think 91 octane will hurt my car?

[RedemptioN]

i have 99 eclipse gs i just replaced my clutch with an act 2100. and now i really want to get a little more hp. now i normaly run 81 octane but i want to run 91 octane. just want to know if its going to kill my injectors or if my car will be fine. also will it idle diff? so i can kinda know what to look for and not think i broke my car thanks in advance for your input.

 

[GsXdSmKingGsX]

No it wont at all .

 

[slow8033]

Nope, it wont hurt your engine, and it wont help your wallet. Your not gonna get any more power from running 91 vs 80 something. It doesn't work that way.

 

[xxxspeedxxx]

it wont matter

 

[RedemptioN]

i guess i was miss led on how the 91vs81 worked thanks for clearing it up for me. i will just stick to my 81 for now

 

[scott90gsx420]

WWhhat?? you should not be running 81.. not even 91 unless you can only get 91. the octane rating is the gases ability to resist detonation(which is very destructive to an engine). you should already be running the highest octane possible let alone if your going to start doing mods. for all your guys who just told him he'd be fine id listen up. read the speed o gauge.. premium gas only. Or read the owners manual it says nothing less then 91. As stated the number is the ability to resist detonation which is commonly called knock/ spark knock and is always misunderstood with pre ignition. when are piston compresses the air/fuel mix the plug ignites it some degree before the piston reaches top dead center. this gives you max power from each combustion cycle. After and only after the plug fires can detonation occur. The gas air mix on a normal combustion stroke will expand slowly and evenly from the spark plug and continue to until all the air fuel mix has disappeared. Detonation is where as the piston goes down the air and fuel gets to hot and spontaneously explodes. this causes a very big spike in pressure some two to three times more then normal. light amounts of knock are common under high boost.Its reaccuring knock that is bad as it WILL kill your ring lands burn holes in pistons blow HG ect. AS you can see knock is bad but preignition is way worse. this is where as the piston is compressing the mix, the mix hits a hotspot in the cylinder and explodes before the piston reach TDC. Of the two pre igniton is way worse it will cause instant damage as it forces the piston the opposite way then the others. Most engines will live with light and even mild knock for some time. Knock though will kill the car and before it does your performance. these cars come with a knock sensor that is designed to listen for detonation.. when it hears it the ECU pulls timing and your power with it. Also detonation will lead to prei gnition as it leads the cylinder walls to extreme heat and melts pistons rings ect.This is why we use egt gauges as the car pulls timing the ignition cycle happens later leading to the exhaust valve getting opened while the mix is still burning. this will cause egts to shy rocket.this is a very short explanation to a very big topic. But i hope you can all gather from this you should not be running anything lower then 91 especially if running higher then stock boost.

 

[slow8033]

WWhhat?? you should not be running 81.. not even 91 unless you can only get 91. the octane rating is the gases ability to resist detonation(which is very destructive to an engine). you should already be running the highest octane possible let alone if your going to start doing mods. for all your guys who just told him he'd be fine id listen up. read the speed o gauge.. premium gas only. Or read the owners manual it says nothing less then 91. As stated the number is the ability to resist detonation which is commonly called knock/ spark knock and is always misunderstood with pre ignition. when are piston compresses the air/fuel mix the plug ignites it some degree before the piston reaches top dead center. this gives you max power from each combustion cycle. After and only after the plug fires can detonation occur. The gas air mix on a normal combustion stroke will expand slowly and evenly from the spark plug and continue to until all the air fuel mix has disappeared. Detonation is where as the piston goes down the air and fuel gets to hot and spontaneously explodes. this causes a very big spike in pressure some two to three times more then normal. light amounts of knock are common under high boost.Its reaccuring knock that is bad as it WILL kill your ring lands burn holes in pistons blow HG ect. AS you can see knock is bad but preignition is way worse. this is where as the piston is compressing the mix, the mix hits a hotspot in the cylinder and explodes before the piston reach TDC. Of the two pre igniton is way worse it will cause instant damage as it forces the piston the opposite way then the others. Most engines will live with light and even mild knock for some time. Knock though will kill the car and before it does your performance. these cars come with a knock sensor that is designed to listen for detonation.. when it hears it the ECU pulls timing and your power with it. Also detonation will lead to prei gnition as it leads the cylinder walls to extreme heat and melts pistons rings ect.This is why we use egt gauges as the car pulls timing the ignition cycle happens later leading to the exhaust valve getting opened while the mix is still burning. this will cause egts to shy rocket.this is a very short explanation to a very big topic. But i hope you can all gather from this you should not be running anything lower then 91 especially if running higher then stock boost.

Um...before you spent 30 minutes typing a response (With no paragraphs I might add) you should check what kind of car the OP is driving. Its Non turbo. He doesn't need premium fuel friend.

 

[scott90gsx420]

Um...before you spent 30 minutes typing a response (With no paragraphs I might add) you should check what kind of car the OP is driving. Its Non turbo. He doesn't need premium fuel friend.

Ah my bad.. Just got off work and I'm tired.. Il look at the OP car next time before posting. Either way Ive always run the highest octane possibly with both my dsm's and my old crx. Cant hurt anything.

 

[slow8033]

Ah my bad.. Just got off work and I'm tired.. Il look at the OP car next time before posting. Either way Ive always run the highest octane possibly with both my dsm's and my old crx. Cant hurt anything.

Lol. No worries. I just didn't want him to get confused.

 

[DSM1G90]

81..? Where can one get fuel with that low of octane?

And WHY would one want to put in 91 for a NT motor and throw away money like that?

You aint going to get extra power with fuel that has more junk in it than 85 or 87 octane, for that junk just protects against knock by decreasing the flammability of the fuel where 81 to 87 burns hotter and quicker.

 

[ktgurl87]

I've actually heard and been told that running premium (whatever the highest octane at the pump is) every once in a while can help clean things out. -shrugs- I don't know for certain. But I know that I personally would not be throwing extra money in my gas tank if it's not required. I hate even filling up the GST. I cry a little bit. I mean... if you've got the extra dollars to toss in there, I don't see where it would hurt, but it's not a requirement.

 

[scott90gsx420]

Lol well il say i did it because my uncles(V8 lovers) told me its give me more power and i was young and nieve and believed them.This was same uncle who still tries telling me turbos give the car power by sucking the exhaust out therefor allowing more flow. And when i switched to it all my other cars ran a lot smoother they revved quicker. just felt better.. Then i got my gsx and started looking into tuning threads and what not and thats when i realized the actually use behind higher octane.
Haha now the only things i ask my uncles for is to use there big tools motor stands ect. and my uncles only want ride in my car or to make excuses why i left them sitting at the starting line..

 

[DSM1G90]

(I had friends that took auto shop in high school and college and I learned a lot from them when I was with them when they had auto projects of all types that they were doing....)

..and what's sorta funny is that stock V8's ran a low 7.8 to 8.2:1 compression ratios and carbureted systems with hi speed jets that had to be changed per altitude for the correct AFR ... You get a car from California to the mountain areas and you had to change out the jets. Otherwise, thing would run horribly lean .. and vice versa if a mountain car when to California...but then you just advanced the timing to compensate ...

Yet, I can also see why they told you 91 plus octane is that if you didn't get on those V8's once in a while to blow out the carbon buildup (which does build up compression to almost 10.5:1 + in a heartbeat) those blocks would knock hard and loud.

Instead of reaching 35mph and jamming the tranny in 2nd gear, slamming on that throttle to the floor to wind that witch up to almost red line and watching the rear end go black from all the carbon that has been built up in the compustion chamber being blown out the tail pipe, it was easier to run 91 octane to rid of the knock that was apparent from thick carbon coated piston tops which raised the compression ratio.

(Dang, been around V8's too much...rofl) I used to do tuneup on a lot of these things due to knocking and before I would begin, I would get in that thing and do the above to see how much carbon came out the tailpipes. 90% of the time after the blowout, the motor had tonnage of more power and ran smoother, but I did an oil change afterwards to rid of the excessive carbon that remained in the block.


-DSM

 

[Boug]

i have 99 eclipse gs i just replaced my clutch with an act 2100. and now i really want to get a little more hp. now i normaly run 81 octane but i want to run 91 octane. just want to know if its going to kill my injectors or if my car will be fine. also will it idle diff? so i can kinda know what to look for and not think i broke my car thanks in advance for your input.

Am I reading things correct...? Did you say 81-octane...?

 

[Quicksilver1695]

most likely means 87 octane.

 

[gusu]

All octane indicates is AKI (Anti-Knock Index), well technically a few more things in the US as we use a very complicated octane rating system here compared to most of the world.

All premium does is lower the point when your car should typically knock. It won't help anything else at all.

You don't make more HP by adding race gas, you make more power by being able to have a more aggressive tune because you will knock much later with better gas. For example people use E85 because it has a higher octane rating of around 105-108 octane (I believe E90 is 108 but could be wrong). E85 does this because it has a continuous explosion as compared to 86-96 octane where it will have a short burst, the reason why you want a long burst is simple, you have a constant/steadier burn of your fuel. The steadier the burn of the fuel is in the combustion chamber the lower the chance of knock will be. Imagine smacking the head of a nail really fast with a hammer and trying to nail it in straight with one hit compared to pushing it in steadily with one strike, this isn't totally 100% what is going on but it is close enough to give you some idea as a newb as to what is going on.

 

[Dhan]

This is kind of an arbitrary question, but at what point do you start to experience knock? Years, months?

The previous owner's wife of my Laser routinely put regular in the tank "because it was the cheaper option" and the owner's manual said regular was okay.

EDIT: does anyone have the original owners manual? I would think it would say to put in premium.

 

[RUBBERtoad]

i guess i was miss led on how the 91vs81 worked thanks for clearing it up for me. i will just stick to my 81 for now

87 is more volatile, burns quicker and 'explodes' faster.

91 is less volatile but holds more energy, however to extract that energy you need a more powerful spark and higher compression (more heat) to get all that 91 is worth.


That's very dumed down but I personally don't feel like writing a small book on what I learned in AIT.

 

[vegeta1170]

Cars are tuned from the factory to many different grades of fuel since different states have different octane ratings at the pump. So putting in 91 octane or even 89 octane when your vehicle isn't tuned just for it, you would be wasting your money.

 

[AK Thunder]

This is kind of an arbitrary question, but at what point do you start to experience knock? Years, months?

The previous owner's wife of my Laser routinely put regular in the tank "because it was the cheaper option" and the owner's manual said regular was okay.

EDIT: does anyone have the original owners manual? I would think it would say to put in premium.

A buddy of mine has his owners manual from his N/T, said regular octane gasoline.
My owners manual, plus my dash and gas cap says premium, but im turbo'd

 

[Dhan]

A buddy of mine has his owners manual from his N/T, said regular octane gasoline.
My owners manual, plus my dash and gas cap says premium, but im turbo'd

Oops, I was referring to my turbo Laser. On the odometer it just says "unleaded only" and on the gas cap and gas cap door it also just says "unleaded fuel only". Kind of misleading if you know nothing about cars.

Sorry, should have been clearer on that one.

 

[scott90gsx420]

This is kind of an arbitrary question, but at what point do you start to experience knock? Years, months?

The previous owner's wife of my Laser routinely put regular in the tank "because it was the cheaper option" and the owner's manual said regular was okay.

EDIT: does anyone have the original owners manual? I would think it would say to put in premium.

I have my original manual and yep it says premium. It says 87 is OK but i don't go by OK. Especially in a modded car. You experience knock when the leading gases in a normal combustion stroke spontaneously explodes instead of burning in a slow expanding burn.
Knock is always confused with pre-ignition as they are closely related. Knock ALWAYS accrues after the spark plug fires where pre-ignition is before the spark plug. They are both destructive but pre-ignition is way worse and will kill your motor the first time it happens. Knock will destroy you motor but is much less likely to do it that fast. Because pre-ignition happens before the spark plug fires it forces the piston the opposite way of proper rotation. Detonation happens after the spark and therefor it pushes the piston the right way, but it causes massive jump in pressure and causes temps to go way up. Therefor as the temps go up you can cause pre-ignition or things to melt. Any knock is bad but a motor will last a long time with slight knock even mediam amounts of it but pre-ignition will kill the motor instantaneously.
That is a VERY SMALL explanation of it. If you got any questions ask and il answer them for ya

 

[DSM1G90]

I have my original manual for my Laser and quote:

"Only Unleaded fuels are to be used

Labels located on the instrument panel and behind the fuel filler door state: "UNLEADED FUEL ONLY".

CARS EQUIPPED WITH A TURBOCHARGED ENGINE:

Your car with operate satisfactorily on preminum unleaded gasoline having a minimum rating of 91 (R+M)/2. These designations are comparable to 95RON (Research Octane Number)

However, you may use unleaded gasoline with an octane rating of at least 87 (91 RON).

If prolonged heavy engine knocking (audible pinging) occurs on your car, consult your dealer."
......

6 bolt turbos had the lower 7.8:1 compression to allow the use of 87 octane in stock form. True, in modded forms, the higher octane fuels are then required.

7 bolt motors had their systems increased - 8.5:1 compression so that 91 octane was a mandantory fuel requirement in stock form.

Pre-ignition - is defined as the ignition of the mixture prior to the spark plug firing. Anytime something causes the mixture in the chamber to ignite prior to the spark plug event it is classified as pre-ignition. Carbon buildup on combustion chamber surfaces are a good cause of pre-ignition since that carbon builds up so much heat that the motor almost acts like a diesel since those form of motors rely on compression (22.0:1) to ignite the fuel.

Knock is when the timing is so far advanced that the spark fires the mixture early and the compression and heat fires the rest of the mixture (giving that metallic "pinging" sound) ..and turbocharged car systems do run their timings way far advanced when needed.

Thus, why the knock sensor is in place to retard the timing (a good 12*) to reduce knock when knock is sensed.

This is combated with the use of premimum fuels if too much knock is present due to early ignition timings.

-DSM

 

[scott90gsx420]

I have my original manual for my Laser and quote:

"Only Unleaded fuels are to be used

Labels located on the instrument panel and behind the fuel filler door state: "UNLEADED FUEL ONLY".

CARS EQUIPPED WITH A TURBOCHARGED ENGINE:

Your car with operate satisfactorily on preminum unleaded gasoline having a minimum rating of 91 (R+M)/2. These designations are comparable to 95RON (Research Octane Number)

However, you may use unleaded gasoline with an octane rating of at least 87 (91 RON).

If prolonged heavy engine knocking (audible pinging) occurs on your car, consult your dealer."
......

6 bolt turbos had the lower 7.8:1 compression to allow the use of 87 octane in stock form. True, in modded forms, the higher octane fuels are then required.

7 bolt motors had their systems increased - 8.5:1 compression so that 91 octane was a mandantory fuel requirement in stock form.

Pre-ignition - is defined as the ignition of the mixture prior to the spark plug firing. Anytime something causes the mixture in the chamber to ignite prior to the spark plug event it is classified as pre-ignition. Carbon buildup on combustion chamber surfaces are a good cause of pre-ignition since that carbon builds up so much heat that the motor almost acts like a diesel since those form of motors rely on compression (22.0:1) to ignite the fuel.

Knock is when the timing is so far advanced that the spark fires the mixture early and the compression and heat fires the rest of the mixture (giving that metallic "pinging" sound) ..and turbocharged car systems do run their timings way far advanced when needed.

Thus, why the knock sensor is in place to retard the timing (a good 12*) to reduce knock when knock is sensed.

This is combated with the use of premimum fuels if too much knock is present due to early ignition timings.

-DSM

Nice writeup. But detonation isn't always caused by to much timing advance. It is also caused by to lean of a AFR for the fuel your running or by to much compression(boost in our case). I run 2g pistons. I run 93 and will never put anything lower in it. NEVER
The knock sensor is very useful for stopping knock AFTER it's happened. As it happens over and over the ecu learns where its happening and then will over time adapt to the lower timing. But until that happens all it takes is 1 good detonation and your piston is gone.
I had issues with my tuning at first i had everything leaned out a lot not thinking about my 2g mas. It would idle a bit ruff but i didn't really think about it. But every time id jam it i would pull nice untill about 4500 then id see lean AFR and at the same time the car would just drop all power. Thats how I knew my timing was being pulled.
Just for your sake whoever reads this, If you are driving a boosted car, run the highest octane fuel you can.

 

[DSM1G90]

If you are driving a boosted car, run the highest octane fuel you can.

Like the Bugatti Veyron 16.4 .. W-16 with four turbochargers pushing the max of 1001 HP out of a 488CID (8.0L) motor

..and uses 100 street premimum octane at the price of 8 bucks/gallon.

Motor, in full explosive force can suck 15 gallons in less than 5 minutes...and push the car at 256mph in stock form.

Agree: full turbo mods needs the high octane fuels...

Drop this W-16 motor in your DSM and see what happens - you probably will not be able to control the car ever again .... rofl

-DSM