I found this episode surprising in that your N/A mid compression build may not benefit from higher octane... what say you?

 

Richard Holdner just had some videos recently that touch on the same thing interesting for sure!

Related! Not sure when the new one comes out, but the latest episode is all about Rec port vs Cathedral port. Nothing super groundbreaking for anyone who reads this site a lot, but still cool to see.

 

Good stuff! Eye opening too...

 

We're talking about an engine that's built for pump gas and it liked E85 which is a higher octane with the added benefits of cooling so no surprise at all.

 

Correct but take E85 and Meth out of the test....

N/A give me 110 octane I'll add degrees of timing and profit... no... profit.. why?

I don't understand how 29* degrees of timing was optimal with the low octane vs high octane

 

Just examples from my past..
From a Fuel engineer,,,, Lower octane fuel ignites to a peak temp faster than high octane fuel, the both release the same BTU of energy per lb, its just the speed it can release it. Chage density on a low CR motor falls off faster with 93-100 octane than 114 octane in a High CR motor.

Example,, I used to drag race a Mazda Rx3 Rotary,, when normally aspirated you can't make one knock( < 8:1 CR stock) . We found a source for 65 octane fuel, bought us 30 HP on a really WELL modified motor, at 12K rpm..... (Tip don't try that RPM at home. it takes a TON of work to get there... ) Stock rotaries damage themselves starting just above about 7800 rpm despite all the myth and legend.. Biggest killer of rotary engines was leaded premium back in the 70's the lead coated the apex seals and ruined them.

On the other hand a Cosworth Twin cam midget I used to take care of had 15.5 to 1 compression and it got pissed with anything less than 100% methanol. (even happier if some Nitro-methane "spilled" in to it.. ) 10K rpm on a 1/8 track. The Piston to head clearance on that motor is scary.

Its all about the build and the fuel. Without 1 the other may or may not give an advantage. I used to see a lot of idiots burn up stock street motors trying to run Nitro.. Convinced they would get 100Giga Horsepower from it.

 

The octane is simply the measure at which a fuel resists auto-ignition. There's no real world effect from it beyond that.

The burn rate of a fuel isn't much related to octane. There's a very slight effect there, but you would never be able to tell the difference in a timing curve over a 30 octane spread. The content of the fuel is the big factor, when looking at just the fuel itself. Sunoco SR18, for example, has a faster burn rate than 87 pump gas. If you want to get a ballpark of the burn rate, look at the fuel's specific gravity, RVP, and distillation. In most cases (some exceptions apply), a lighter fuel with higher vapor and lower boiling point will tend to have a faster burn rate.

That said, the chamber shape, turbulence, temperature, and pressure have far higher effects on the burn rate than the fuel itself. That's why you don't see a difference in timing across the fuels in that episode. The engine wants what the engine wants. The fuel can be a factor though if it's not able to be burned efficiently due to the chamber variables. Toluene, for example, has a high boiling point, is rather dense, and has poor RVP which makes it difficult to vaporize and burn efficiently. This can hurt power in an NA engine that doesn't have the heat and cylinder pressure to vaporize it and burn it, but great for a boosted engine looking to open up the tuning window. In the EM episode, the E85 and methanol are both restricted in what they can do because of the engine chosen. They both have a slower burn rate than pump gas. The pump gas was already burning slower than the chamber will accommodate so the other two fuels don't fare any better. The power bump comes from the cooling effect of the alcohol, which was also restricted by the air not being that hot to begin with. The E85 was able to cool the air about as much as could be done so the methanol wasn't going to improve on that, hence the power numbers between them were about the same. Compare those two fuels in a 14:1 engine, it's a different story.

The oil has a factor in this too. (You should expect an oil note from me by this point.) Any oil that gets past the rings, clung to the cylinder walls, can effect the octane and burn rate. There's power to be found here as well.

 

Great post here. Well said. Combustion chamber design and shape will dictate overall timing. Doesn’t matter if you add 15 octane to the fuel, the chamber wants the timing that it wants. Adding more octane does nothing…ASSuming that the correct octane is being used for the dynamic compression of the given engine setup. The cooling effect of a high oxygenated fuel will help a little if it’s July-august.
I enjoy the EM show, but I find it’s (mostly) more entry level testing of stuff that’s common sense related in this industry. Nothing cutting edge to be found there.

 

I love the show also and you're right that most of what they cover should be common knowledge to most people who are true gear heads. There have been some episodes I found very interesting and made me really think past the obvious and one that really sticks out to me anyway was the header bash episode, I'm sure had it been done with a max effort engine the results might have been different, They beat those headers to death and after a couple of those hits I said to myself....that's surely going to kill power and then they run it and nothing changed. I couldn't tell you how many times I've had to ding headers for clearance on my stuff or other people and wondered if it really did have an effect.

I had an uncle that drove and worked on drag cars in 60's and then turned his talents to dirt cars, No matter what team he was working for they always seen a huge improvement in their programs. His success was in knowing how to make everything work together on the car and that included the driver. I couldn't tell you how many times car owners and drivers were pissed because he made a bunch of changes without telling them, He did some things that most people would say was not going to work or *** backwards. In the end they had to admit what he was doing got them wins and championships.

 

I wish Engine Masters would get into more technical things, and they do occasionally. With the simple, common knowledge things, they could at least go into more detail as to why things are the way they are. People tend to remember things better, and apply them more effectively, when they understand the reasoning behind it. When people don't understand the why and how, if something doesn't go according to plan, that's how myths and misinformation are created. A good example is people who bash any kind of gasohol but run avgas that contains blends of alcohols and glycols. Avgas is a funny one to me as a lot of people don't realize how unregulated it is and how much it can vary from one batch to another. One batch may have a stoich of 13.5 and the next be 15.2. One may have 5% toluene/xylene and the next 35%. It's all over the place. About the only thing that is consistent is the alcohol/glycol used as anti-freezing agents.

The bashed headers episode didn't have much effect because the headers weren't having much effect to begin with. The intake and cam used didn't pair really well with the headers used so you had this conflict of wave tuning that didn't allow the headers to scavenge as well as they could. Combine that with headers likely a little oversized to begin with, it's not being very demanding. That same engine with tuned intake runner and header lengths and a custom cam would likely be a different story. However, I understand why they didn't do that. They wanted to replicate what >90% of combos are on the street which is common (non-matched) parts from a catalog with headers designed around engine bay fitment over wave tuning.

My favorite episode will always be the air filter shootout with the salad bowl.

 

That was a good one, Filters can be a packaging nightmare at times but it make no sense when people have the room to run a good filter and they choose something that's obviously restrictive because they like how it looks or they just don't understand how much it's killing power.

I like your posts, They are always informative and to the point.

 

For a fact!