Possible to have too much octane?

[turbojimmy]

I've been poking around the site looking for advice on EGTs and WB02 readings and found a couple of vague references to boost and octane. Things like if you're running 116 then you should have a minimum of x-PSI and that 116 will raise EGTs.

I have a few race chips: 108, 110 and 114 octane. I realize that these numbers are guidelines but am I hurting performance by always running 116 octane? I figure the 116 gives me a lot of breathing room boost-wise though lately I've been running relatively low boost at the track (like 22-24 PSI).

Just curious....

Jim

 

[gnx139]

I believe that excessive octane to boost ration will hurt performance. It has simething to do with higher octane burning slower internally. I've recently wondered if anyone has an octane:boost map that would help people with a question like yours. Something like 15-16psi on 93, 17-18 on 97 and 19-20psi on 100 octane. This is without alki of course. I currently run 18psi using a xylene mixture that gives me 98 octane.

 

[Adam Connell]

You always want to use the minimum octane you can get away with without detonation... atleast thats the rule of thumb in the N/A world. Octane is actually a rating that determines how fast the fuel burns. 93 octane burns slower at the same pressure than 87 octane. Now, if you are getting detonation then you're fuel is burning too fast or cannot stand up to the cyl. pressure and pre-detonates. Pretty much, if you're not running at the maximum of a given fuel, it's a waste, and you should run a lower grade fuel... Im sure someone will pipe in and tell me Im wrong, but thats how this board goes.

Also just because you switch from 116 to 110 or to 104 does not mean the actual quality of the fuel degrades, Especially in race gas. If you dont need 116 at a given boost, then run something lower...

I dont know where that bull**** about 87 being lower quality than 93 came from, but the modern day truth is that it's just NOT true. 93 just has more additives to get the octane rating up, and SOMETIMES has added detergents to clean fuel systems and such... People dont like to hear this, but ALL gasoline(all grades, companies, ect...) are shipped in the same pipeline from the same places. The difference only comes when the individual companies buy it. They add what they want to the gas to get it to their desired specs... Basically if you run 93 in a car rated for 87 you are wasting your money, hurting performance, and lowering the all important MPG because you are not getting a complete burn out of the fuel. This can also be bad for cat converters...

 

[Blown&Injected]

Higher octane DOES NOT equal slower burn

It just means it is more resistant to knock. Yes the knock flame is a fast burn but that is because the fuel detonated instead of burned not because the fuel is designed to burn fast or slow.

Indeed some of the fastest burning fuels are very high octane. The reason the speed of the fuel burn is fast is because it is designed for extremely high RPM engines and is an independent concern from the octane level.

 

[d0n_3d]

Correct...the higher the octane, the higher the resistance to detonation. As far as how fast a fuel burns, I'm not quite sure on that but I always thought the more lead the fuel had, the slower it burned. In fact I'm pretty sure 93 octane burns slower than 87.

N/A cars don't require as high of octane as the turbo cars do. Turbo cars generally run much higher compression ratios when the turbo kicks in compared to static N/A compression motors. Sure you can build 11, 12, 13:1 ratio motors N/A but take a 8:1 compression ratio and add a turbo to it. Run about 25 psi and then let's talk compression ratio!

 

[TurboDave]

Higher octane DOES NOT equal slower burn

It just means it is more resistant to knock. Yes the knock flame is a fast burn but that is because the fuel detonated instead of burned not because the fuel is designed to burn fast or slow.

Indeed some of the fastest burning fuels are very high octane. The reason the speed of the fuel burn is fast is because it is designed for extremely high RPM engines and is an independent concern from the octane level.

That was kinda what I've always been told by race fuel vendors. As a matter of fact they warned me away from running anything more than what the car needed. ESPECIALLY the really high octanes like 118. He told me that stuff was designed for REALLY high rpm applications (Pro stock specifically) where it's fast burn is needed.

 

[turbojimmy]

Thanks for all the info. I think I'll take it down to 110 or 112 octane and mix in some alky if necessary.

Jim

 

[turbofabricator]

Read VP face fuels site. There are SPECIFIC fuel blends for each type of engine. VP Racing Fuels Contact VP directly BEFORE you change fuel blends. There are 60 blends of fuel available. You can get into serious trouble using the wrong fuel blend. Just because it's rated at 110 octane, doesn't mean it will work good in a turbocharged application. Most turbo cars run better on 93 octane pump gas then 100LL Aviation fuel. That stuff really needs help to work good in a strong turbo Buick. I use to blend 100LL with a few other chemicals to get it to perform good. I wouldn't recommend that anyone do that, when you can order VP (X) and have a custom taylored fuel for your application. I even use to add octane booster to C-16 to keep it from detonating back in the days of 28 lb. injectors. I was running 11.70's @112 on a stock turbo and stock intercooler, and stock injectors, using a modified C-16 or special blend of "stuff" in 100LL Av gas. Much easier today to get the right fuel. Back when I was using wierd fuel stuff, I changed head gaskets like most people change oil. Would have been nice to have 60 lb injectors back then.

 

[BlackBandit]

Run about 25 psi and then let's talk compression ratio!

I am not trying to be a dick but for the sake of clarity I think you mean cylinder pressure not compression ratio. An engine with an 8:1 comp. ratio has that same ratio with the engine idling or running 35 psi of boost. The cylinder pressure is what goes up and causes detonation. HTH. james

 

[SVORay]

I dont know where that bull**** about 87 being lower quality than 93 came from,

It's my guess that people usualy tend to think anything that cost more has to be better...and people always want to have it better than the next guy etc. So they run higher octane in vehicles that don't really need it. Now with that in mind, I'm actually having detoning issues in my wife's Tahoe and it's completely stock? If it's weird it will always happen to me lol

 

[Blown&Injected]

It's my guess that people usualy tend to think anything that cost more has to be better...and people always want to have it better than the next guy etc. So they run higher octane in vehicles that don't really need it. Now with that in mind, I'm actually having detoning issues in my wife's Tahoe and it's completely stock? If it's weird it will always happen to me lol

I agree!

I think 25 years ago when one could still find leaded at some stations, they may have added some better additives to the hi-test fuel but today - it's all the same stuff at the pumps