markyerger

I always run premium (93 octane) in the ZR-1.

if I put 104+ octane boost or some other kind of booster, am I doing good or harm??

Sgreg

Probably don't need it if you are running a good grade of 93 octane gas. JMO.

Paul Workman

The LT5 was designed to operate 87 octane**. If you're having knock issues with 93 and especially if you aren't running a "93 octane chip", you have other problems, and you should look to finding the cause. That 104+ stuff is not only a BandAid, but back in the day, it resulted in a rust-colored residue on my spark plugs (L79 BBC), and I wonder what it might do to O2 sensors? (I dunno)

If I'm not mistaken, the late mo C4s and for "sure" the C5s programs will push the spark advance to the point where knocks are detected and back off from there and put it in the "learn" bin. Therefore, although the engines were designed to operate on 87, they will push the envelope so that 93 octane will result in the "learned" spark advance will take advantage of 93 octane, resulting in more efficiency (output).

Bottom line: If it ain't knockin w/ 93, putting "booster" in the fuel is a total waste, not to mention possible sensor issues.

FWIW,

P.

glass slipper

You're likely to do more harm than good but if you aren't having any problems with knock retard, you'll just lighten your wallet. Most octane boosters don't do anything at all and the ones that do have MMT which has a bad reputation. In low doses and occasional use, MMT won't have any negative effects and can raise octane from 93 to 95 (not really much is it)...high doses used regularly will cause a multitude of problems due to the rust colored manganese deposits from clogging the catalytic converter to engine failure while raising octane from 93 to 96. MMT is like TEL (lead) in that it has decreasing effectiveness as concentration levels increase. You would be better off getting unleaded race gas for the times you need it (like high temperatures in the summer where you may get knock retard) and save your money. Here's a good link to read through:
http://www.idavette.net/hib/fuel/index.htm

C1ANDZR1

Not to hijack this thread, but would blending a 3-4 gallons of the VP "Street Blaze 100" 96 octane unleaded to a tank of 93 octane help performance or would I just be throwing money away?

Jason

glass slipper

That's going to cause a few raised eyebrows.

But you are correct, I've had to get a link to the EPA website law section to prove to others in the C6 section that ALL cars sold in the US are required to be capable of running on 87 octane. Doesn't mean they have to ever run 87 octane, they just have to be capable of it which is why knock sensors exist.

Blown67427

In order to get the absolute right answer to this, you'd have to know if your engine is detonating presently with the fuel you're using. If it is not detonating, then it would be a waste of $$ and may even hurt performance. The fuel or octane you use, has alot to do with the burn rate, and in the timing in which the head was designed to perform, or any imperfections within the chamber etc. The pent roof design of the LT-5 allows for a more complete burn, which is why it gets away with so much compression, and yet can burn lower octanes. Generally, the more octane, the slower the fuel burns, the less octane the faster it burns. Octane these days is the amount of chemicals, that control the burn rate. Any burning before or after it's proper time is called pre-ignition, this is one of the causes of detonation, and can be very harmful to your engine,especially if you are hearing it. Hook it up to a diagnostic equipment, and look for knock. If you have none, don't waste your money.

glass slipper

If you're not getting any knock retard, it'll be a waste of money. If you mix 4 gallons of 96 octane with 16 gallons of 93 octane, you'll end up with only 93.6 octane...I'm not sure you would see much difference even if you were getting knock retard.

glass slipper

Octane is a measure of a fuels' resistance to self-ignition/detonation. The octane rating of a fuel has nothing to do with the burn rate/flame speed. Increases in octane cause a delay in the ignition of the fuel but from a temperature perspective...not from a time perspective. Once the fuel has ignited, the flame speed is governed by the chemicals in the fuel. Gasoline is a combination of over 500 different hydrocarbons as well as other chemicals that can be combined to vary octane and flame speed independantly. Rocket Brand has a 118 octane fuel used by Pro Stock 500 cubic inch 10,000 RPM engines that burns much faster than 87 octane fuel. In fact, cars running 9:1 compression and 87 octane fuel will see HP gains with the 118 race gas and decreased timing to take advantage of the faster flame speed. The decreased timing reduces the negative work done on the crankshaft as the piston is approaching TDC on the compression stroke which has the net effect of increasing HP.

PS Pre-ignition is when the mixture ignites before the spark plug fires. You may or may not have detonation with pre-ignition. Detonation can lead to pre-ignition, but they are two completely different forms of abnormal combustion.

Blown67427

Never fails. It always turns into a big dick contest.

glass slipper

http://www.repairfaq.org/filipg/AUTO/F_Gasoline.html
http://www.repairfaq.org/filipg/AUTO...l#GASOLINE_004

From the second link:

"The antiknock ability is related to the "autoignition temperature" of the hydrocarbons. Antiknock ability is _not_ substantially related to:

1) The energy content of fuel, this should be obvious, as oxygenates have lower energy contents, but high octanes.

2) The flame speed of the conventionally ignited mixture, this should be evident from the similarities of the two reference hydrocarbons. Although flame speed does play a minor part, there are many other factors that are far more important. ( such as compression ratio, stoichiometry, combustion chamber shape, chemical structure of the fuel, presence of antiknock additives, number and position of spark plugs, turbulence etc.) Flame speed does not correlate with octane."

Read the above links and maybe you'll measure up for the next contest.

Aurora40

The crux of his point about datalogging the car to see if knock is even an issue was right on, though. And I'd toss out if your LT5 is getting knock, often the best fix is to go drive the hell out of it. They seem prone to knock after light use as I guess carbon builds up and needs to be blasted out.

As an aside, here's an article on the subject I always find interesting:
http://members.aol.com/aurora402002/...ine_basics.pdf

Blown67427

I was just giving a simplified explanation. I could have gotten extremely technical without having to use a link, as I'm well versed on this issue.

Maybe you should have read my comment a bit more carefully

glass slipper

Except he never said anything about datalogging. He did mention knock as an issue but it had been mentioned twice already. I didn't have an issue with that, I only took issue with him perpetuating the myth of higher octane fuels burning slower. It's like the myth that people believe about higher octane gas making more power because it has more energy. I read through your link, excellent article as it's very well written and factual.

glass slipper

I'm not trying to get into a pissing contest with you, but I invite you to get as technical as you want to back up your correlation of octane rating to flame speed theory. What you are suggesting is counter to what needs to happen in the combustion chamber. The longer it takes for the fuel mixture to burn, the longer the end gasses are exposed to higher and higher pressures and temperatures which increases the chance for self ignition of the end gasses leading to detonation/knock. Read the link provided by Aurora above...it's all in there.

I did read your comment very carefully and this is the only part I have a problem with: "The fuel or octane you use, has alot to do with the burn rate". It simply isn't true concerning octane leading me to believe you aren't as well versed as you think on this issue. There are plenty of technical publications that prove octane rating has no correlation to flame speed.

We can always agree to disagree.

Blown67427

Sorry, but I have other things to occupy my time with. I think the readers got the jist of how it works. Bottom line, if the engine is knocking, and timing is being pulled it will cost you power. In most cases, concerning a "stock" LT-5, the ecm thru the knock sensor is capable of backing enough timing, so that the engine does not injure itself. This is true, if everything is functioning properly. Like I mentioned above, the only way to know if there is enough detonation is by hooking diagnostic equipment, and monitoring the data.

Another note. The ecm is programmed to advance the timing till it picks up a knock, as a reference point. This is not what we're talking about here, just to make it clear.

This I agree with

drmcar

To get back on subject I was at a dragstrip many years ago before my mods and ran all morning. In the PM had low gas and added 3 gallons of 100 octane to @ 3 gallons of 93. Next three runs were the best of the day! Not scientific, but it worked for me. Garth

Blown67427

It may be that the engine was backing timing due to detonation, untill you corrected it with a better fuel mixture, or it could be the result of cooler denser air, which helps all the way around.

GTB/ZR-1

Shoot, I run 93 w/ 12:1 compression & spray a 120 dry shot--no hints of detonation...

I know, I'm a madman, but the LT5s just don't seem to have detonation issues.

C1ANDZR1

George,
Mike P. told me you got the JSB Z06....that color is awesome!! What got all of this started was that I am going to get a drum of VP 114 for the race car tomorrow, and was going to get some of the 100 unleaded to blend while I was there, but I think that the 93 octane will do just fine in my stock Z.

Jason