L Head on the dyno

Very true.

AND are his numbers on a stand or at the wheels.

Would love to spend some time tweaking and tuning on the dyno to see what gains we could make. the problem is time............
D

 

Lower octane fuel has nothing to do with horsepower, there is the same amount of BTU's in premium as regular, only difference is the ability to maintain the compressed pressure until it is electrically ignited instead of mechanically ignited. He could have used low grade and had the same hp rating.
Just to put this out there, my Suzuki is recommended for 87 octane, runs fine on it and the motor has 11.3:1 compression. Alot of pre detonation has to do with port and chamber shape as well as fuel grade and how much swirl, movement and temperature it has when entering the chamber. I love the stories about guys saying I get better mileage and power on premium than low grade, if your engine isn't knocking or sufering from pre detonation it will make no difference, its mostly all in there head.

 

From my understanding and reading higher octane fuels burn a little slower then lower octane fuels. Could be wrong could have been websites put up by those guys thinking they get worse mileage with lower octane fuels, Which BTW my car I swear gets worse with higher octane fuels, could be that I am heavier on the gas when I have more octane? I know I know it is probably in my head.

 

The burn rates and resistance to ignition can have an effect on how an engine runs, how much hp it can generate, etc. Another laymans way of describing octane in lots of text books I've seen and used describes in a nutshell as octane rating "a rating to resistance to ignition". In other words, a lower octane rating fuel has a lower resistance to ignition and higher rating a higher resistance to ignition. That's why many engines require a higher octane rating. A higher compression engine, different combustion chamber design, etc. etc. can cause detonation issues with lower octane rated fuels because it has less resistance to ignition so can pre-ignite or detonate. This is a very simplified explanation but should get the basic idea.

 

That would be why you need higher octane fuel, pre ignition or detonation due to the pressure put on the fuel from turbo boost. Higher or lower octane fuel does not burn slower or faster it is only resistant to igntion under pressure, think about it, diesel fuel packs more btu and is slower igniting than gas, in fact the reason diesels are generally slower at winding up is due to the slower burn rate of diesel fuel. If you get more power from hi octane fuel it is due to the engines inabiltiy to run on regualr fuel and pre ignition problems. it literally is that simple.

As I said the engine will be the judge of what fuel it needs and if it is running with no pre detonation on regualr it will not get any more hp from running on hi octane fuel, thats simple physics. Both have the same btu so both fuels have the same potential for hp.

 

That and they tend to run better with pistons and rings in their normal positionsR)

 

I think I was something in print recently about Jeep experimenting with a turbo on the F head, don't rember where.
Found it.

Peterson's 4wheel and Off-Road, Jan 2012, pg 51.