To me, LSPI just means detonation under load at lower rpm. Especially since manufacturers make a lot of vehicles stay in the lowest possible rpm range while cruising. I've build probably ten high performance small blocks including the 434 sbc in my 72 camaro rsZ/28. We had detonation then on pump gas if you ran too much timing. I ran a msd digital 6 ignition with a locked timing at 28⁰ with a 15⁰ start retard and never had any issues. The only thing I ever had to do was switch plugs when running nitrous. So did manufacturers just "fancy up" the word detonation to LSPI?
LSPI a boutique word for detonation?
- Thread starter Jmoney7269
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Its a case of they are similar but different. Detonation refers to abnormal combustion caused by overly advanced spark or fuel octane below what is required for engine compression/timing. Retarding spark timing and increasing fuel octane rating are the cure. LSPI is more like engine dieseling back in carb days when the mixture explodes without a spark occuring. Timing has no direct effect on LSPI but increasing octane helps decrease the problem.
It's different. The idea is small displacement motors running a ton of boost at low rpm. Like a 2.0 liter motor making 300hp running 25psi of boost in high gear at 2000rpm. I think it's more of a design flaw
the difference is, lspi isn't cured by pulling timing, and might even get worse. You're giving the oil and fuel mixture more time to evaporate and become combustible. And the oil contains catalysts for oxidation (calcium and sodium) in larger quantity than anti-oxidants like zddp and organic moly compounds.
There is info claiming oil too thick can cause LSPI on a cold engine.
That doesn’t sound right
The claim is cold thick oil is harder for the piston rings to scrape compared to a thinner oil. The oil that doesn't get scraped normally burns off without issue but can cause LSPI.
those claims need to be quantified. Every oil is thick when cold, so what are we talking about? 20 cSt, 1,000 cSt or 60,000 cSt?
even so, there has to be boost involved, and likely lugging. I run my engines at a light load until they get warm, and the tcu luckily favours a downshift over boosting so I'm not concerned.
Remember, these are boosted, high compression, direct injected engines, often with low tension piston rings. So while the old rules still apply, there is a new twist here, as the cylinder pressures are rather high.
Bottom line LSPI is associated with excessive cylinder pressures. 1400-2200PSI is common during modest LSPI events and 3000PSI+ before destruction.
Calcium in the oil has been a contributing factor.
By way of comparison, a 427 Chevy tuned to make 550HP might reach a peak cylinder pressure of 1100PSI at peak torque. About 3x lower than a destructive LSPI event.
Bottom line LSPI is associated with excessive cylinder pressures. 1400-2200PSI is common during modest LSPI events and 3000PSI+ before destruction.
Calcium in the oil has been a contributing factor.
By way of comparison, a 427 Chevy tuned to make 550HP might reach a peak cylinder pressure of 1100PSI at peak torque. About 3x lower than a destructive LSPI event.
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The 70-73 generation is my favorite. My second favorite is 78-81.
I'm also keen on the split bumpers.
That oil stops being cold the moment it touches those 450°F cylinder walls and top rings. The oil in the sump may still be 20°F but the oil around the rings gets hot very quickly.
If there is an increase in LSPI when the engine is cold, I'd think it's more related to engine warmup programming. You shouldn't be WOT and full boost at 1500 rpm on a cold engine anyway, regardless if GDI or not.
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Engineer here.
Broadly speaking, there's 2 combustion regimes:
Deflagration - Normally Occurring combustion of fuel/air mixture where the flamefront travels subsonically. Pressure delta is typically small and is assumed zero for simple analyses.
Detonation - Flamefront travels @ supersonic speed and pressure rises sharply, and can/is harmful to the piston & cylinder.
Broadly speaking, there's 2 combustion regimes:
Deflagration - Normally Occurring combustion of fuel/air mixture where the flamefront travels subsonically. Pressure delta is typically small and is assumed zero for simple analyses.
Detonation - Flamefront travels @ supersonic speed and pressure rises sharply, and can/is harmful to the piston & cylinder.
This tells me that LSPI is detonation ignoring the ΔP from boost.
I recall reading some post that it's CAFE fault. Lug it baby!
Since in Europe they didn't have as much problem with the small displacement Turbo DI engines. And over there, the ECU / Engine / Trans are programmed not to lug as much for a little mpg gain.
Conclusion:
No replacement for displacement & back to manual transmission! No?
Since in Europe they didn't have as much problem with the small displacement Turbo DI engines. And over there, the ECU / Engine / Trans are programmed not to lug as much for a little mpg gain.
Conclusion:
No replacement for displacement & back to manual transmission! No?
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