11 replies to this topic

[matty121]

Hi there,

Have read through a lot of topics but am still unclear as to what electronic ignition systems are needed for a turbo conversion...

I have a 1986 998 piccadilly and will be using a t3 turbo with a metro engine and head

Ill be using the distributor from my old standard engine, the points and condenser have been replaced with a electronic ignition unit.

Will I be able to use this distributor, or is megajolt needed?

chears matt

[Ethel]

Ignition timing on any engine is about igniting the charge so that gives the maximum push on the piston after it has passed TDC while avoiding excess combustion pressure before tdc - that would waste power by trying to push the piston against the engine's rotation and the prolonged high pressure would create enough heat to melt things.

As the revs increase the piston gets to tdc faster which means the ignition timing can be advanced (by angle of rotation) so the time between the spark and TDC remains much the same. A more full combustion chamber will also burn quicker, hence vacuum advance which compensates for the less full cylinders at part throttle.

A normally aspirated engine reaches a point where the induction system can't keep up with the engine speed and cylinder pressures start to drop, even with a fully open throttle: the point where maximum torque occurs.

If you have a turbo you can counteract this tail off by increasing the boost therefore turbo engine's can have complex ignition timing needs and will generally need less overall advance and a more linear advance curve.

Programmable ignition, like MJ, is particularly useful with forced induction.

[wolfie]

Ignition timing on any engine is about igniting the charge so that gives the maximum push on the piston after it has passed TDC while avoiding excess combustion pressure before tdc - that would waste power by trying to push the piston against the engine's rotation and the prolonged high pressure would create enough heat to melt things.

As the revs increase the piston gets to tdc faster which means the ignition timing can be advanced (by angle of rotation) so the time between the spark and TDC remains much the same. A more full combustion chamber will also burn quicker, hence vacuum advance which compensates for the less full cylinders at part throttle.

A normally aspirated engine reaches a point where the induction system can't keep up with the engine speed and cylinder pressures start to drop, even with a fully open throttle: the point where maximum torque occurs.

If you have a turbo you can counteract this tail off by increasing the boost therefore turbo engine's can have complex ignition timing needs and will generally need less overall advance and a more linear advance curve.

Programmable ignition, like MJ, is particularly useful with forced induction.

Hmmm i dont see why you have to try and make yourself look clever again not everyone is stupid, not everyone needs an explanation that looks copy and paste job, the above does not answer the question.

Matty

A Dizzy will be fine if it has the right advance curve, your not running silly boost and its set up correctly, engine managment (of any manufacturer) will optimise the ignition setup and actually is not to hard to set up, my original setup a GEMs unit i did the basics myself with just a laptop timing light and a book i am now on my second unit an omex 500 and will shortly be buying an emerald to run fuel injection i am personally not a fan of the mega range but thats just personal choice and what suits me.

For a comparison the same turbo engine in my car gave 148brake on the dizzy and 158 on the gems after final setup on the same RR about 14lb of boost iirc.

[Wil_h]

As above you need the correct advanve curve to match the specification of your engine. In theory there should be no power difference between a dizzy and mapped ignition if both optimised, but dizzys are a bit crap and you get a stronger spark with mapped systems, so power can be made. I personally made *melons*all extra maximum power when I swapped from a dizzy fixed at 25 deg to a fully mapped system, but I did gain low and midrange.

The dizzy you plan to use will be next to useless on a forced induction engine, it will need to be so retarded to limit the maximum advance that you will suffer off boost and on cruise (infact everywhere other than what).

If you want to use a dizzy then the Metro turbo one is the best to use. But I'd advise mapped ignition, worth every penny.

[matty121]

Ignition timing on any engine is about igniting the charge so that gives the maximum push on the piston after it has passed TDC while avoiding excess combustion pressure before tdc - that would waste power by trying to push the piston against the engine's rotation and the prolonged high pressure would create enough heat to melt things.

As the revs increase the piston gets to tdc faster which means the ignition timing can be advanced (by angle of rotation) so the time between the spark and TDC remains much the same. A more full combustion chamber will also burn quicker, hence vacuum advance which compensates for the less full cylinders at part throttle.

A normally aspirated engine reaches a point where the induction system can't keep up with the engine speed and cylinder pressures start to drop, even with a fully open throttle: the point where maximum torque occurs.

If you have a turbo you can counteract this tail off by increasing the boost therefore turbo engine's can have complex ignition timing needs and will generally need less overall advance and a more linear advance curve.

Programmable ignition, like MJ, is particularly useful with forced induction.

Hmmm i dont see why you have to try and make yourself look clever again not everyone is stupid, not everyone needs an explanation that looks copy and paste job, the above does not answer the question.

Matty

A Dizzy will be fine if it has the right advance curve, your not running silly boost and its set up correctly, engine managment (of any manufacturer) will optimise the ignition setup and actually is not to hard to set up, my original setup a GEMs unit i did the basics myself with just a laptop timing light and a book i am now on my second unit an omex 500 and will shortly be buying an emerald to run fuel injection i am personally not a fan of the mega range but thats just personal choice and what suits me.

For a comparison the same turbo engine in my car gave 148brake on the dizzy and 158 on the gems after final setup on the same RR about 14lb of boost iirc.

thanks for the input! what book did you refer to? looking at the performance figures you have given looks like ill be using a metro dizzy for the moment as i'm not after massive power gains at the moment, and am on a budget so i could do without the ECU at the moment.

how will i go about getting the correct advance curve? will it just be playing about with the dizzy with a timing light?

chears matt

[matty121]

As above you need the correct advanve curve to match the specification of your engine. In theory there should be no power difference between a dizzy and mapped ignition if both optimised, but dizzys are a bit crap and you get a stronger spark with mapped systems, so power can be made. I personally made *melons*all extra maximum power when I swapped from a dizzy fixed at 25 deg to a fully mapped system, but I did gain low and midrange.

The dizzy you plan to use will be next to useless on a forced induction engine, it will need to be so retarded to limit the maximum advance that you will suffer off boost and on cruise (infact everywhere other than what).

If you want to use a dizzy then the Metro turbo one is the best to use. But I'd advise mapped ignition, worth every penny.

really helpful stuff! ill be going for a metro turbo dizzy then until I can afford mappable ignition.

do you have a estimate round figure of how much it cost you to set up the mapped ignition?

chears matt

[Ethel]

Thanks for the compliment Wolfie, I write my own replies.

I could have just said use a Metro Turbo distributor, but that would assume Matty is aiming to build a similar spec engine and wouldn't help him to decide what his requirements are. Of course plenty of people understand what an ignition system does; I'd be wasting my time writing a reply for them. If you fall in to that category, I wasn't writing it for you so why take offence?

I hope readers use all the info on the forum to improve their own understanding and make their own decisions; it's the most effective and rewarding way.


Matty,

The last Turbo dizzy I watched on Ebay went for £60, the cost of Megajolt can vary a lot, depending on what you can rustle up for yourself. Trigger-wheels do the cheapest timing wheel I've seen; you can buy a self assembly MJ from Autosportlabs (you might get stung a bit of import duty on top), that leaves EDIS to find on a scrap Ford and some brackets and wiring to make.

A stop gap alternative would be to modify an existing dizzy by putting a couple of stops on the baseplate to limit the travel of the centrifugal advance.

[wolfie]

Thanks for the compliment Wolfie, I write my own replies.

I could have just said use a Metro Turbo distributor, but that would assume Matty is aiming to build a similar spec engine and wouldn't help him to decide what his requirements are. Of course plenty of people understand what an ignition system does; I'd be wasting my time writing a reply for them. If you fall in to that category, I wasn't writing it for you so why take offence?

I hope readers use all the info on the forum to improve their own understanding and make their own decisions; it's the most effective and rewarding way.

sorry but thats total tosh, you on a number of occations have written or copied a drawn out explanation of something that he no relation to the question asked you have done it to me, i asked Phil in relation to a megasquirt question if it did MAP and TPS as all my ecu's ive had have done both, the answer was clearly no theres two different boards however you have to do a drawn out and unnecessary explanation that again looks like a copy on MAP and TPS when that was not the question i asked, if someone needs an explanation on the workings of an ecu they will ask for it the same goes for MAP TPS ect ect you dont need to try and belittle or try and make yourself out to be better!

Matty

The book i refer to was actually the ECU installation manual my error sorry, however a good book to get is the engine managment haynes manual written by Dave Walker IMO and arguably one of the most innative and experianced engine tuners in the UK

[ivanhoew]

mattty ,the cheapest and easiest way to do it is lock the advance mechanism with a dab of weld ,so it does not advance ,then fix the timing at around 24 degrees ,run 8.5:1 cr and around 10 psi .

this will make a bit less average powerand mpg than a total recurve .but will work .and be fun .

you can run more boost ,or less ,and will have to retard or advance to suit ,but this is a good ball park figure .

[matty121]

mattty ,the cheapest and easiest way to do it is lock the advance mechanism with a dab of weld ,so it does not advance ,then fix the timing at around 24 degrees ,run 8.5:1 cr and around 10 psi .

this will make a bit less average powerand mpg than a total recurve .but will work .and be fun .

you can run more boost ,or less ,and will have to retard or advance to suit ,but this is a good ball park figure .

great can this be done on any distributor? or particular ones..

do you have any pictures if you have done this yourself?

chears matt

[Ethel]

sorry but thats total tosh, you on a number of occations have written or copied a drawn out explanation of something that he no relation to the question asked you have done it to me, i asked Phil in relation to a megasquirt question if it did MAP and TPS as all my ecu's ive had have done both, the answer was clearly no theres two different boards however you have to do a drawn out and unnecessary explanation that again looks like a copy on MAP and TPS when that was not the question i asked, if someone needs an explanation on the workings of an ecu they will ask for it the same goes for MAP TPS ect ect you dont need to try and belittle or try and make yourself out to be better!

Matty

The book i refer to was actually the ECU installation manual my error sorry, however a good book to get is the engine managment haynes manual written by Dave Walker IMO and arguably one of the most innative and experianced engine tuners in the UK

Think what you like, it's no skin off my nose. Both versions of Megajolt are built on the same circuit board - it may be of no interest to you, but it may be useful info to someone else who wants to swap from TPS to MAP and is a matter of fact. Facts are independent of opinion.

If you think I cut 'n paste my posts, then cut 'n paste them into Google and you'll find the source, if there is one - or you'll find out your opinion is wrong.


Yes you can put a stop on any dizzy's advance with a spot of weld, solder etc. You'll have to strip the shaft out to expose the centrifugal advance. By turning one of the shafts against the other it will be obvious what's needed. Just remember the dizzy does one revolution to every two the crank does, so half the angle is needed, i.e. if you want to limit the advance by a further 10 degrees you need to reduce the movement of the rotor arm by 5 degrees.

[ivanhoew]

mattty ,the cheapest and easiest way to do it is lock the advance mechanism with a dab of weld ,so it does not advance ,then fix the timing at around 24 degrees ,run 8.5:1 cr and around 10 psi .

this will make a bit less average powerand mpg than a total recurve .but will work .and be fun .

you can run more boost ,or less ,and will have to retard or advance to suit ,but this is a good ball park figure .

great can this be done on any distributor? or particular ones..

do you have any pictures if you have done this yourself?

chears matt

hi matty ,this can be done on any distributor. i have done this myself on several different turbo engines , i have no pictures to be honest ,its so simple that i didnt think it interesting enough to take a picture .lol