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?
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
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
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
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
OK well I'll go for the simple option then of sticking with high octane petrol and not worrying. Which I was doing anyway; I have always put 97+ in the Alpina and other performance cars. (Although bizarrely my 928GTS was noticeably quicker on normal unleaded but that's another story)
As Brian has driven the car for 27K miles without damaging anything it can't be that fragile!
As Brian has driven the car for 27K miles without damaging anything it can't be that fragile!
I don't know what was in the tank when I collected the car and experienced the rattle, I didn't put it in. I haven't noticed the rattle with 97RON, I prefer Optimax so will use that when I can find it. I guess the way to look at it is: if putting 97 in made the rattle go away, then I can be even more confident with Optimax or 99RON... I just hope that no damage was done during that first drive when I was deliberately making it rattle in an effort to identify the source of the noise. Probably only did it 7 or 8 times, for about 2 or 3 seconds each time so fingers crossed.
Brian - I assume that all of your testing, dyno time etc was done on higher octane fuel? Hence you would not have seen any detonation that might be caused by SUL, or by fuel that had deteriorated in the tank whilst standing for a while...?
By the way, did you tend to use only Optimax, or 99RON, or 97RON or what?
"Beginning to wonder what I had been doing for 4 years" -
Anyone who knows your car is aware of how good a job you did, and I feel very fortunate to have been able to take the car over from you. And the reliability speaks for itself.
Neverthless I experienced something which is apparently very bad for an engine so it's only right for me to ask about it so I can avoid it happening again. This in no way indicates a criticism of your work. As we have said, you have presumably mapped the car for high octane fuel (correct?) which in my mind is a perfectly reasonable assumption to make on a car like this. I always use 97RON or higher anyway. In which case the problem goes away.
By the way, did you tend to use only Optimax, or 99RON, or 97RON or what?
"Beginning to wonder what I had been doing for 4 years" -
Anyone who knows your car is aware of how good a job you did, and I feel very fortunate to have been able to take the car over from you. And the reliability speaks for itself.
Neverthless I experienced something which is apparently very bad for an engine so it's only right for me to ask about it so I can avoid it happening again. This in no way indicates a criticism of your work. As we have said, you have presumably mapped the car for high octane fuel (correct?) which in my mind is a perfectly reasonable assumption to make on a car like this. I always use 97RON or higher anyway. In which case the problem goes away.
So would that rattling definitely have been detonation, or could it have been something less damaging? I'm not sure if you can have "mild" detonation - presumably detonation is detonation....?
If the compression check is OK, am I in the clear? Presumably there could be some minor damage to the pistons, pitting etc which a compression check wouldn't show up?
>> Edited by gregwatson on Tuesday 13th December 23:07
If the compression check is OK, am I in the clear? Presumably there could be some minor damage to the pistons, pitting etc which a compression check wouldn't show up?
>> Edited by gregwatson on Tuesday 13th December 23:07
Hmmm. Well, I guess I've either damaged it or I haven't. Higher octane should stop it happening again. I like to think that if significant damage had been caused, I'd notice something.
It wasn't a heavy hammering sound - I thought it was some sort of undertray or heat shield rattling because I've had that before in another car - a very light, tinny rattling sound. In terms of it happening at peak torque - remember that this car develops over 500 lb-ft by 2,300 rpm so there's a lot of torque pretty much everywhere.
It wasn't a heavy hammering sound - I thought it was some sort of undertray or heat shield rattling because I've had that before in another car - a very light, tinny rattling sound. In terms of it happening at peak torque - remember that this car develops over 500 lb-ft by 2,300 rpm so there's a lot of torque pretty much everywhere.
Yep, I guess that could have caused it. I can't imagine there has been any significant damage done though since the car still pulls incredibly hard and there aren't any funny noises or misfires or rough idling or anything. Just a tapping noise when warm (only noticeable at idle) which I don't think is related. I would have thought that if one or two cylinders had been damaged, I'd notice something when accelerating hard...
There's also a couple of videos and sound recordings of my car (Brian's at the time) on a dyno somewhere. I could not believe my ears when I heard that sound. Made me think of a fighter jet. If you haven't heard it, you should have a listen. It's an unbelievable noise.
Oh and of course the torque - 515lb-ft available from 2,300 rpm. That's the real beauty of the twin screw supercharger.
;->
Most of you have probably heard them already but those who haven't can go here:
gallery
Look for anything with "pomona" in the title. I think it's the long one (27MB) that's best.
>> Edited by gregwatson on Tuesday 20th December 21:47
Oh and of course the torque - 515lb-ft available from 2,300 rpm. That's the real beauty of the twin screw supercharger.
;->
Most of you have probably heard them already but those who haven't can go here:
gallery
Look for anything with "pomona" in the title. I think it's the long one (27MB) that's best.
>> Edited by gregwatson on Tuesday 20th December 21:47
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