Octane Boosters

[BIG-G]

How many of you guys run an occasional octane booster?? Favorite brand??

I do it about once a week and always use moble 93 octane fuel. 4.0L H.O. 1995 bolt on mods; just incase u were wondering.

 

[RichP]

Why ? The 4.0 is not made to run high octane and the computer system is not setup for it. If you are doing it to cut down on knock then you have a carbon problem usually. A good cleaning with GM Top Engine cleaner, Sea Foam followed by a BIG bottle of Chevron Techron followed by a good off the engine throttle body cleaning is usually a good solution. Putting the occasional tank of 'high octane' is a waste of money.
I used to think I was 'treating and being nice' to my engines by putting in premium fuel then I started studying what high octane really does. That said, some of the fuel companies do put in more detergents but I think thats part of the higher octane rating additives, the increased detergents retard early detonation by glowing carbon deposits by making the fuel harder to ignite.
Back in the day I had a 427 in a 67 mustang, the compression ratio was 11.5:1 and it would not run on anything except sunoco 260 or amaco high test, it ran like crap with anything below 95 octane, the 4.0L in stock form is like 8:1
Some good info HERE

 

[BIG-G]

Well i have NO knocing. I just had a compression test done and got 160's on all 6 cyl ! Also had a head check and shes good 2 go 100%. So its mainly for an added jolt in acceleration and nothing more.

 

[Sarge]

Considering the higher octane burns slower I don't see how you get any extra acceleration either.

Sarge

 

[Cjmartz2k]

Higher octane won't do squat for acceleration unless you can adjust your timing to take advantage of it, which there is only one way to do an a 4.0--high altitude/adjustable crank position sensor (the later of which I have, and it's adjusted all the way advanced and I still run 87). Just run the lowest octane you can without it pinging. If you are dead set on it, however, just know those little cans you buy at autozone only bump it up from .1-.3 of a full octane number. Try looking for tolulene on the internet and read up on it.

 

[Cjmartz2k]

BTW, good info Rich. It doesn't get any more official than that.:thumbup:

 

[dmillion]

Well i have NO knocing... So its mainly for an added jolt in acceleration and nothing more.

Don't feel bad, because this is a VERY common misconception. But it IS a misconception. Higher octane fuel will do nothing for your acceleration, nor will it help your engine in any way (unless you have knocking or pinging problems). You should use the lowest octane fuel that does not knock or ping.

 

[BIG-G]

Ok, so no octane fuel snymore for my XJ.

 

[5-90]

No need - the basic compression ratio of the 4.0 (about 8.8:1) will run well on pretty much anything - and the dynamic compression ratio (taking into account cam duration) is even lower. Basic 87 octane is nearly too rich for the 4.0 - and most strokers, if set up properly for quench, should run just fine on 87 octane as well - unless you get silly with compression.

You don't need 89 octane until you start seeing dynamic compression of about 9.5:1 (not static compression - that's determined without accounting for camshaft dynamics. Dynamic compression is calculated as compression taking place AFTER the intake valve closes - and is a much more reliable indicator of fuel octane requirements,) and even that can be reduced by quench setup (creating a good deal of "swirl" in the combustion chamber - the idea behind the old Ford "HSC" - "High Swirl Combustion" engines) and keeping your engine from accumulating carbon deposits by using good gasoline (minimal crap) and keeping things cleaned regularly.

Detergent and cleaning additives are pretty much all the same for all grades of gasoline, and octane is often "improved" by blending - common octane improvers are acetone, toluene, and methyl tertiary butyl ether (MTBE.) Octane improvement is determined by the "blending" octane numbers of the fuel and additive, and the ratio(s) in which they are used.

I've been doing some fuel research for additions to my book, and it's amazing what you can find out with a little research - and access to university libraries...

5-90

 

[85xjwoody]

My 85 2.5 carbed engine I have always put 89 octane in with ten percent being ethanol. I used to run 87 but my jeep would run rougher at idle and the same at a steady highway speed. I switched to the 89 and have had no more problems like that. My question is did the switch make the difference or did something clean out of my fuel system and make it run better? Both of my engines have done the same on the 87 and 89. I use the same gas station everytime for my jeep unless I am up north wheeling and I usually have to full up once at a different station but show no differences. Sorry for the thread hijack but thought this post was close to what is already being talked about.

Kim.

 

[bjoehandley]

I've used some in my Turbo K's, but the only one worth waisting money on it is Nitrous Oxide System's booster in the blue box/can. All the other ones I tried killed performance in those cars. Haven't tried any in my '98 yet, but don't plan on changing anyhting in the motor to make it neccesary either.