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OK, tried doing the search and didn't find exactly what I was looking for so here goes........my question is do you need to upgrade your octane grade (other than 89 or whatever) if you have an aftermarket intake and exhaust only? Some say yes and some say no. I've been using 91 oct. (which I've read on here is a waste of my money), but am just used to it b/c that is all I can use in my Mercedes so I just continued that trend when I got this car. What is the general consensus?:dontknow:
 

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Well some ppl will say using 89 is the best for the car with no mods or alil mods. I use 93 in my car and i havent even put a mod on the car yet. I use 93 because it burns cleaner and I feel its better for the car. Same with the oil, in my past car i had a few mods, used 93 and used mobil 1 synthetic in it starting at 9000miles and when it was sold it had 70,000miles and still ran like new. Alotta ppl have diff opinions on this.
 

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It's preference. Higher octane has been dyno proven at least 2-3 HP across the rev board...at least on the EP's K20A3. Here's a direct quote from Hondata "In the graph above, the change in octane was worth about 2hp and the tuning 8-10." That's from the Civic Si K20A3 page. I've always used 91 octane (Highest we get here in Ca) because it's only a few cents more per gallon and it will prevent all detonation at the highest timing setting the computer can give before detonation. Not that it matters much but detonation leaves carbon buildup in your combustion chambers. Which in the future will give you poor performance if you plan on keeping the car long. I use 91 octane to prevent that as much as possible. But also the higher octane makes your car burn "dirtier" out the tailpipe though ;)
 

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Discussion Starter #4
And the other thing I've always "heard" is that using lower octane leaves a sludge at the bottom of you gas tank so if you let your fuel run low, you may essentially suck sludge into your system. Not sure how true that one is, sounds more like an old wives tale than a statement of fact. And no, I don't have anything againist the "elderly" or "wives" so keep the slams to yourself........LOL.
 

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I'd say 91; or in my case 93 here in GA, only with the Hondata ecu flash due to the advance in the timing.
 

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Discussion Starter #6
Does an Intake and Exhaust cause the engine to run any leaner due to the increase in airflow?
 

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From what I've heard 87 should be fine, I remember a while back reading an article about how oil companys spend millions each year promoting their high octane gas when in fact most cars don't need it. That having been said the dealership told that its best to use high octane gas, I fill up with 91 octane every so often and use 87 the rest of the time.
 

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YOU DO NOT NEED A HIGHER OCTANE.

87 Octane will run perfectly.

THE ONLY TIME YOU NEED TO GET A HIGHER OCTANE is if you purchased an ECU upgrade or have a Turbo or Supercharger!

And actually, 87 octane leaves fewer deposites than 91/93 because higher octanes have more detergents per part than lower octane. Lower octanes burn warmer and cleaner, higher octanes burn colder and leave junk behind because of the extra additives.

Some cars require a higher octane because of their compression or boost characteristics. A higher octane ignites at a higher temperature. If you put a low octane in an engine that has a high compression ratio then the compression inside the engine cylinder will ignite the gas before the spark-plugs fire. Engines with advanced timing (I.E. Hondata ECU mod advances engine time) will need a higher octane so that it ignites with the proper timing. Engines that are boosting increase compression because it jams more into the cylinders.

Intakes and Exhausts do not increase compression and do not advance timing.
 

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Higher octane does not increase horsepower, either. I've seen 3 back to back dynoes that have varied between 6 horsepower and 14 pounds of torque with under 5 minutes between dynoes and no change in condition or parameters.

You cannot tell me that 2 to 3 horsepower difference on a dyno was because of higher octane, that is ridiculous and has no grounds in any kind of chemistry or mechanics.
 

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89 octane will make the engine run "smoother", don't know about any power gains.
 

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James do you understand that our engines are equipped with knock sensors, and when the sensor sends a signal to the ECU saying it detects knock the ECU automatically retards timing and also makes VTC adjustments until the knock sensor reads no more pinging.

However, at WOT, the ECU advances timing as much as possible before detonation. With higher octane it's ability to advance the timing higher is greater than with lower octane. It also gives off more aggressive VTC adjustments too.

What Hondata does is set the "preset" timing higher than the factory setting so it's preset is always higher meaning the computer will adjust/retard from a higher timing degree than before. There are many debates on this but that's how I see it. Our OBDII cars are pretty advanced compared to OBD0 and OBDI cars. I'm an entry level Honda PACT student with a year left before my Honda certifications and that's how I was taught at Honda school ;)
 

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Summarize what DAVIDT just posted.

Daily Driving = 87

hitting the track = 91+

I don't think it's a wise idea running 91+ all the time
it can lead to problems because it leaves junk behind like James posted.
 

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The knock sensors, thanks to vibration and extreme engine noise, cannot detect knocks above around 6,000 RPMs.

THAT'S the reason you might be able to get away with saying you should use a higher octane when you're racing, because it will help ensure against knocking and give you peace of mind about your engine life. But higher octanes do not increase horsepower, they are unneeded for best performance on the track, and it doesn't give you better economy because it COSTS MORE even if you get 2 miles per gallon better you're still wasting more money than that will give you.

I am fully aware that the engine alters timing based on the fuel quality it detects, but I honestly do not believe that it will INCREASE valve timing beyond regular timing with a higher than adequate octane. If you affirm so, with your Honda schooling, then I'll believe you, but don't throw this out there unless you know for sure that it does. Because there is evidence to the contrary:

Some people are throwing dyno claims out that are nill, meaningless, and are well within regular dyno variances. So if it DOES advance timing with higher octane then it obviously isn't showing up on any measureable scale, and thus not a performance variable.
 

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James you are correct that each dyno run will be different, especially between 2-5 HP even on the same car because of engine down time, cool ins, etc etc. The Honda ODBII ECU is very smart and will infact retard/advance timing based on TPS, airflow, engine RPM, o2 readings, knock sensor readings, etc. Hondata is a very recognized tuning company and I believe them when they say it claims 2-3 HP on the dyno. It's not much, and yes you probably won't be able to feel it but it's something :) Like I stated before it's mainly preference.
 

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Uhm... it won't change timing based on airflow/O2 sensor readings. The ECU will change how lean or rich the engine runs, but it will not impact engine timing one iota.

Can you link me to this info from Hondata? I'd be very curious to see it.
 

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James S said:
Uhm... it won't change timing based on airflow/O2 sensor readings. The ECU will change how lean or rich the engine runs, but it will not impact engine timing one iota.

Can you link me to this info from Hondata? I'd be very curious to see it.
Wanna make a bet? The ECU can only go so rich or lean during a certain engine speed especially steady cruising because it's only getting a certain amount of airflow. It will retard/advance timing to help the situation, especially when the motor is running poorly.

Here is a link to Hondata's info: http://www.hondata.com/k20a3civicsirelease.html

It's the first paragragh under "tune notes" :) I didn't believe all the ECU mombo jumbo either until I hook'd up a Honda scanner to one of the 02 Accords and school and drove around with the scanner hooked up. The Honda scanner is trick, it gives real time reading of all the sensors, timing, engine speed, vehicle speed, it's really cool. To see all the numbers jumping around while driving :)
 
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