What Octane?

Topic: What Octane? (Read 16982 times) previous topic - next topic

Reply #15 – December 27, 2011, 09:38:55 PM

My car has ported E7s with GT40 valves, speed pro flat tops, heads are milled (9.5-1 compression), HO cam advance 2*, 1.6 roller rockers, and trickflow valve springs and I run 89 at 16* advanced. When I had the SO motor I couldnt run more than 12* of timing on 93. The only thing I can think that would cause that is carbon build up.

What Octane?

Reply #16 – December 27, 2011, 10:04:20 PM

All

What Octane?

Reply #17 – December 27, 2011, 10:28:46 PM

87 cause I'm cheap. And the guy with the right foot thinks its supposed to go to the floor regularly. Once in a while Ill throw in some 89 for the detergents. What do I know I'm no engine builder when this one falls apart we'll look inside and see what I did wrong.
:burnout:

What Octane?

Reply #18 – December 27, 2011, 11:16:14 PM

You're misunderstanding me Tom Renzo. There are reward/drawback situations where modifying and engine to the point where you have to use higher octane fuel ISN'T worth it and there are modifications you can make to an engine that require you to use higher octane fuel that ARE worthwhile. Installing a power adder like a blower, nitrous or turbo would be a situation where you would experience a gain in power even though you'd have to run a fuel with lower combustability (higher octane fuel). In my last post, I used the example of raising your compression ratio as being another worthwhile and effective way to improve the power of an engine, even though you'd have to run higher octane fuel if you raised the comression ratio much. Situations like advancing your timing so much, you have to run higher octane fuel to keep pinging at bay, are NOT worthwhile however. All I was trying to convey, is the point that you've got to pick your battles. The reason why octane is added to fuels, is to decrease their volatility. If you decrease the volatility of a fuel, you've decreased how much energy is released when it combusts.

AvGas is gasoline with a super high octane rating. Other than having tons of octane, it IS gasoline, just like what you fill your car's tank with. With that in mind, the little test I mentioned in my last post was a comparison of a low octane gasoline to a very high octane gasoline. In other words, it was an apples, to apples test. Gas to gas.

To address your tailpipe example; if you used Zonda's car as a test platform and ran it on 87 octane gasoline, an emissions test WOULD detect more polutants than it would if Zonda had his car tested with 87 octane in the tank. Hell, do the test yourself and the spark plugs will tell you that. When you run a higher than required octane fuel in your car, you WILL build up more deposits in your engine than you would with a lower octane. Like I covered earlier, higher octane fuels are DESIGNED to burn slower and with less energy. The drawback is that they don't burn as completely as lower grades. It's no different than setting your car on 10 tons of dynamite and lighting the fuse. You're car is going to be more thoroughly destroyed from the explosion, than it would be if you only used 2 tons of dynamite. Whether you're talking dynamite, or fuel, more energy being released means more thorough destruction.

To get my powerplant license, I had to sit through way too many classes on fuel theory. You could say I'm more than a little familiar with how all this works Tom. :)

What Octane?

Reply #19 – December 28, 2011, 07:07:26 AM

What Octane?

Reply #20 – December 28, 2011, 09:54:10 AM

Good morning Tom. Considering that EGR valves are part-throttle devices, anyone who removes their EGR valve in hopes of gaining horsepower doesn't know much about cars. At idle and full-throttle, the EGR isn't even working. The only things you'll accomplish by removing your EGR valve would be 1. Increasing the amount of polutants your car puts out. 2. Worsening your gas mileage and 3. Cleaning up the looks of your engine compartment. You DON'T improve performance by removing your EGR. That's NOT how cars work.

If you're looking for maximum horse, you SHOULD advance your timing as much as you can. As much as you can without increasing the octane requirements of your car. If you've been reading car blogs and magazine articles for so long Tom, you should have noticed how many times people reported an IMPROVEMENT in power/throttle response when they switched to using a lower octane fuel.

To address your comment about carbon being off the table; are you trying to tell me that hydrocarbons AREN'T tested for when an emmissions test is performed? Please tell me you're not trying to tell me that. YES. Modern gasolines do have additives that are designed to reduce carbon emmissions, but they don't totally remove carbon emmissions.

What Octane?

Reply #21 – December 28, 2011, 09:54:37 AM

What Octane?

Reply #22 – December 28, 2011, 10:01:18 AM

This is all chemistry. And chemistry is a nice can o' worms with a lot of hard data to chew through. If we really want to understand this issue we need to know the potential energies of compounds, the energy densities as these compounds exist, and in what ratios they're found at the pump.

http://motorcycleinfo.calsci.com/Gasoline.html Read "Octane Ratings"...Some history, and an "a-ha!!!!" moment, yes that is how industry tells you 0-100 the rating. Keep that maximum in mind.
http://books.google.com/books?id=J_AkNu-Y1wQC&pg=PA62&lpg=PA62&dq=1927+graham+edgar+105+octane&source=bl&ots=j0Au5QzTbq&sig=DLNHRF3MqfgkuoAdyEAix6euKTQ&hl=en&sa=X&ei=Ax_7TtCmAcXt0gHIrJibCg&ved=0CCYQ6AEwAQ#v=onepage&q=1927%20graham%20edgar%20105%20octane&f=false
Read page 62. 100 Octane, classically, should be the maximum you ever see. Adding other things, *mainly* lead, brought the performance you could make ABOVE "100% octane", equivalent to dumping 100% iso-octane in your tank. That was the best anti-knocking combustible one could technically "use" at the time.

NOW......here is our biggest talking point!!!!!!!!!!!!!!!!!
Low octane we're arguing is potentially more energetic but too volatile. High octane, low volatility is apparently less energetic. We can take advantage of the good part and bump timing and compression...maybe make a net gain, is it enough though?
http://en.wikipedia.org/wiki/Octane_rating

Look down at the chart of different materials, from actual pure compounds to end products you buy at the pump. Lets compare Methane and 2,2,4-Trimethylpentane. That mouthful is actually pure iso-octane, 100% Octane as we would say.
http://en.wikipedia.org/wiki/2,2,4-Trimethylpentane
http://en.wikipedia.org/wiki/Methane

(now yes I am grossly overusing Wikipedia....but I'll give it the benefit of the doubt for chemical pages...enough people in the know watch those pages carefully)

Iso-octane has 5461 Kilo-joules of energy per mole. Methane has only 891. Methane has a Research Octane Number of 120 and Iso-octane is as we know 100. So, this case supports our argument. Higher octane and less energy. But wait.
Look at the g/mol rating. Grams per mole. This tells you how dense the material is. Divide the energy per mole by the grams per mole, you get the energy density. Iso-octane has an energy density of about 44 KJ/mole. 5461/114 = 44

..........Methane has a density of 55.7 KJ/mole.

So IN THIS CASE, the one with lower volatility actually is more "powerful" as well! This is one case. And gasoline is composed of as many as 500 different hydrocarbons. You would have to at least have a rough idea of the majority of the makeup of any given gallon of gasoline, know each energy and energy density of each....and come to a conclusion on the overall effect. For a scientist or an engineer like me, it's interesting and frighteningly....beckoning.

FOR A HOTRODDER?

Quote from: "thewestie"

we'll look inside and see what i did wrong

I think this is much more reasonable and prudent.

Slam it together, stand on the shoulders of giants as much as you can, run it, see what happens. Build it, hammer down, grenade it, and build it better.

What Octane?

Reply #23 – December 28, 2011, 10:49:02 AM

That's some good reading Zonda.

What Octane?

Reply #24 – December 28, 2011, 10:55:03 AM

I....do have an excuse lol. I'm on the third and final day of being paid to do absolutely nothing at my new job. Long story short, some BS happened, so now I have to wait til tomorrow for my safety training, then I can go back in the cleanroom and LEARN STUFF again!!! For now I'm wasting taxpayers' and investor's money :(

What Octane?

Reply #25 – December 28, 2011, 10:59:59 AM

Well... I think I'm gonna start calling you "Easy Money!"

What Octane?

Reply #26 – December 28, 2011, 11:05:22 AM

No just call me "Tweek" from south park like my friend and his dad do because I can't sit the hell still, can't ever get comfortable, have to adjust my seatbelt like 1,233,895 times and fidget endlessly during a 15 minute drive.

EDIT: If you're reeeeeeaaalllly bored this is a good read too http://www.faqs.org/faqs/autos/gasoline-faq/part3/preamble.html

Quote from: "Aviation Fuel stuff"

The
Performance Number indicates the maximum knock-free power obtainable from a
fuel compared to iso-octane = 100. Thus, a PN = 150 indicates that an engine
designed to utilise the fuel can obtain 150% of the knock-limited power of
iso-octane at the same mixture ratio. This is an arbitrary scale based on
iso-octane + varying amounts of TEL, derived from a survey of engines
performed decades ago.

What Octane?

Reply #27 – December 28, 2011, 05:01:01 PM

I could not tell any differance or emissions change between egr working and not. Best mileage I averaged over my 100 miles commute, was 35mpg without functioning egr at between 55 and 70mph.

What Octane?

Reply #28 – December 28, 2011, 05:30:32 PM

By recirculating exhaust gasses the way it's designed to do, an EGR valve will decrease the amount of polutants comming out the tailpipe Haystack. That's why you have to have one on your car to pass the visual inspection part of an emmissions test. You might not have been able to notice a difference with your nose, by an emmission sniffer would detect the difference.

When an EGR valve recirculates exhaust gasses through your engine, that leans out your mixture a little. When you lean the mixture, you burn less fuel. Less fuel also means less power though. A hair less power cruising down the road doesn't matter. At full throttle though, it does. That's why your car's EGR valve is closed by the ECM when the engine is at full throttle.

If you didn't lose a little gas mileage when you removed your EGR valve, your EGR wasn't working properly. Increasing gas mileage and decreasing emmissions is what a properly working EGR does and is designed to do.

What Octane?

Reply #29 – December 28, 2011, 05:31:08 PM

It is best to have highest timing possible prior to ping. As for EGR, I have found that more power can be found without it. I understand it does not function at idle or full throttle, however when you first go to full throttle, the mixture that is remaining in the cylinder is diluted. Not to mention, if it is malfunctioning it could cause all sorts of issues. I have never had the privledge of using a dyno on anything I have worked on. Just going by power difference that I have felt. Normally only minor improvements, but had a major improvemet with a 350 Chevy a friend of mine owns. Have never had gas milage decrease from removing EGR. I would think the lower octane would burn more completely as it is more volitile thus decreasing emmissions as long as there is no detination.