Curious Question - Avoiding Detonation with timing
05-08-2015, 12:25 PM
#1
Curious Question - Avoiding Detonation with timing Is there math or reasonable rules that allows one to determine if x amount of boost is in no way controllable with pump fuel?
fake values example:
e.g. 8.1 DCR ... 10 psi xxx amount of cylinder pressure and have timing at 13°
increase to 15psi xxxx amount of cylinder pressure and have to reduce timing to 8°.
rules or threshold to say.. if there is this (xx) much boost (or cyl pressure) that no matter how far you pull timing, you will have detonation?
Or does power simply decay from too much timing retard?
I guess I am asking, can one calibrate the engine for Not using any octane assisted fuel.. (methanol injection) on higher boosted/ medium compression ratio scenarios.
fake values example:
e.g. 8.1 DCR ... 10 psi xxx amount of cylinder pressure and have timing at 13°
increase to 15psi xxxx amount of cylinder pressure and have to reduce timing to 8°.
rules or threshold to say.. if there is this (xx) much boost (or cyl pressure) that no matter how far you pull timing, you will have detonation?
Or does power simply decay from too much timing retard?
I guess I am asking, can one calibrate the engine for Not using any octane assisted fuel.. (methanol injection) on higher boosted/ medium compression ratio scenarios.
05-08-2015, 02:18 PM
#2
Restricted User
Formulas don't typically work.
Even if you have an equal dynamic compression ratio on 2 completely different setups with wildly varying static compression ratios, one is going to make a lot more power and generate a lot more heat.
You also don't get to factor in things like quench, or piston material/shape which will have an effect on how much timing you want to run, and formulas don't exactly work in a linear manner with octane rating.
Most people will say raise timing and then back it off a bit when the HP per degree starts to diminish a bit. This is a major gamble on pump gas.
The key is to just not get greedy with your timing. Most people slowly slope down to 14 degrees or so by the time they hit 100 kPa, and then maybe go down further from there depending on how high they're running.
Also, since water/meth injection can be done fairly cheap, there isn't any reason not to do it. Water does wonders for cast pistons and detonation.
Even if you have an equal dynamic compression ratio on 2 completely different setups with wildly varying static compression ratios, one is going to make a lot more power and generate a lot more heat.
You also don't get to factor in things like quench, or piston material/shape which will have an effect on how much timing you want to run, and formulas don't exactly work in a linear manner with octane rating.
Most people will say raise timing and then back it off a bit when the HP per degree starts to diminish a bit. This is a major gamble on pump gas.
The key is to just not get greedy with your timing. Most people slowly slope down to 14 degrees or so by the time they hit 100 kPa, and then maybe go down further from there depending on how high they're running.
Also, since water/meth injection can be done fairly cheap, there isn't any reason not to do it. Water does wonders for cast pistons and detonation.
05-08-2015, 04:11 PM
#3
9 Second Club
Is there math or reasonable rules that allows one to determine if x amount of boost is in no way controllable with pump fuel?
fake values example:
e.g. 8.1 DCR ... 10 psi xxx amount of cylinder pressure and have timing at 13°
increase to 15psi xxxx amount of cylinder pressure and have to reduce timing to 8°.
rules or threshold to say.. if there is this (xx) much boost (or cyl pressure) that no matter how far you pull timing, you will have detonation?
Or does power simply decay from too much timing retard?
I guess I am asking, can one calibrate the engine for Not using any octane assisted fuel.. (methanol injection) on higher boosted/ medium compression ratio scenarios.
fake values example:
e.g. 8.1 DCR ... 10 psi xxx amount of cylinder pressure and have timing at 13°
increase to 15psi xxxx amount of cylinder pressure and have to reduce timing to 8°.
rules or threshold to say.. if there is this (xx) much boost (or cyl pressure) that no matter how far you pull timing, you will have detonation?
Or does power simply decay from too much timing retard?
I guess I am asking, can one calibrate the engine for Not using any octane assisted fuel.. (methanol injection) on higher boosted/ medium compression ratio scenarios.
Tuning experience would cover a lot of the answer. I would doubt there are calculations for what you are asking....but then I wonder what some of the engine dyno sim type products/software might say ?
And of course it will depend on what octane fuel you intend to use.
What do you deem as "higher" boost, and what you deem as "medium" compression ?
05-08-2015, 06:30 PM
#4
Rather than asking an extrememeememely vague question...
Tuning experience would cover a lot of the answer. I would doubt there are calculations for what you are asking....but then I wonder what some of the engine dyno sim type products/software might say ?
And of course it will depend on what octane fuel you intend to use.
What do you deem as "higher" boost, and what you deem as "medium" compression ?
Tuning experience would cover a lot of the answer. I would doubt there are calculations for what you are asking....but then I wonder what some of the engine dyno sim type products/software might say ?
And of course it will depend on what octane fuel you intend to use.
What do you deem as "higher" boost, and what you deem as "medium" compression ?
92 octane gasoline - 15psi medium compression as in a calculated static compression of 9.9716 // A Dynamic Compression of 7.31342
Im sure the next thing you would ask is FI type... Centrifugal-- so belt RPM - through a front mounted intercooler
Last edited by vmapper; 05-08-2015 at 06:38 PM.
05-08-2015, 06:35 PM
#5
Formulas don't typically work.
Even if you have an equal dynamic compression ratio on 2 completely different setups with wildly varying static compression ratios, one is going to make a lot more power and generate a lot more heat.
You also don't get to factor in things like quench, or piston material/shape which will have an effect on how much timing you want to run, and formulas don't exactly work in a linear manner with octane rating.
Most people will say raise timing and then back it off a bit when the HP per degree starts to diminish a bit. This is a major gamble on pump gas.
The key is to just not get greedy with your timing. Most people slowly slope down to 14 degrees or so by the time they hit 100 kPa, and then maybe go down further from there depending on how high they're running.
Also, since water/meth injection can be done fairly cheap, there isn't any reason not to do it. Water does wonders for cast pistons and detonation.
Even if you have an equal dynamic compression ratio on 2 completely different setups with wildly varying static compression ratios, one is going to make a lot more power and generate a lot more heat.
You also don't get to factor in things like quench, or piston material/shape which will have an effect on how much timing you want to run, and formulas don't exactly work in a linear manner with octane rating.
Most people will say raise timing and then back it off a bit when the HP per degree starts to diminish a bit. This is a major gamble on pump gas.
The key is to just not get greedy with your timing. Most people slowly slope down to 14 degrees or so by the time they hit 100 kPa, and then maybe go down further from there depending on how high they're running.
Also, since water/meth injection can be done fairly cheap, there isn't any reason not to do it. Water does wonders for cast pistons and detonation.
Quench is 0.051.
I was told by Arrun that a tighter quench doesnt really do much.
The pistons are not cast.
why does one have to use Meth injection? .. can one run without meth (I am not interested in the debate of but you are leaving XX power on table etc...) I am 'curious' as the title says...
Last edited by vmapper; 05-08-2015 at 06:41 PM.
05-08-2015, 06:44 PM
#6
To many factors to consider, Even two identical engines may want something different.
Then you can also factor in outside air temperature and humidity. So what may work one day will not work when it's hotter or colder or more or less humid. For the most part there is no reason to tune to the ragged edge unless you can afford to rebuild/replace and engine.
Then you can also factor in outside air temperature and humidity. So what may work one day will not work when it's hotter or colder or more or less humid. For the most part there is no reason to tune to the ragged edge unless you can afford to rebuild/replace and engine.
05-08-2015, 07:06 PM
#7
To many factors to consider, Even two identical engines may want something different.
Then you can also factor in outside air temperature and humidity. So what may work one day will not work when it's hotter or colder or more or less humid. For the most part there is no reason to tune to the ragged edge unless you can afford to rebuild/replace and engine.
Then you can also factor in outside air temperature and humidity. So what may work one day will not work when it's hotter or colder or more or less humid. For the most part there is no reason to tune to the ragged edge unless you can afford to rebuild/replace and engine.
but what is considered the ragged edge? is 13° of timing ok? is 10? is 2? This is exactly what I am asking, if this generates xx amount of boost... I dont want to put in 5° timing and it still grenades. Starting point perhaps is the better question?
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05-08-2015, 08:30 PM
#8
I guess i missed the mark on asking the question.. lol.
but what is considered the ragged edge? is 13° of timing ok? is 10? is 2? This is exactly what I am asking, if this generates xx amount of boost... I dont want to put in 5° timing and it still grenades. Starting point perhaps is the better question?
but what is considered the ragged edge? is 13° of timing ok? is 10? is 2? This is exactly what I am asking, if this generates xx amount of boost... I dont want to put in 5° timing and it still grenades. Starting point perhaps is the better question?
05-09-2015, 03:08 AM
#10
9 Second Club
I am merely asking is there a LIMIT as in, no matter how much timing one pulls is there a threshold where detonation is uncontrollable...meaning.. always there. not sure how tuning experience would cover this (shrug) it is not every day I come across this.
92 octane gasoline - 15psi medium compression as in a calculated static compression of 9.9716 // A Dynamic Compression of 7.31342
Im sure the next thing you would ask is FI type... Centrifugal-- so belt RPM - through a front mounted intercooler
92 octane gasoline - 15psi medium compression as in a calculated static compression of 9.9716 // A Dynamic Compression of 7.31342
Im sure the next thing you would ask is FI type... Centrifugal-- so belt RPM - through a front mounted intercooler
And FI type is important too. 15psi at 1000rpm is going to be more challenging than 15psi at 7000rpm.
But as you're now saying a centri blower, that simply isnt going to make the boost low down, then I would see no major problem at all with the 92/15psi/10.0:1 CR you are thinking as long as chargecooling is good.
Will the engine be knock limited ? No doubt it will, but most of them will be anyway so that isnt a big deal in itself.
But for those engines that are heavily knock limited and running quite low timing, they should keep an eye on EGT's to make sure things dong get out of hand during hard use.
If you're starting to get into single digit timing figures then I'd think you need to start a different approach though