Discussion
When I collected my car from pomona and was driving home, I noticed a "rattle" from underneath the car when accelerating hard from low revs in 5th and 6th gear. Sounded a bit like a loose shield or undertray or something. Asked Brian when I got home and he remembered putting in some standard unleaded and suggested if I refill with higher octane petrol the sound would go away. He was right, so I assume this was pinking.
My question is - how quickly do you do damage to an engine if it's pinking? From what I have read, it's about the worst thing you can do to an engine aside from not putting any oil in! Am I likely to have done any damage already? And should I be nervous about driving a car that will pink on lower octane fuel? Anyone else get pinking on lower octane fuel?
My question is - how quickly do you do damage to an engine if it's pinking? From what I have read, it's about the worst thing you can do to an engine aside from not putting any oil in! Am I likely to have done any damage already? And should I be nervous about driving a car that will pink on lower octane fuel? Anyone else get pinking on lower octane fuel?
The pinking you heard is from timing being 'on the edge' and causes a minor? rattle at bottom end.
Unlikely to do damage unless it is continuous and long-term.
The american racers used to call it "the rattle of power" as it meant that the timing was as advanced as it could be before detonation.
If it was detonation you would hear it at the top end and after a few seconds you would notice a severe drop in power and a sudden tug in the wallet.
I assume Brian's motor still runs the knock sensors??? (although some supercharged engines don't because the sensors get confused by rotor noises and are either re-sited or removed -not good).
It is a good idea to run 97 octane or higher as Brian probably told you.
Cheers
Eric
Unlikely to do damage unless it is continuous and long-term.
The american racers used to call it "the rattle of power" as it meant that the timing was as advanced as it could be before detonation.
If it was detonation you would hear it at the top end and after a few seconds you would notice a severe drop in power and a sudden tug in the wallet.
I assume Brian's motor still runs the knock sensors??? (although some supercharged engines don't because the sensors get confused by rotor noises and are either re-sited or removed -not good).
It is a good idea to run 97 octane or higher as Brian probably told you.
Cheers
Eric
All you wanted to know about detonation and pre-ignition here (and probably loads of stuff you don't want to know about 
www.streetrodstuff.com/Articles/Engine/Detonation/
www.streetrodstuff.com/Articles/Engine/Detonation/pinking under light throttle wont usually do any harm, but it is to be avoided, and teh car should never do it.
If you car is detonating whilst on boost, expect to blow your engine up pretty quickly. You will destroy your pistons, or if you are lucky, just blow a head gasket.
No engine, especially a forced induction engine should suffer from detonation.
If you car is detonating whilst on boost, expect to blow your engine up pretty quickly. You will destroy your pistons, or if you are lucky, just blow a head gasket.
No engine, especially a forced induction engine should suffer from detonation.
That's a very interesting article.... What worried me a little was this :
"An engine that is making 0.5 HP/in3 or less can sustain moderate levels of detonation without any damage; but an engine that is making 1.5 HP/in3, if it detonates, it will probably be damaged fairly quickly, here I mean within minutes."
By my calculations my engine is making 1.56 HP/in3.... so sounds like this is definitely to be avoided. I guess I can just ensure I always stick with high octane and try to avoid loading the engine at low revs....
"An engine that is making 0.5 HP/in3 or less can sustain moderate levels of detonation without any damage; but an engine that is making 1.5 HP/in3, if it detonates, it will probably be damaged fairly quickly, here I mean within minutes."
By my calculations my engine is making 1.56 HP/in3.... so sounds like this is definitely to be avoided. I guess I can just ensure I always stick with high octane and try to avoid loading the engine at low revs....
Interesting, found this article about "spark knock" which also seems to describe exactly what I experienced: Supercharger spark knock
Basically, recommendations so far to avoid detonation include:
1. Retarding the ignition (with loss of power/torque)
2. Cooling the inlet air (Brian already fitted a charge cooler and aquamist)
3. Use high octane fuel (or even octane additives)
4. Avoid using boost at low revs, ie select the appropriate gear!
But apparently you can also use “cold” spark plugs like NGK Iridiums. Does anyone know anything about this approach? Got this from the NGK website:
"With modified engines (those engines that have increased their compression) more heat is a by-product of the added power that normally comes with increased compression. In short, select one heat range colder for every 75-100 hp you add, or when you significantly raise compression. Also remember to retard the timing a little and to increase fuel enrichment and octane. These tips are critical when adding forced induction (turbos, superchargers or nitrous kits), and failure to address ALL of these areas will virtually guarantee engine damage."
I should state for the record that I am but a curious amateur, and Brian knows vastly more about this stuff than I ever will.... But as I said I'm curious about things and like reading up on them.
>> Edited by gregwatson on Monday 12th December 21:18
>> Edited by gregwatson on Monday 12th December 21:43
Basically, recommendations so far to avoid detonation include:
1. Retarding the ignition (with loss of power/torque)
2. Cooling the inlet air (Brian already fitted a charge cooler and aquamist)
3. Use high octane fuel (or even octane additives)
4. Avoid using boost at low revs, ie select the appropriate gear!
But apparently you can also use “cold” spark plugs like NGK Iridiums. Does anyone know anything about this approach? Got this from the NGK website:
"With modified engines (those engines that have increased their compression) more heat is a by-product of the added power that normally comes with increased compression. In short, select one heat range colder for every 75-100 hp you add, or when you significantly raise compression. Also remember to retard the timing a little and to increase fuel enrichment and octane. These tips are critical when adding forced induction (turbos, superchargers or nitrous kits), and failure to address ALL of these areas will virtually guarantee engine damage."
I should state for the record that I am but a curious amateur, and Brian knows vastly more about this stuff than I ever will.... But as I said I'm curious about things and like reading up on them.
>> Edited by gregwatson on Monday 12th December 21:18
>> Edited by gregwatson on Monday 12th December 21:43
I think colder plugs will help prevent preignition which is caused by localised hot spots, but not detonation which is due to instantanous ignition rather than a controlled ignition. Or something like that anyway. Lots of cool info on ls1tech.com if you really want to know more. Basically preignition and detonation are 2 different things.
Reccomendations to avoid detonation.
Simple, make sure the damn thing is mapped properly for the fuel you are using.
If it is detonating due to too much ignition advance, it will not cost you power by retarding it. Detonation will lose you power, as well as destroy your engine.
If its due to excessive air temps. Well again, it should be mapped properly that this isnt an issue. But you cant say they are excessive without actually monitoring them.
Water injection helps, just make sure it is actually working. Although in a way it is also a band aid fix to the problem, although it can also be useful too.
Use of high octane fuel. Yes thats nice. But again, if its mapped properly for SUL fuel, then it shouldnt happen in the first place to require higher octane fuel.
As for boost in a low gear. The twin screw could achieve this, but as with everything, the engine should be mapped accordingly so it doesnt become an issue.
Put it this way. I dont know of any forced induction cars that pink or detonate when they leave the factory.
If its built properly and mapped properly, it shouldnt be an issue. It should never do it unless a problem arises elsewhere.
Simple, make sure the damn thing is mapped properly for the fuel you are using.
If it is detonating due to too much ignition advance, it will not cost you power by retarding it. Detonation will lose you power, as well as destroy your engine.
If its due to excessive air temps. Well again, it should be mapped properly that this isnt an issue. But you cant say they are excessive without actually monitoring them.
Water injection helps, just make sure it is actually working. Although in a way it is also a band aid fix to the problem, although it can also be useful too.
Use of high octane fuel. Yes thats nice. But again, if its mapped properly for SUL fuel, then it shouldnt happen in the first place to require higher octane fuel.
As for boost in a low gear. The twin screw could achieve this, but as with everything, the engine should be mapped accordingly so it doesnt become an issue.
Put it this way. I dont know of any forced induction cars that pink or detonate when they leave the factory.
If its built properly and mapped properly, it shouldnt be an issue. It should never do it unless a problem arises elsewhere.
If it's just a matter of sticking to 97 RON or better, and that will guarantee no detonation under any circumstances, then I'm perfectly happy with that. (Although I guess there is always the chance I might get stuck and not have access to 97 RON but then I guess I'd drive carefully until I'd filled up again with the good stuff)
After all, Brian has tuned this car amazingly well and has presumably set it up to take advantage of high octane fuel. The scenario that worries me is that 97RON might appear to eliminate detonation, but it might still happen when I can't hear it (maybe at higher revs?) and cause damage. I'd be happy if I knew it simply could not happen under any circumstances.
Should also point out that Brian has done 27,000 miles in the car as it stands without blowing the engine up....
>> Edited by gregwatson on Monday 12th December 21:50
>> Edited by gregwatson on Monday 12th December 21:52
After all, Brian has tuned this car amazingly well and has presumably set it up to take advantage of high octane fuel. The scenario that worries me is that 97RON might appear to eliminate detonation, but it might still happen when I can't hear it (maybe at higher revs?) and cause damage. I'd be happy if I knew it simply could not happen under any circumstances.
Should also point out that Brian has done 27,000 miles in the car as it stands without blowing the engine up....
>> Edited by gregwatson on Monday 12th December 21:50
>> Edited by gregwatson on Monday 12th December 21:52
I see nothing wrong with requiring 97 for max power. Im not sure what the tune is but some boost tunes can run dual maps so they will scale down in timing for lower octane fuel. Im tossing up trying out 98 octane to wring a little more power myself. I guess the moral is forewarned is forearmed.
Paul - agreed.
Hence my comment re 27,000 miles without blowing the engine. One of the many things that I like about this car is that Brian did a 110% proper job. He didn't just stick a supercharger on... there are so many things he added to support the extra power (pistons, gaskets, arp con rod bolts, high performance fuel pump, aquamist, AP racing 6-pots etc etc not to mention a LOT of dyno time...). Heck, he even tried several superchargers before settling on the Whipple... But then you guys know all of this better than I do!
Doesn't stop me being curious though, and worrying that I might damage the car if I don't know enough about it, hence the questions.
(PS before some joker beats me to it.. I am aware that the car had pistons and gaskets before Brian worked on it, you know what I meant!!!!!!!!!)
>> Edited by gregwatson on Monday 12th December 22:27
Hence my comment re 27,000 miles without blowing the engine. One of the many things that I like about this car is that Brian did a 110% proper job. He didn't just stick a supercharger on... there are so many things he added to support the extra power (pistons, gaskets, arp con rod bolts, high performance fuel pump, aquamist, AP racing 6-pots etc etc not to mention a LOT of dyno time...). Heck, he even tried several superchargers before settling on the Whipple... But then you guys know all of this better than I do!
Doesn't stop me being curious though, and worrying that I might damage the car if I don't know enough about it, hence the questions.
(PS before some joker beats me to it.. I am aware that the car had pistons and gaskets before Brian worked on it, you know what I meant!!!!!!!!!)
>> Edited by gregwatson on Monday 12th December 22:27
"gregwatson" car runs in "Speed Density Mode" and in this mode the PCM only uses one spark table.
As part of a "Speed Density" tune it is standard practise to retain an aggressive knock retard setting (normally the PCM will remove 5deg the moment it detects knock)....
The Knock sensors are not fool proof but if anything they are over sensitive so they pull timing at the first hint of knock......making the car safe.
As part of a "Speed Density" tune it is standard practise to retain an aggressive knock retard setting (normally the PCM will remove 5deg the moment it detects knock)....
The Knock sensors are not fool proof but if anything they are over sensitive so they pull timing at the first hint of knock......making the car safe.
So how come I could reproduce the rattling at will by accelerating hard at low revs in 5th and 6th gear? Surely if the system were picking that up and reacting quickly I would barely notice it let alone be able to reproduce it at will (albeit with cheap petrol)?
According to the engine manual (Brian pointed me to it) :
The processed knock sensor signal is then supplied to the PCM. The PCM then adjusts the ignition control system to reduce the spark advance. How much the timing is retarded is based upon the amount of time knock is detected. After the detonation stops, the timing will gradually return to its calibrated value of spark advance. The Knock Sensor system will only retard timing after the following conditions are met:
• The engine run time is greater than 20 seconds.
• The engine coolant temperature is greater than 70°C.
• The engine speed is greater 1650 RPM.
• The manifold absolute pressure is less than 60 kPa.
Is there something in that last point that might prevent it from retarding?
Also, from what I have read, whilst a little knock is considered acceptable on some cars it is considered a very bad thing on high power output engines (see earlier post) so perhaps it's not sufficient to assume the PCM will sort it out eventually if it goes on long enough?
According to the engine manual (Brian pointed me to it) :
The processed knock sensor signal is then supplied to the PCM. The PCM then adjusts the ignition control system to reduce the spark advance. How much the timing is retarded is based upon the amount of time knock is detected. After the detonation stops, the timing will gradually return to its calibrated value of spark advance. The Knock Sensor system will only retard timing after the following conditions are met:
• The engine run time is greater than 20 seconds.
• The engine coolant temperature is greater than 70°C.
• The engine speed is greater 1650 RPM.
• The manifold absolute pressure is less than 60 kPa.
Is there something in that last point that might prevent it from retarding?
Also, from what I have read, whilst a little knock is considered acceptable on some cars it is considered a very bad thing on high power output engines (see earlier post) so perhaps it's not sufficient to assume the PCM will sort it out eventually if it goes on long enough?
But how quickly is it supposed to react and deal with the problem? Because it didn't seem to deal with it at all... As I said the event seemed to last until I eased up on the throttle or possibly as the revs reached a more suitable level. This was accelerating from say 2k rpm in 6th (approx 80mph).
Plus - if the detonation pressure spike is bad enough, surely you only need one to cause damage?
>> Edited by gregwatson on Monday 12th December 22:57
Plus - if the detonation pressure spike is bad enough, surely you only need one to cause damage?
>> Edited by gregwatson on Monday 12th December 22:57
gregwatson said:
• The manifold absolute pressure is less than 60 kPa.
Is there something in that last point that might prevent it from retarding?
That is the minimum MAP before the Knock sensors work.....so above 60 Kpa the sensors work.
You could be suffering "Tip In Knock"........if you back off the gas and then re apply the gas does the noise continue?
ps. what brand of fuel are you using?
>> Edited by wortec1 on Monday 12th December 23:00
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