Hi All,
I am trying to get a better understanding of initial timing for my set-up.
fiat twincam 2.0
twin 40 webers
lotus 7 kit car (circa 600kg)
megajoltE
I have been advised to set initial at 10 deg @ 850..........however if i sit in the car with the megalot running and slowly nudge my initial timing up 1 degree at a time, my revs increase also...at present i have settled at 18 deg at 1000 rpm...............(i could go higher but worried about knocking)
The simple fact the revs increase as i increase the initial timing tells me the engine is making more power because it is better burning the fuel..............
I still plan on keeping total advance at 35 deg at 3000 rpm
Another theory i want to table.............my car being so light results in minimal load on the engine............should this warrant running with higher initial timing.....?
look forward to your thoughts guys..
Initial timing....go higher or lower.........fiat twin cam
Moderators: JeffC, rdoherty, stieg, brentp
To find out what your car wants for initial timing, first get the engine up to operating temperature. Then increase the timing 2*. Shut off the engine for a minute or so to allow it to heat soak, then try to restart. If it starts easily increase the timing 2* more, shut off and allow to heat soak. Keep doing this until the engine either drags the starter or it spits out through the carb. When that happens back off 2*. The only time that hasn't worked for me was when I was running a cam with 300* advertised intake duration. I was up to 22* initial and it was still starting easily. I backed off to 18* and left it there. The rule-of-thumb us old folks use is initial timing should never be less than 10 or more than 20.
Hello,
I think you need to educate yourself first. Please, do not take it as a rude comment, this is absolutely not my intent
We all start somewhere and your comment made me feel that you do not yet understand exactly how timing & knock work.
Here are my best books. They are very well done with many pictures & drawings to explain you how engine works. They're talking about fuel injection but timing is also part of the tuning process for any engine.
Designing and Tuning High-Performance Fuel Injection Systems by Greg Banish
Performance Fuel Injection Systems by Matt Cramer
Engine Management: Optimizing Modern Fuel and Ignition Systems by Dave Walker (not as good as the 2 first ones but it starts with carbs to extrapolate with FI which can be good also to read)
Ideally you want timing at idle (and everywhere else on the map) to be as efficient as possible.
If rpm increase with timing, it means you're becoming more efficient with better torque output, so it is going the right way. At some point, it will start becoming steady until it start decreasing. You want your timing at be right where rpm starts to be steady.
If rpm are too high, you need to play with carbs to lower rpm (the sync bolt)
With MJLJ (and any programmable ECU) you can find best timing, lower it a little at 1000rpm for instance and make it ideal below, let say 700rpm, this will give an extra torque supply if something turn on at idle (alternator, lights, AC, etc)
Regarding knock, it happens when fuel mix burn increase pressure inside combustion chamber to a point where unburnt fuel self ignite.
To have this condition happening, you need to have enough pressure (=enough fuel & air) to get to the point where pressure could make fuel mix to self ignite. Bottom line, it won't happen at idle where there's only enough fuel to make the engine runs, same goes for cruising conditions. It would only happen with higher loads during high acceleration in high gears for instance.
Engine also have to be knock limited. Some engine will never knock because they would never reach pressure high enough (low compression ratio engine for instance)
You'll also see that fuel mix does not burn at the same speed depending on load (air available). Low load conditions could (and must!) run much higher timing. For instance, with my setup, I run max timing at WOT around 33° whereas I'm running as much as 49° at cruise at 3000 rpm. This is one of the main benefit of such system, cruising & transient states are much more controlled with MJLJ. That would reduce fuel consumption & increase performance
I think you need to educate yourself first. Please, do not take it as a rude comment, this is absolutely not my intent
We all start somewhere and your comment made me feel that you do not yet understand exactly how timing & knock work.Here are my best books. They are very well done with many pictures & drawings to explain you how engine works. They're talking about fuel injection but timing is also part of the tuning process for any engine.
Designing and Tuning High-Performance Fuel Injection Systems by Greg Banish
Performance Fuel Injection Systems by Matt Cramer
Engine Management: Optimizing Modern Fuel and Ignition Systems by Dave Walker (not as good as the 2 first ones but it starts with carbs to extrapolate with FI which can be good also to read)
Ideally you want timing at idle (and everywhere else on the map) to be as efficient as possible.
If rpm increase with timing, it means you're becoming more efficient with better torque output, so it is going the right way. At some point, it will start becoming steady until it start decreasing. You want your timing at be right where rpm starts to be steady.
If rpm are too high, you need to play with carbs to lower rpm (the sync bolt)
With MJLJ (and any programmable ECU) you can find best timing, lower it a little at 1000rpm for instance and make it ideal below, let say 700rpm, this will give an extra torque supply if something turn on at idle (alternator, lights, AC, etc)
Regarding knock, it happens when fuel mix burn increase pressure inside combustion chamber to a point where unburnt fuel self ignite.
To have this condition happening, you need to have enough pressure (=enough fuel & air) to get to the point where pressure could make fuel mix to self ignite. Bottom line, it won't happen at idle where there's only enough fuel to make the engine runs, same goes for cruising conditions. It would only happen with higher loads during high acceleration in high gears for instance.
Engine also have to be knock limited. Some engine will never knock because they would never reach pressure high enough (low compression ratio engine for instance)
You'll also see that fuel mix does not burn at the same speed depending on load (air available). Low load conditions could (and must!) run much higher timing. For instance, with my setup, I run max timing at WOT around 33° whereas I'm running as much as 49° at cruise at 3000 rpm. This is one of the main benefit of such system, cruising & transient states are much more controlled with MJLJ. That would reduce fuel consumption & increase performance
Mathieu