View Full Version : Gas octane

08-09-2002, 09:37 PM
The other post reminded me to ask this. So i have a completely stock d16a6 Si engine, with only like 40K miles on the engine total in the last 11 years. I have ONLY run 87 gas on it since i got it, even during races. I have a CAI, header and gutted cat that eventually goes to a stock muffler. So when do you think I should start using higher octane gas? I am planning on installing a 89 integra ECU in and see what that does.

08-09-2002, 11:58 PM
Frankly, Tyson, I would be more than a little surprised if you found much praactical (or speed) advantage in running higher octane gas. Your car, in stock form, is pretty much engineered to run on plain ol' unleaded. My wife has a CR-V and only occasionally do we get a tank of cheap unleaded (we always buy the lowest grade available) that causes any kind of problem.

Something like the unleaded race fuels that you can buy are, in my experience, only valuable because they are less likely to contain nasty petrochemicals that refiners are trying to get rid of (including them is a common practice with pump gas, from what I understand) and batch consistency is better. Higher octane commercial pump gas is just as likely to include garbage chemicals - probably.

If you increase your compression ratio or change your timing, you might well reach a point where a higher octane would be required but, if the car's operating parameters don't require it, there is little if anything to be gained by running high-test gas.


08-10-2002, 01:54 PM
40k miles? Damn Tyson, I want your motor. Mine has like 120k!

B Breon
08-12-2002, 09:05 AM
If you still have your owners manual, check it, I think the manual calls for Premium. Have had ignition knocking on hot days in my street ride on 87 before but the motor had a lot more miles!

08-12-2002, 01:04 PM
actually i can run 86 if i wanted according to the manual.

08-12-2002, 07:57 PM
This is food for thought, as I am NOT familiar with the car.

Does the car have some method of knock detection? If so running low octane under load at high rpms might cause the computer to retard the timing. You would think that the low octane is fine (it's not pinging) when in fact, you are losing power.

If it doesn't and it's not pinging you will gain zero HP by using higher octane and not changing anything else.

Chris Sawatsky
08-12-2002, 08:28 PM
no knock detector on our engines.
I ran this weekend with a bottle of NOS octane booster in my gas tank (sponsor gave it to me to try free)
I ran slightly better than usual, but it may have been due to weather/tires/witchcraft etc

I would say there isn't much to be gained by using high octane fuel in a ITA crx

08-12-2002, 08:56 PM
120k jasonb? I want your motor. Mine has 188k and it's still going strong. Well, strong enough to finish anyway.

1994 Civic DX - ITA #93

08-12-2002, 09:17 PM
ok, this is gonna lead to another discussion, but what about advancing the timing? how much have you guys gone and tested effectively?

Jon Nelson
08-22-2002, 09:53 AM

Witchcraft? Sheesh... I need some of that! Perhaps you should try a curse on Dave! Or his right rear tire, at least....... BTW, have you heard how the gang made out at the Canadian GT championship in Calgary?

Seriously, though, you're getting pretty quick... get a proper set of sticky tires and you should be able to catch Dave.....or ME!!! (Assuming I can keep it on the track and near the front for more than a lap!!)

As for the octane, Tyson, get premium pump gas. Cheap insurance, especially under racing conditions, I don't think the factory recommendations accounted for race abuse.



Jon Nelson
08-22-2002, 09:58 AM
I re-read your post, Tyson...

Stock muffler?! No wonder you're car is overweight!!! Not to mention the power loss from using the stock exhaust!

I built a thin-guage stainless 2-1/4" collector-back system that saved me something like 15 pounds or so over a full steel system with a resonator and heavy chambered muffler. Supertrapp on the end for driving to/from races.


08-22-2002, 10:33 AM
Higher Octane doesn't = more power in and of itself. The Octane rating of a fuel refers to its ability to resist knock, based upon the stability of its hydrocarbon chains and the resulting number of free radicals. Running a fuel w/ higher resistance to knock allows one to run the motor with more ignition timing advance, higher compression (static and dynamic) etc etc...which in turn can allow you to make more power. But simply adding higher octane fuel w/o other changes will not make more power alone. This is why SCCA (via the GCR) does not categorize legal fuels by octane rating, but instead by Dielectric Constant. The DC is a measurment of the amount of hyrdocarbons in the fuel...which is what makes more power.


Greg Gauper
08-22-2002, 01:05 PM
Originally posted by johng:
120k jasonb? I want your motor. Mine has 188k and it's still going strong. Well, strong enough to finish anyway.

188K!!! I want your motor (for my parts car at least http://Forums.ImprovedTouring.com/it/smile.gif It has 220K miles and two cylinders are down to 60lbs of compression and it drinks a qt of oil every 300 miles.

Funny thing is, it sill gets over 30mpg which is 15 more than my truck gets....so the parts car will be run until it dies since I come out ahead $10 a week in gas money.

[This message has been edited by Greg Gauper (edited August 22, 2002).]

08-22-2002, 01:10 PM
If it doesn't and it's not pinging you will gain zero HP by using higher octane and not changing anything else.

yes, i realize where im at now higher octane isnt gonna do me anything, so what must change in order to utilize/necessitate higher octane... (im indirectly asking how to make more power people!)

08-22-2002, 05:49 PM
Allow me to join in here. Just finished a chat with Sunoco Race Fuels and their tech guru. I asked what would happen if I used GT100 unleaded in both my CRX and 99 Prelude. His answer was very simple-nothing bad as the computers will detect the change in burn point and adjust the timing. Race fuels are blended as a "pump-DOT legal" street fuel. The difference is that they start to burn at a lower temperature and will burn more completely than ordinary pump gas. Yes, you can blend it with your daily fuel as well. Race fuel also contains the required additive package and the DC (dielectric constant)check will read the same as pump. The Sunoco website has a lot of good info in the race fuel area. Do we need 100 octane in an Si 1.6 motor-probably not if it has not been race prepped. It is good to know that we can use it without harm during a track event. Will it increase performance-I suspect the answer can only be seen on a chassis dynamometer.
As to using 87 octane in any of my cars-forget it. The techs at my Honda dealership say to run 89 in both the CRX and Civc with their 1.6 D series engines. The Prelude requires 91+ fuel and has labels telling you this.

'96 Civic HB Just cruising daily
'99 Prelude=a sweet song in motion

08-22-2002, 07:50 PM
JC...i'm sorry but I just don't agree with much of what you posted. Our Computers are not magical, and cannot "detect a change in burn point" ??? they can only detect audible knock and retard the ignition timing a few degrees to try and stop it when octane is too low for the conditions.

For much usefull info on gasoline formulations and octane ratings and the effects of changing compression, timing, etc...I suggest you check out:


For a list of dielectric contstants of the most common race fuels go here:

www.ridgenet.net/~hideseng/dc_list.htm (http://www.ridgenet.net/~hideseng/dc_list.htm)

other usefull info is at:

From the SCCA board minutes in 1999 when fuel rule was submitted in some form.

From Nov 13, 2000 board meeting. Rule 17.4.1 corrected concerning fuel. It's about half way down.
http://www.scca.org/news/tech/club_racing/...g/11-13-00.html (http://www.scca.org/news/tech/club_racing/11-13-00.html)


Gord Galloway
08-23-2002, 10:34 AM
I will admit I run Premium in my cars. 2 reasons: 1-I have advanced my timing as much as the distributor slots will allow, 2-In the event of an overheat situation or a slightly lean burn situation (such as a momentary fuel starve) there is a less likely chance of lean detonation which could be catasrauphic. It may be overprcautionary and may not even work but for the few extra cents it costs it is worth the possible peace of mind.

Gordon Galloway
Honda CRXsi
IT2 #32

08-24-2002, 06:27 AM
Thanks for posting the references.
I only presented the position of Sunoco here. I will agree the computer in a CRX is not as sophisticated as one for a 99 Prelude. However, as far as I can determine the usefulness of 100+ octane in anything other than a race prepped motor is overkill without specific dyno numbers.

'96 Civic HB Just cruising daily
'99 Prelude=a sweet song in motion

08-27-2002, 08:12 AM
At a recent regional event I was suprised to see two of the top ITA cars (one integra and one a crx) using LEADED race gas! What's up with that?

Greg Gauper
08-27-2002, 08:46 AM
Leaded racing fuel is permitted it IT. In fact leaded racing fuel is more strict in terms of meeting the fuels rules. It's the unleaded pump gas that SCCA doesn't like cuz the additives and stuff can hide the rocket fuel . That's why 'pump' fuel isn't permitted in Production/GT/Formula. Only SS/IT/Touring where the O2 sensors are still in use.

The only thing I'm not looking forward to next year when I convert to Limited Prep G-Prod is that I will be forced to run leaded racing fuel in a 10:1 compression motor. I have been following the FF web site and a lot of those guys run AV gas (They have 9:1 or 10:1 motors I think) and some of the AV gas blends are legal. Good info over on FF/DSR/S2000 web sites regarding racing fuels, specifications, definitions, etc.

08-27-2002, 10:54 AM
Nothing wrong with using leaded race gas.
Advantages: Higer octane resists detonation;
Lead lubricates the valves

Diadvantages: Higher Octane makes less power(yes...but less octane promotes destructive detonation);
Lead promotes corrosion in exhaust systems.

Actually, I use leaded race gas (VP) for a strange reason--almost infinite shelf-life.

08-27-2002, 02:06 PM
Thanks for the info. I must not be as old and knowledgable as I think I am 'caus I still manage to learn new stuff every time out. I guess my point was that these cars use Oxygen sensors and the lead should kill them very quickly. Maybe with the single wire O2 sensors it doesn't matter that much?

08-27-2002, 04:36 PM
I forgot to add that as a "diadvantage"--contaminates O2 Sensors.

Actually, it doesn't destroy them because I understand you can clean the lead off the sensor with a torch or something. Also, it takes a while for the lead to affect the sensor. If you carry enough spare sensors and know their useful life as exposed to lead, it is probably not much of a handicap.

08-28-2002, 08:58 AM
Hm-I wonder about the question concerning the O2 sensor and its survival. Does anyone have any hard data on this? Sunoco has several different unleaded fuels that will not harm the sensors. The price of a sensor from Honda (wholesale) for my Si was $150 and I would not feel good about destroying it. Then again I also still have the catalytic convertor on the car as it is still street legal.
I too must not be as old and wise as my years would lead me to think-I also just keep learning every day.

'96 Civic HB Just cruising daily
'99 Prelude=a sweet song in motion

[This message has been edited by jc836 (edited August 28, 2002).]