LSPI questions

[Wiring3826]

Hi everyone,

Hopefully this is the right sub -forum for this question. I have a 100% stock FiSt and am wondering about LSPI. This is the first turbo AND manual car I've owned, and LSPI is a new concept to me. I understand the basic premise (high load at low rpm could result in high boost condition that leads to pre-detonation), but I don't have a great feel for what constitutes "low" rpm and "high load."

On motorcycles it is very obvious to me when I "lug" the engine - it feels/sounds almost like a stuttering. If I'm rolling along at 2k rpm and gradually increase throttle as the rpms increase, is this ok? Will an LSPI event be very obvious to the driver, i.e. loud pinging, etc?

I've also noticed that the shift indicator wants you to shift VERY early. I assume this is optimized for firm efficiency over anything else. It feels "right" to me to hang on to a gear until 3k rpm or so before I upshift.

Regarding engine oils, I've read just enough to know that I need to do more research about anti-LSPI oils. Considering my engine is stock and I don't plan to modify it, I was thinking any 5w20 synthetic that meets the specs in the manuals should be fine. Not sure if the listed specs cover LSPI or not, which is another thing I need to research.

I guess that was more of a ramble than I anticipated, but any and all input about the subjects above would be greatly appreciated!

 

[SteveS]

If you're just doing ordinary around-town driving it is perfectly alright to let the revs drop and then gently accelerate. It's also perfectly fine to shift early without running to the redline. In fact if you do run to the redline or at least to high rpm, you will not be fitting in the flow of traffic very well. Ford tuned this engine the way they have always done them as far as I can tell. They like to make engines flexible and make all the torque down low, not high rpm screamers. I find that I can loaf along a side street at 25 mph in 5th no problem, even with a gentle hill. On a 45 mph boulevard, 6th is no problem even if you have to slow a little and then accelerate back up with traffic. We have a road like that which turns into a merge lane for a freeway, and I don't have to downshift from 6th to accelerate briskly to 65 mph. What you'll hear when the engine does start to lug is a lot of noise from the sound symposer but not much action from the car. You'll also see the intantaneous fuel economy plummet, but if you downshift you'll see better acceleration, less cow-moaning noises, and better fuel economy.

Note that when I accelerate in these conditions, it's with just part throttle. If you go full throttle then you're going to have more problems. If you need that much acceleration, you need to drop a gear or two.

 

[ansibe]

I don't think LSPI is well understood by anyone, but it is very real and can cost you an engine!
I believe it is caused by an emulsification of fuel and oil, which is a very very low octane mixture. Modern turbos like ours develop a lot of boost at low rpm which causes the emulsified mixture to ignite way before tdc. kaboom.
Oil type is very important to avoid the emulsification. I use Amsoil Signature, but there are plenty of others. Liquid fuel and oil are needed for the condition to occur, so make sure your engine oil is up to temp before beating on the car.
Try not to flat foot your car at 1500rpm.

 

[M-Sport fan]

There is A LOT of controversy, conjecture, and theorizing over what properties of an engine oil help stave off (or promote) the LSPI event.

From the limited research I have done, the consensus seems to be that the lower an oil's NOACK volatility number is, the less chance there is of that oil being a factor in LSPI.

Sulfated ash (SA) and the Total Base Number (TBN) may also come into play regarding LSPI, but there is not a lot of agreement on those metrics having a direct impact.

Most of the premium synthetic oils out there today are very good in this respect, but some are exceptional, albeit under a certain NOACK number (like ~10%) it may not matter much.

Most premium synthetic 5W-30s seem to have lower NOACK percentages than most 5W-20s, but there are exceptions to that generality.

Of course, it you habitually and drastically lug the engine, and try to go WOT from very low (like under 2K revs), even an oil with a nonexistent 0.5% NOACK will not help you.

 

[Wiring3826]

Thanks for the input, everyone. Sounds like a little bit of common sense driving habits will go a long ways here.

@M-Sport fan very detailed response re: engine oils, appreciate it. I think for my use case "very good" is probably good enough. If I were pushing the car hard regularly at track days or modding the motor I would do more research into specific oil properties.

 

[Dialcaliper]

From the info I can find, LSPI is a result of engine oil that stays in the cylinder has time to absorb heat and offgas volatiles off the hot cylinder walls at low engine speed during the compression stroke before the DI injectors deliver fuel.

Oil has fairly high resistance to vaporizing, but once atomized it has effectively low octane, so it preignites before the spark plug (igniting any fuel injected, similar to classic pre ignition/detonation.

“LSPI-safe” oils seem to use some
combination of base oil with low volatiles (low NOACK), and additives that are effectively acting as an “octane booster” for the oil vapor, both of which help to prevent oil vapor preignition.

TBN itself is just a measure of oil on the acidic/basic scale (measured as mg of potassium hydroxide needed to neutralize it). Essentially a measure of how much buffering additive is left in the oil to prevent the PH from dropping to levels acidic enough to allow/cause corrosion. It has nothing directly to do with LSPI behavior, however used oil with a very low base number indicates that it’s been in the engine a long time under use, which means its base oil has been degraded and additives exhausted, making it more likely to suffer from LSPI issues. However, in a *new* oil of any kind, the starting TBN is not really directly relevant.

 

[Wiring3826]

Excellent info, thank you.

 

[M-Sport fan]

From the info I can find, LSPI is a result of engine oil that stays in the cylinder has time to absorb heat and offgas volatiles off the hot cylinder walls at low engine speed during the compression stroke before the DI injectors deliver fuel.

Oil has fairly high resistance to vaporizing, but once atomized it has effectively low octane, so it preignites before the spark plug (igniting any fuel injected, similar to classic pre ignition/detonation.

“LSPI-safe” oils seem to use some
combination of base oil with low volatiles (low NOACK), and additives that are effectively acting as an “octane booster” for the oil vapor, both of which help to prevent oil vapor preignition.

TBN itself is just a measure of oil on the acidic/basic scale (measured as mg of potassium hydroxide needed to neutralize it). Essentially a measure of how much buffering additive is left in the oil to prevent the PH from dropping to levels acidic enough to allow/cause corrosion. It has nothing directly to do with LSPI behavior, however used oil with a very low base number indicates that it’s been in the engine a long time under use, which means its base oil has been degraded and additives exhausted, making it more likely to suffer from LSPI issues. However, in a *new* oil of any kind, the starting TBN is not really directly relevant.

Yes, THANK YOU for 'getting into the weeds' technically as to both the direct and specific causes of LSPI, and the oil add pack 'cures'.

I did not know that some blenders throw an octane booster type/'acting' additive compound into the oil to further try and stave off LSPI, on top of the use of high quality, and low volatility PAO/POE content base oils.

The only speculation I have ever heard in the past about how a high TBN can hurt was that when high doses of calcium are used to achieve said high starting TBN (vs. using the more modern/recent magnesium to get the same result), it can possibly exacerbate LSPI, but .