yeah I wish people would understand what octane really means..
But people just dont get it..


But the day pigs fly is when people understand Hp = ( Torque * RPM ) / 5252..

I love asking people, if your engine made 100 HP at 5252 RPMS how much torque would you make at that RPM.. The answer is always funny..

 

Tooleman - While that formula is technically correct, many people misinterpret it to mean that it will calculate the maximum engine HP, when in actuallity it only calculates the engines Horsepower at that specific RPM

So in order to find the maximum HP of an engine, you would have to know at what RPM it occurs, and the specific torque rating at that RPM. From there you could plug it in to the formula and find the maximum HP.

 

I know, but its fun anyways haha..

 

Any car with a high CR would need more precise detonation timing. With a turboed/SC'd engine, you're effectively creating a high compression ratio because everything in your cylinder is more pressurized.

Probably quite a bit. Lots of modern engines have knock sensors and will adjust timing accordingly.

Arg... Everything I've said was already covered...

 

Most Hondas are typically considered torqueless. But then they also rev much higher. So lets say you use a gear to halve the rotational speed of your driveshaft. Would that increase torque? Because everything goes through different gearing.

This I want to truly understand. I haven't gotten a proper explanation yet.

 

The engine would still make the same amount of power, but if I understand what your saying, the engine would rev faster..

 

Perhaps I can help. Basically you have to think of it like this: Engine torque (as well as Horsepower) are completely independent of gearing. No matter what the gearbox ratios are, the engine can only make so much power and torque, no amount of gear ratios can change that.

What gear ratios can do is this: Increase the useabiliy of torque/horsepower that the engine is making. Lower gears ratios can help a low-torque engine (Honda S2000) get off of the line faster, because they allow the engine to get up to peak revs much faster and more efficiently. However, this is by no means a substitute for torque.

Example: when in 4th gear (on most transmissions 4th is a 1:1 ratio) in an S2K, if you punch the gas from 1800RPM, its probably not going to do much. You would have to downshift in order to bring the rev's up into the power band, allowing the engine to spin faster and make more power. Try the same thing in a GTO or Corvette, and the results will be quite different. Even from 1800RPM in 4th, the engine will start to pull, and as the revs go up it will just continue to make power. Most times a downshift is not even required, because the engine makes lots of torque down low.

The bottom line is this - Torque is low-end to mid-range grunt, horsepower is mid-range to top-end power. Gearing can effectively make up for lack of torque in many applications, but it is no real substitute.

Hope that helps

 

no replacement for displacement..

 

Yes, there is. It's called BOOST.

 

nope you are wrong..

anything that can be done to a small engine, can be done to a big engine..

once boost goes on both engines, the small engine will never make as much power..

 

a 2 stroke or a rotary engine makes twice the power per displacement than a 4stroke.

 

diesel cars do it, except no spark plugs at all. whats their compression ratio 16 to 1 or something like that.

 

2 strokers also blow up really easy, and rotery engines have seal problems and need to be rebuilt all the time..

 

Maybe but they are still a replacement for raw displacement. 1/2 the volume 100% of the power.

 

why couldnt you do a big V8 2 stroker.. hehe..

also id like to see a 2 liter rotory engine make the same power with the same mods as a 4.0 rotory engine..

there is no replacement for displacement..

 

Rotary engines are insane. They are in the Mazda RX 7s and other cars. Cool engines. They only have like 5-7 moving parts in the engine, they can up to a no ending RPM (until it self destructs) and they can make some serious power. Learned all about them when I went to AMT tech school (Aircraft Maintenance Technician).
But about the whole Detonation thing... someone said it was when the gas fires too early. Well that is wrong. When the gas burns/ignites before its supposed to, that’s referred to as Pre-ignition. Detonation is when the Fuel/Air mixture explodes due to really high pressures and temperatures in the combustion chamber. Detonation is the principle of operation to diesel engines, like someone else said they do not have spark plugs. They have Glow-plugs to help start the engine when its cold, but other then that they produce a lot of Power/ Displacement because of the Explosions/ Controlled burn. But the downside to those engines is the weight factor.

And on the Octane rating. The octane rating of a fuel refers to the performance rating of the fuel. And the performance rating of a fuel reflects on the operating abilities of the fuel. Basically in short form, Different fuels are used in different engines to prevent detonation. Racecars use higher-octane fuels because of their higher compression rations, and the higher operating temperatures. Engines that are equipped with supercharger/turbochargers need higher-octane fuel due to mainly the higher operating temperatures. The forced air is hotter then naturally aspirated and can lead to detonation problems.

Well, I’ll wait for the critism...
Hope some people learn something after reading this.

 

I have been reading this forum for awhile, I am a student at Universal Technical Institute in AZ hence the username. I do not own a cobalt but I will as soon as I get out of college, I am not here to add my 2 cents or opinions on anything I just wanted to try to simplify things to better understand them for everyone. So I hope this helps...

I was going to write a long explanation but I will just paste the site where I learned some of it from a long time ago. I suggest everyone read it and my apologies if it was a waste of time but I doubt anyone will read it and come out without learning anything. http://auto.howstuffworks.com/question90.htm

Simply said as you need a higher octane based on temperature and pressure in the combustion area. Higher temps and pressures are caused by forced induction as well as compression ratio as everyone has already figured. An engine with a low compression ratio say 8:1 that has a lot of boost for example may need a higher octane than an engine with 12:1 compression. These are just ways to increase cylinder pressure or temp. I can go into more detail but if you read that link it pretty much explains everything.

As for the mention of diesels, I am not positive but I think that all diesels have a compression ratio of 20:1 minimum, they also mostly have turbos. So if you are asking yourself how they can have that much compression and forced induction with diesel fuel that has a low compression point of ignition.... the reason is that the fuel injector is a direct inject, the injector sprays directly into the combustion chamber instead of at the back of the valve. The injector sprays at an extremely high pressure at a pre-determined time when proper ignition would be acheived. ... So the injector sprays when the piston is at near top dead center and the fuel that enters the cylinder combusts instantaniously and forces the piston down. The time that the injector sprays the fuel in a diesel, is per say the ignition timing that a spark would have in a gasoline engine.... in comparison

sorry if you thought that was too long, just tryin to help those that were wondering

I agree with everything 05 Blue B10wn ss said.

 

also for all of you that are in the Pheonix area (there was an earier thread on where to find better gas) you can get very high octane fuel at the glendale airport off of litchfield .. West of Avondale. I think it is 101 or 104 octane, anyway you should bring some gas cans and mix it with the shitty 91 they sell down here at the pumps. My teacher goes there to get gas for his chevelle.

 

I had a tank of 87 last week, and I thought there was no difference in performance. This week I put 91 octane in it and I could tell the lower octane stuff was crippling the engine.

 

Yeah Woodio, I know what ya mean. I always run 93 Octane, but a few days ago i got a really good deal on 91 ( like 2.40$ Gal "What a deal") and i am noticing a power decrease, and i think my gas milage went down a lil bit. But other then that, the engine still runs fine.