I have been thinking about ignition timing and the advised maximum amounts necessary to deliver peak performance.
If my understanding is correct, for best performance total advance should be all in by the rpm in which the engine delivers maximum torque, and then essentially stays at the figure right through to red line and maximum power.
What if a distributor delivers the necessary advance at the rpm corresponding with maximum torque, but then continues to build by a further 8 to 10 degrees by red line and maximum power.
Pinging is far less likely once the rpm exceeds the maximum torque point, so is it detrimental to run additional timing from the aforementioned point to red line?
As an example, 28 degrees maximum advance is the quoted figure to provide maximum torque for the 4.6, but what if timing continued from that point to a maximum of say 38 degrees at say 5500 rpm?
I appreciate your views.
Ron.
Ignition Timing,..how much is too much?
Moderator: phpBB2 - Administrators
Hi
The ignition curve along with the mixture will dictate where peak torque will occour and what happens to the torque curve before and after. It is therefor a bit non sensicle to say timing will be "all in " by peak torque as in some cases you may need the extra timing after and in some cases you may need to retard timing at peek torque.
The real answer is to get it on a dyno and set the advance for max power at a number of rev points using a locked distributor, tweek the mixture to match and plot this out. Then get a distributor re curved to match what the engine wants.
Or did I miss your point?
Mike
The ignition curve along with the mixture will dictate where peak torque will occour and what happens to the torque curve before and after. It is therefor a bit non sensicle to say timing will be "all in " by peak torque as in some cases you may need the extra timing after and in some cases you may need to retard timing at peek torque.
The real answer is to get it on a dyno and set the advance for max power at a number of rev points using a locked distributor, tweek the mixture to match and plot this out. Then get a distributor re curved to match what the engine wants.
Or did I miss your point?
Mike
poppet valves rule!
Hello Mike,
I am just trying to gain a better understanding of ignition timing and its significance to engine performance. I have read the excellent article that Pete posted the link to regarding re curving Lucas distributors but I wanted to know more.
When my 4.6 was built by the Range Rover specialist here in Sydney (they have a Dyno for 4 wheel drives on site) , I was discussing the ignition timing with the Service Manager. I mentioned that the 4.6 required 28 degrees maximum advance, as this is the usual figure that is quoted, although I know that small variations in maximum can occur. The Service Manager said that each engine must be taken on its own merits and tuned accordingly, using the rolling road, setting the fuel map etc. He pointed to a late 1980s Range Rover which was home to a new 4.6. He explained that the timing on that engine was set to 38 degrees maximum advance, and that at lesser degrees the maximum power was also less.
Ron.
I am just trying to gain a better understanding of ignition timing and its significance to engine performance. I have read the excellent article that Pete posted the link to regarding re curving Lucas distributors but I wanted to know more.
When my 4.6 was built by the Range Rover specialist here in Sydney (they have a Dyno for 4 wheel drives on site) , I was discussing the ignition timing with the Service Manager. I mentioned that the 4.6 required 28 degrees maximum advance, as this is the usual figure that is quoted, although I know that small variations in maximum can occur. The Service Manager said that each engine must be taken on its own merits and tuned accordingly, using the rolling road, setting the fuel map etc. He pointed to a late 1980s Range Rover which was home to a new 4.6. He explained that the timing on that engine was set to 38 degrees maximum advance, and that at lesser degrees the maximum power was also less.
Ron.
4.6 Rover 3500 P6B
Re: Ignition Timing,..how much is too much?
Thanks for the comments on my article! Please bear in mind that the information is only what I have gathered from books and during my own testing on various RV8 lumps. It could all be rubbish!RoverP6B wrote:I have been thinking about ignition timing and the advised maximum amounts necessary to deliver peak performance.
If my understanding is correct, for best performance total advance should be all in by the rpm in which the engine delivers maximum torque, and then essentially stays at the figure right through to red line and maximum power.
What if a distributor delivers the necessary advance at the rpm corresponding with maximum torque, but then continues to build by a further 8 to 10 degrees by red line and maximum power.
Pinging is far less likely once the rpm exceeds the maximum torque point, so is it detrimental to run additional timing from the aforementioned point to red line?
As an example, 28 degrees maximum advance is the quoted figure to provide maximum torque for the 4.6, but what if timing continued from that point to a maximum of say 38 degrees at say 5500 rpm?
I appreciate your views.
Ron.
From gumph that I've read the max advance seems to boil down to many things, some of them being the following:
1. The fuel being used...some fuels burn slower than others
2. The CR, high CR's produce high flame speeds
3. The chamber shape and squish band design
4. The conrod ratio as this determines the piston dwell.
5. The AFR
6. The bore to stroke ratio
7. The sparkplug location
8. The running temperature of the engine
9. The turbulence in the chambers, the turbulence is low up to around peak torque but then increases as the revs increase after this. So even though there is less and less time to complete the burn after say 3000 RPM the increase in turbulence compensates for this. (This is what I've read, I'm not 100% sure that I believe it!
)As to how much advance you can run, well you should bear in mind that even if your engine will take 38 degrees it does not follow that it will make more power than say 32 degrees. Some engines will not detonate even with a massive amount of advance, its still no good for it.
I run my 4.6 at 32 degrees, it lost 4 BHP on the dyno when I knocked it back to the "magic" 28 that most people quote.
In fact I had set my engine up using an Innovate LC1 and a "seat of the pants" dyno. When I stuck the car on the rollers every single thing I tried lost BHP and torque. (I even swapped carbs, they had both been setup using the LC1. The Eddy 600 made 16-20 ftlbs more torque at 2500 RPM but no difference at all at 5500 RPM over the 500 carb)
Pete
