87 vs 93
- Thread starter zach98
- Start date
rdss
Junior Member
severous01
New member
o wow....another one of these???
there's a lot of speculation on running high octane vs low. personally if you're not tuned, there's no reason to run high. the difference in octane ratins is DETONATION PREVENTION...that's it. it burns slightly slower to prevent detonation in increased timing for TDC. the higher the octane rating, the further before TDC you can go with spark, and the bigger the 'boom' due to compression of ignited fuel within the cylinder.
for example...a 350 v8 engine that has a CR of 9 psi and has a timing setup of 19* BTDC will yield about 250hp/torque. increase compression to 11 psi and you get about 315hp/tq. that same 11 psi and bump timing to 29* will give you a required 93 octane and about 400hp/tq
so, the CR of the v8 was theoretical (actual CR depends on the engine builder, heads, pistons and whatever else) but the CR issues was really a way to introduce boost...and the timing issue was relative to going from 87-93.
ALSO...timing is a major player on fuel economy. fuel starts burning BEFORE maximum compression is reached, and forces the piston down harder/faster...using less fuel due to expansion of gasses happening sooner in the up motion of the piston. in this case you ask 'why cant i just bump timing on regular fuel'...well, that's where detonation comes into play. 93 octane is 93% resistant to detonation. 87 is 87% resistant to detonation. i use resistant loosely here...as it's hard to explain octane...WHICH IS WHY YOU NEED TO RESEARCH IT...
if you get better running/performance with high octane you most likely have an issue with detonation/misfire. you 'may' get better economy with high vs regular. and you 'may' get smoother running with high vs low. personally it's all a 'butt=dyno' situation and is more or less a percieved notion than actual numbers/performance. but to each his own, do as you will, and good luck with your choices.
there's a lot of speculation on running high octane vs low. personally if you're not tuned, there's no reason to run high. the difference in octane ratins is DETONATION PREVENTION...that's it. it burns slightly slower to prevent detonation in increased timing for TDC. the higher the octane rating, the further before TDC you can go with spark, and the bigger the 'boom' due to compression of ignited fuel within the cylinder.
for example...a 350 v8 engine that has a CR of 9 psi and has a timing setup of 19* BTDC will yield about 250hp/torque. increase compression to 11 psi and you get about 315hp/tq. that same 11 psi and bump timing to 29* will give you a required 93 octane and about 400hp/tq
so, the CR of the v8 was theoretical (actual CR depends on the engine builder, heads, pistons and whatever else) but the CR issues was really a way to introduce boost...and the timing issue was relative to going from 87-93.
ALSO...timing is a major player on fuel economy. fuel starts burning BEFORE maximum compression is reached, and forces the piston down harder/faster...using less fuel due to expansion of gasses happening sooner in the up motion of the piston. in this case you ask 'why cant i just bump timing on regular fuel'...well, that's where detonation comes into play. 93 octane is 93% resistant to detonation. 87 is 87% resistant to detonation. i use resistant loosely here...as it's hard to explain octane...WHICH IS WHY YOU NEED TO RESEARCH IT...
if you get better running/performance with high octane you most likely have an issue with detonation/misfire. you 'may' get better economy with high vs regular. and you 'may' get smoother running with high vs low. personally it's all a 'butt=dyno' situation and is more or less a percieved notion than actual numbers/performance. but to each his own, do as you will, and good luck with your choices.
severous01
New member
personally i use 93 octane. also, i get an average of 2.5mpg better with 93. now...yes it's colder outside, and most of the time i'm not using AC,
theoretical...if the ac uses 30% power to run ac, and it cycles 50% of the time...i get a net gain of 15% fuel economy for just turning off the ac during the winter.
also, i installed an injen CAI a few weeks ago. my car also has only 5000 miles on it and i'm sure it's just broken in because until about 1000 miles ago i was steady 27mpg, and am now running 29.5...and it's steadily goin up about .2mpg/tank
theoretical...if the ac uses 30% power to run ac, and it cycles 50% of the time...i get a net gain of 15% fuel economy for just turning off the ac during the winter.
also, i installed an injen CAI a few weeks ago. my car also has only 5000 miles on it and i'm sure it's just broken in because until about 1000 miles ago i was steady 27mpg, and am now running 29.5...and it's steadily goin up about .2mpg/tank
severous01
New member
yeah....it's hard to teach someone octane/cetane ratings if they have no idea about compression, timing, valvetrain, adjustable cams, or whatever else. i always relate to the SBC/SBF issues. mostly because they're basic and will always remain the same.
also the 'showdown' is full of a bunch of useless posts and opinions. i got to page 3 and couldnt read any more.
Octane rating - Wikipedia, the free encyclopedia
Octane ratings explained
The Low-Down on High Octane Gasoline
Octane Ratings - What Should I Know About Premium vs. Regular Gasoline? - Epinions.com
also the 'showdown' is full of a bunch of useless posts and opinions. i got to page 3 and couldnt read any more.
Octane rating - Wikipedia, the free encyclopedia
Octane ratings explained
The Low-Down on High Octane Gasoline
Octane Ratings - What Should I Know About Premium vs. Regular Gasoline? - Epinions.com
severous01
New member
there's no sensor for fuel rating in the sonic. you have the e85 setup, and you know you had to enable the fuel rating option and install the sensor. stock ECM is a wonderful thing and can do many things...but without the sensor it can do NOTHING. so sarcasm out the window and useless info down the drain...the stock ecm is limited to program from the factory. and that's 87 octane...no matter how far the knock sensor and fuel parameters go, it will never go above or below 20% from factory settings in the o2 sensor monitors without setting a SES light.
severous01
New member
i'm outta here...if the OP wants my opinion...or anyone else for that matter i wont be returning here and you can PM me
octane is a HEATED DEBATE and has been since someone decided to say 'i get better performance/mileage with premium vs regular'...and all the zombies flollow. without flex fuel and the sensors involved a factory tuned car will NEVER get 'better' fuel economy or performance with permium fuel. it will always inject a SPECIFIC amount of fuel a SPECIFIC amount of time at a SPECIFIED timing interval NO MATTER WHAT...based on conditions from all sensors involved in the SES system. if you get out of those parameters for ANY reason you will get a SES light with a trip code (higher or lower doesnt matter).
it's simple, easy, and reliable. your engine will not 'assume' that without a knock sensor it can increase timing and boost performance. it doesnt work like that. it works how it's programmed and that's set on parameters based on a specific fuel rating for a specific engine/car combo...set from factory. if you change it good. if not...still good. just because you put better/expensive fuel in the car and you do a simple mpg test proves nothing except you had a better day/week/month with that tank than the last. temp, elevation, pressures, throttle response all matter. the possibilities are endless.
octane is a HEATED DEBATE and has been since someone decided to say 'i get better performance/mileage with premium vs regular'...and all the zombies flollow. without flex fuel and the sensors involved a factory tuned car will NEVER get 'better' fuel economy or performance with permium fuel. it will always inject a SPECIFIC amount of fuel a SPECIFIC amount of time at a SPECIFIED timing interval NO MATTER WHAT...based on conditions from all sensors involved in the SES system. if you get out of those parameters for ANY reason you will get a SES light with a trip code (higher or lower doesnt matter).
it's simple, easy, and reliable. your engine will not 'assume' that without a knock sensor it can increase timing and boost performance. it doesnt work like that. it works how it's programmed and that's set on parameters based on a specific fuel rating for a specific engine/car combo...set from factory. if you change it good. if not...still good. just because you put better/expensive fuel in the car and you do a simple mpg test proves nothing except you had a better day/week/month with that tank than the last. temp, elevation, pressures, throttle response all matter. the possibilities are endless.
smsfabrication
New member
The car runs smoother, is more powerful and gets better mileage on 93.
Its verifiable through many sources. Regardless of how many Chevy V8s you want to bring up, my Sonic gets 4mpg better and runs 16psi, not 10, on premium. So that's what I run.
Its verifiable through many sources. Regardless of how many Chevy V8s you want to bring up, my Sonic gets 4mpg better and runs 16psi, not 10, on premium. So that's what I run.
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sx sonic
New member
I believe the dual map Eric was talking about is seperate of the alochol sensor system. From what I've gathered the intial startiing map is more aggressive (for 91+oct or possibly running closer to absolute ideal for 87 w/o margin for error bad gas, high int temps, etc). Then if the ECM detects knock it triggers a less aggresive/pulled back map, and then if knock is detected it will pull timing the conventional way. I've heard filling the tank is what resets the system back to the more aggressive map.
Note that is just an educated guess on my part based on what I've read with some insight added in.
I was a skeptic of this feature on the sonic as well but after seeing a dyno chart posted by what I consider a reliable/unbiased source I now believ otherwise.. pretty sure it was LaborSmith who posted it from a dyno run he did stock. 1 on 87 one on 91/93 and there was a 10-20hp difference.
And as you know octane does not have a direct impact on power by itself I then became a believer, well sorta and atleast in regards to the dual map programming.
Personally I've never felt a difference or seen any quantifiable difference in my MPGs but I will acknowledge their is a possibilty for higher octane to yield better results.
Not disagreeing with the majority of your post severous, just pointing out a possible/likely awnser for yoye debate as regarding our particular cars. Also thanks for the links, I dig that sh!t
-tyler
Note that is just an educated guess on my part based on what I've read with some insight added in.
I was a skeptic of this feature on the sonic as well but after seeing a dyno chart posted by what I consider a reliable/unbiased source I now believ otherwise.. pretty sure it was LaborSmith who posted it from a dyno run he did stock. 1 on 87 one on 91/93 and there was a 10-20hp difference.
And as you know octane does not have a direct impact on power by itself I then became a believer, well sorta and atleast in regards to the dual map programming.
Personally I've never felt a difference or seen any quantifiable difference in my MPGs but I will acknowledge their is a possibilty for higher octane to yield better results.
Not disagreeing with the majority of your post severous, just pointing out a possible/likely awnser for yoye debate as regarding our particular cars. Also thanks for the links, I dig that sh!t
-tyler
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