Compression of our motor and octane

Ahhh possibly another '16 M/T guy who has felt the "stuttering" or "slight miss" hesitations under consistent load, like pulling up a slight hill in 5th/6th gear (~1500-2000rpm). My (former) truck would do this like crazy right from the factory and on 87 fuel. Put 91 in the tank, and the effect would be noticeably reduced under the same conditions. Now, that premium fuel (in my area) was also E0 as compared to the 87 which is up to 10% ethanol.

 

The direct injection has a combustion chamber cooling effect, but this engine uses both port and direct injection. The direct injection isn't always in play. It's part of it, but the the aluminum engine is a big factor. Aluminum has a higher rate of thermal conduction than cast iron which other engines are typically made of. The heat is pulled from the combustion chamber so quickly, it is less likely to develop a hot spot that would cause pre-ignition. Because of this, you can run a higher C/R in an aluminum or aluminum head engine without detonating on a lower octane fuel. An iron engine (with all other things being equal) would require higher octane at that C/R simply because of the combustion chamber heat. Other factors that affect potential for detonation would be cam lobe overlap, timing, head design, exhaust, exhaust valve design, and plug heat range.

My carburated CBR 600R is 11.5:1 and is designated as 87 only. No injection, no variable ignition timing, just a liquid-cooled aluminum engine and a relatively cold plug.

There is nothing wrong with running a higher octane fuel, it won't hurt anything, it just costs a little more. Realistically, premium is 20 cents per gallon more than regular. It's four dollars per tank more - who cares? I typically run mid grade, but If I were towing a heavy load I would use premium as a little extra insurance against detonation when really loading the engine. My last truck was premium only, 25 gal tank, and got 10 MPG so I don't worry about the fuel cost in this thing; it's like a gift.

 

One note on the direct versus port injection on the 2GR-FKS - if you watch/log the injection mode PID while driving, you'll notice that it doesn't take much application of engine load to induce "direct". The other two possibilities are "port" and "either". The only time I recall seeing "port" was during idle, when not in DI cleaning mode.

 

My new 600 plus hp 406 sbc with 10.9:1 compression was built as a pump gas race engine but can run race fuel for more hp

 

Ethanol content would make a difference as it has lower energy potential than gasoline. Ethanol content is 10% I believe. There is no difference in power potential between grades of gasoline (all things being equal in terms of ethanol content). The octane number only relates to resistance to detonation. A no ethanol fuel would be better in that you would probably see a small boost in mileage. Ethanol is also hydroscopic, meaning is pulls water from the atmosphere which is no bueno and further degrades your fuel quality.

 

I'm in.

 

I love 2 strokes, but I'm old. I've heard the emission problems have been solved with new fuel injected models. In CA they red sticker 2 strokes made after... 2002 I think. I wonder, though, if the factories would be interested in a true 2 stroke resurgence? There is more money to be made in 4 strokes between increased service intervals and parts. In the end it's usually money, but with dirt bikes it's also about racing and winning, so maybe...?

 

When Hurricane Dorian was approaching earlier this summer all the local stations ran out of all grades except premium so I had no choice but to fill up with it. I was expecting a warm fuzzy feeling but it never happened. Think I'll stick with 87.

 

So tell me, where is this place where “Premium” is only .20 cents more per gallon? I wanna live there.

just jumping from regular to mid grade ( which is 87 octane here btw) alone will set you back over .30 cents a gallon. Premium - we’ll see for yourself.

I pulled this just a few minutes ago where gas is relatively inexpensive.

 

That information might be in the 'How much is your gas thread'

Here's the link :https://www.tacomaworld.com/threads/how-much-is-your-gas.632795/page-11#post-21796218



Since regular is hitting 163.9 a liter here, or $6.21 per gallon $, I will stay with regular and not take the hit for premium.

With gas prices so high, I might have to start bottling up farts to sell!

 

Yes but, as a few here know camshaft and computer timing can change that 11.8:1.

 

My point is that topping of with premium vs. regular is not anywheres near only four dollars more per tank. At least not anywhere I’ve been lately and I just got back from a multi state trip. Cheapest I found was right here at home and the difference is more like .60 cents per gallon not .20 as he claimed.

states I was at where the gas cost more the difference was even more significant.

 

The compression ratio is a fixed figure. The intake valve timing changes the combustion chamber pressure, not the compression ratio.

 

Fairbanks Alaska is still a place, yes?

Filled up today for $3.25 for 90, 87 was $3.05. The difference for me is roughly $171 per year for premium vs 87. My truck runs better on it, so it’s worth it to me. If yours doesn’t, or your math doesn’t work in your favor, buy the gas you want.

 

My Trans Am is 11.5:1 and runs fine on 93 octane. 112º LSA and decent duration makes dynamic compression much less. With a smaller cam I'd have to change heads to drop compression.

 

Ok I’ll be right there. Just a hop, skip and jump.

 

https://youtu.be/Bb5VfiFy0kY

 

noun

1. the ratio of the maximum to minimum volume in the cylinder of an internal combustion engine.

Now, bear with me here. Does that volume of charge air that's expelled back out into the intake manifold count, or do you have to subtract that from the maximum volume? To be fair, that small volume of air is not being compressed when the intake valves are hanging open after BDC on the compression stroke when the intake cam VVT angles are retarded.

 

We have 87, 89 & 93 here. Choosing has never been very fun for me, so I’ve always mixed equal parts of each up to 20 gallons, which gives me an octane of about 90(89.6666667 to be exact), which i think is perfect. Then i top the last gallon off with diesel because 4 is my lucky number. Works great for me.

 

You are very hard pressed to find a new gasoline V6 vehicle with a cast iron block. Tell me I am wrong. (And yes I know about the 2.7L 4-banger)