How many degrees advance - change in RON
Discussion
Right then.......my cologne engined Capri hasn't been tuned since leaded petrol was de rigeur.
I consulted my Haynes and they have it as wanting 12* BTDC.
Now IIRC leaded was 98RON.
I want to run 95.
So I've found a strobe and chalked it up and had a little google.........
which took me to an Integra tuning site that advocated advancing until it pinked at idle and then backing off 2*.
I haven't gone that far but I have left it at 15*.
What does the house think the correct angle is, is the 2* thing correct and any other tips/hints for something that can be done with a strobe, some dodgy spanners and an old stick. All in language that a complete dumbass like me can understand.
I thank you
I consulted my Haynes and they have it as wanting 12* BTDC.
Now IIRC leaded was 98RON.
I want to run 95.
So I've found a strobe and chalked it up and had a little google.........
which took me to an Integra tuning site that advocated advancing until it pinked at idle and then backing off 2*.
I haven't gone that far but I have left it at 15*.
What does the house think the correct angle is, is the 2* thing correct and any other tips/hints for something that can be done with a strobe, some dodgy spanners and an old stick. All in language that a complete dumbass like me can understand.
I thank you
For carb you want lean best idle. Usually means tuning for near MBT at idle and leaning it out. Try and get max vacuum. I think there are a few posts around on the net on the topic.
EFI cars you want something different, you kind of want the mid point between MBT and where retard slows things down, so that the ECM can move spark around to raise or lower rpm from various idle loads like ac, power steering etc.
EFI cars you want something different, you kind of want the mid point between MBT and where retard slows things down, so that the ECM can move spark around to raise or lower rpm from various idle loads like ac, power steering etc.
It's a mechanical injection and I don't think there is scope for changing the mixture.
It's also a Capri........the ancils are simple and the only loads you can apply are the heater fan/wipers/lights and demister.
I think I'm stuck with playing with the advance. Unless you have some cunning (and simple) plan.
It's also a Capri........the ancils are simple and the only loads you can apply are the heater fan/wipers/lights and demister.
I think I'm stuck with playing with the advance. Unless you have some cunning (and simple) plan.
So you're running three degrees more advance than standard, and on a lower octane fuel? I would go with the idea of advance until you hear light linking and then back two degrees, but bear in mind it'll be more vulnerable in hot weather so if you're setting it now you might need to bring it back another degree or two in the summer.
planetdave said:
I thought lower octane = slower flame front = more advance.
I haven't gone the wrong way, have I?
and now I've got the strobe and marked the pulley it's only a couple of minutes work to rectify
Usually, the knock limit will prevent you from running the optimum advance for full power so you just run as much advance as you can get away with. In areas where knock is not an issue, yes the lower octane will prefer more advance. I assume you're just swinging the dizzy though so you will just be looking for as much advance as you can get away with without knocking anywhere.I haven't gone the wrong way, have I?
and now I've got the strobe and marked the pulley it's only a couple of minutes work to rectify
Dude lower octane requires less advance as its more volotile. Higher octane burns more controlled but with less intensity.
You dont want as much advance as possible, you want advance set to Max Break Torque which is not as close as you can get to pinging!
Usually MBT is where peak pressure arrives around 14* ATDC. It depends on combustion chamber design, quench, octane etc.
You can only really find it on a dyno. That being said 95 to 98 octane probably relates to "around" 2* difference.
If your engine is designed for 95 octane and you run it on 98 you wont necessarily get more power, in fact the fuel will burn with less energy so you may actually lose power! Do your research before changing octane for no reason. Dynamic compression ratio, cam timing etc.
You dont want as much advance as possible, you want advance set to Max Break Torque which is not as close as you can get to pinging!
Usually MBT is where peak pressure arrives around 14* ATDC. It depends on combustion chamber design, quench, octane etc.
You can only really find it on a dyno. That being said 95 to 98 octane probably relates to "around" 2* difference.
If your engine is designed for 95 octane and you run it on 98 you wont necessarily get more power, in fact the fuel will burn with less energy so you may actually lose power! Do your research before changing octane for no reason. Dynamic compression ratio, cam timing etc.
ringram said:
Dude lower octane requires less advance as its more volotile. Higher octane burns more controlled but with less intensity.
You dont want as much advance as possible, you want advance set to Max Break Torque which is not as close as you can get to pinging!
Usually MBT is where peak pressure arrives around 14* ATDC. It depends on combustion chamber design, quench, octane etc.
You can only really find it on a dyno. That being said 95 to 98 octane probably relates to "around" 2* difference.
If your engine is designed for 95 octane and you run it on 98 you wont necessarily get more power, in fact the fuel will burn with less energy so you may actually lose power! Do your research before changing octane for no reason. Dynamic compression ratio, cam timing etc.
What on earth are you talking about?You dont want as much advance as possible, you want advance set to Max Break Torque which is not as close as you can get to pinging!
Usually MBT is where peak pressure arrives around 14* ATDC. It depends on combustion chamber design, quench, octane etc.
You can only really find it on a dyno. That being said 95 to 98 octane probably relates to "around" 2* difference.
If your engine is designed for 95 octane and you run it on 98 you wont necessarily get more power, in fact the fuel will burn with less energy so you may actually lose power! Do your research before changing octane for no reason. Dynamic compression ratio, cam timing etc.
GreenV8S said:
ringram said:
Dude lower octane requires less advance as its more volotile. Higher octane burns more controlled but with less intensity.
You dont want as much advance as possible, you want advance set to Max Break Torque which is not as close as you can get to pinging!
Usually MBT is where peak pressure arrives around 14* ATDC. It depends on combustion chamber design, quench, octane etc.
You can only really find it on a dyno. That being said 95 to 98 octane probably relates to "around" 2* difference.
If your engine is designed for 95 octane and you run it on 98 you wont necessarily get more power, in fact the fuel will burn with less energy so you may actually lose power! Do your research before changing octane for no reason. Dynamic compression ratio, cam timing etc.
What on earth are you talking about?You dont want as much advance as possible, you want advance set to Max Break Torque which is not as close as you can get to pinging!
Usually MBT is where peak pressure arrives around 14* ATDC. It depends on combustion chamber design, quench, octane etc.
You can only really find it on a dyno. That being said 95 to 98 octane probably relates to "around" 2* difference.
If your engine is designed for 95 octane and you run it on 98 you wont necessarily get more power, in fact the fuel will burn with less energy so you may actually lose power! Do your research before changing octane for no reason. Dynamic compression ratio, cam timing etc.
poor guy only wants to set his timing for unleaded fuel
Edited by That Daddy on Tuesday 11th December 15:16
"Octane rating is a measure of detonation resistance, not deflagration characteristics.
It might seem odd that fuels with higher octane ratings explode less easily, yet are popularly thought of as more powerful. The misunderstanding is caused by confusing the ability of the fuel to resist compression detonation as opposed to the ability of the fuel to burn (combustion).
A simple explanation is that carbon-carbon bonds contain more energy than carbon-hydrogen bonds. Hence a fuel with a greater number of carbon bonds will carry more energy regardless of the octane rating."
http://en.wikipedia.org/wiki/Octane_rating
It might seem odd that fuels with higher octane ratings explode less easily, yet are popularly thought of as more powerful. The misunderstanding is caused by confusing the ability of the fuel to resist compression detonation as opposed to the ability of the fuel to burn (combustion).
A simple explanation is that carbon-carbon bonds contain more energy than carbon-hydrogen bonds. Hence a fuel with a greater number of carbon bonds will carry more energy regardless of the octane rating."
http://en.wikipedia.org/wiki/Octane_rating
ringram said:
What exactly is incorrect about what I said BTW?
ringram said:
Dude lower octane requires less advance as its more volotile.
Ignoring the spelling, volatility is a measure of the ability to evaporate and nothing to do with calorific value or octane rating.ringram said:
Higher octane burns more controlled but with less intensity.
Or to put it another way, higher octane fuel burns very slightly faster, is more susceptible to knock, and for all practical purposes can be treated as releasing the same amount of energy. I'm not sure what 'controlled' and 'intensity' mean in this context but it's not obvious that your use of either term is (a) accurate or (b) relevent. ringram said:
You dont want as much advance as possible, you want advance set to Max Break Torque which is not as close as you can get to pinging!
Assuming you mean Maximum Brake Torque, when tuning for maximum power what's normally tuned for is Minimum Best Torque i.e. the point at which you are *just* starting to lose power as you move a parameter from the absolute optimum towards a safer region. Typically, in high performance engines the knock limit will be encountered before peak torque is achieved i.e. the fuel and timing are set to achieve MBT relative to the onset of knock.ringram said:
If your engine is designed for 95 octane and you run it on 98 you wont necessarily get more power, in fact the fuel will burn with less energy so you may actually lose power!
If your engine is limited by knock then using a higher octane fuel will delay the onset of knock slightly and enable you to move the fuel and ignition settings slightly closer to the optimum for peak power. The slightly slower combustion speed will move the optimum ignition timing. I think you will struggle to show any effect from changes in calorific value of the fuel.ringram said:
Do your research before changing octane for no reason. Dynamic compression ratio, cam timing etc.
So basically if we go away and learn all sorts of stuff about engines, your point will suddenly become clear? Or is your point that you know a lot of terms and must therefore be right?Edited by GreenV8S on Wednesday 12th December 00:35
Ok agreed on calorific value point 
MBT yes you want minimum timing that gives you best torque. Its still best torque though.
"For every operating condition of an internal combustion engine there exists an optimal spark timing, called maximum brake torque (MBT), which maximises the output torque and the efficiency of the engine." http://www.ep.liu.se/undergraduate/abstract.xsql?d...
And from the master of combustion engines
pp. 18-19 of Internal Combustion Engine Fundamentals, Intl. Ed., 1988, by John B. Heywood.
"There is an optimum spark timing which, for a given mass of fuel and air inside the cylinder, gives maximum torque. More advanced (earlier) timing or retarded (later) timing than this optimum gives lower output. Called maximum brake-torque (MBT) timing,† this optimum timing is an empirical compromise between starting combustion too early in the compression stroke (when the work transfer is to the cylinder gases) and completing combustion too late in the expansion stroke (and so lowering peak expansion stroke pressures).
_____________________
† MBT timing has traditionally been defined as the minimum spark advance for best torque. Since the torque first increases and then decreases as spark timing is advanced [from traditionally defined MBT], the definition used here is more precise."
You are correct that "if the engine is limited by knock" a higher octane will help. However there is no evidence to suggest that is the case, hence my comments in regards to verifying this before blindly using higher octanes. I also stated that if an engine was designed for 95 octane that using 98 would most likely be a waste of time. Or do you disagree?
You also say "higher octane fuel burns very slightly faster, is more susceptible to knock"
However higher octane is LESS susceptible to knock surely?
Anyway, its clear to me that while the odd term was used inaccurately the basic gist of what I was saying is correct. We can be anal about terms till the cows come home. If you want to waste your money on higher octane without figuring out if you actually need it then thats fine. At least Ive made people think (including myself and thanks for pointing out my slack use of terminology!)
MBT yes you want minimum timing that gives you best torque. Its still best torque though.
"For every operating condition of an internal combustion engine there exists an optimal spark timing, called maximum brake torque (MBT), which maximises the output torque and the efficiency of the engine." http://www.ep.liu.se/undergraduate/abstract.xsql?d...
And from the master of combustion engines
pp. 18-19 of Internal Combustion Engine Fundamentals, Intl. Ed., 1988, by John B. Heywood.
"There is an optimum spark timing which, for a given mass of fuel and air inside the cylinder, gives maximum torque. More advanced (earlier) timing or retarded (later) timing than this optimum gives lower output. Called maximum brake-torque (MBT) timing,† this optimum timing is an empirical compromise between starting combustion too early in the compression stroke (when the work transfer is to the cylinder gases) and completing combustion too late in the expansion stroke (and so lowering peak expansion stroke pressures).
_____________________
† MBT timing has traditionally been defined as the minimum spark advance for best torque. Since the torque first increases and then decreases as spark timing is advanced [from traditionally defined MBT], the definition used here is more precise."
You are correct that "if the engine is limited by knock" a higher octane will help. However there is no evidence to suggest that is the case, hence my comments in regards to verifying this before blindly using higher octanes. I also stated that if an engine was designed for 95 octane that using 98 would most likely be a waste of time. Or do you disagree?
You also say "higher octane fuel burns very slightly faster, is more susceptible to knock"
However higher octane is LESS susceptible to knock surely?
Anyway, its clear to me that while the odd term was used inaccurately the basic gist of what I was saying is correct. We can be anal about terms till the cows come home. If you want to waste your money on higher octane without figuring out if you actually need it then thats fine. At least Ive made people think (including myself and thanks for pointing out my slack use of terminology!)
GreenV8S said:
yes the lower octane will prefer more advance.
"Low octane rating requires a more retarded ignition timing and a high Octane rating allows a more advanced timing to be used"http://mg-tri-jag.net/tech6.htm
Im sorry you are therefore wrong Sir.
"The higher the octane rating on fuel the less volatile (evaporative qualities) and the slower the fuel burns."
http://dnr.louisiana.gov/sec/EXECDIV/TECHASMT/ecep...
My volatile comment still stands as well.
GreenV8S said:
higher octane fuel burns very slightly faster
"it's easier to ignite a low octane fuel than a high octane fuel and that the higher octane fuel burns slower."http://kapitalmoto.co.uk/node/24
and again.
Its easy to condem someone without checking facts isnt it!?
Oh dear, why did I write that? Too much late night posting, I seem to have switched my 'higher' and 'lower' around half way through.
Lower octane fuel burns slightly quicker which means that other things being equal, peak power will be achieved with slightly less advance. However, lower octane obviously is more prone to detonation, so where the engine is knock limited the timing will need to be retarded and/or fuel added to avoid detonation. Both of these measures cost power, in effect the theoretical optimum is in a running area that can't be used because of detonation. In practice high performance engines are usually knock limited around peak torque. Raising the octane moves the optimum timing very slightly, but more importantly it means that it is possible to get closer to the optimum without detonation occurring.
Naturally you need to retune to take advantage of this in order to get any power benefit. If you just raise the octane rating without making any other changes then you wouldn't expect to gain any power, and you could expect to lose some because the optimum has moved further away. However, that loss is small compared to the amount you stand to gain if the engine is knock limited and you retune to take advantage of the higher octane rating.
Lower octane fuel burns slightly quicker which means that other things being equal, peak power will be achieved with slightly less advance. However, lower octane obviously is more prone to detonation, so where the engine is knock limited the timing will need to be retarded and/or fuel added to avoid detonation. Both of these measures cost power, in effect the theoretical optimum is in a running area that can't be used because of detonation. In practice high performance engines are usually knock limited around peak torque. Raising the octane moves the optimum timing very slightly, but more importantly it means that it is possible to get closer to the optimum without detonation occurring.
Naturally you need to retune to take advantage of this in order to get any power benefit. If you just raise the octane rating without making any other changes then you wouldn't expect to gain any power, and you could expect to lose some because the optimum has moved further away. However, that loss is small compared to the amount you stand to gain if the engine is knock limited and you retune to take advantage of the higher octane rating.
Pigeon said:
I once experimented with attaching strain gauges to the head of my MZ to see if I could detect the deformation due to combustion pressure and use that as feedback to adjust the ignition timing to give the pressure peak at 15 deg ATDC. Unfortunately I couldn't detect a thing...
You could put a pressure transducer inside the chamber, but you would need very fast monitoring to get the timing accurately enough. Ion detection seems to be the fashionable way to do this now.Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff