Compression Ratio

[njv]

hi.
here in germany i am lucky in as much as we have optimax at every shell station here it is super plus with an octane rating of 98 ron and i have had no problems with it what so ever some of the high performance audi bmw etc etc run really high comp ratio here from the factory if i have to wait at the petrol station to fill up i like to spot whos filling with super plus whos using super and whos using benzine its allways the top end cars with the super plus being poured in.
ray your explaination of the ron system was exactly as i understand it as well. only bit that confuses me on this is when you get into fuel with a 104 ron rating or so as it is then resistant to pre ignition 104% of the time? i do realise our european ratings are slightly diferent 4 higher in general i beleive and this may explain it.

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neil verdon 66 sqr on irs

[ray greenwood]

Yeah Neil...I'm not 100% on the over 100 octane explanation either. The people I have spoken to say that it is more of an expression of potential stability marked by the fact that the fuel repeatably ignites 100% of the time in the test cyl. at the correct point, and because of other stabilizing components has extra meaures of pre-detonation protection from compression and heat levels, that may be non standard to most auto industries....its probably just a math thing...or maybe it was just an advertising ploy on the Oil companies part. Hee Hee ..maybe racing fuel has always been a max. of 100 octane..and we are using fuel six octane #'s lower from the pump?!!That would sound poor wouldn't it? Ray

[VBCurtis914]

Back to CR issues..
How strong is the effect of cam duration on dynamic CR? For instance, let's say a motor with a 260 duration cam runs safely at 8.5 CR on pump gas. How much higher could static CR be set if the cam were 280 or 290 duration?
Are we talking .1 or .2 bump in "safe" static CR, or can we get into the 9's with a 290-300 degree hot-street cam?

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[njv]

nice.
your gonna run sweet with a high comp ratio and wild cam .
but possibly short if you dont addrese the cylinder seating .
if like me your gonna take your engine apart regular you can just lap in and go again i dont see a problem.
its a trade off it is a game e=mc2.

im gonna be running a web 163 grind the duration is not huge at 284o but it lifts .5 and i will be setting my cr to 9:1.

the best engines are like light bulbs that are just about to burn out they shine very very bright just before they blow.,
sorry :¬)

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neil verdon 66 sqr on irs

[ray greenwood]

I am running 8.33:1 with 262 duration. I have had no problems with cyl. seating on the 1.7 liter 90mm. I am wondering, with those kind of pressures..how much of the cyl. seating problem is due to just the extra heat..and the the subsequent extra expansion problems with the larger diameter cyl? I may have less effecticve compression than I figure or at least for less time due to a good bit of valve overlap...but 262 is the advertized..Ray

[phybertek]

Spyke,

I'm no expert, I actually asked the question in the first place. Correct me if I am wrong anyone or you spyke. What I think was implied by the 89 Octane vs 92 Octane. When it was said that 92 octane burns faster because it is a more pure substance than a lower Octane level gasoline. Chemically, I will use the composition of H20 (water) to explain. If you have a glass of water and boiled it at 212 degree Fahrenheit at sea level, the water, because of its properties will always boil at 212 F. I am talking about pure H20. At this point in which water begins to boil is called the critical point. The same applies to freezing. Now, if you add some other compound to the water, it will make the solution (water) unpure. The boiling point of water will decrease or increase depending on compound X. If the compound X is H30, then the boiling point will increase in result having a higher critical point. The same applies to Gasoline. The lower the Octane, the hire the critical point; which means slower burning gasoline. One can not imagine gas burning slow, but when compared to 6000 rpm, it will show up.

The vapor pressure octane is a whole school of thought. I know that VP (mm Hg at 20 degree Celsius of Alkylates (isoctane, octane number 100) is like 70-72. Vapors are good. But i'll only begin to sound like a fool because I forgot my chemistry

Now, let just say gas ignites at 99.2 degrees (don't remember the actual energy required to ignite the chain, but lets just say 99.2 (octane number 100)). Now you have a spark that ignites the gasoline, but her gasoline burns way to slow. You will have residual remaining in the combustion chamber. Then on top of that, you heads and cylinders are runing at 300 Degrees. The remaining gas could in fact and will burn in the chamber during the exhaust cycle causing knocking.

I'm thinking from a chemical prospective, not from automotive experience.

[phybertek]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by phybertek:
<B>Spyke,

I'm no expert, I actually asked the question in the first place. Correct me if I am wrong anyone or you spyke. What I think was implied by the 89 Octane vs 92 Octane. When it was said that 92 octane burns faster because it is a more pure substance than a lower Octane level gasoline. Chemically, I will use the composition of H20 (water) to explain. If you have a glass of water and boiled it at 212 degree Fahrenheit at sea level, the water, because of its properties will always boil at 212 F. I am talking about pure H20. At this point in which water begins to boil is called the critical point. The same applies to freezing. Now, if you add some other compound to the water, it will make the solution (water) unpure. The boiling point of water will decrease or increase depending on compound X. If the compound X is H30, then the boiling point will increase in result having a higher critical point. The same applies to Gasoline. The lower the Octane, the hire the critical point; which means slower burning gasoline. One can not imagine gas burning slow, but when compared to 6000 rpm, it will show up.

The vapor pressure octane is a whole school of thought. I know that VP (mm Hg at 20 degree Celsius of Alkylates (isoctane, octane number 100) is like 70-72. Vapors are good. But i'll only begin to sound like a fool because I forgot my chemistry

Now, let just say gas ignites at 99.2 degrees (don't remember the actual energy required to ignite the chain, but lets just say 99.2 (octane number 100)). Now you have a spark that ignites the gasoline, but her gasoline burns way to slow. You will have residual remaining in the combustion chamber. Then on top of that, your heads and cylinders are runing at 300 Degrees. The remaining gas could in fact and will burn in the chamber during the exhaust cycle causing knocking.

I'm thinking from a chemical prospective, not from automotive experience.</B><HR></BLOCKQUOTE>

[Shiver]

Many years ago when I was in a vocational auto mechanics course in my local college, we had a rep. from Chevron come in and talk about fuels/octane ratings. He did a demonstration that I found very interesting... He had a pyrex tube 2.5" in dia. about 3.5' long, a rubber ball that fit inside the tube and 2 samples of gas, one was about 90 octane and the other was 102 octane if I remember correctly. He squirted a small amount of the 90 octane into the tube, placed the ball in the tube and rolled it back and forth a couple of times to mix the air in the tube with the fuel, then lit the mixture from the bottom of the tube...the result was a violent explosion out both ends of the tube. He went through the same procedure with the 102 octane but when he lit the mixture the result was a nice even flame that burned from the lower opening to the top opening....it was a very rapid burn but no explosion and only a little whooshing sound. My point is that your engine needs higher octane when the mixture explodes before the piston reaches TDC causing the explosion to push back on the piston (that's the pinging you hear!) Higher octate causes a slower more controled burn so the cylinder pressure is still rising as the piston reaches TDC and peaks shortly after causing the force to the piston just as it starts down. Higher compression ratios increase the intensity of the explosion and advanced timing gives the explosion more time to build pressure. There is no extra power (BTUs) in higher octane fuel and using a higher octane than needed will actually loose power because the piston is already on the way down when the max burn is taking place causing cylinder pressure to be lower. This is straight from the Chevron rep.
I long for the days of 104 octane at the local pump for less than .50 cents a gallon and I could run 13-1 compression on the street!
ken

This seems like it's not really accurate. A diesel engine wants this to happen. It's not premature detonation in a Diesel engine so why is it in a gas engine. If the timing is set like a diesel and low octane is used to create a bigger explosion then the spark should be set for when the detonation happens to creat a big explosion. People are actually trying to merge the way diesel work in a gas engine. The other question is using a low compression ratio 7.6:1 and adding a supercharger to it should change the ratio on a 4 cylinder carburetor Holley engine. If the fuel pump, air from supercharger, and high performance spark with the detonation, shouldn't this create a very high performance engine? Theoretically looking at a diesel and trying to match it in a gas engine should give a high torque engine with great milage. Only thing I can think of, the engine wouldn't last very long due to the high psi.

[Shiver]

Sorry a stupid question, but if the spark plug fired for a longer time, wouldn't most if not all fuel detonate rather then a fast spark that doesnt? If you wait for the compressed fuel to detonate and have the sparkplug fire at the same time with a lower octane to create an explosion rather then slower burn, shouldn't this be more burned fuel and higher psi that will mimic more of a diesel engine?

[Wally]

You're quoting a post from 22 years ago?? Are you a bot?

[dstar5000]

You're quoting a post from 22 years ago?? Are you a bot?

DON

[AdminSteve]

This is strange but it doesn't read like a bot.

AdminSteve

[dstar5000]

I WAS HERE 22 YRS AGO....

DON

[raygreenwood]

I was here too! This was a really good thread overall!

I may identify as a bot...but I'm not!

Ray

[Clatter]

Takes you back, don’t it?

To a quaint simpler time of the Internet..