Understanding Ignition Timing

[martin_t]

Hi

I am trying to understand ignition timing but am struggling!! There are a few very knowledgeable guys on the forums I use, who have helped me massively, but I am still not sure about the timing side. I have a RV8 3.5. how do I know what the total advance timing should be set at? I have just watched a youtube video where they use a strobe light and turn the dizzy round to achieve change on a small block Chevy, but how do I know what is the perfect setting? My engine is not standard so the Haynes is not helpful.
If its simple, by all means tell me I'm being a bit dim (!!), but I just need to understand so I can get my motor running better (hopefully!).
Also, it looks like a lousy weekend ahead and Newark kit Car Show could be a washout, so I need something to fiddle about with in the garage!!!

Many thanks

Martin

[mgbv8]

No two dissy engines perform the same with the same timing Martin. They all have their little quirks, especially after they have been tweaked a bit.

Go for a fairly standard setup to start with. 8-10 BTDC for idle advance. And aim for 28-30 BTDC for max advance at 3000 rpm.

Do you have a strobe light?
Is the engine already a runner?

If the answer to the above is yes to both you are on the right track.

If its not a runner yet we can advise on the basic setting in order to get it running.

Perry

[martin_t]

Hi

Yes the engine runs and seems fine. Just feel from what people have said that maybe it will run better (?) with the right timing setup.

thanks

Martin

[ramon alban]

this might help you

http://www.vintagemodelairplane.com/pag ... ion04.html

http://www.vintagemodelairplane.com/pag ... ion05.html

[sidecar]

You want to be running more than 30 degrees on a 3.5 lump, 36 would be a better bet. I have also found that they idle is best with around 14. (quite a bit more than Rover specify).

The Eddy 500 carb that you are running does not suit the Lucas vac advance very well at all. You are best off not using it but using quite 'light' dizzy springs so the all in is around 2700-3000 RPM. I believe that JE Developments also does not use the vac system.

Before you do any messing about with the timing you must be sure that your TDC mark really is at TDC, you will then need some sort of timing tape. (or a dial back strobe).

Have a read of this. (The bit under braided hoses)

http://how-to-build-a-pilgrim-sumo.wiki ... by-members

I wrote it ages ago when I was running a Lucas dizzy with a Lucas amp, I now run MSD as you know.

[martin_t]

You want to be running more than 30 degrees on a 3.5 lump, 36 would be a better bet. I have also found that they idle is best with around 14. (quite a bit more than Rover specify).

The Eddy 500 carb that you are running does not suit the Lucas vac advance very well at all. You are best off not using it but using quite 'light' dizzy springs so the all in is around 2700-3000 RPM. I believe that JE Developments also does not use the vac system.

Before you do any messing about with the timing you must be sure that your TDC mark really is at TDC, you will then need some sort of timing tape. (or a dial back strobe).

Have a read of this. (The bit under braided hoses)

http://how-to-build-a-pilgrim-sumo.wiki ... by-members

I wrote it ages ago when I was running a Lucas dizzy with a Lucas amp, I now run MSD as you know.

Thanks Pete

The bit I don't understand is the idle setting. If I loosen the dizzy, use a timing light and aim for 12-14 at idle, that obviously moves when you set the timing (moving the dizzy again) at 2700-3000rpm. the idle will have changed so I'm not understanding why you set it in the first place?
Does that make sense? Please bare with me!!!

Thanks

Martin

[sidecar]

You want to be running more than 30 degrees on a 3.5 lump, 36 would be a better bet. I have also found that they idle is best with around 14. (quite a bit more than Rover specify).

The Eddy 500 carb that you are running does not suit the Lucas vac advance very well at all. You are best off not using it but using quite 'light' dizzy springs so the all in is around 2700-3000 RPM. I believe that JE Developments also does not use the vac system.

Before you do any messing about with the timing you must be sure that your TDC mark really is at TDC, you will then need some sort of timing tape. (or a dial back strobe).

Have a read of this. (The bit under braided hoses)

http://how-to-build-a-pilgrim-sumo.wiki ... by-members

I wrote it ages ago when I was running a Lucas dizzy with a Lucas amp, I now run MSD as you know.

Thanks Pete

The bit I don't understand is the idle setting. If I loosen the dizzy, use a timing light and aim for 12-14 at idle, that obviously moves when you set the timing (moving the dizzy again) at 2700-3000rpm. the idle will have changed so I'm not understanding why you set it in the first place?
Does that make sense? Please bare with me!!!

Thanks

Martin

Hi Martin,

You don't re-set the dizzy at 2700, the mechanical advance will have been 'adding' advance as the revs rise, what you need to do is check when all of the advance has been added (what RPM it as all been added by) AND what the all-in figure for the timing actually is. (You could rev the engine to 4000 RPM, if all the advance has been added by 3000 RPM then it won't be any higher at 4000 RPM).

The problem is that you might set the timing up to say 14 degrees at tickover but you then find at the all-in figure is say 40 degrees and is only all-in at 4000 RPM. You then start having to get clever! You would need to restrict the total advance by use of sleeves and fit lighter bob-weight springs. I have worked on many Rover dizzies, quite a lot of them seem to actualyl give the required all-in figure of 36 when set to 14 static, usually the bob weight springs will need changing though because they are too stiff. The Lucas dizzy is a bit more of a pain on the 4.6 lump because it then needs the sleeves fitting as the 4.6 only needs 28-30 degrees all-in. Lucas made 'flavours' of the dizzy, each having different mechanical advance 'sweep figures' (How much advance they can have) and different bob weight springs.

Regards,

Pete

[Cobratone]

Pete, do you have any info/websites that show how different advance settings affect cruise and acceleration? i.e. if setting afr for maximum economy at cruise then timing be should be "X" etc? I know you use a programmable system so wondered whether you had looked into this or not??

[martin_t]

You want to be running more than 30 degrees on a 3.5 lump, 36 would be a better bet. I have also found that they idle is best with around 14. (quite a bit more than Rover specify).

The Eddy 500 carb that you are running does not suit the Lucas vac advance very well at all. You are best off not using it but using quite 'light' dizzy springs so the all in is around 2700-3000 RPM. I believe that JE Developments also does not use the vac system.

Before you do any messing about with the timing you must be sure that your TDC mark really is at TDC, you will then need some sort of timing tape. (or a dial back strobe).

Have a read of this. (The bit under braided hoses)

http://how-to-build-a-pilgrim-sumo.wiki ... by-members

I wrote it ages ago when I was running a Lucas dizzy with a Lucas amp, I now run MSD as you know.

Thanks Pete

The bit I don't understand is the idle setting. If I loosen the dizzy, use a timing light and aim for 12-14 at idle, that obviously moves when you set the timing (moving the dizzy again) at 2700-3000rpm. the idle will have changed so I'm not understanding why you set it in the first place?
Does that make sense? Please bare with me!!!

Thanks

Martin

Hi Martin,

You don't re-set the dizzy at 2700, the mechanical advance will have been 'adding' advance as the revs rise, what you need to do is check when all of the advance has been added (what RPM it as all been added by) AND what the all-in figure for the timing actually is. (You could rev the engine to 4000 RPM, if all the advance has been added by 3000 RPM then it won't be any higher at 4000 RPM).

The problem is that you might set the timing up to say 14 degrees at tickover but you then find at the all-in figure is say 40 degrees and is only all-in at 4000 RPM. You then start having to get clever! You would need to restrict the total advance by use of sleeves and fit lighter bob-weight springs. I have worked on many Rover dizzies, quite a lot of them seem to actualyl give the required all-in figure of 36 when set to 14 static, usually the bob weight springs will need changing though because they are too stiff. The Lucas dizzy is a bit more of a pain on the 4.6 lump because it then needs the sleeves fitting as the 4.6 only needs 28-30 degrees all-in. Lucas made 'flavours' of the dizzy, each having different mechanical advance 'sweep figures' (How much advance they can have) and different bob weight springs.

Regards,

Pete

Actually Pete, the mist is starting to clear!!! Thanks mate, I think I am starting to understand. (putting it into practice is something else though!!!).
One quick question, while gathering bits for the new engine, what dizzy would you suggest? Don't think I will stretch my knowledge going with an MSD solution to start with. The three options I have been looking for are either the Lucas 35DM8, 35DLM8, or the Mallory Magnetic. Any thoughts? My current Opus will be going.


Cheers

Martin

[sidecar]

Pete, do you have any info/websites that show how different advance settings affect cruise and acceleration? i.e. if setting afr for maximum economy at cruise then timing be should be "X" etc? I know you use a programmable system so wondered whether you had looked into this or not??

Hi Tone,

I'm on my hol's in Spain at the moment, most of the info that I spout comes from several books that I've read along with any other info that I can pick up along the way!

I guess really the only way to know for sure is to spend hours on a dyno with your own motor trying out all the combinations that are possible. (This would be very expensive!)


With regards to cruise timing well I've never been too bothered about MPG so I have not spent hours fiddling with it but my mate runs the same engine as me in a Manta along with and MSD setup. He also runs a MAP system, we set it up to give 14 degrees more advance as long as the manifold was at 20 inches of mercury vacuum. He can get 27 MPG at 60-70 MPH which ain't bad! With regards to AFR and ignition advance the quickest burning ratio is 14.7:1 anything either side of that will burn slower and I guess the further away from 14.7 that you are the slow it will burn. I can not get the AFR any leaner than 15:1 with the Eddy carb and still have decent engine response, I'm sure that with multipoint EFI you could go a fair bit leaner which will then require a bit more advance. As you are going to use a 'clever' system on your new engine you could run alot of advance whenever the AFR is lean and the manifold vacuum is high, you could then peg back the advance as soon as the vacuum level drops. This is what we did on the Manta, in order to get 20" of vacuum the throttle must only be just cracked open, the advance is dropped like a hot stone as soon as the throttle is opened any more.

With regards to the ignition settings for acceleration and peak revs really I have just gone for what others have said. (In 'the book' JE has been quoted with regards to peak advance figures, 28-30 degrees for a 4.6 lump so I went with that).

There is a chap round here that has a dyno that bolts to the wheel hubs, one day I'll stick my car on it and have a fiddle.

As my MSD has loads of adjustments I did set it up with a bump in the timing, I reckon that the VE must be dropping like a stone at anything over 5k RPM so I get the system to push the timing up from 28 to 32 from 5000 to 5500 RPM. The top end from 5000 to 6000 RPM 'seems' a bit better but of course it is easy to just think that it is better because 'it must be'

BTW, the gearbox mods went completely wrong!

[sidecar]

Actually Pete, the mist is starting to clear!!! Thanks mate, I think I am starting to understand. (putting it into practice is something else though!!!).
One quick question, while gathering bits for the new engine, what dizzy would you suggest? Don't think I will stretch my knowledge going with an MSD solution to start with. The three options I have been looking for are either the Lucas 35DM8, 35DLM8, or the Mallory Magnetic. Any thoughts? My current Opus will be going.


Cheers

Martin

A year ago I would have said that the Lucas dizzies are fine, I thought that there was no more power to be had out of my engine via the ignition, however I was proved wrong when I went to MSD. (The increase was not from different settings, both my Lucas and the MSD initially ran the same settings.

I have worked on one Mallory system, it seemed well made and was adjustable in all the respects that you require, the Lucas dizzies are only adjustable by 'modification' which ain't the same thing.

Personally out of the choices that you have given I'd go for a Mallory without a vac system. (Just don't go for a twin points Mallory!)

[martin_t]

Actually Pete, the mist is starting to clear!!! Thanks mate, I think I am starting to understand. (putting it into practice is something else though!!!).
One quick question, while gathering bits for the new engine, what dizzy would you suggest? Don't think I will stretch my knowledge going with an MSD solution to start with. The three options I have been looking for are either the Lucas 35DM8, 35DLM8, or the Mallory Magnetic. Any thoughts? My current Opus will be going.


Cheers

Martin

A year ago I would have said that the Lucas dizzies are fine, I thought that there was no more power to be had out of my engine via the ignition, however I was proved wrong when I went to MSD. (The increase was not from different settings, both my Lucas and the MSD initially ran the same settings.

I have worked on one Mallory system, it seemed well made and was adjustable in all the respects that you require, the Lucas dizzies are only adjustable by 'modification' which ain't the same thing.

Personally out of the choices that you have given I'd go for a Mallory without a vac system. (Just don't go for a twin points Mallory!)

Pete

Like the idea of the MSD, but considering I am struggling to get my head round straight dizzy setup, it may be a step to far initially!!

Cheers

Martin