AcuraTLFan

I was browsing throught Honda's and Acura's website and found something i don't quite understand.

Gas octane rating, the higher the octane the less chance of detenation occuring due to high temp. So one might conclude, like i did, that the higher the compression ratio, resulting in more heat would likly require higher octane; however, this isn't the case.

Acura TL-P
Compression Ratio 9.8:1
Octane Premium 91

Acura TL-S
Compression Ratio 10.5:1
Octane Premium 91

New Honda Accord V6
Compression Ratio 10:1
Octane Regular 87

At first i thought, there's something wrong. Since the TL-P with lower CR require higher Octane then AV6 with higher CR. Figured that CR is not proportional to octane. But then i thought that Acura is 3.2 liter and Honda is 3.0 liter, so it's fairly close, shouldn't matter.

Does anyone know any factors or why the Accord would require less octane while the specs. are almost identical to a TL which require higher octane. I would understand if it required Supreme octane 89, but 87, the same stuff 4 cylinders Civic with 115 HP are using??!?!?

typeR

on the accord...apperantly the ecu can advance and retard timing based on fuel,so it doesnt "require" premium it just backs off timing...however add premium and you gain a reported 10hp/10lb.ft., the marketing here was we make "x" amount of power and only require regular unleaded....with the price of gas its a good idea...the TL/CL's however i dont think can turn back timing enough to not be adversly affected by low octane such as 87

ShaguraTL

Yes, the 240hp stated for the new Accord V6 is with 91 octane. The ECU was given a larger authority range on timing adjustments. Meaning it can retard the timing enough to handle 87 octane. The TL & CL ECU has a smaller authority range and can only compensate enough for 89 octane. It's range isn't large enough to handle 87. Granted, you can run 87 but you'll be detonating past 3,500 rpm or so.

Are there any companies out there that offer reprogramming services for the factory TL/CL ECU? If so, then they could increase the authority range a little further. Possibly enough for 87 octane. The only reason I can see why Honda/Acura didn't do this from factory is for emissions purposes. If you retard the timing enough, it hurts emissions and the EPA, etc. would be complaining. I'm guessing the new Accord has enough emissions control that it can get away with the more retarded timing on 87 without making excessive polution.

T Ho

Advances are being made in engine design (cooling systems, combustion chamber shapes, camshaft timing, etc) that are allowing higher and higher compression, with the same octane gas. The Civic Hybrid uses 11.3:1, and only 87 octane suggested per the manual. It's not just about the ability to retard timing. The ability to maintain tight control over combustion chamber jacket cooling, evenly at all cylinders, is a GIANT factor here in preventing detonation, and manufacturers are getting better and better. And that's good for power and efficiency. Increasing compression ratio by one full point will typically add over 5% HP, and gain fuel economy as well. The downside is that as compression rises, so does NOx emissions. That's one thing that's preventing them from going even higher right now- they could probably do an 11.5:1 to 12:1 Accord motor and require 93, if not for NOx emissions.

Heck, back in the '80s, you couldn't rely on 93 octane to prevent a 10.5:1 motor from knocking itself into oblivion.

ShaguraTL

Yes, very good point. I just assumed Honda would look for the easy way out rather than redesign a better cooling system, combustion chamber design, etc. I'm looking forward to the day 100+ octane will be avail at all gas stations.

::stabs at the voodoo doll he made of the EPA::

T Ho

Don't ever hold your breath for higher octane than we have now. I'd be surprised if it ever happens.

Higher octane fuel burns more slowly- that's the way it resists engine knock/detonation. It's not "better," it's just necessary for high compression engines. As engine makers learn ways around this, it's better all-around. Being able to run the lowest octane fuel in the highest compression engine is the way to go.

Todd

Ray_Khan

you can always find the stations who sell 100 octane Even better when you have an ECu that has program to take adcantage of 100 and 104 octane

T Ho

Running higher octane than an engine requires will not gain performance, regardless of ECU tuning. In fact, it can hurt it. I've personally tried this, and can confirm those results.

In other words, 100 octane in the TL-S may well slow you down, even with a new timing curve.

Ray_Khan

I'm pretty sure 100 octane is safe as it is unleaded...104 is leaded I believe and this will destroy your catalytic converters. I am willing to bet the TLS wil benefit from 100 octane. I believe the ecu will advance timing a little to compensate for the 100 octane. I'm pretty sure all the CLS guys (the ones with the better times) are running 100 octane at the strip. I'm not saying there is a night and day differnece with 100 octane, but I'd bet on about 10 hp or so.

I have some ecu mods to my car that help me benefit from runnign higher octane gas. I have special programs for running 100 and 104. But I don't have them in a TLS.

power3dfx

higher octane will give more power, i too have tested. but it can be dangerous, so its something you probably wouldnt want to do.
100+ octance usually costs 3 to 4 times as much as the 91, with those outrageous prices, you are better off getting an intake for your car or spending the money on another mod. better yet, save some gas and dont drive as much!

Gilgamesh

Doesn't running the higer grade also keep your fuel-delivery equipment generally cleaner as well?

T Ho

Interesting. In my "other" car, dropping from 93 to 89, after having the timing curve all over the place looking for the sweet spot, picked me up two tenths.

I'd like to see ECU data logs for various octanes for drag runs- knock sensor hits, timing variations, etc. How far are you running the timing up, and what are the increases at the track?

EDIT- to achieve anything over 100 octane, lead must be added.

Todd

ShaguraTL

I wasn't hoping to use 100+ octane in my TL...I know that won't yield any performance gain. I'm planning on buying a turbocharged car soon and if I turn up the boost, I'm gonna need more than 93 octane. I live in the northwest tip of Florida and haven't seen *ANY* gas stations around here with higher than 93. Oh well. I guess I'll have to go with octane boosters. Just trying to think ahead for the future.

AcuraTLFan

Thanks for the helpful info...didn't know that the ecu could modify the timing

Ray_Khan

which turbo charged car? As for octane booster, they are crap. Tolulene what seens to be the "octane booster of choice with teh folks I know. But don't add too much...it's not healthy to try to go from 87-100...I'd use it to go from 100 to something a litlte higher. Too much tolulene is bad for the car.

what equoment is used to log this? We have a nice way to do it with Audis, there is a guy who writes software that is basically an OBDII interface with a great graphical readouts and tools. It basically copies what the dealer OBD (VAG tool for VW and AUdi) tools can do. It's pretty nice and only about $150 for software and cable. So you can sit in the car and get some cool data logs on anytihng going on in the car with a laptop. It will even tell engine timing, but I don't know if it logs requested timing.

dean078

using 100 octane will not give you more power because the air/fuel mixture will still be ignited by the spark plugs at the compression ratio (actually, i think it's a little before the full compression ratio).

unless you have a variable compression engine to increase the compression ratio past 10.5:1, 100 octane won't do jack.

Ray_Khan

the engine control unit (ECU) control when the spark is ignited and how long the fuel injecter is spraying fuel (pulse width). It has a knock sensot to detect when the timing is causing knocking and it will then retard (pull back a few degrees) the sprark timing until no more knoching is detected. I'm not sure how the TLS meters air to determine correct pulse width.

Turboara

Octane boosters are worth crap, I remember reading several articles that they barely add 1 octane, even the "108 boosters". Like everyone said, putting over 91 in a stck tl may even impede performance, but on a supercharged or turbocharges car you could easily get 20+ hp with using racing gas. On my DSM, I run 16psi of boost on 93 pump gas, any higher boost and I get engine knock, which retards timing and detonation, as I see the exhaust gas temerature skyrocketing. With 100+ octane, I could run 21psi of boost with 0 knock. The difference in power between 16psi and 21 psi is insane. If you check around carefully, you may find a couple of gas stations or race shops that regularly stock 100+ octane in your neighborhood.

typeR

im not stock.but i always add a gallon or two of 105 GT plus unleaded (sunoco) and show improved times,this is added to a nearly empty tank...at ACL some are experimenting with lower tem Tstat/fan switch the fact is our car sees knock atleast moddified TL/CL-S' and alittle increase in octane seems to cure the KR

typeR

oh BTW the accord V6 is rated at 240 on 87 octane

sparky57

Hogwash. That is nothing more than good marketing. It is important, however, to find a brand that contains detergent additives and uses newer, well maintainted pumps. I avoid any pump that looks like it dates back to the Eisenhower administration.

Some older cars do require a higher octane gas than was originally specified due to carbon deposit buildup in the cylinders. Those deposits effectively increase the compression ratio.

rw

ShaguraTL

I'm trying to get my career in line first before I ditch my TL. I was going to get a 2003 WRX but now that the new Impreza (WRX and STi) were announced at noon this Monday, I'm definitely going to opt for the STi.

As for the octane booster, I was refering to tolulene. It's cheaper too (if you find the right places that sell it) than octane booster bottled stuff you buy @ auto stores.

My fiance is wanting a WRX for herself (how lucky am I to find a car chick eh?) In the hot florida heat, I'm not a fan of knock and more than 93 octane would give me a little piece of mind as detonation would be less of a worry. The top mount intercooler becomes a interheater when it comes to traffic in the summer.

Ray_Khan

I'm liking the STi myself.....but in building a house this year, i chose to keep my A4 and mod it. Not quite an Sti, but 300 hp nonetheless

T Ho

If you can see actual, real time spark timing, you can compare it with the "best case" timing map, and see if timing is being pulled back.

And you are talking about boosted cars. That's a different discussion than NA engines, with regard to the usefulness of higher octane.

dean078

Yes, it can retard timing (firing the spark before normal) to prevent compressing the air/fuel mix further.

Under normal circumstances, the engine will not retard timing and fire the spark close to top dead center of the cylinder (TDC = the max. compression).

using 93 octane, it will fire at this same optimum point.

using 100 octane, it will still fire at this optimum point.

the engine will not advance timing (fire after normal) just because you are using 100 octane, it will fire at the same time as using 93 octane. If you modify your engine to advance the timing and use higher octane, that would help, but then you won't be able to go back to lower octane.

the engine will not adjust this for you because you put in different gas, it will not know the difference unless the octane is too low.

typeR

you're close the car does see knock at higher temps/humidity and does have a couple of degrees of KR and so under these circumstances 100+ may bring timing to optimum

dean078

agreed...under those circumstances, higher octane would bring the timing to optimum.

but where does it add power? it just didn't lose it under those circumstances.


the case that i'm arguing is that under normal circumstances with a stock engine, using 100 octane over 93 gives you jack.

T Ho

Increased humidity will tend to reduce spark knock, not increase it. Wetter air slows the flame travel. I can actually tell this in the idle speed of my old Z28.
That description is backwards. If timing is changed from 15 deg BTDC to 10deg BTDC, it is said to be retarded five degrees. In "engine time" 10BTDC is after 15BTDC, not before.

*BTDC- Before Top Dead Center

Here's something not brought up- running higher than required octane and advancing the timing to try and get something from it also increases emissions. It can be substantial (2-3x).

dean078

when the car retards the timing, it will fire before the optimum compression because at the optimum (or near optimum) compression would cause the a/f mix to auto-ignite (cuasing engine knock).

according to you, 10BTDC is after 15BTDC, which means the compression at 10BTDC is higher than 15BTDC.

so according to what you said, if the timing is retarded 5 degrees the compression would be higher. why would the compression be higher when the spark plugs fire when it's being retarded? the spark plugs wouldn't need to fire because the gas would have already self-ignited at this compression.

it's been a long time since my thermo class, so I dont' remember the terminology, but seems like what you stated was advancing the timing (firing later rather than sooner).

dean078

and if you read my statement again, it doesn't deal with degrees (as i'm not an auto engine specialist and i'm not sure which way is which), but it's not backwards because if the knock sensors sense knock, it has to ignite the fuel at a lower compression, meaning that it will fire BEFORE normal/optimum compression.

T Ho

But, your understanding is mistaken.
That's not correct.
Engine knock is essentially the fuel/air mixture being ignited before the optimum time. If it happens too soon (meaning too long before the piston travels upward to TDC), combustion pressure peaks too early, and actually attempts to force the piston back down, AGAINST the rotation of the crank. The timing being over-advanced (again, too long before TDC) is one of the things that can cause this to happen.
You're thinking strictly in terms of compression, and not in terms of flame front travel, mixture ignition rate, and how it relates to the rotation of the crank.

dean078

you're right, it retards it to fire later in the comrpession cycle.

it's been several years out of thermo class, so i just vaguely remember this stuff.

wv5b

These cars can easily adjust their computer settings to any octane 87 and higher. The reason premium fuel is recommeded in some sports sedans is because they can advertise the higher horsepower that is produced by premium fuel. You can safely use 87 or 89 fuel and most people will never notice the difference. I burn 89 in mine. My daughter has an 03 honda accord v-6 and it runs great on 87. BTW. the nav. system on the new accord blows the old nav. system on my tl-s away. It responds to 180 voice commands and will even change the radio and climate controls by audible commands. It will respond to find the nearest atm, restuarant, hospital, police station and many more. It is awsmome and I think it has about as much pep as my tl-s.

PeterUbers

iTrader: (1)

So you're saying on premium this bad boy has the "potential" to produce additional hp??

WTF.... this '04 TypeS better be the shiznitz or I'll be embarrassed pulling up to a new Accord w/ a) better gearing in their 5-spd autos, b) about the same hp and better hp/wt ratios....

ugh, and it'll probably be a mom on her way to soccer practice!!!!!!!!aaaaaaaaaaaaargg

typeR

yes it's been reported that there is a 10/10 bump by going to premium...
peak numbers however are not the end all...the typeS still has a longer flater power band

PeterUbers

iTrader: (1)

this is true

enbe

higher octane yields more power as the bonds of the carbon will burn evenly rather than detonate; higher octane numbers reflect that more even and controlled burn.

Karanx7

iTrader: (2)

Thanks for your info. I'm sure he's been waiting 14 years for it.

enbe

And I personally would not want to do that; having driven both I prefer the response of the higher compression of the premium fuel. Drive both and the A-B will is noticeable easily.

justnspace

iTrader: (1)