Does higher octane fuel help prevent LSPI?

[OppositeLocK]

What do you mean by “worth it?”

If 93 is available in your area, there will be very few stations selling 91, so you’d have to hunt for 91 if you wanted to run it.

In that respect, yes, 93 is worth it. If for no other reason than it’s the easiest supreme grade gasoline to buy, assuming it is sold in your area.

Worth it in the sense as, for example, if a car is tuned for 91 max, running higher octane than that won't give it more power. But perhaps it will make it less prone to LSPI. So it's worth it from that sense. But if it won't help LSPI at all, then why would I put it in my car? That's just throwing money away.

Where I'm at, it's very easy to buy 87/89/91/93/94 whenever, wherever I want. So it's not a matter of convenience or hunting anything down.

But it might not be worth it to pay a few bucks per tank for extra octane that serves no benefit at all.

 

[gathermewool]

As others have said, octane likely has no effect on LSPI. LSPI is more a function of pre-ignition of a fuel mist or buildup, i.e., it's not the fuel that's pre-igniting, but the volatile oil constituents that enter the combustion chamber, mostly from the PCV system.

Actually, the modern autos/dual-clutches are brutal for this - they upshift v. quickly and require at times a lot of pedal input to shift down. One has to think that LSPI has been considered by the manufacturers in their shift map logic.

I really like the CVT in my '14 FXT; however, I did experience some form of low-speed, high load knock once, and inaudible power loss at times, while running 93 AKI that scared the hell out of me! Unfortunately, the solution to that was one of many ECM updates that fixed the issue (I haven't experienced any low-speed knock since), but also lowered performance. Because an ECM update fixed the issue AND I don't have any perceptible oil consumption, LSPI wasn't likely the issue for me, but there's no way I can know that for sure. The ECM update could also have changed the RPM/load relationship to prevent LSPI, if what I experienced was in fact LSPI.

Regardless and surprising to me, is that the CVT will still try to maintain a relatively low RPM (HP curve, is to please those who perceive a loud engine near redline as providing the power they're asking for. There's a huge difference in engine sound between 3.5-4.5K where the engine produces the most power and near 6k.

 

[TiGeo]

Worth it in the sense as, for example, if a car is tuned for 91 max, running higher octane than that won't give it more power. But perhaps it will make it less prone to LSPI. So it's worth it from that sense. But if it won't help LSPI at all, then why would I put it in my car? That's just throwing money away.

Where I'm at, it's very easy to buy 87/89/91/93/94 whenever, wherever I want. So it's not a matter of convenience or hunting anything down.

But it might not be worth it to pay a few bucks per tank for extra octane that serves no benefit at all.

Some vehicles certainly have more timing advance possible in their ECM logic so running higher octane than the min required *can* allow a little more power, typically on the top end/under heavy load. I know our VW Atlas is that way and I've got the logs to show it - more timing correction on 87 than 93. I still run 87 as it's just an around-town vehicle and that's the min required but there is more power there to be had which is clearly shown by my logging.

 

[TiGeo]

As others have said, octane likely has no effect on LSPI. LSPI is more a function of pre-ignition of a fuel mist or buildup, i.e., it's not the fuel that's pre-igniting, but the volatile oil constituents that enter the combustion chamber, mostly from the PCV system.



I really like the CVT in my '14 FXT; however, I did experience some form of low-speed, high load knock once, and inaudible power loss at times, while running 93 AKI that scared the hell out of me! Unfortunately, the solution to that was one of many ECM updates that fixed the issue (I haven't experienced any low-speed knock since), but also lowered performance. Because an ECM update fixed the issue AND I don't have any perceptible oil consumption, LSPI wasn't likely the issue for me, but there's no way I can know that for sure. The ECM update could also have changed the RPM/load relationship to prevent LSPI, if what I experienced was in fact LSPI.

Regardless and surprising to me, is that the CVT will still try to maintain a relatively low RPM (HP curve, is to please those who perceive a loud engine near redline as providing the power they're asking for. There's a huge difference in engine sound between 3.5-4.5K where the engine produces the most power and near 6k.

I can ease into the throttle in my Sportwagen and see 20psi at low rpms as it tried to catch up when it should shift down routinely (it's tuned so not the stock ECU map).

 

[gathermewool]

I can ease into the throttle in my Sportwagen and see 20psi at low rpms as it tried to catch up when it should shift down routinely (it's tuned so not the stock ECU map).

Good point! Especially in Intelligent-mode (tamer than Sport and S# modes), it helps to either use the paddle shifters or change pedal position at a moderate rate instead of mashing the go pedal.

 

[OppositeLocK]

There's a huge difference in engine sound between 3.5-4.5K where the engine produces the most power and near 6k.

Power meaning what? While torque usually drops off at higher RPM, it doesn't mean HP does.

 

[JT20]

What do you mean by “worth it?”

If 93 is available in your area, there will be very few stations selling 91, so you’d have to hunt for 91 if you wanted to run it.

In that respect, yes, 93 is worth it. If for no other reason than it’s the easiest supreme grade gasoline to buy, assuming it is sold in your area.

They are usually selling 92 when some stations sell 93.

 

[gathermewool]

Power meaning what? While torque usually drops off at higher RPM, it doesn't mean HP does.

They’re directly related.

 

[OppositeLocK]

They’re directly related.

 

[gathermewool]

My FXT doesn‘t have gears

Here’s Cobb’s dyno (not my vehicle) that shows the non-flatness of the torque curve):

 

[el Nuke]

They are usually selling 92 when some stations sell 93.

Never seen an area with supreme gas options like that, what geographical area is this located in?

Almost everywhere in Texas I’ve been has 93 as the supreme and the only non-93 supreme selling stations are all the same brand (Allsups/Alon selling Fina gas).

Abilene‘s gas stations’ supreme is the outlier, being only 91 (with the Allsups/Fina stations there selling 90 octane as their supreme for some odd reason). I cannot find a reason why they are different from almost every other city in the state, but they are, and it displeases me greatly.

Brady was like Abilene for the longest time, but I noticed a new Valero station there now which sells 93 as its supreme. But that is the only one out of a dozen or so of all brands of gas that has 93. The rest only sell 91 as supreme.

 

[bbhero]

In my area Pilot truck stop sells 92 octane. And Love's used to and I believe Wawa did sell 92 too.

Strange because everywhere else it is 93. Which is like a lot of other gas stations.

 

[OppositeLocK]

My FXT doesn‘t have gears

Here’s Cobb’s dyno (not my vehicle) that shows the non-flatness of the torque curve):View attachment 30269

Okay, let's call it a ratio instead, the logic is the same. Holding it at redline is more efficient for a CVT than being at a lower RPM no matter than it's not at peak torque. Your chart proves exactly what I said:

Power meaning what? While torque usually drops off at higher RPM, it doesn't mean HP does.

On your chart HP passes torque at around 5.2K and keeps going up, that's why holding at redline and expanding the gear ratio (i.e., shifting at redline) puts down more power. You can picture it as many small shifts occurring, all at redline.

 

[bbhero]

I believe the max torque on my car is at 4,400 rpm. Redline starts at 6,500 rpm.

I agree that hammer down in this circumstance is more efficient for a CVT...

 

[JT20]

Never seen an area with supreme gas options like that, what geographical area is this located in?

Almost everywhere in Texas I’ve been has 93 as the supreme and the only non-93 supreme selling stations are all the same brand (Allsups/Alon selling Fina gas).

Abilene‘s gas stations’ supreme is the outlier, being only 91 (with the Allsups/Fina stations there selling 90 octane as their supreme for some odd reason). I cannot find a reason why they are different from almost every other city in the state, but they are, and it displeases me greatly.

Brady was like Abilene for the longest time, but I noticed a new Valero station there now which sells 93 as its supreme. But that is the only one out of a dozen or so of all brands of gas that has 93. The rest only sell 91 as supreme.

Go to Indianapolis, Indiana. There are several stations where you can have your choice of.. 87, (skip 88,) then 89, 90, 91, 92, or 93 octane fuels.

Yes, 6 selections.

Keystone Ave and elsewhere..

As to 92 octane fuels, Marathon as well as many truck stops have that as the Premium offering. Usually same price as 93.

I have both purchased it, and waited for a station where 93 was cheaper.. It's all over the Midwest, this.

One thing I have never seen in person is 86 octane gas. And I am not sure I trust it.

 

[JT20]

In my area Pilot truck stop sells 92 octane. And Love's used to and I believe Wawa did sell 92 too.

Strange because everywhere else it is 93. Which is like a lot of other gas stations.

I was going to say, Pilot is a couple of towns over and it has 92. It might even be a Flying J. It has 92.

There are... 5 other gas stations, all closer than the other one, in about a 5 mile radius a Speedway (actually two Speedways? Or a Raceway Gas) a BP a Shell and a Marathon (I am sure there are more in any direction) and all of them have the standard 93.

It is weird.

 

[gathermewool]

I don’t know the ratio difference between 3k RPM (max torque) and 6K RPM (same torque as ~2.2k RPM). Someone would have to do back-to-back runs to find out whether 4.5k RPM is faster than 5.9k RPM, considering the ratio change torque multiplication posited in your Youtube video, minus losses.