Engine downsizing comes with downside

[Delta]

Originally Posted By: gregk24
Originally Posted By: Kibitoshin
Not really a huge fan where a turbo on a tiny engine makes most of it's power. I doubt morons who drive these things will keep it out of boost to reap the fuel economy benefits.


Morons? Wow thanks! I'm a fan of VW turbos, they seem to be tuned very well.


Hah, I had to chuckle at this one!

Even on boost the VW engines return good fuel economy, not that I'd know or anything...


(Premium fuel is the bees knees on them too...)

 

[Jarlaxle]

Originally Posted By: Virtus_Probi
Originally Posted By: Linctex
Originally Posted By: meep

turbocharging is not new---


Just think - the 1987 Buick GNX (underrated at 276 hp from 231 cubes) was 30 YEARS ago!!!


My FXT makes 250HP (probably accurately reported) from 122 cubes and has the benefit of water cooling for the turbo...one of the advances made in the last 30 years. The supposed 420 lb-ft that the GNX made is much closer to the FXT per cube, though.
I actually made a rash decision to go find myself a new Grand National when I was a young punk, but this was around 1988 and their last model year was '87...probably lucky for me, would have been "fun" dealing with that RWD power in snow and ice when I moved back North. Actually, I probably would have crashed and died right away in Dallas...


Chrysler had water-cooled turbochargers 30+ years ago. (And managed 224HP from a 2.2 litre engine.)

 

[Jarlaxle]

Originally Posted By: rooflessVW
Originally Posted By: Kibitoshin
Not really a huge fan where a turbo on a tiny engine makes most of it's power. I doubt morons who drive these things will keep it out of boost to reap the fuel economy benefits.

You don't like peak torque just off idle? :screwy:


I have it...no turbo, no waiting...LOTS of torque.

 

[Ducked]

Originally Posted By: PimTac
I'm guessing it's the newer materials in engines that cannot hold up under knocking. Those of us who drove in the 70-80's will remember engines that knocked constantly. It was actually said that light pinging meant good fuel economy. Back then they didn't have lightweight pistons, low friction rings, and other components that are in modern engines today. Knock sensors are standard as well.


This isn't knocking. This is pre-ignition. Thats why they call it LSPI

Different, and much more destructive.

 

[Ducked]

Originally Posted By: SonofJoe


Given that there are already hundreds of thousands of potentially LSPI-susceptable TGDI engined vehicles already out there on the roads, how many have seen severe engine damage? Hmmm...either no-one knows or the people that might know aren't saying. I think the people that are most affected (people who make pistons like Mahle and the OEMs) are deliberately hyping LSPI up to get attention focussed on the issue.


They make aftermarket pistons, correct?

If so, I can't see the motivation for hyping this. Broken engines might mean more parts sales.

If they are an OEM supplier and they are having to pick up the tab on warranty claims then I could see they'd want it fixed, but that'd imply its on a scale significant enough to bother them.

 

[Cujet]

Originally Posted By: Virtus_Probi
One way to help avoid LSPI in a DIT engine is to use oil that doesn't promote it.
dexos1 Gen 2 includes an LSPI test in a GM DIT engine and I will sure be looking for that license when it goes live in September. Interestingly enough, it looks like M1 5W30 AP already has a Gen 2 license number.
Here is a good thread that wemay started discussing LSPI and oil, there are more in the "Interesting Articles" forum.

Oronite on LSPI

dexos1 Gen 2 Licenses

BTW, I am interested in LSPI because my car was recalled for it...


I think that's true. Also more frequent oil changes to avoid fuel dilution of the oil. Possibly a slightly higher viscosity.

 

[CT8]

High octane engine oil ! Problem solved.

 

[Kuato]

Originally Posted By: CR94
Originally Posted By: Kuato
Nothing new really..."don't lug your engine" is something our granddads said way back when.
What's new is that modern LSPI destroys the engine, whereas way back when "lugging," if not extreme, didn't, and was more efficient than the opposite error of needless high revs.


True that it's more severe now, considering the amount power potentially generated at low rpm.



Originally Posted By: cb_13
Originally Posted By: Lolvoguy
"there's no replacement for displacement"

I'm pretty sure every modern engine has proven that to be false.

Technology is the replacement.


I4 vs V8, same technology, no contest whether it's a 1960s engine or a 2018 engine.

 

[DweezilAZ]

Don't forget the Olds F85 turboed 215.

 

[DweezilAZ]

Exactly as mentioned in the owner's manual of the 84 Citation I had. "Some pinging is acceptable as the engine is operating as designed for best fuel economy and power", or something of that sort.

 

[neo3]

Originally Posted By: Ducked
Originally Posted By: PimTac
I'm guessing it's the newer materials in engines that cannot hold up under knocking. Those of us who drove in the 70-80's will remember engines that knocked constantly. It was actually said that light pinging meant good fuel economy. Back then they didn't have lightweight pistons, low friction rings, and other components that are in modern engines today. Knock sensors are standard as well.


This isn't knocking. This is pre-ignition. Thats why they call it LSPI

Different, and much more destructive.


Please explain the difference.

 

[SonofJoe]

Classic knock (or pinking) is caused by pre-ignition of the fuel, usually at high load. It's initiated by 'hot spots' like bits of glowing ash on the top of the piston. The octane rating of the gasoline is it's ability to resist pre-combustion.

LSPI is pre-ignition that's caused by a mix of engine oil/unburnt fuel that first collects in the space between the top land and the bore and then at low speed, gets 'thrown off' into into the compressing air/fuel mix to act as a combustion initiator. Low speed is an essential component of this type of knock as oil migration via the process of 'throw off' declines with increasing engine speed.

 

[barryh]

My understanding of pinking is it's abnormal combustion that occurs after normal combustion has already been initiated by the spark. As the combustion pressure rises spontaneous combustion occurs in some parts of the combustion chamber before the normal flame front has managed to get there. The noise you hear is a pinging metallic resonance of the cylinder affected and it is characteristic of the noise that unlike a bearing knock it sounds to be at a faster frequency than the cylinder firing frequency. The reason for this is there is more than once instance of detonation occurring in different parts of the combustion chamber on each cycle.

Pre-Ignition or knock is abnormal combustion that occurs before the normal ignition spark. In fact it can be a long way before perhaps not that much past BDC. Pre-ignition is initiated by glowing carbon or a spark plug that is too hot. Because the mixture is ignited far too early it builds pressure for most of the compression stroke and so can be very destructive melting plugs and holing pistons.

 

[4ever4d]

Originally Posted By: Alfred_B
Electric cars will fix this issue.

 

[4ever4d]

Keep the small displacement turbo engines, back off the DI, and go to diesel fuel.

 

[PimTac]

Originally Posted By: SonofJoe
Classic knock (or pinking) is caused by pre-ignition of the fuel, usually at high load. It's initiated by 'hot spots' like bits of glowing ash on the top of the piston. The octane rating of the gasoline is it's ability to resist pre-combustion.

LSPI is pre-ignition that's caused by a mix of engine oil/unburnt fuel that first collects in the space between the top land and the bore and then at low speed, gets 'thrown off' into into the compressing air/fuel mix to act as a combustion initiator. Low speed is an essential component of this type of knock as oil migration via the process of 'throw off' declines with increasing engine speed.



Thanks SonofJoe for that clear explanation.

 

[Shannow]

Originally Posted By: barryh
My understanding of pinking is it's abnormal combustion that occurs after normal combustion has already been initiated by the spark. As the combustion pressure rises spontaneous combustion occurs in some parts of the combustion chamber before the normal flame front has managed to get there. The noise you hear is a pinging metallic resonance of the cylinder affected and it is characteristic of the noise that unlike a bearing knock it sounds to be at a faster frequency than the cylinder firing frequency. The reason for this is there is more than once instance of detonation occurring in different parts of the combustion chamber on each cycle.

Pre-Ignition or knock is abnormal combustion that occurs before the normal ignition spark. In fact it can be a long way before perhaps not that much past BDC. Pre-ignition is initiated by glowing carbon or a spark plug that is too hot. Because the mixture is ignited far too early it builds pressure for most of the compression stroke and so can be very destructive melting plugs and holing pistons.


Yep, there's pre-ignition, and "end gas autoignition"...

The latter is when the air fuel mix away from the spark plug (end gasses) are compressed as the expanding already burned/burning gasses increase the cylinder pressure. The pressure wave that they experience travels across the chamber a the local speed of sound (KRT^0.5 - as the temperture rises, so does the local speed of sound), while the flame front moves at around 40fps.

The pressure increase causes the gasses to heat, until sometimes they reach the auto-ignition point.

Thus "end gas" "autoignition"...it's the largely destructive force, as that isn't controlled, and it's instantaneous, and the two fronts then collide.

Look at the difference in allowable compression ratio between large bore engines with open and closed chambers (closed chambers were to keep the combustion volume close to the spark plug flame initiation site...the squish/quench areas had to be 0.040" or thereabouts to ensure that the rising pressure in the end gasses was matched with the heat being absorbed into the head metal syrfaces so that they wouldn't ignite...the flame couldn't propogate through the "quench' area (thus the name "quench").

Other solutions were twin plugs to shorten the flame propagation time as well.

 

[Ducked]

Originally Posted By: PimTac
Originally Posted By: SonofJoe
Classic knock (or pinking) is caused by pre-ignition of the fuel, usually at high load. It's initiated by 'hot spots' like bits of glowing ash on the top of the piston. The octane rating of the gasoline is it's ability to resist pre-combustion.

LSPI is pre-ignition that's caused by a mix of engine oil/unburnt fuel that first collects in the space between the top land and the bore and then at low speed, gets 'thrown off' into into the compressing air/fuel mix to act as a combustion initiator. Low speed is an essential component of this type of knock as oil migration via the process of 'throw off' declines with increasing engine speed.





Thanks SonofJoe for that clear explanation.


OK, but you'd have done better to thank Barryh, since his accurately described the difference between detonation and pre-ignition.

The terms in this area are used so inconsistently that it can be almost impossible to discuss, but, 4WIW

detonation=knocking=pinging=pinking=probably other synonyms that I've forgotten

=rapid explosive combustion of the gases ahead of the expanding flame front.

It can be destructive because it happens very rapidly, delivering a shock to the cylinder and piston which causes it to "ring" at a characteristic frequency detected by knock sensors, but because it happens after the timed ignition from the spark plug, its not nearly as destructive as

Pre-ignition, which, as the name implies, happens before timed ignition when the piston is on its way up the cylinder, opposing its motion and generating huge pressures and stresses which can be very rapidly fatal.

Classic knock (or pinking) is NOT caused by pre-ignition. Its caused by detonation.

 

[PimTac]

I think the problem here is that terms are being used to describe a scenario. A knock is the sound. Detonation is the act. Pre ignition is the cause. LSPI is the phenomena.

 

[Ducked]

Originally Posted By: PimTac
I think the problem here is that terms are being used to describe a scenario. A knock is the sound. Detonation is the act. Pre ignition is the cause. LSPI is the phenomena.



Nope. Wrong in at least a couple of places. Detonation isn't "the act". It isn't anything. It isn't involved in pre-ignition.

Knock is the sound of detonation.