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Old 09-15-2021, 10:56 PM   #1
sebastian323
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Default does using 87 octane on a turbo EJ engine actually lead to engine damage

Does pouring 87 octane into a stock tune turbo Subaru actually damage the car ? I imagine the ECU can roll back the ignition timing quickly enough to prevent significant detonation. I can see where you will lose power, but where does the actual damage come in. I suppose people concerned with this are on tuned cars that are pushing the knock threshold more aggressively
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Old 09-15-2021, 11:02 PM   #2
K3rm1tth3fr0g
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Yes. It's not good. you're going to start knocking
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Old 09-15-2021, 11:13 PM   #3
djoye
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Check the manual, pretty sure it will say that lower-grade fuel can be used temporarily and may also say something about not driving hard; I would certainly stay out of boost.
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Old 09-16-2021, 12:51 AM   #4
AliBenn
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I can see why OP is getting/not getting exact answers on google

Currently, multiple manufacturers are using turbos but saying ok to use regular unleaded
On these late model vehicles, the engines have 2 fuel pumps. A pick up pump in the tank AND a high pressure pump on engine.
Your 2006 has one pump and provides 40lbs of pressure
A 2018 Chevy Malibu has a pick up FP plus a HP pump which provides 10000 lbs of pressure
(Diesel HP pumps provide 25000plus pressure)
Bc pressure is so high, premium unleaded not needed

So look at the issue this way
If you have 2 FPs your good with 87oct
If you have 1 FP AND are forced induction you need premium
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Old 09-17-2021, 02:18 PM   #5
sebastian323
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Quote:
Originally Posted by AliBenn View Post
I can see why OP is getting/not getting exact answers on google

Currently, multiple manufacturers are using turbos but saying ok to use regular unleaded
On these late model vehicles, the engines have 2 fuel pumps. A pick up pump in the tank AND a high pressure pump on engine.
Your 2006 has one pump and provides 40lbs of pressure
A 2018 Chevy Malibu has a pick up FP plus a HP pump which provides 10000 lbs of pressure
(Diesel HP pumps provide 25000plus pressure)
Bc pressure is so high, premium unleaded not needed

So look at the issue this way
If you have 2 FPs your good with 87oct
If you have 1 FP AND are forced induction you need premium

I believe this is because that chevy malibu is a direct injection vehicle so the fuel is injected at the precise moment it is needed, reducing the chances of detonation. the high pressure fuel pump is for the direct injection as pressures at the injector inlet must be much higher in order to successfully push fuel into the pressurized cylinder
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Old 09-22-2021, 03:59 PM   #6
DFrat
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why are you trying to use lowmoctane fuel? just wondering
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Old 09-22-2021, 04:08 PM   #7
blurred
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Quote:
Originally Posted by sebastian323 View Post
I imagine the ECU can roll back the ignition timing quickly enough to prevent significant detonation. I can see where you will lose power, but where does the actual damage come in.
If I try to punch you in the face 5 times but only land 1 hard right before you dodge the rest it would describe how a knock sensor works in older cars.

After you dodged the remaining 4 punches I move slightly and try again, landing the first 2 massive hits before you dodge the rest.


So yes, you dodged 7 punches
...But you still have a broken jaw, and a black eye.
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Old 09-23-2021, 02:43 AM   #8
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If the car was tuned for low octane fuel it is possible to run BUT performance will be WAY WAY down even compared to 91 octane.

When i tune a car on east coast 93 octane the engine will generally make more power with 1-3* more timing than the exact same engine on west coast 91 octane. To use even lower octane will require even less timing to prevent knock.

In stock form the ECU is able to pull timing out when it see's knock BUT it does not do it fast enough to prevent damage or problems. I would personally never even recommend running a stock tune on a stock car that would see track time. The oem subi calibrations are not very good and even worse on low octane fuel.

I would highly recommend doing some data logs with your car and then review the data to understand exactly what the ECU is doing and why. Have a read through this article for some extra insight on what you'll see in a data log. Subaru data logging explained, learn to analyze your own logs
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Old 09-23-2021, 02:43 AM   #9
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sorry double posted
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Old 09-23-2021, 02:42 PM   #10
rtv900
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Quote:
Originally Posted by AliBenn View Post
Bc pressure is so high, premium unleaded not needed

So look at the issue this way
If you have 2 FPs your good with 87oct
If you have 1 FP AND are forced induction you need premium

This is really misleading, the pressure of the injection system has less than nothing to do with what he is asking about octane.
Can direct injection allow slightly less octane. . . .yes, because it provides better mixing so there aren't sparse lean areas within the cylinder.
It's just better mixing.
Forced induction still needs the octane due to the effective compression ratio at full boost.
The ECU can adjust to a point, but I seriously doubt you can throw 87 in a turbo car and not have problems.

Quote:
Originally Posted by sebastian323 View Post
I believe this is because that chevy malibu is a direct injection vehicle so the fuel is injected at the precise moment it is needed, reducing the chances of detonation. the high pressure fuel pump is for the direct injection as pressures at the injector inlet must be much higher in order to successfully push fuel into the pressurized cylinder
NO, direct gas injection does NOT make a gas engine into a compression ignition engine.
No clue where this idea came from.
Direct injection still injects during the intake stroke while the valve is open. It just goes right in the cylinder rather than on the back of the valve.
All it does is creates a better more even mix, that's it.
Gas engines, direct or port, still have fuel in the entire time until the spark occurs.

If it weren't until it was needed it would be a diesel.
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Old 10-06-2021, 02:57 PM   #11
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Quote:
Originally Posted by rtv900 View Post
...Forced induction still needs the octane due to the *effective compression ratio* at full boost...
*Cylinder pressure*.

That is all.
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Old 10-13-2021, 02:25 PM   #12
StarkWRX
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As stated before, we have static compression ratios of around 8.4:1. So, if you drive under 0 psi relative manifold pressure, you are essentially driving a NA car (of sorts). Could you drive with 87 octanes without harming the engine? Possibly. Would I do it? Not unless it's an emergency.

Knocking comes from the charge igniting prematurely (usually from high temperature). So, with that in mind, what you *may* be able to do is increase the octane of your fuel with ethanol (flex fuel) and at the same time decrease the charge temperature (by way of the same ethanol).

I run E30 every now and then, tuned my IDC a bit and I keep an eye on my AFR.
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