ymeski56

Your not taking into consideration, different compression rates of the engines dynoed. A stock compression engine vs. a built engine w/ a high rate of compression will render two very different outcomes w/ 91 octane! One of their results will be rather dismal comparatively. Anybody want to guess which? And juxtapose, run the same two engines once more w/ 87 octane and see what happens! This time it's not going to be very pretty for the other one. Anybody want to guess which? As far as octane choice, the only thing these two engines have in common is they are in fact both internal combustion.

dr_bowtie

I agree with you ymeski56....

and when I get home today I will school all the others on Octane of fuels...but given your last 2 post you ARE 100% correct...Octane goes hand in hand with compression...and the lower the Octane the hotter the fuel burns NOT colder as many presume or assume

fuels have ranges of use just like camshafts have a range of use...this is measured in Octane ratings...

I would recommend you others research fuels and Octane and what it means and why 87 octane will make more power in a 8:1 compression motor and any higher will make NO difference...you can even build an engine to run 11:1 compression and live happily on 87 octane and feeding it any higher will NOT make any more horsepower...

Fact is...if you dyno an engine and it make more power on a higher octane fuel that tells you 1 important thing...the engine exceeds the fuel requirements for the lower octane fuel...or exceeds the octane requirements for the fuel it was using... in simple terms it was exceeding the fuel....

This IS YOUR JOB as an engine builder/assembler to know when this will happen....or you end up with broken parts racing and you end up blaming it on bad parts or something else when in pure simple terms you exceeded the fuel and it burnt up...Detonated!

ymeski56

What he said!!!!And there it is, in one big nut shell! This post of yours, aught to be a "permanent sticky." It's a hard act to fallow. I got nuthin! Ok, maybe one thing: "The correct octane should be viewed as use of the correct part, based on the individual application". Does that work? But if the general populist actually digested this post information, the forum would likely loose 1/2 it's troubleshooting posts. But there's always poorly maintained Transmissions to pick up the slack! I do wish your post became a permanent "sticky", as I'm really tired of turning into a ranting Evangelist every time the subject rears it's ugly head! That way we could refer them to the sticky. Although there will always be the few. Those that think the world is still, and will ever remain flat. It reminds me of an old polish saying, "Never try to teach a pig to sing. Your not only wasting your time, but your annoying the poor pig!" Anyway, well done, and have a great day!

dr_bowtie

I will try to make this as easy as possible....

1st of all let me explain Octane...the lower the number IE: 87 the QUICKER the fuel will ignite and the hotter it burns...on the other hand the Higher the Octane number the Slow the fuel is to ignite and the colder it burns...

the Octane rating of Gasoline or other fuels can quickly be derived from 2 parts...Compression and heat...The Octane rating of the fuel dictates how much Compression it can handle with Heat of the compression DIRECTLY related to it...

This means that 87 Octane can handle 8:1 compression with a higher cylinder heat rating than 89 Octane...

Now as you give the engine more RPM and it starts making power the cylinder temp elevates...the hottest point MUST be within the spec of the fuel or you get...? Detonation thats right...

87 octane will give you the best performance off the line but even 86 or even 85 will do even better...but the trade off is the heat rating...they simply cannot handle the same heat load....

As the Octane rating increases so does the heat range and compression the octane can support...this is why when you run higher compression you need higher octane fuel...simply to stay within the heat rating of the fuel at the engines maximum cylinder temps...

Now you ask can a lower octane support Higher Compression....simple terms yes...but to do so we MUST stay within the heat range...but we all know higher compression equals more power...actually it equals heat which in turn decides the power...Heat = Power...more heat more power usually...

Now since we decide we want to run higher compression on lower octane the simple thing to do is regulate the cylinder temp...but how do we do that? many ways...either dont run the engine into the RPM range where the heat will exceed the fuel....lessen the amount of ignition timing...but that makes less power all around and defeats using lower octane fuel...

The most common practice is to run the engine colder...IE lower Thermostat...lower engine temps mean lower cylinder temps normally...this is not taking into account racing or forced induction...this is stock normally aspirated engines...

So it is possible to happily run 87 Octane in an engine with 11:1 compression as long as you can control cylinder temps...there are much more factors that come into play as well like the "Squish" or "Quench" of the combustion chamber....

Basically like a camshafts Duration sets the Usable RPM range of the cam the Octane rating sets the Usable heat range of an engine...


But as I basically said the lower the Octane rating the Quicker and hotter the fuel burns but less pressure and heat it can handle....where as the Higher the Octane the more pressure and heat it can handle but slower it burns...

the difference would be like lighting 87 octane and watch it flash and then lighting Kerosene....but on a much bigger scale...

then there are fuels like Diesel with a very high rating that will not burn under its own....throw a match in diesel and it will go out...but atomize it and fireball...

Alcohol is a whole different breed...mostly because it is an Oxygenated fuel....

dr_bowtie

you got 2 different things going on here....performance injectors do very little differently than stock injectors...there are only 3 companies that make injectors and most are either low impedance or high impedance...

Stock are usuall high and aftermarket are generally low and the 2 cannot be interchanged...

even teh statement about the molecules and fuel pump have more to do with the fuel Density that Octane...

simply put you can cover up and Octane issue by feeding it more fuel or fuel at a different density...making a finer mist as you try to say does nothing for the Octane issue if heat keeps coming on...you will still exceed the fuel and detonate... you will just do it later in the rpm range where Damage will be more prone...the higher the rpm that detonation occurs the more damage will be done...

If you are running more compression and/or heat than the fuel can support the only approach is to step up the fuel...not add more...

Trapper

You probably meant to say Chemtool Fuel Additive and not Gumout. Gumout has several on the market and they all are petroleum based, not keytone based. Gumout with Regane is one of the best out there with Polyether Amine as the active ingredient. PEAs are in a lot of the better fuel cleaners as well as Stoddard Solvent types like BG44 or some of the Techrons. The Regane cost a small fraction of the others though and works just as good.

As you stated, acetone is also a plasticizer and can do damage to the plastic parts of the fuel system. It also is a great paint remover so getting any on the side of the truck certainly won't help the paint. As far as acetone relieving surface tension, in the lab it's possible but not in your fuel system. Any gains that folks "feel" from the use of it is probably that it is an almost instant solvent and it can clean a fuel system quick. Obviously, a clean fuel system and injection system is going to run better. Although acetone has a much higher octane rating, about 140, you'd need to add gallons to your fuel tank to effectually raise the octane level of the fuel in the tank. Adding 8 oz of acetone to a gas tank of 25 gallons (which is also 3200 oz) is not going to do much if anything to the fuel. The percentages just aren't in it's favor.

In regards to your comments about 87 gas burning hotter. There are about 119,000 btus in 87 octane gas. A 93 octane gas has about 127,000 btus. While theoretically the higher octane fuel has more energy in it, unless the engine is designed to use that octane level, it is wasted energy in an engine designed for 87.

While we are approaching this from different angles, I think we're beating the same horse with different sticks.

dr_bowtie

actually you have the BTUs backwards and off... the 87 Octane carries 125,000BTUs and they go down from there...but reamain around 120,000BTUs there isnt enough difference to make notice...

event eh addition of 10% ethanol it goes to 120,000 even though Ethanol is an Oxygen carrying fuel....


here is a good LONG read for info....

http://en.wikipedia.org/wiki/Gasoline

Trapper

The numbers I quoted were from Mobil Exxon SW Region office. I would never use Wiki as a reference as any idiot with a computer and able to type can post "documents". And a bigger idiot can get on Wiki and change the first idiots "documents". Not a good source of info. FWIW the US DOE shows BTU rating at 115,000 for all gasoline and ethanol at 76,000 absolute. I highly doubt that they take into consideration the 26 different blends that are formulated across the USA. Around here we have a max pump octane rating of 93 but a lot of areas in the higher elevations have only 91 because of the ethanol content or oxygenates.

dr_bowtie

wiki was just the easiest and simplest for the general public to understand....doesnt matter really where the info comes from as long as it is relatively truthful.

we have 95 octane at the pump....but we also have 100, 104 and 108 at select gas stations....100 can be put in your tank while 104 and 108 cannot....it is off-road use only....

we have to get 112, 114 and 116 from a dealer....I run 114 in my car with 13.8:1 compression..

racin4ds

iTrader: (1)

dr bowtie and trapper- are you guys chemists by chance??