Naturally aspirated and 87 octane...
 

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?

Why would you even spend the time and money to tune for 87? Its less than 5$ difference to fill up. Since its on average 250$ for a tune. It would be a complete waste of money to detune the car to save a few dollars.

Personally I wish they would just change to 93 octane only everywhere and get rid of this 3 tier bs.

If you want to do a tune to have cheaper fill ups then go with e85, then you get more power and a lower fillup. Actual MPG tho I have seen everywhere from better to worse on the car.

Also people are running 7-8.5 psi on pump gas, maybe more I havent really looked that far.


But Im gonna go with yes.... if you really wanted to spend the money on a tune Im sure someone like Visconti could make a map.

between 87 octane and 93 octane you only save $3 per gas tank, if you are that CHEAP go buy another car.

Would you design a motor with fairly nice technology to handicap it to 87 octane? I know I wouldn't. Also, if I can advertise a motor to do 200 crank HP, why would I say no, I want it to be tuned to the cheapest gas, I'm gonna tune it to 87 octane even though then I can only advertise it making 185 crank HP. It just doesn't make any kind of sense.

Ok, what part of this:
" 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?"
did you not understand? I'm not saying I want this, I'm wondering how much power you would actually lose. I'm also not cheap, I stated very clearly that I did not have a problem putting 93 octane gas in my car. It was more of a technical question.

Is it really a question worth answering though? I think that is a better question.

If you (factory and tuners) are going to spend the time and money to do it, spend that time to improve it to its best.

I'm going to drive backwards to work tomorrow. I wonder what my MPG will be like?

Well, here's my train of thought...if the aftermarket can get the electronics to cope with increased cylinder pressures of FI through tuning while still using 93 octane gasoline, why can't the engine be tuned to use 87 octane at the decreased cylinder pressures that a N/A motor has. It's not like 93 octane has any more power potential than 87, in fact it may have less power potential do do its slower burn rate. I think direct injection motors have a lot more leeway in the compression/octane relationship due to the way fuel is introduced into the cylinders. If you can get the same amount of power with lower octane gas, why wouldn't you? I'm talking about from the factory. I wouldn't spend the money on an aftermarket tune to get the motor to produce 200 HP on 87 octane. But I think the factory could do it. So, just to be clear. I am not looking for an aftermarket tune for 87 octane, I am fine with the car the way it is, I have no problem buying 93 octane either. This is just a thought experiment on what I've seen boosted motors doing with 12.5 to 1 compression and pump gas.

this motors CR is not for 87

Just...nevermind.

ha, that was entertaining.

i think its a good question

When you bought your FR-S/BRZ, the dealer probably put 87 in it and your car didn't blow up. The Mustang 5.0 pulls timing and runs on 87 fine; just less HP. Until we have the software available for logging, we just don't know. The logic might be there now.

I'm not sure if ECUTEK found the memory location where timing is stored. If they did, we can look at the difference between the exptected timing and actual. See if the timing is pulled with 87 octane once pinging is detected. The Turbo Subaru's have a software tool called Learning View that does this.

If you really stay off the throttle you might even be able to burn a whole tank of 87 and not have the car misbehave...

It might be possible to save gas money by blending in 1 gallon of E85 into each tank, especially since the motor is direct injected you can raise the knock resistance quite a bit. For best results use a new ignition map of course, but it shouldn't be off by too much.

so why the question? that was rediculous. If you can/want to put 93 in your car, then why not just do it? This motor was made to use 93 and thats why its rated at 200 crank. That was a foolish question... Just put what it asks for and your all set. No need to wonder about something you don't/won't do.

You must have some really shady dealers around you.... The Mustang also isnt running the same compression ratio nor the same type of fuel injection set up.

If the Mustang can do it without direct injection, the FA20 should have no problem with 87.

All car dealerships says the put in premium, but they always put in the cheapest gas they can get.

Why 93 octane?

Because race car.

Short answer: Yes it will work, and you will lose power.

I know a guy who had his WRX tuned for 87. Thing is, he didn't tell the tuner before the session, just filled it up. Tuner was disappointed with the power he got, and probably spent longer than normal tuning. He was noticeably upset once the guy told him why it was so low. It was a good 87 map, but I recommend informing the tuner of your fuel choice before attempting.

If thats what you want to believe thats fine. Most dealers arent like that tho. I saw mine filled up with prem, as have others. I was out walking around looking at used cars and one of the techs were over filling it up.

Also, if they are caught going against correct servicing specs it should be brought up to their supervisors.

Never mind guys, sorry for having a curious mind. Please go back to arguing over which air filter makes 1 more HP than another. I appreciate all the thoughtful replies.

@zooki.. Not too long ago, I was being absent minded and told the gas station attendant to fill up with $15 regular (87 octane and here in Oregon you cannot pump your own gas). I didn't realize what I said until he gave me the receipt. Guess what happened to the motor? Nothing. It was fine. I just didn't go WOT until it all burned away. I'm nearly certain that Toyota/Subaru have already accounted for the fact that people might do this occasionally. I'm sure the motor can be tuned to run on a lower octane of gas, but (as you prob already know) you will make less power. The motor is high compression. If we were talking about a 8.5:1 motor, different story of course. I have also researched differences in behavior in this regard with iron vs aluminum heads.

Good thought experiment. Just not sure that any tuners would be willing to put much effort into an 87 tune on 12.5:1.

You can put 87 octane in the stock motor, but you shouldn't make a habit of it. A dealership that I used to work for would put regular gas in the engine for it's first fill-up. I can't say I agreed with it, but I'm sure it wouldn't do too much harm.

It isn't cylinder pressures that require higher octane, it's the amount of spark advance that requires higher octane. Yes increasing boost will create more opportunity for knock/detonation, but that can be fixed by pulling a bit of timing back.

It isn't an issue on boosted cars because they're adding a lot more power already, so pulling timing back to avoid detonation isn't an issue.

On an N/A engine you would have to pull timing to prevent detonation, but without the boost there's no way to get that power back. If you were to run an N/A engine on the timing tables from a boosted tune you would be losing quite a lot of power across the board.

The stock ECU will pull timing back if it detects any knock, so it's "safe" to run it on 87 octane, but you'll get worse mileage and less power since the ECU isn't running on the optimal maps.

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.

I always thought that the relationship of spark advance to cylinder pressure was inverse.

I'm wondering how much direct injection changes this. Just a few years ago you would have never thought we could boost a 12.5 to 1 compression motor with 5-8 lbs. of boost on 93 octane, but yet here we are, doing it reliably. I would guess(just a guess) that a DI motor can use a lot less spark timing since the ability to control the injector timing and precise amount of fuel injected seems to help control detonation in a big way. I have been trying to find info on how spark timing relates to fuel injector timing on a DI motor in the context of crank degrees. Plus the advances in combustion chamber design that promotes fast, even burns. But I'm still looking for that info. Anyway, I was just curious, and thought I'd throw it out here. I guess I should have expected some of the replies I got....

lol I feel your pain... Trying to get a technical thought discussion going on the internet is... painful.

I don't have the answer but I thought I'd help clear up some confusion.
I too don't quite understand all the intricacies of engineering and tuning a modern DI internal combustion engine, but I get what the OP is saying. Most of you boneheads need to read the question and stop staring at your own colons.

If a high compression engine requires 93 octane at stock power levels @ 12.5:1 CR, but 93 octane is also stable enough for bolt on FI at 12.5:1 CR, why isn't the inverse true? IF an OEM engine were designed at 12.5:1 CR boosted and required 93oct, wouldn't we expect to be able to run lower octanes if it were changed to NA and produced less power?

It's an exercise in engineering thought, the question is not "hai guyz will it go OK on 87? derp? And the answer is not "OMG RTFM NOOB".

Anyways, it's obvious that high compression and high heat require more stable octane ratings, but the (perfectly legitimate) question still stands: How much has DI changed this train if thought? Could DI allow us enough finite control of what's happening in the cylinder to improve efficiencies and net the same power from lower octanes?

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.

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

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.

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.

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.

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

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.

http://www.ft86club.com/forums/attac...1&d=1357926869

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.

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.

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

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).