Naturally aspirated and 87 octane...

[xwd]

DI is why this motor can run 12.5:1 on 91 to begin with and why engines like the new 2L DIT turbo motor from Subaru runs like 10.8:1 versus the old 2L turbo motor which runs 8:1...

They are designing an engine with DI in mind to begin with and the requirement is 91 octane.

[Gixxersixxerman]

Originally Posted by dwx

DI is why this motor can run 12.5:1 on 91 to begin with and why engines like the new 2L DIT turbo motor from Subaru runs like 10.8:1 versus the old 2L turbo motor which runs 8:1...

I can't agree 100% on DI being the reason these can run 12.5:1.. Motorcycles have been running 12.5:1 for awhile .. My friends r6 runs 13.1:1 on 91 pump and my 03 GSXR 600 ran 12.3:1 on manufactor recommended 87 pump

[usptwins]

Tell you what, if your car thows a CEL and you bring it in to the dealership, and they find out that you put 87 in it and have been running it, then its not the cars fault. Thats why the car is made and produced with the octane that they are SUPPOSE to use. Otherwise it will give you problems later. Just spend the money to use what it needs. Im getting tired of people trying to cheap out on this car. Its not a civic or a honda. hell.

[xwd]

Originally Posted by Gixxersixxerman

I can't agree 100% on DI being the reason these can run 12.5:1.. Motorcycles have been running 12.5:1 for awhile .. My friends r6 runs 13.1:1 on 91 pump and my 03 GSXR 600 ran 12.3:1 on manufactor recommended 87 pump

Those are very different engines. Mazda runs 13:1 in their Skyactiv 2L but it only makes 155hp. It runs on 87, they have a 14:1 version which runs on 91. DI is the main reason they can pull it off.

[bigjake]

i live in a small town, and most stations carry 87 and 89, more are starting to carry 91, but no one in a 60 mile raduis has 93 octane gas.

[wparsons]

Originally Posted by dwx

It's absolutely cylinder pressures which require higher octane...

Spark advance can cause detonation, but the reason you have to pull back timing is based on cylinder pressure, whether it's a NA or FI application.

87 octane fuel doesn't burn correctly with higher cylinder pressures and spark, it explodes, which causes detonation. To say you could tune a car for 87 octane and get the same amount of power as a car tuned on 93 is completely incorrect.

How does pulling timing lower cylinder pressures? Higher octane fuel isn't more resistant to cylinder pressures, but it does burn slower. Running richer can prevent detonation, which actually increases cylinder pressures since there is more fuel (which can't be compressed).

I 100% agree that you won't get the same power (assuming equal quality tunes on the same engine) on 87 octane as 93, I already said that above.

[serialk11r]

Originally Posted by wparsons

How does pulling timing lower cylinder pressures? Higher octane fuel isn't more resistant to cylinder pressures, but it does burn slower. Running richer can prevent detonation, which actually increases cylinder pressures since there is more fuel (which can't be compressed).

I 100% agree that you won't get the same power (assuming equal quality tunes on the same engine) on 87 octane as 93, I already said that above.

It lowers peak cylinder pressure by dumping more heat out the exhaust, not good. Best way to lower cylinder pressure is to reduce the desired torque output :P

[arghx7]

Retarding ignition timing lowers cylinder pressure. It changes the combustion phasing. Here are some representative indicator diagrams which help illustrate the concept. I'll have to see if I can find some good heat release charts as well.



The OP's question is perfectly reasonable, considering that Ford Ecoboost engines are running on regular fuel.

What you have to remember though is that those type of engines are specifically designed for low octane use. For one thing, they use a lot of charge motion (port masking etc), basically a restrictive intake port meant for low-mid rpm use, to help reduce knock. Also, exhaust manifold and valve timing configuration reduce residual gases in the combustion chamber to mitigate knock.

Now, recall the basic idea of the D-4S combustion system. It is a system based on a high flow intake ports, with comparatively poor charge motion. It's not designed for really high knock resistance, it's designed for high filling efficiency.

[Boosted2.0]

Originally Posted by zooki

So, after reading on the Forced Induction forum about how much boost is safe to run on pump gas, I have a question. If you can run around 5lbs. of boost(roughly) on a stock motor with 93 octane, why couldn't the factory engineers have tuned the stock motor to run on 87 octane? If aftermarket tuners can deal with the increased cylinder pressure using pump gas, it seems that a N/A motor could run on 87 octane, even with 12.5 to 1 compression. I realize that there would be a loss in power, but technically it should be able to be done, right? And yes, I realize its a sports car, and yes, I like all the power I can get, and I don't mind paying for Premium, I was just wondering if its possible, and how much power it would give up. Any tuners ever try this?

Its a bad idea. Midgrade and premium tend to have higher quality and detergent levels. Given the carbon issues they have been dealing with on the early 3.5L direct injection designs, sticking with high quality fuel seems adviseable.

[OrbitalEllipses]

Originally Posted by Boosted2.0

Its a bad idea. Midgrade and premium tend to have higher quality and detergent levels. Given the carbon issues they have been dealing with on the early 3.5L direct injection designs, sticking with high quality fuel seems adviseable.

Yo dawg just pour in some Tide (no bleach) with your next fill up on 87 to get those detergents.

[NYCsubaruBRZ]

87 will give u poor gas mileage and less power
it wont hurt your car because the ecu will adjust but no point to put 87 unless its all the gas station has. you wont save money, u will just use more gas. you might actually spend more.

you might get 80 miles less on a tank of 87. so was saving the 4 bucks on fill up worth it? nope. and it makes the car slower. this car is slow enough lol

[mad_sb]

It certainly can be done. The reason it is not... you would have to retard the timing under load so far away from MBT it would kill the efficiency of the engine. With boost people are retarding timing as well, but making up for it with a massive increase in VE. Without boost, every degree of timing you drop away from MBT costs you a couple hp.

It would be a nice experiment to tune the same stock car on 87, 89, 91, 93.. though i think it would meed to be done on an engine dyno to really safely get the most out of the lower octane under all driving conditions.

Also of note, if you want to get an idea of what it might feel like, just ask your tuner to give you a stock map with the ignition advance table set to all zero's (setting IAM to zero will only work for about 10 minutes until IAM works back up to normal levels).

[Draco-REX]

Originally Posted by zooki

So, after reading on the Forced Induction forum about how much boost is safe to run on pump gas, I have a question. If you can run around 5lbs. of boost(roughly) on a stock motor with 93 octane, why couldn't the factory engineers have tuned the stock motor to run on 87 octane? If aftermarket tuners can deal with the increased cylinder pressure using pump gas, it seems that a N/A motor could run on 87 octane, even with 12.5 to 1 compression. I realize that there would be a loss in power, but technically it should be able to be done, right? And yes, I realize its a sports car, and yes, I like all the power I can get, and I don't mind paying for Premium, I was just wondering if its possible, and how much power it would give up. Any tuners ever try this?

Because they wouldn't have been able to hit their power target with crap 87.

They're also realists that realize that if someone can't afford $3 per tank to get the most performance and reliability from their car, then they probably can't afford the car. I mean, really, it's such a non-issue I don't know why people are even thinking about 87.

[InvalidJohnny5]

I've seen people cheap out on the car and put "autozone mods" sadly this great car is getting in the hands of former civic owners...