93 Octane Premium Unleaded.....

Do they even sell leaded at gas stations anymore?

 

Not around here they don't. But i'm sure some small towns have it still.

 

I use Sunoco Ultra 94. I was told by my PCM tuner that really Texaco 91, or is it 92? actually gives better performance. I tried it but couldn't really make myself believe it was better, so back to Ultra 94. Maybe it's just me, but it seems that on WOT runs, I felt something different....for the better. He!!, maybe I'm just wasting $ on the 94, at least the voices in my head are telling me I know what I'm doing.

 

This has been beaten to death in many other places, but there's no reason to use any more than what's required.. We ran my bike on a dyno (all stock except a pipe and power commander) back to back with 87 and 92 octane (5 pulls with each). It made an average of 2.7 more horsepower with the 87... Granted, that's not much of a difference, but why pay more for less.. If you car doesn't ping on 91 (and it shouldn't), the additional octane is wasted -- and could be detrimental..Why people think 93 equals higher performance is confusing to me..

 

I use 93 because that's what the station closest to me has. I don't feel like downgrading to 89 octane because it's below the required level, although I hear it does just fine. So it just gets premium regardless.

 

Probably because on the gas pumps it'll read "87 Unleaded, 89 Unleaded Plus, and 92 Super Duper High Performance Unleaded" (and usually the label on the 92 will look cool compared to the others)

 

When I had my tuning done for the hotcam Bryan at PCMforless told me specifically that I would need to run 93 or higher octance with the cam and his tuning. Around here the choices are either 87,89,93 or 94. There is no 91 or 92, unless you go to some of the cheapo stations where who knows where some of those places get there gas. I was running Sunoco 94 anyway and still do and couldnt be any happier with his tuning and advice

 

What kind of compression ratio does your bike run at, or most bikes in general? I'm not into bikes but I get the feeling they are not high compression engines being that some of them run up around 15k rpms. I thought higher octance was necessary to prevent detonation in higher compression motors. Maybe octane isn't as important in a lower compression bike motor.

 

Bikes have higher compression engines than cars (in general).. but they have more efficient combustion chambers, so they're able to run that compression with lower octane gas.. Many bikes are over 12:1, and they function fine on 90 octane...

 

I thought we were talking about Chevrolet 5.7 L LT1 V-8 engines?

 

If you read the entire thread, you know I was just making a point.. It seemed pretty simple to me, but maybe.....

 

Not necessarily correct. The only way you can determine the true octane requirement of a specific engine it to monitor for knock retard. If you are getting "true" knock retard, you will benefit from increased octane.

Octane requirement changes.... as carbon builds up, as cooling system deposits create hot spots in the heads, you may need a higher octane. Elevated coolant temps, elevated inlet air temps also raise the octane requiement. Unless you actively monitor for knock retard, you are just guessing as to whether you are making the maximum possible power for your specific engine conditions. Yes, 91 octane may satisfy the vast majority of the typical LT1 population, but to make a blanket statement is incorrect.

Its not always necessary to run 93 either... in the winter, when inlet air temps and coolant temps fall, the octane requirement falls. Simply by using a scanner to monitor knock retard, you can insure you are using the correct fuel for the conditions.

And octane does NOT correlate to burn speed. Octane defines - at least with regard to detonation - the tendancy of the fuel to form new compounds (end gasses) under the high pressure and temperature conditons of the initial spark ignition, that will auto-ignite and form a second flame front, remote from the first. Its a function of chemical composition, not burn speed.

And octane does not correlate to energy content of the fuel. You need to look at the fuel's specific gravity, and the heating value (BTU/#) to determine the specific energy content of the fuel, which still is not dependant on "octane".

For a very good reference on the subject, check out the Gasoline FAQ , focusing on section "6. What do Fuel Octane ratings really indicate?" Good reading, if you have the time....

 

I'll assume that you know some things I don't, but, if the higher octane doesn't slow burn speed, what causes the reduced horsepower/performance on higher octane gas? It isn't just my experiment that proves this -- it's been shown time and again that octane in excess of what's needed can decrease your horsepower/torque...

With regard to your other point.... Yes, I agree that engines with the conditions you noted would require higher octane, but it was my assumption that the question asked (what kind of fuel do I need??) was a general one -- I answered it that way. I thought I was clear in that I stated, as did you, that "91 octane will satisfy the vast majority of LT1 motors". I guess if you really break it down, almost all "blanket statements" are incorrect, but people use them to satisfy the majority of situations -- that's what I was doing.

Incidently, if I am wrong about the "burn speed" thing regarding octane (and several "educated" people told me that's what it was), I'd appreciate your interpretation of what really is happening.. I understand why it wouldn't give any additional performance, but why it hinders it, I'm confused...

 

I Goofed. I meant Regular or Premium. Thanks guys.

I don't have an LT1, yet. I have a third gen. www.geocities.com/akshay95624/index.html

I forgot that the compression ratio on the LT1 is 10.x
That's a sign to run 91 octane.

Akshay

 

Not sure if you want info, or just want to argue about "blanket statements".

It is entirely possible for a higher octane fuel to either increase or decrease power output. The "secret" is in what I described above, with regard to "specific energy content". Some high octane fuels (but no all) achieve the higher octane by using hydrocarbon components that have a low density (LB/GAL), or a lower heat content (BTU/LB), or both.... there are not as many "pounds" of fuel in a given volume. There are not as many BTU of energy in each gallon. A fuel injector delivers fuel on a "volume" basis, not a "pounds" basis (contrary to the way they are rated). If you use a fuel with a low density or a lower heating value, you may have less BTU's in the cylinder to produce the heat that produces the pressure rise that produces the power - E-I-E-I-O.

But not all high octane fuels are of a lower density or of a lower heating value (energy content). Some are extremely dense and are blended for high specific energy content (BTU/GAL).

My experinence with my own engine, on the dyno might suggest that not all engines lose HP with higher octane, nor do they necessarily gain HP with higher octane.

With the engine on an engine dyno, we tuned it for max HP on 93 octane pump gas. Then we tried 94 octane, and were able to get a decent increase in HP by adding more timing. The HP did not increase because of the energy content of the fuel, or the burn speed of the fuel, but because of the improved timing. Then we tried upping the fuel to 100-octane VP Fuels unleaded. No gains, or loss of any kind, and it did not respond to timing changes.... a 10.8:1 engine doesn't need 100 octane fuel.

Then we started the nitrous tuning. In order to "baseline" the engine before we sprayed any nitrous, we simply took the NA tune that produced max HP on 94 octane fuel, and ran the engine on VP Fuels C-16.... 117.5 (R+M)/2. With no changes of any kind, the engine picked up 6HP. It did this because C-16 is an extremely dense, high energy fuel. It increases octane with 6g/gal of lead, not a lot of lightend hydrocarbons. It was simply getting more BTU in the combustion chamber.

There are fuels that do "burn slower" and are high octane..... I've done some work with VP Fuels "Air Race".... and based on input direct from VP Fuels, this will slow down combustion, when used as a buffer in the fuels like C-16.

My favorite quote from the Gasoline FAQ: