I know that running higher than needed octane fuel can actually result in a loss of horse power. Has anybody ever actually proven this to be the case on a dyno??? If so, high much horse power was lost??

 

I dont know about a loss in power , I think the high octane gas burns slower / cleaner

I know my gas mileage improves a lot with high octane

 

You can not generalize about either energy content or burn speed vs. octane rating. Octane rating depends almost exclusiely on "chemistry" and finding flammable compounds that do not form "end gasses" at high temperature and pressure, that will auto-ignite and form a second flame front in the combustion chamber. Has nothing to do with energy content, nothing to do with flame speed.

What costs you HP with SOME high octane racing fuels is the fact that they achieve the octane ratings with "light end" hydrocarbons, that are not very dense. As a result, the fuel has a low specific gravity.... there are less pounds of fuel in a cubic foot (or in a gallon, which is a volume measurement). Since a carb or a fuel injector is essentially a volume based fuel delivery system, using a low density fuel means you are putting less pounds of fuel into the chamber. And since energy content is generally referenced in BTU/pound, you are putting less energy into the mix. You could overcome this by simply putting a larger volume of fuel into the chamber, but neither the carb or the FI system will do this on its own... you need to rejet or reprogram.

My engine was tuned NA for optimum performance on 94 octane (480HP). Since we knew the nitrous tune would use C16 (117.5 R+M/2) we rebaselined the engine with C16... no changes other than fuel. It picked up 6HP, primarily because C16 is blended for high density.

The thing you need to look at in a fuel is "specific energy content".... BTU/gallon.

 

Well, you would not believe....
I ran out of gas the other day in my Z28, called my daughter to come bring me my gas can from home. Se brought me my 110 octane racing fuel can instead of my lawnmower gas can.
I put it in anyway and drove 1/2 mile to the gas station and filled it up with 93. MAN did it make a difference!!!
Now you just touch the gas pedal and this thing jumps!!!
I am also getting better milage too.
I don't know if I would do it all the time, 110 Octane is $6.95/Gal. here in Atlanta. But for now I will enjoy this tank.

 

I wouldn't do it "all the time".... the lead will kill the O2 sensors and the cats.

 

Fred,
I plan on using wet n2o but with my stroker CR of 11.35 I don't think i can go much over 100 shot without racing fuel. The thing is there's no racing fuel here, but I can get c14 or c16. My ? is how much of this stuff should I blend with regular fuel say 95 octane? or is it clean c16 when nitrous is on?

Thanks

 

Yes, lower octane more violent burn, higher octane less violent smoother burn. Sounds like this thread should be in advance tech.

 

[thread hijack]

Fred: would running leaded 110 octane on race day hurt my O2s !?

how should i mix it with 94 octane ?

i wont be running leaded fuel consistently but as a added saftey measure (along with 150 jets on as tock bottom end) i wanna mix some in with my pump gas

[/thread hijack]

thanx

 

Good info, Injuneer.

As I understand it, you can get the 92 (or whatever) (R+M)/2 rating by blending more or less Research octane number (RON) gas with more/less Motor octane number (MON). Research numbers are generally 8-10 points higher than Motor numbers because of the test conditions. Motor numbers generally relate to WOT or full power detonation, so a refinery could easily blend gas that tested at 92 (R+M)/2 and be more WOT detonation resistant than pump 94 (R+M)/2.

What SG was your 94? Many pump 92s are .75 or higher, while 87 and unleaded racing gas is generally below .75. We had some experience with .735SG 92 (R+M)/2 which was quite detonation resistant.

 

You can buy VP Fuel products in containers ranging from 5 - 55 gallons. I buy C16 ($7/gal) in a 30gal drum, and Air Race ($9.50/gallon) in a 5-gallon container. They can ship it. I just get mine through a local speed shop... they pick it up at the distributor in Delaware (??).

With a 135-shot on top of the 480HP NA, we were able to run fine on 100 octane unleaded. I'm a little lower on CR at 10.8:1, but you shouldn't need to use anything like C16 for a 100-shot. Run straight 100 unleaded.

I've run quite a bit of C16 (6 grams/gallon lead) through my engine, and one of the O2 sensors still appears to be reading fine. The other one is reading way low.... I don't use the sensors.... I run open loop on a MoTeC computer, but the sensors are still connected to the stock PCM, and I can look at them with my ScanMaster. I wouldn't risk running leaded fuel for a street car that relies on the O2 sensors for keeping the A/F ratio in line.

I think for the most part you can just prorate the number of gallons to get the approximate blended octane.....

10gal 94 + 5gal 110 = 15gal 99.3

Very rough, but you'd need a degree in chemistry to figure it out in any detail, and a complete composition of each fuel.

Just don't make the mistake a lot of people make..... they see C-10, and assume it is 110 octane.... it isn't. It is 100 octane (M+R/2). 96 motor octane, 104 research octane - see next comment.

And the comment about motor vs. research octane is an excellent one.... for performance tuning, you need to look at the "motor" octane. Research octane is a measure primarily for part/moderate load driving. The thing I like about the C16 is that it is dense and it is 117 motor octane, 118 research octane - 117.5 (R+M)/2. The Sunoco equvialent has the same (R+M)/2, but the motor octane is nowhere near 117.

I'll have to check the SG they used on the dyno sheets for both the 94 octane Sunoco and the VP C16.