Have I caused damage?
12-13-2005, 04:24 PM
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Have I caused damage? Hello all.
I have just bought a supercharged HSV GTS-R with an LS1 5.7L engine. It currently puts out 545bhp with 14psi supercharger boost (twin-screw Whipple). It has forged pistons, ARP con rod bolts and steel gasket shims. It also has a chargecooler and water injection.
Anyway when I drove the car home after buying it, I noticed that if I used a lot of throttle when in low revs in a high gear, I could hear a rattle that sounded like a loose undertray or heat shield or something. Anyway I did this a few times to try and pin down what was making the noise. Maybe 7 or 8 times, for 2 or 3 seconds each time. The supercharge was providing a lot of boost even this low down the rpm range (about 2k) and the water injection was active.
Anyway when I got home I spoke to the previous owner and he remembered putting in standard unleaded into the tank and suggested I use premium (97RON) which would probably make the problem go away. And the problem did seem to go away with higher octane.
My research since then indicates that this was almost certainly detonation, and that detonation with a high power output engine (this has about 1.5hp/in3) is lethal.
I have three questions:
1. Am I likely to have caused damage already during those initial rattles?
2. Should I be relaxed about it moving forwards, and just stick with high octane, and keep off boost at low rpms or do I really need to get the mapping adjusted? I'm worried that I might not hear it any more with higher octane, but perhaps it's still happening at higher rpm when I can't hear it.
3 The knock sensors have not been disabled, so I'm wondering why they didn't intervene and retard the ignition?
Many thanks for any help you can offer
Greg
I have just bought a supercharged HSV GTS-R with an LS1 5.7L engine. It currently puts out 545bhp with 14psi supercharger boost (twin-screw Whipple). It has forged pistons, ARP con rod bolts and steel gasket shims. It also has a chargecooler and water injection.
Anyway when I drove the car home after buying it, I noticed that if I used a lot of throttle when in low revs in a high gear, I could hear a rattle that sounded like a loose undertray or heat shield or something. Anyway I did this a few times to try and pin down what was making the noise. Maybe 7 or 8 times, for 2 or 3 seconds each time. The supercharge was providing a lot of boost even this low down the rpm range (about 2k) and the water injection was active.
Anyway when I got home I spoke to the previous owner and he remembered putting in standard unleaded into the tank and suggested I use premium (97RON) which would probably make the problem go away. And the problem did seem to go away with higher octane.
My research since then indicates that this was almost certainly detonation, and that detonation with a high power output engine (this has about 1.5hp/in3) is lethal.
I have three questions:
1. Am I likely to have caused damage already during those initial rattles?
2. Should I be relaxed about it moving forwards, and just stick with high octane, and keep off boost at low rpms or do I really need to get the mapping adjusted? I'm worried that I might not hear it any more with higher octane, but perhaps it's still happening at higher rpm when I can't hear it.
3 The knock sensors have not been disabled, so I'm wondering why they didn't intervene and retard the ignition?
Many thanks for any help you can offer
Greg
12-13-2005, 05:58 PM
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Probably not significant damage no, but pull all the sparkplugs and check them carefully. Forged pistons will usually hang in there a little longer than the average spark plug, so if the plugs aren't damaged then the pistons probably aren't.
Detonation is sort of like hammering on the bearings, so it's possible for them to take some damage, but for only a few seconds at a time I doubt anything serious happened.
You might want to consider running the engine a little cooler, and richen up the high load - low RPM section of your VE table. This would probably let you get away with the cheaper gas.
Detonation is sort of like hammering on the bearings, so it's possible for them to take some damage, but for only a few seconds at a time I doubt anything serious happened.
You might want to consider running the engine a little cooler, and richen up the high load - low RPM section of your VE table. This would probably let you get away with the cheaper gas.
12-14-2005, 02:10 AM
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OK, thanks.
I was worried about cracking the cylinder liinings, pitting the pistons etc.
I guess that knocking can't instantly destroy engines because (as I understand it) when tuning them, it's quite common to advance ignition until they start to knock, and then retard it a little..?
I was worried about cracking the cylinder liinings, pitting the pistons etc.
I guess that knocking can't instantly destroy engines because (as I understand it) when tuning them, it's quite common to advance ignition until they start to knock, and then retard it a little..?