Ignition timing
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Ignition timing
Its probably been covered before but can anyone tell me the correct ignition setting for my engine? Its a 4.6 (9.35 to 1 comp) running on 97octane fuel, and yes I'm using a dizzy! Cant find a definite answer anywhere. Thanks
Triumph TR7 V8 3.9efi
Hi
any more information like cam timing, weight of car, is it manual or auto???
If it is an auto with a near stock cam and genuinely 9.35:1 (did you measure it or is it from the Haynes manual? what is the stall on the torque converter if it has one) and the car is under a ton and a half then start at about 14 to 16 at fast idle with the vac advance disconnected, have about 32 to 34 degrees in by 3200 revs and have about another 10 come in with the vac advance at 1200 revs and the throttle nearly closed. no vac advance then take out 2 more degrees at 3200. listen to see if it is detonating as you open the throttle and take out timing if it does.
Personally I would ignore what I have just said and book it in for a dyno session as every timing curve is different.
Best regards
Mike
any more information like cam timing, weight of car, is it manual or auto???
If it is an auto with a near stock cam and genuinely 9.35:1 (did you measure it or is it from the Haynes manual? what is the stall on the torque converter if it has one) and the car is under a ton and a half then start at about 14 to 16 at fast idle with the vac advance disconnected, have about 32 to 34 degrees in by 3200 revs and have about another 10 come in with the vac advance at 1200 revs and the throttle nearly closed. no vac advance then take out 2 more degrees at 3200. listen to see if it is detonating as you open the throttle and take out timing if it does.
Personally I would ignore what I have just said and book it in for a dyno session as every timing curve is different.
Best regards
Mike
poppet valves rule!
Ok, its a p6 so well under ton and half and manual. I was planning a trip to a rolling road after mot etc. Its booked in for test on Thursday, been off the road since 2008. My localish rolling road didnt bother answering my email - I think he prefers rally cars etc. I will probably have to trailer the car around 100 miles to near Cardiff. If I could set it at idle ( with vac pipe off ) then it should be ok?
Triumph TR7 V8 3.9efi
The above figures are nothing like the ones that Rover specify however I'm with Mike on this one. But like he says it depends on loads of stuff!kiwicar wrote:Hi
any more information like cam timing, weight of car, is it manual or auto???
If it is an auto with a near stock cam and genuinely 9.35:1 (did you measure it or is it from the Haynes manual? what is the stall on the torque converter if it has one) and the car is under a ton and a half then start at about 14 to 16 at fast idle with the vac advance disconnected, have about 32 to 34 degrees in by 3200 revs and have about another 10 come in with the vac advance at 1200 revs and the throttle nearly closed. no vac advance then take out 2 more degrees at 3200. listen to see if it is detonating as you open the throttle and take out timing if it does.
Personally I would ignore what I have just said and book it in for a dyno session as every timing curve is different.
Best regards
Mike
I run 18 degrees at idle 28 at 5500 which then advances to 32 from 5500 to 6000 RPM. 18 is a lot for idle but its what my engine 'wants'. My ignition system will allow me to run at around 10 degrees when at cranking revs which helps give the starter motor an easy time.
So basically your question is opening a 'can of worms'!!
Last edited by sidecar on Fri Jan 23, 2015 5:31 pm, edited 1 time in total.
Yes, sorry! There is no black and white answer I suppose. I'll try and get it close then book in a dyno sessionsidecar wrote:kiwicar wrote:Hi
any more information like cam timing, weight of car, is it manual or auto???
If it is an auto with a near stock cam and genuinely 9.35:1 (did you measure it or is it from the Haynes manual? what is the stall on the torque converter if it has one) and the car is under a ton and a half then start at about 14 to 16 at fast idle with the vac advance disconnected, have about 32 to 34 degrees in by 3200 revs and have about another 10 come in with the vac advance at 1200 revs and the throttle nearly closed. no vac advance then take out 2 more degrees at 3200. listen to see if it is detonating as you open the throttle and take out timing if it does.
Personally I would ignore what I have just said and book it in for a dyno session as every timing curve is different.
Best regards
Mike
The above figures are nothing like the ones that Rover specify however I'm with Mike on this one. But like he says it depends on loads of stuff!
I run 18 degrees at idle 28 at 5500 which then advances to 32 from 5500 to 6000 RPM. 18 is a lot for idle but its what my engine 'wants'. My ignition system will allow me to run at around 10 degrees when at cranking revs which helps give the starter motor an easy time.
So basically your question is opening a 'can of worms'!!
Triumph TR7 V8 3.9efi
Dunno why people think that running the motor just off the point of pinking will give the best timing figure, its just not true, well not unless you are running way too much compression in which case you are just running a compromised setup. Just off pinking is an 'old school' setup method when people did not know any better.
The likes of Ricardo have done loads of research into this, any petrol engine produces the the highest torque figure at any given revs when the peak cylinder pressure is reached when the piston is 14-20 degrees ATDC. (You need to light the mixture BTDC in order to allow time for it to burn and generate pressure).
So if you use the 'just off pinking method' you could end up advancing the ignition too far, you could and up with the peak cylinder pressure at 6 degrees or something like that. On the flip side some engines will never go into 'pinking' mode so how would you setup the timing on such an engine?
If your engine has been built with too much static compression for the fuel being used then you might have no choice but to use this method, the engine might pink when the peak cylinder pressure is reached at 24 degrees ATDC but the lump won't tolerate any more advance, such an engine would run better with a lower CR or a higher octane fuel and more ignition advance.
I guess there might be some engines where the just off pinking point just happens to be around the same 14-20 degree ATDC peak cylinder pressure point but without a lot of dyno testing you would never know whether you had such an engine.
This wiki link talks about peak cylinder pressue so it must be true!...
http://en.wikipedia.org/wiki/Ignition_timing
The likes of Ricardo have done loads of research into this, any petrol engine produces the the highest torque figure at any given revs when the peak cylinder pressure is reached when the piston is 14-20 degrees ATDC. (You need to light the mixture BTDC in order to allow time for it to burn and generate pressure).
So if you use the 'just off pinking method' you could end up advancing the ignition too far, you could and up with the peak cylinder pressure at 6 degrees or something like that. On the flip side some engines will never go into 'pinking' mode so how would you setup the timing on such an engine?
If your engine has been built with too much static compression for the fuel being used then you might have no choice but to use this method, the engine might pink when the peak cylinder pressure is reached at 24 degrees ATDC but the lump won't tolerate any more advance, such an engine would run better with a lower CR or a higher octane fuel and more ignition advance.
I guess there might be some engines where the just off pinking point just happens to be around the same 14-20 degree ATDC peak cylinder pressure point but without a lot of dyno testing you would never know whether you had such an engine.
This wiki link talks about peak cylinder pressue so it must be true!...
http://en.wikipedia.org/wiki/Ignition_timing
LOL, Sorry about that!Andrewrv8 wrote:I'm really confused nowI dont have a figure from a book for the 4.6 but for the 3.5 it states 8btdc (where is degrees on keyboard?) 18 sounds a lot to me, if I aim for 14btdc it should be safe. I will get it set up properly though and get carb jetted. Hope she passes mot!!
18 is quite a lot, one of the main things that determines the advance that the engine wants at tickover is the cam duration. A long duration cam leads to poor cylinder pressure at tickover along with exhaust gasses left in the combustion chamber, more advance helps the engine run well under these conditions.
When you get your ear 'in tune' with your engine you can hear what it wants at tickover just by adjusting the timing whilst listening to how the engine responds. Basically you can start fairly retarded then slowly wind in the timing, the engine will respond by speeding up, keep advancing the timing and listen for the RATE that the engine revs speed up, at some point the RATE will reduce. The engine will still speed up as you wind in more timing but the rate of this increase in RPM will fall off. The ideal tickover timing is just at the point the rate falls off. It can be a bit tricky to find this point and you can end up winding the timing to 30 degrees, the engine will still be running very well but clearly you can not leave the timing like this!
Now this is all great but its no good if the all-in ends up being 38 degrees or something like that. This is when you have to get clever, these dizzies can be modified so you can get both the idle and the all-in figures that you are looking for. Personally I would not run a 4.6 at more than 30 degrees all- in. I know I do but only at high RPM where the VE is dropping right off.
As you car is probably not all that light you might want the all in at 3-3.5k RPM and not earlier. So you are looking at something like 12-14 at tickover, 30 degrees all-in at 3000-3500 RPM (vac disconnected during the setup and only connected back to a timed port if it suits the vac canister)
Then there is the carb, if you you are running an Eddy 500 the non-timed port and timed-port vac advance takes offs don't really suit the Lucas vac canister very well at all! What carb are you running?
I wrote this yonks ago.. .
http://how-to-build-a-pilgrim-sumo.wiki ... by-members
I run an MSD unit now with a locked out Lucas dizzy, looking back I think that I just about squeezed all the performance I could out of the Lucas dizzy along with its standard ignitor but going to an MSD unit must have added about 15 BHP to the output of my car. (guesimation here). I find it hard to get excited about the standard system, they are not all that good in my humble, I guess they were built to a price and to suit a standard engine blimbling around for most of its life!
Not having a go at anyone here, its just what I found by spending months messing about with this stuff.Andrew,
As others have said this is not a question with a straight forwards answer.
Did I miss it or do you know what engine the Dizzy came from?
If it's from a 3.5 then it will have advance settings to give about 35 degrees total.
If it's from a 3.9 then it will have advance settings to give about 32 degrees total.
High and low compression versions of these engines will again have different setting in the dizzy.
As Sidecar said the 4.6 will need about 30 degrees total advance and as a starting point using a strobe you could set the idle to 10 degrees. Then put a 30 degrees mark on your crank pulley and with the engine at 3000 - 3500RPM rotate the dizzy to spot this mark. (Vacuum disconnected off course).
Return the engine to tick over and take another reading. It will be higher or lower than 10 degrees. If it at about 12 degrees then the pick up from idle will be good. If it's 6-8 degrees then the engine will not be as responsive.
I suspect that if the dizzy is originally from a smaller engine the idle timing will read lower than the initial 10 degrees.
To get the idle timing up a bit to give better response you will need to put a stop inside the dizzy to limit the total advance and then reset the dizzy to give 30 degrees at 3000-3500 RPM. This will then give a higher idle reading.
This should give a reasonable starting point for a standard road going 4.6.
Inside the dizzy on the baseplate under the weights you will find a number stamped. This could be 9, 11, 13 etc., depending on the max advance it was set to max at. (If the number is 9 this represents 18 degrees in engine degrees so add the idle degree of say 12 degrees and that will give 30 degrees total. If the number is higher than 9 then you will need to put a stop inside the dizzy to reduce the maximum advance and thereby allow a better idle setting.
As stated by Sidecar, connecting the vacuum advance with certain carbs will give way too much light load advance so you need to check how much added advance you are getting at light load.
Regards Denis
As others have said this is not a question with a straight forwards answer.
Did I miss it or do you know what engine the Dizzy came from?
If it's from a 3.5 then it will have advance settings to give about 35 degrees total.
If it's from a 3.9 then it will have advance settings to give about 32 degrees total.
High and low compression versions of these engines will again have different setting in the dizzy.
As Sidecar said the 4.6 will need about 30 degrees total advance and as a starting point using a strobe you could set the idle to 10 degrees. Then put a 30 degrees mark on your crank pulley and with the engine at 3000 - 3500RPM rotate the dizzy to spot this mark. (Vacuum disconnected off course).
Return the engine to tick over and take another reading. It will be higher or lower than 10 degrees. If it at about 12 degrees then the pick up from idle will be good. If it's 6-8 degrees then the engine will not be as responsive.
I suspect that if the dizzy is originally from a smaller engine the idle timing will read lower than the initial 10 degrees.
To get the idle timing up a bit to give better response you will need to put a stop inside the dizzy to limit the total advance and then reset the dizzy to give 30 degrees at 3000-3500 RPM. This will then give a higher idle reading.
This should give a reasonable starting point for a standard road going 4.6.
Inside the dizzy on the baseplate under the weights you will find a number stamped. This could be 9, 11, 13 etc., depending on the max advance it was set to max at. (If the number is 9 this represents 18 degrees in engine degrees so add the idle degree of say 12 degrees and that will give 30 degrees total. If the number is higher than 9 then you will need to put a stop inside the dizzy to reduce the maximum advance and thereby allow a better idle setting.
As stated by Sidecar, connecting the vacuum advance with certain carbs will give way too much light load advance so you need to check how much added advance you are getting at light load.
Regards Denis
1950 A40 Devon Hotrod with 5.0 twin turbo RV8.
EDIS8 wasted spark, Holley Injection.
Been as far as the Moon and back in 57 years of driving. Same Car, 5 engine upgrades !!!
EDIS8 wasted spark, Holley Injection.
Been as far as the Moon and back in 57 years of driving. Same Car, 5 engine upgrades !!!
This is interesting reading, thanks guys, I am understanding it in principle which is a good place to start. Just to clarify, I'm using a standard 4.2 camshaft (long nose) with cam timing at factory setting. And a Rangey 3.5 pointless dizzy, I will set idle at 10 then check at 3000rpm.
I was recommended the MSD set up but feel it would be wasted as the P6 has some restrictions, limited options with headers etc and a fragile diff. I do have another 4.6 with some interesting bits for my next project so who knows? Thanks to everyone for responses.
I was recommended the MSD set up but feel it would be wasted as the P6 has some restrictions, limited options with headers etc and a fragile diff. I do have another 4.6 with some interesting bits for my next project so who knows? Thanks to everyone for responses.
Triumph TR7 V8 3.9efi
DEVONMAN wrote:Andrew,
As others have said this is not a question with a straight forwards answer.
Did I miss it or do you know what engine the Dizzy came from?
If it's from a 3.5 then it will have advance settings to give about 35 degrees total.
If it's from a 3.9 then it will have advance settings to give about 32 degrees total.
High and low compression versions of these engines will again have different setting in the dizzy.
As Sidecar said the 4.6 will need about 30 degrees total advance and as a starting point using a strobe you could set the idle to 10 degrees. Then put a 30 degrees mark on your crank pulley and with the engine at 3000 - 3500RPM rotate the dizzy to spot this mark. (Vacuum disconnected off course).
Return the engine to tick over and take another reading. It will be higher or lower than 10 degrees. If it at about 12 degrees then the pick up from idle will be good. If it's 6-8 degrees then the engine will not be as responsive.
I suspect that if the dizzy is originally from a smaller engine the idle timing will read lower than the initial 10 degrees.
To get the idle timing up a bit to give better response you will need to put a stop inside the dizzy to limit the total advance and then reset the dizzy to give 30 degrees at 3000-3500 RPM. This will then give a higher idle reading.
This should give a reasonable starting point for a standard road going 4.6.
Inside the dizzy on the baseplate under the weights you will find a number stamped. This could be 9, 11, 13 etc., depending on the max advance it was set to max at. (If the number is 9 this represents 18 degrees in engine degrees so add the idle degree of say 12 degrees and that will give 30 degrees total. If the number is higher than 9 then you will need to put a stop inside the dizzy to reduce the maximum advance and thereby allow a better idle setting.
As stated by Sidecar, connecting the vacuum advance with certain carbs will give way too much light load advance so you need to check how much added advance you are getting at light load.
Regards Denis
All sound advice, the link that I posted up in one of my threads shows where the stopper needs to go, you can also change the bob weight springs in order to tweak the timing curve, again the wiki site (how to build a Sumo) shows the springs that you can use.
The issue that I have found with the vac systems on the Eddy carb is that just as you are cracking the thottle open the vac port send too strong a signal to the vac canister. What this means is that you maybe comming out of a bend at say 3000 rpm with all of the mechanical advance running (so at 30 degrees advance) then the vac system goes and dumps another 12 degrees of advance in just as the engine is comming under load, the result is that the engine kicks back which is not good for it. Then as you open the throttle more that vac system backs off which is fine. I tried all sorts of 'clever' bodges to get round this including restrictor jets and bleed systems, nothing really worked too well. The one thing that I did not try was a delay valve, some Rovers have them fitted, I'm not sure how they work! My MSD runs with a MAP system which I can program so after some tests with a vac gauge I could work out exactly how to set the system up to avoid issues yet still run an extra 14 degrees when the manifold is under high vacuum. MuscleManta ran the same setup on his 4.6 Manta along with an Eddy 500 carb, he managed to get 27mpg whilst driving on a motorway which I think is pretty good!
I have another dizzy in my garage which I will take a look at, the link suggests running vac-less, particularly if using Eddy 500. Interesting, that could be the answer to the harsh vacuum from carb. The carb does need setting up properly (jets etc) as its still from the box, probably running lean. I will look into MSD for next engine, quite simple to hook up I understand. Damn, I had a lovely lightened flywheel hidden away
Triumph TR7 V8 3.9efi
