bikes bikes do this.
It's also what the Leburg aircraft electronic ignition system does.
By the way, I'm assuming in a Jodel D150 we are talking about a 4 cylinder horizontally opposed (flat) four stroke engine.
If the Potez engine you are referring to is not one of these (radial? rotary?) then you may need to think again, although I wouldn't rule out something similar!
Rob Swain
If the good Lord had intended man to fly, He would have given him more money.
If the good Lord had intended man to fly, He would have given him more money.
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Steve Brown
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Re: Megajolt Ignition
Hi Gary
Yes Rob is correct - the Megajolt and the Leburg use identical Ford coil packs.
The missing tooth of the ring needs to align with the relevant VRS at 90 deg before relevant TDC - this gives the software about 30 - 40 degrees to decide (based on the current rpm and MP) when to fire the relevant coil in the pack.
It is indeed wasted spark ie so one of the coils in the pack fires 2 'TDC paired' cylinders on both compression and exhaust stroke but even on a single EDIS/Megajolt, the EDIS relies on automatically firing a second spark (of the other coil in the pack /'TDC paired' cylinders) at exactly 180 deg (NOT 18 teeth!) after the first spark advance point (that was calculated by the earlier missing tooth/VRS sensing position and based on the rpm/MP data at that time).
So for your second Megajolt , just mount the second VRS at 180 deg to the other one, keep the standard 36-1 tooth ring and it will function perfectly.
The software even enables you to electronically fine tune the VRS positions, in case you don't quite get them physically mounted exactly 180 deg apart.
You will need to think through which ignition lead goes to which plug - which all depends on the firing order of your engine. Work out which pair of coils/HT lead connections in the coil pack fire together
Have fun!
Steve
Yes Rob is correct - the Megajolt and the Leburg use identical Ford coil packs.
The missing tooth of the ring needs to align with the relevant VRS at 90 deg before relevant TDC - this gives the software about 30 - 40 degrees to decide (based on the current rpm and MP) when to fire the relevant coil in the pack.
It is indeed wasted spark ie so one of the coils in the pack fires 2 'TDC paired' cylinders on both compression and exhaust stroke but even on a single EDIS/Megajolt, the EDIS relies on automatically firing a second spark (of the other coil in the pack /'TDC paired' cylinders) at exactly 180 deg (NOT 18 teeth!) after the first spark advance point (that was calculated by the earlier missing tooth/VRS sensing position and based on the rpm/MP data at that time).
So for your second Megajolt , just mount the second VRS at 180 deg to the other one, keep the standard 36-1 tooth ring and it will function perfectly.
The software even enables you to electronically fine tune the VRS positions, in case you don't quite get them physically mounted exactly 180 deg apart.
You will need to think through which ignition lead goes to which plug - which all depends on the firing order of your engine. Work out which pair of coils/HT lead connections in the coil pack fire together
Have fun!
Steve
Re: Megajolt Ignition
Wasn't sure about the coils used by the Megajolt, but mostly agree about the Leburg.Steve Brown wrote: - the Megajolt and the Leburg use identical Ford coil packs.
Why "mostly"? Because Dave Mickleburgh advised that it was possible to use 4 Honda (CBR600 or Fireblade) coils if you so wished. This saves weight over 2 Ford units which are quite substantial. I believe he used them on his VW conversions.
The Ford units are used on recent ('05) Fiestas, but probably on lots of other 4 cylinder petrol engined ones too. I found my 1.4 Duratec engined Fiesta had the right coil pack, so bought 2 new ones for the Leburg installation on G-BAPP. Dave even supplied the correct connector leads for ignition to coil connections, and would provide bespoke length ones if required. He was an awfully nice chap, and sadly missed.
Rob Swain
If the good Lord had intended man to fly, He would have given him more money.
If the good Lord had intended man to fly, He would have given him more money.
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James Wilshaw
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Re: Megajolt Ignition
Can somebody tell me which issue of the magazine contains steves article, as I cannot recall reading it... Had a look through the pile of LAA mags and can't locate it!
Thanks.
Thanks.
Regards,
James Wilshaw
James Wilshaw
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Steve Brown
- Posts: 257
- Joined: Wed Jan 02, 2008 11:00 am
Re: Megajolt Ignition
Hi James - it was August 2011.
Time flies!
Regards
Steve
Time flies!
Regards
Steve
Re: Megajolt Ignition
Noooooooooooo!Steve Brown wrote:...it was August 2011.
Can't be that long ago!
Beginning to know how my folks felt when they used to say things like that!
If I recall correctly there was an element of work-in-progress (or approval-in-progress) about the whole megajolt for aircraft project. Any chance of an update article?
Rob Swain
If the good Lord had intended man to fly, He would have given him more money.
If the good Lord had intended man to fly, He would have given him more money.
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Brian Hope
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Re: Megajolt Ignition
Steve's a busy guy but he has promised a follow up article. The system has been on the Eze for a while now and is running very well, Mike, Steve's partner in the aircraft, told me a couple of weeks ago they were planning to run an air test to get some definitive figures for an article, so fingers crossed we can report on how the unit is performing later in the summer.
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