pimpin-tl

Nah, meet Mike Murillo. He is a friend of mine. He ran the fastest street legal mustang down the track.

Atrain

Abnmarine,

Yes, that's the J-Man.

He knows the know for sure.

A-Train

Abnmarine

He wrote the codes for the Mustang's computer. He tuned my car in under 30 minutes with impressive results.

Atrain

Jerry knows more about the Ford EEC-IV & EEC-V systems than anybody on the planet.

We had a long talk about octane and guess what he had to say?

End of story.

A-Train

SouthernBoy

Ah yes, the EEC-IV ECU. My '88 Mustang used this system and it was the last year for it. The '89's went to Mass Air with the EEC-V.

Atrain

Southernboy,

That is incorrect.

The 5.0L Mustang received mass air in 1988, however the EEC-IV was still in use all the way to 1995. In 1996, when the Mustang switched to the 4.6L V-8, the EEC went to EEC-V and OBD-II.

FYI, The 1994 T-Bird used the 4.6L V-8 with EEC-V and OBD-II. Yeap, OBD-II on the '94/'95 T-Bird LX. We were the test mules for the Mustang.

Now the Mustang uses the Black Oak Processor (aka Spanish Oak).

A-Train

SouthernBoy

I am going to have to disagree with you on the 1988 302 Mustang LX. Mine did not have MAF.. it had the speed density system. I have a bunch of writeups in my basement (magazines) about this. But I do have to tell you that my '88 302 LX most definitely did not have MAF.

Abnmarine

Here are a few pics of my last Mustang. Made 750 rwhp on 93 octane. It started as a 4 cylinder the day I bought it. Ended up selling it last year for 15k. I'm out of the stang scene now.

Abnmarine

Oh and I did all of the work myself to include the paint.

Atrain

Abnmarine,

I stand corrected. Speed density was used up to 1988. They switched to mass air in 1989.

The EEC-IV however was still used until 1995 for the Mustang.

Nice car.

A-Train

rbpeirce

I have an RL, NSX and a Prelude. All specify 91 octane. In the Pittsburgh area, and I suspect in most parts of the country, I have a choice of 87, 89, 93 and sometimes 94 or higher. I always burned 89 and have never had a problem. I have been told there is a slight drop in horsepower, but I can't say it is noticable.

rbpeirce

That's not entirely true. Modern engine management systems can adjust to different octane ratings, within limits. If the car calls for 91, there is almost no difference going to 89 but a greater difference going to 87. OTOH, there will be an improvement on 93 or 94. I have heard, but not tested, that there is improvement all the way up to at least 100. However, it isn't sufficiently important to me to make it worth the extra money unless I am going to the track. Even then, I never run more than 93.

Atrain

rbpeirce,

Look I don't know how else to say this. Higher octane does not add more power, period.

What determines power output of ANY gasoline engine is how efficiently it burns fuel. 99% of cars cannot detect octane. Many cars can ONLY detect knock and retard the spark timing which reduces power. If the knock goes away with higher octane fuel, the PCM adds back the spark timing.

You don't gain anything, you get back what you lost.

That is a blanket statement.

My car requires 93 octane fuel since it was dyno tuned to use premium 93 octane fuel. If I use 91 octane or lower the engine will knock and I'll crack a piston ring land. I've done it before and hypereutectic pistons are very unforgiving.

I have also tested with 100 octane unleaded race fuels from Sunoco and they have never added any horsepower by themselves. Only when more spark advance can be dialed in (if possible at all).

A-Train

rbpeirce

Which is one of the things modern engine management systems do. I'm sure there are limits, and I am talking about stock cars, not modified cars, but every Honda/Acura automobile I have ever owned could run fine on slightly lower octane gas and could run better on slightly higher. I can't comment on extremes. All I am ssaying is you can use 89 and you can benefit from 93.

Atrain

rbpeirce,

Back up your statement with facts. Show me the hex code from the Honda ECM that allows it to detect octane and dial in more spark timing.

I have never seen any production vehicle that runs on gasoline use a PCM that could detect OCTANE and dial in MORE spark timing based on say 116 octane fuel.

The cars today cannot detect octane they simply dial in more spark if knock IS NOT present. That is not gaining over the baseline. You are receiving the claimed power the engine can make, not any more.

I've had Lincoln Mark VIII guys argue with me in the same matter. They claimed the SOTP meter (seat of the pants) went up when they added more octane. What they didn't know is the cars are into the KS from the factory and adding more octane stops the KS from triggering. That dials back in the spark timing it was supposed to have from the factory.

NO extra power is made, just what was advertised before some final programming was made to the FN10 chassis.

A-Train

rbpeirce

I can't back it up with code. It is anecdotal.

What I have read, which may in fact be wrong, is that the engine management system can detect knock and adjust the spark accordingly. I have also read, again perhaps in error, that Honda engines have the capability to produce more output on slightly higher octane fuel. I specifically used a range of 87-93, which is all I have read about. I have no idea what would happen with 116, but I can't imagine it would be any more than whatever the maximum is.

I imagine, although I don't know, that there is some limit to how far the system can advance the spark. For all I know, the thing is set at 93 or 94 or whatever and when we use the suggested 91 octane fuel the spark gets dialed back to prevent knock. However, I don't know if that is the case either, and I don't know why the factory would resort to such a practice except possibly to keep horsepower below some target level.

I agree that the useable octane rating is a function of the engine, where it might tend to knock and what adjustments can be made to prevent that. Unfotunately, I lack the necessary specifics to know exactly what goes on in a Honda system to do that.

SouthernBoy

Advancing the "spark" (initial timing and therefore spark advance) beyond the capabilities of the fuel in an engine of a given design and in a given state of tune will bring on the onset of pre-ignition. For example, my 1988 Mustang LX 302CID (5.0 for you liter lovers) was the last car I have owned where you could manually advance or retard initial timing. Just like the "old" days, you loosened the distributor yoke, then using a timing light pointed at the timing marks on the crank pulley, you turned the distributor to the desired setting.

The factory spec on that car was 10 degrees BTDC. I set it to 12 degrees since I had a setup that cooled the intake charge. This increased throttle response and yes, made more power. But there is a limit to how far I would be able to set the timing. For a short while, I ran a Hyper-Tech chip which required you to set your timing to 8 degrees because it would take over and jump the timing significantly. Not good for normal around town driving but not too bad for WOT runs. Still it was not the best chip and I soon removed it and went back to my 12 degree setting.

The point here is that manufacturers design their engines and ECUs to get the most out of the installed environment (your car and all of its hookups like intakes, exhaust, etc) and to do this while being able to give the best possible performance over the very wide variety of conditions found in street use. If they have spec'd the engine to operate best at 12 degrees initial advance, this may equate to, say, 22 degrees total advance at full throttle (this is an example, friends). In order for the engine to deliver with this timing, it requires a certain grade of fuel to be used. If you lower the grade, as in less octane, the ECU will sense this when the engine is put under load conditions, such as WOT and instead of advancing the timing to 22 degrees, it may only advance it to, say, 19 degrees. It does this if it detects ping or knock. Once this occurs, the ability of the engine to produce the power it was designed and tuned to produce is reduced.

Now if you were to use 104 octane fuel, your engine will still not advance the timing beyond 22 degrees (again, our example here) because that was how it was tuned to operate. So what happens is a loss of power and greater fuel consumption, along with more carbon buildup and more unburned fuel exiting the exhaust to be burned by the cats, because of the higher octane fuel's reduced volatility.

So if your engine fuel recommendation is 91 octane, that is the grade of fuel that the manufacturer had found to be best suited to allowing the engine to operate at its most efficient and satisfactory manner where all of its performance features can best be utilitized.

Atrain

SouthernBoy,

I agree 100%.

A-Train

SouthernBoy

Thank you A-Train.

I would like to add that temperature also plays a roll here. Cooler temperatures mean more molecules of oxygen per cubic foot of air. This forces the ECU to increase the fuel shot to try to maintain the desired ratio of approximately 14.7:1 (air to fuel). It will also advance the timing a little to take advantage (i.e. start the burn earlier) of the increased air/fuel mix. This means more power and an increase in throttle response... at the expense of lower fuel milege. This is why modern cars get better gas mileage in the warmer months.

Also, I suspect a lot of people may not be familiar with the term,"state of tune" when speaking about an engine. This has nothing to do with a "tune-up". What it means is everything from the compression ratio to camshaft timing, lift, and duration, to inake and exhaust design. In other words, state of tune is the state of your engine as installed in your car.