89 octane

BrentSC

Registered User
i put 89 octane fuel in my SC by accident and it seemd like it ran just fine, do i really need to put 92+ octane in it? is there a difference? thanks

brent
 
i run 91, its the best i can do in california

but, i have heard, that with a lower ctane rating, your car may be more likley to ping, or detonate, causing problems down the line. like bad headgaskets..

this is only what ive read on this board, never tried it myself.
 
Gas

I tried mid level gas in my 92'.....................ran ok.

Didn't have that "edge" you feel with premium gas.

Mixing mid and premium don't give good results either.

At $3.39 for the moment, I'll bite the bullet and go for the octane.

Might try adding octane boost and see what it does.
 
I got some BAD 93 octane from a station in SC recently.....

My engine sounded like it was gonna lose it's guts when you went WOT.....:eek:

I put a bottle of octane booster in and it ran alright for the rest of the tank.....
 
There's usually about a 20 cents a gallon difference between low octane and premium fuel. For the prce you pay to buy a bottle of octane boost; you would be better off just to pay for the premium fuel.
 
yeah its probably worth it to bite the bullet and go with premium to aviod future problems. thanks guys
 
If you look at the cans, Octane booster provides only Point increases. So that 89 octane with a 4 point increase becomes 89.4 octane. Um, not worth it.

89 octane won't provide the necessary detonation protection necessary for WOT runs with the standard SC motor. It may require more timing to be pulled than the knock sensor is able to have be done.

Since you can't assume you will always find 92 or 93 octane fuel, the EEC has support for the Octane plug. this is a resistor plug hooked into the harness. If you pull this plug, the EEC will retard timing across the board by 4 degrees.
Here is a thread that tells you where it is:
http://www.sccoa.com/forums/showthread.php?s=&threadid=6782
 
Store bought octane boosters are worthless, not enough quantity. Take a tip from Formula 1, use Toluene. You can get it cheap if you buy it in 5 gallon drums. It is what is in the octane boosters you buy at the store. Not sure that it is any cheaper than just buying premium, but if you need higher than 93 (or 91), its an easy solution.

Jason
 
Also, when the computer pulls timing, it's unfortunately because knocking was detected (sort of a reactive approach). So, although the knocking was only momentary until the timing was pulled, there was still some knocking which can eventually damage the head gaskets, etc.
 
Posted by someone who is smart. And by smart, I mean, if I knew 1/10th of what he knows, I would die a happy man. (and this isn't just theory)
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I've never liked octane boosters as a substitute for race gas, but given the number of people who send e-mails asking about them it's apparent that people want to know more. They will never replace the real thing, but octane boosters can be useful at preventing knock if you only need to raise the octane a few points, but they come with a host of caveats.

The pros:
- Conveniently located at your local dealer or auto parts store
- Easy to transport
- They are cost effective if your octane needs are minimal

The cons:
- Most boosters raise the RON octane more than the MON octane, which
makes them fairly useless for most race applications, or high load
high heat situations
- Most of the better additives at this point are either Toluene or MMT
based. Toluene has the advantage of being relatively cheap, and fairly
effective at raising the octane even in fairly high percentages. Plus
it has good resistance to pre ignition which is an important consideration
in a two stroke. The downside is as you raise the percentage of Toluene
(or most aromatic hydrocarbon based additives) , the throttle response
quickly becomes flat and mushy. The snap goes BYE BYE.
So the engine won't knock, but it probably won't run worth a damn either.
- MMT based boosters (the most common today) quickly reach a point of
diminishing returns (i.e. the more you add the less it helps)
- Organometallic boosters like MMT can cause a huge increase in engine
deposits, and increase the risk of plug fouling and pre ignition
- Most boosters tend to kill the throttle response and make it
difficult to jet. Mix in the constantly changing base fuel your mixing
it in and you have a constantly moving target.
- Most octane boosters (especially toluene based) have high solvent
properties which can raise hell with reeds and crank seals in two-strokes
- If you need to raise the octane a significant amount, octane boosters
are much more expensive and much less effective than race fuels

There's more to it than this but I'm sure you get the point. Basically
it boils down to this, if your engine only needs a small increase in
octane as a safety margin then using octane booster is still better than blowing it up, but you'll likely give up throttle response for the
convenience. If you need a large increase in MON octane you won't get it from octane booster without paying more than you would for real race gas in the first place, plus it will run BAD. No snap, and an impossible to read plug.

During some testing with VP "Octane Power Boost" (MMT based) on my YZ417 (13.25 :1 CR). I've also noticed a reluctance to start when the engine is cold, although this may be application specific. The throttle response isn't as good as running
VP-C18 or C-12 but it doesn't knock, and the power you give up on the top end would only be noticeable to guys running flat out all the time.

Even though I hate to recommend octane boosters, if you have to use them here's some things you can try in order of my preference based on my testing on a 92mm stock compression YZ400, and a 94 mm 13.25 compression YZ417. I used Amoco Premium MTBE based (non-alcohol) as my base fuel in all tests, which were done in fairly warm 80-95 degree weather. My results probably aren't really useful to anyone who isn't running a similar combination, but they hopefully will shed a little light on the subject.

VP - "Octane Power Boost" - MMT based mixed 1 OZ./gal.
Pretty good throttle response once you get the jetting sorted out which tended to lean out on this combination. This was probably the closest to good race gas that I've seen. Raising the percentage of VP quickly killed the throttle response and made it much more difficult to start cold. This would be a reasonable choice if you can't get race gas or just feel cheap. Street price $10 for a 16oz bottle.

Snap "The Outlaw Racing Formula" - MMT based mixed .75 OZ./gal. Reasonable throttle response not quite as sharp as the VP additive but close. Jetting tended to lean out on this combination. Raising the percentage killed the throttle response and made it much more difficult to start cold. This is easy to find at most auto parts stores and speed shops. Street price $10 for a 16oz bottle.


PJ1 - "Gas Energizer Octane Plus" Toluene based mixed 2 OZ./ gal.
Throttle response is fairly soft when mixed at 1 OZ./gal and gets worse as you increase the percentage, jetting tended to less sensitve to this additive. Top end pull was a better than the MMT based additives at 2 OZ./gal. I've heard that this product has been discontinued, but no confirmation at this point. Street price $6 for an 18oz bottle.

Maxima - "Hi-test Octane Booster" mixed 2 OZ./ gal.
This appears to be a Toluene based additive, but Maxima doesn't list the specifics in their literature. Like the PJ1 additive throttle response is fairly soft when mixed at 1 OZ./gal and gets worse as you increase the percentage, jetting tended to be less sensitve to this additive. Top end pull was a better than the MMT based additives at 2 OZ./gal. Street price $4.50 for a 16oz bottle.
 
IF if you want more on the "why"

-----------

The octane rating of a fuel will give you no indication of the combustion speed , regardless of the way the octane number was attained.

It’s common practice for writers in popular press to summon the gods of combustion speed to try and explain the magic powers of toluene, acetone and any number of octane boosters and Home Depot speed secrets they are trying to foist off on an unknowing audience. They’ll tell you that these compounds raise the octane of the fuel and as a result slow down combustion and fend off detonation as a result. It’s just more pseudo-science BS from people who would have done well to pay more attention in Chemistry 101 in high school.

Real combustion events follow the real laws of chemistry, and while it’s a pretty complex set of interactions there are a few things that are easy to explain and understand.

It's a commonly held misconception that higher Octane fuel slows down the flame speed, which keeps the engine from knocking. What a load of crap.
A fuel's laminar Flame speed (basically fuel burning without the influence of combustion swirl or tumble) is a function of fuel chemistry (specifically Hydrogen/Carbon ratio), not the Octane rating.

The Hydrogen/Carbon make up of the fuel will determine it’s flame speed and the energy release whether it's a high-octane fuel or not. You can have fast and slow burning high octane fuels, but in most cases the differences are so slight as to not be an issue.

The heat of combustion at a simple level is basically a function of combustion efficiency and the calorific (energy) value of a fuel. There isn't a lot of energy difference between most conventional fuels, but combustion efficiency can sometimes be improved with race fuels so a bit more heat release is possible. Overall it's pretty much a wash in most cases though.

In other words, you aren't going to change the energy release or the speed of combustion in any significant way by switching from 87 to 110 octane gasoline, or anything in between . If you lose or gain power by switching fuels there are other things at work.

The way octane influences knock has to do with the way fuel is burned (well it’s really REACTED in the chamber) in the combustion chamber. The components in higher-octane fuels are less likely to have weak molecular bonds that can break easily and form active radicals. Higher-octane fuel is just made up of components that are (for lack of a better term) stouter under high temperatures and high cylinder pressures. Things like our long lost friend lead and metallic additives like MMT (common in octane boosters) tend to work as an anti-catalyst and block the formation of the active radicals that lead to auto-ignition of the fuel and ultimately detonation. The longer it takes to react all the fuel the greater the chances are that heat will accelerate the reactions beyond what the fuel components can bear. The idea that purposely SLOWING things down in the chamber is somehow beneficial in light of the reactions taking place is pretty funny really

Heat , pressure, and time tend to be the driving force in all of this. The more heat and pressure you subject the fuel to and the longer you keep the temps elevated the better and more stable the fuel you need . That's why engines that run at high rpm and have small bores can run very low octane fuels even with high compression ratios.

It's just simple chemistry really. If you look at the chemistry of explosives you can see a lot of similar reactions taking place, and it can give you some real insights into what's happening inside the combustion chamber when things go wrong. It's a fine line between engine tuner and explosives engineer.
 
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