Ignition timing
Discussion
Depends on how you want to set it up- you can use the stock method of setting it at idle and no vacuum with a strobe, in which case about 8' btd will be OK. If you want to tweak it as close as you can then its set at the point of maximum advance- this is normally about 3400 RPM or above and about 28' would be a safe value. The smaller 3.9 engines will take about 32' but its really pushing the limits and the bigger engines need less advance as the flame front is slower in the bigger combustion chamber. Well worth having a dig around for Chimp on Gas topic on ported vacuum , its affect on timing and its removal-- as it makes the engine run much smoother and cooler.
For the record on a TVR Chimaera, V8S or Griffith there's absolutely no point in disconnecting the vacuum advance when you set your timing at idle.
The advice to disconnect the vacuum advance when setting your ignition timing is only relevant on a car where the vacuum advance unit is connected to full vacuum, the standard arrangement on all Griffs and Chims is ported vacuum where at idle the position of the vacuum port is actually at the atmopheric pressure side of the throttle butterfly.
As such on our cars the vacuum applied to the vacuum advance unit at idle is zero, so disconnected or connected it's not changing your timing by one single degree.
To answer the OP's question five litre and four litre RV8 TVRs have the same distributor, the exact same distributor as fitted to a Range Rover or Discovery in fact. This distributor only gives 18 degrees of mechanical advance over your base timing at idle, it's also all done advancing at 3,250rpm so whatever it gives you at 3,250rpm is exactly the same total timing number it gives at 6,250rpm.
Now we now know the window of mechanical advance is from idle to 3,250rpm and within that window the distributor can only ever give you an additional 18 degrees of mechanical advance we can set our idle timing as a subtraction of safe total timing which is 28 degrees for a 500 and 30 degrees for a 400.
For a 500 thats: 28 - 18 = 10 degrees at a 900rpm idle
For a 400 thats: 30 - 18 = 12 degrees at a 900rpm idle
I strongly recommend investing in a dial back timing light with a tacho, if I'm setting up the timing on a car with a distributor I always reach for my trusty INNOVA 3568 Digital Timing Light which allows you to dial up and down, this arrangement is what we used to call a dial back timing light.
Once you've used a dial back timing light you will never want to use a basic strobe without this feature, with a dial back timing light you only really need a clear TDC mark on the pulley but ultimately it also allows you to double check your timing setting if you've used the traditional method of finding your 10 or 12 degrees mark which can be difficult to see.
As we know a distributor advances in response to engine speed so the tacho feature on the INNOVA 3568 is also extremely useful, make sure the engine is fully warm before attempting to set your timing and the engine is idling at a steady 900rpm. Like all timing lights the INNOVA 3568 has an inductive pickup you clip to no1 HT lead but on the 3568 it's metal not plastic which on a TVR Chim or Griff is useful to avoid a melted pickup.
I recommend setting your timing using the traditional method by finding your 10 degrees mark at idle on your 97 500 Griff pulley using the strobe , but because this can be tricky to see and there may be some bouncing use a dial back timing light to dial in the much clearer TDC mark, now read whats on the screen and if it shows 10 degrees your good to pinch up your distributor clamp bolt.
Now seek the help of a friend to hold engine speed at 3,500rpm, again use the dial back timing light to dial in TDC, in your case the screen on your timing light should read 28 degrees total timing ie 10 + 18 = 28 degrees of safe total timing for a Griffith/Chimaera 500.
Finally always follow with an on road load test, a long straight open road going up a hill at speed is best so you can put the engine at load at engine speeds of 3,500rpm or above. While it's true the onset of detonation is inaudible to the human ear it's always good practice to drive and test, if you do hear any detonation (pinking) at all you absolutely must retard your timing by a degree or two until no audible detonation can be detected under load at or above 3,500rpm.
The advice to disconnect the vacuum advance when setting your ignition timing is only relevant on a car where the vacuum advance unit is connected to full vacuum, the standard arrangement on all Griffs and Chims is ported vacuum where at idle the position of the vacuum port is actually at the atmopheric pressure side of the throttle butterfly.
As such on our cars the vacuum applied to the vacuum advance unit at idle is zero, so disconnected or connected it's not changing your timing by one single degree.
To answer the OP's question five litre and four litre RV8 TVRs have the same distributor, the exact same distributor as fitted to a Range Rover or Discovery in fact. This distributor only gives 18 degrees of mechanical advance over your base timing at idle, it's also all done advancing at 3,250rpm so whatever it gives you at 3,250rpm is exactly the same total timing number it gives at 6,250rpm.
Now we now know the window of mechanical advance is from idle to 3,250rpm and within that window the distributor can only ever give you an additional 18 degrees of mechanical advance we can set our idle timing as a subtraction of safe total timing which is 28 degrees for a 500 and 30 degrees for a 400.
For a 500 thats: 28 - 18 = 10 degrees at a 900rpm idle
For a 400 thats: 30 - 18 = 12 degrees at a 900rpm idle
I strongly recommend investing in a dial back timing light with a tacho, if I'm setting up the timing on a car with a distributor I always reach for my trusty INNOVA 3568 Digital Timing Light which allows you to dial up and down, this arrangement is what we used to call a dial back timing light.
Once you've used a dial back timing light you will never want to use a basic strobe without this feature, with a dial back timing light you only really need a clear TDC mark on the pulley but ultimately it also allows you to double check your timing setting if you've used the traditional method of finding your 10 or 12 degrees mark which can be difficult to see.
As we know a distributor advances in response to engine speed so the tacho feature on the INNOVA 3568 is also extremely useful, make sure the engine is fully warm before attempting to set your timing and the engine is idling at a steady 900rpm. Like all timing lights the INNOVA 3568 has an inductive pickup you clip to no1 HT lead but on the 3568 it's metal not plastic which on a TVR Chim or Griff is useful to avoid a melted pickup.
I recommend setting your timing using the traditional method by finding your 10 degrees mark at idle on your 97 500 Griff pulley using the strobe , but because this can be tricky to see and there may be some bouncing use a dial back timing light to dial in the much clearer TDC mark, now read whats on the screen and if it shows 10 degrees your good to pinch up your distributor clamp bolt.
Now seek the help of a friend to hold engine speed at 3,500rpm, again use the dial back timing light to dial in TDC, in your case the screen on your timing light should read 28 degrees total timing ie 10 + 18 = 28 degrees of safe total timing for a Griffith/Chimaera 500.
Finally always follow with an on road load test, a long straight open road going up a hill at speed is best so you can put the engine at load at engine speeds of 3,500rpm or above. While it's true the onset of detonation is inaudible to the human ear it's always good practice to drive and test, if you do hear any detonation (pinking) at all you absolutely must retard your timing by a degree or two until no audible detonation can be detected under load at or above 3,500rpm.
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