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 Post subject: Low comp. & fuel
 Post Posted: Sat Feb 19, 2011 5:46 am 
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I have been thinking lately, for the stock compression or low compression 8 - 9 or so static compression limited classes, among other factory engine beginner racing classes. My sisters oval track 305 Chevy bomber did well with just 93 octane pump gasoline, I didn't see the need for us to buy racing fuel. I realize racing gasoline is composed mostly of components that vaporize more quickly to keep up with the high engine speeds, but with an engine that will not see absolutely more than 6,000rpms with factory compression.

I ask this,

Is the specially designed racing fuel really worth the extra money when the engine is only operating with, for example, 9:1 at an average window of 4500 to 5500rpms?

Thanks!

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 Post subject: Re: Low comp. & fuel
 Post Posted: Sat Feb 19, 2011 7:30 am 
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Too high an octane gas will actually slow you down! I don't think I'd run anything but 93 octane pump gas in it. You might try some 100LL aviation gas or even the 110 race gas but you're not likely to see any benefit from either but then again, only testing it will prove this one way or the other. ;-)

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 Post subject: Re: Low comp. & fuel
 Post Posted: Sat Feb 19, 2011 7:44 pm 
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All gasoline's (except av-gas) have very nearly the same heating value per quantity of air burnt. The difference is so small its not worth listing. The way to view engines is this, they are not just an air pump, they are a machine to raise the energy level of liquid fuel to the state of combustion. What that sentence means is the primary function of an engine is to burn fuel. To do that the fuel has to be turned into a gas, to so that the fuel has to have its energy level raised to boiling point. Thats what the job of an engine is. Air flow into an engine is the reason why the fuel energy is raised. if the air flow is reduced the energy input to the fuel is reduced, thats why you can throttle it. The throttle controls air flow thus controlling energy input to the fuel. the piston still does the same motions etc and compresses whatever is in the cylinder etc, there are no mechanical devices in the engine that can vary the energy input to the fuel other than the throttle valve. Ok so now we have that point clear, so we have to consider that the engine is actually there to input energy to fuel, now what that means is different engine combinations need to run different fuels.

Because all gasolines have similar energy output doesnt mean they need similar energy input. Low octane doesnt mean the fuel needs less energy input. Low octane means it has a detonation point that is lower than a high octane fuel. The point of detonation in the test engines used is found by varying the compression ratio as the only factor changing. That situation doesn't occur in hotrodders engines. The tests are done with constant inlet air temperature and constant carburetion and valve event timing and motion. The octane rating of the fuel is thus only comparable under those conditions. Looking at octane ratings as an assessment of suitability for low compression racing is not a good indicator.
What you need to look at is distillation point data. Racing fuels convert to gas at lower temperature than street fuels, thats a critical difference especially when the heat input is low because of low compression.
What is important especially when using low compression is to get the right camshaft into the engine. The camshafts ability to fill the cylinder and then adequately compress the mixture to create sufficient heat to vaporize the fuel must be understood.


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 Post subject: Re: Low comp. & fuel
 Post Posted: Sat Feb 19, 2011 9:00 pm 
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In my 2 stroke development days I managed to get high octane fuels to make the engine detonation limited at 12.5:1 compression and street fuels to not be at 21:1 compression. High octane fuel to run to max power at 14000 rpm and low octane street fuel to max power at 21000 rpm; all on the same engine with the same porting and ignition system and timing etc. All done by changing exhaust pipe shape(not cone timings) and carburetion and fuel selection.

Anything can be done with anything is all I have ever been able to figure out.

Low compression certainly has an effect upon the RPM range but its not the reason why. Alter the carburetion and valve timings to suit low compression and the revs potential will go up.
The compression ratio rule your under is certainly enough compression to run an engine for max power at 8500 rpm, I've done that to stock compression rule classes where other competitors are running max of 6800 rpm and we were doing 8300. Taking out the track records in the process. They changed the rules and banned our carburetion and intake and exhausts and other things after that. It's the price you have to pay sometimes in racing so you move on.

So to answer your question exactly, racing fuels are not needed if you do the right things to street fuel even in a limited compression engine. Its very difficult to do the right things though, it took me decades of research and work. Its easier to use racing fuels that are designed for low compression. Street fuel is not designed for the reasons you want for racing, its designed for emissions. If you want to be top dog then you have to experiment and research and learn and invent.


Last edited by shrinker on Sat Feb 19, 2011 9:19 pm, edited 1 time in total.

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 Post subject: Re: Low comp. & fuel
 Post Posted: Sat Feb 19, 2011 9:04 pm 
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Thank you for the replies.

Ken wrote:
Quote:
Too high an octane gas will actually slow you down!


I wonder how many people know this? This sounds familar to me, but, I just havent put much thought into the answers to why until now I suppose. For the recreational performance enthusiast, this thought probably takes the backseat. I know R&D will be the decider on which octane is going to perform the best, that should be a fun couple practice days!

Shrinker wrote:
Quote:
...the fuel has to have its energy level raised to boiling point...


Are you speaking of alcohol fuels? if I remember correctly, gasolines have a vaporization point. Please do explain Shrinker.

Going by octane may not be the best way of choosing which level of fuel is the best, but its probably the easiest way a person could dial in something that doesn't have the time to go forward with a thorough R&D session. If somebody is very competitive, they will probably go the full nine yards and investigate what they have as far as camshaft, induction and fuel ignition system to make a choice.

Thank you \:D/

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 Post subject: Re: Low comp. & fuel
 Post Posted: Sat Feb 19, 2011 9:06 pm 
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I see you replied about the same time I have. I am exhausted at the moment from the day, I will read your new post and reply at a later time.

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 Post subject: Re: Low comp. & fuel
 Post Posted: Sat Feb 19, 2011 9:18 pm 
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Raising the energy level of a fuel to boiling point is the process of rapid vaporization. One and the same thing just different words, I was just using common language not technical.

The thing to take away from what been said by all on this thread so far is all Gasoline's have the same power producing potential. You have to condition them right and control the factors in the engine right and then they all make the same power. The only exception to this rule is compression limits the maximum power. Its not compression ratio its the dynamic compression. Its the mass of air you induct and then compress that matters BUT you have to have the fuel conditioned correctly along with the mass of air other wise its a messy scene that has problems.
What people fail to add to the commonly said statement " an engine is just an air pump" Is "that has to maintain combustion integrity". Think about that for a bit.


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 Post subject: Re: Low comp. & fuel
 Post Posted: Sun Feb 20, 2011 12:24 am 
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Ken0069 wrote:
Too high an octane gas will actually slow you down!

That is partly true. There is a general trend that higher octane fuel blends require more energy to vaporize but that is not the same for all blends. For instance methane is a high octane fuel and it requires virtually nothing to vaporize it because its already a gas at room temp. For liquid fuels the rule sort of applies but once again there are differences. Hydrocarbons can be of different types of molecular bonds or shapes if you will. Its mainly to do with the connections of the carbon elements. Some are straight line like a chain, some are branched like a tree with limbs and branches and twigs, some are rings like a circle joined together and then they may have branches coming off of the circle. There are over 7000 combination's possible and around 5000 known combination's. The fuel companies claim to only know about 450 of the 530 odd combination's that are present in gasoline. Your just left to fly blind on the remainder.

Its not what you buy in a gallon of gas thats important its what it turns into as its burning that matters. The molecules dont 'explode' all at once, they sort of fizz away like a fuse. Its the aggressiveness of the Oxygen that controls the destruction of the molecule. Oxygen aggression is related to the heat. Hotter is more aggressive.
As the molecules 'burn' they change from one chemical to another. If you remove or add an element from or to the molecule its another chemical after that. If you cease stuffing around with the molecule part way through and dont get the job done then your left with an unknown substance, so take pot luck as to what its octane rating is. Thats the problem encountered with street fuels. Street unleaded has a fraction of the fuel that is meant to not get burnt thats why its got high distillation temperature for the final 10%. If you evaporate street unleaded in a tin your left with a oily substance. That stuff is meant to not be burnt in the chamber its meant to feed the red hot catalytic convertor. Thats all fine and works a treat in a low power per cubic inch street engine that doesnt make much cylinder pressure ( read heat), use that fuel in a race engine with a high power per cubic inch and your going to reach a point somewhere where that oily goo starts to burn. If you dont complete the burn on that oily goo you will end up with radicals. They cause detonation. So if your going to use street fuel in high power engines you have to have no wet fuel trails or turbulence puddles and you have to have complete vaporization and combustion close to stoich. That is very hard to do. But if its done then you can run street fuels at very high compression pressures and power outputs.


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 Post subject: Re: Low comp. & fuel
 Post Posted: Sun Feb 20, 2011 7:57 am 
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shrinker wrote:
Raising the energy level of a fuel to boiling point is the process of rapid vaporization. One and the same thing just different words, I was just using common language not technical.

The thing to take away from what been said by all on this thread so far is all Gasoline's have the same power producing potential. You have to condition them right and control the factors in the engine right and then they all make the same power. The only exception to this rule is compression limits the maximum power. Its not compression ratio its the dynamic compression. Its the mass of air you induct and then compress that matters BUT you have to have the fuel conditioned correctly along with the mass of air other wise its a messy scene that has problems.
What people fail to add to the commonly said statement " an engine is just an air pump" Is "that has to maintain combustion integrity". Think about that for a bit.


Very insightlful Shrinker, learned something new today! I see how you were applying the 'boiling point' comment earlier. I guess I have neglected the complete thought of the fuel boiling in terms of reaching the vaporization point during my studies ](*,) Smokey's hot vapor engine is great representation of the beginning to end vaporization process in an internal combustion engine. I see where you are going with mentioning of the manipulation of timing, atomization and exhuasting the gases for playing with compression & octane. What you have responded with is great, especially for the young gearhead/racers like myself, very intuitive!

Quote:
Anything can be done with anything is all I have ever been able to figure out.

This opens my view even further on engines, but, factory restricted parts hinder this unless the racer is allowed to modify the components appropriately. I will do some R&D, hopefully soon, to see how much the factory parts restrict the engines possibility of breathing adequately.

Quote:
Low compression certainly has an effect upon the RPM range but its not the reason why. Alter the carburetion and valve timings to suit low compression and the revs potential will go up.
The compression ratio rule your under is certainly enough compression to run an engine for max power at 8500 rpm, I've done that to stock compression rule classes where other competitors are running max of 6800 rpm and we were doing 8300.

When you did this, how much did you experiment in the squish and quench area of the chamber? There had to have been more than just set the quench and move on wasn't there?

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 Post subject: Re: Low comp. & fuel
 Post Posted: Sun Feb 20, 2011 2:36 pm 
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Fahlin Racing wrote:
Quote:
Low compression certainly has an effect upon the RPM range but its not the reason why. Alter the carburetion and valve timings to suit low compression and the revs potential will go up.
The compression ratio rule your under is certainly enough compression to run an engine for max power at 8500 rpm, I've done that to stock compression rule classes where other competitors are running max of 6800 rpm and we were doing 8300.

When you did this, how much did you experiment in the squish and quench area of the chamber? There had to have been more than just set the quench and move on wasn't there?

No alterations allowed to the heads or porting or anything etc. Stock cams everything stock. Only modifications allowed were sections of the intake manifold. The rules restricted the carburetion to 2 Stromberg single barrels. Carburetors were allowed to be modified. The engines were all the V6 3 litre mitsubishi.
We made a water heated intake manifold plenum where the fuel exited side draft carbys and impacted upon the water plate, The corrosion on the plate was high so the methanol was being vaporized effectively. The plenum volume was 8 times one cylinder, the carburetors were internally modified to decrease droplet size using my Smartcarby technology.
The purpose of the modifications we did was to decrease droplet size considerably thus decreasing vaporization time, that allowed high RPM. The limitation of the engines was vaporization not breathing.


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 Post subject: Re: Low comp. & fuel
 Post Posted: Thu Feb 24, 2011 5:15 am 
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Interesting, and very easy to grasp the concept.

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 Post subject: Re: Low comp. & fuel
 Post Posted: Sat Jan 07, 2012 3:22 pm 
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Note that the plenum had a heating plate that the fuel blasted onto. The heating plate vaporized the fuel entirely as it was methanol and the water temp is enough to do that. When the plenum fuel condition is mostly gas there is no throttle delay. The carburetors were sidedraft Constant Velocity type (CV)not downdraft booster emulsion type(yours). The CV type carby doesnt have an accelerator pump and doesnt need one. When we ran the engine without the water heated plate (it developed a crack one day so we bypassed it for the race) the engine lost performance, it was obviously slower on the track. We then made a new plenum without heating but it was as small a volume as possible and the performance picked back up but not to the level of the first design. The performance without the heating was mainly worse in the lower RPM range. The top end eventually became about the same but it was far harder to tune it to do that. The engine reacted to atmosphere much more. Then the season was over and they banned our technology so we sold the car and left the class.

Most people dont know how much the power changes by running a 8 times plenum because they never go that big. You dont know what your missing unless you do stuff.


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 Post subject: Re: Low comp. & fuel
 Post Posted: Sun Jan 08, 2012 7:14 am 
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Shrinker in regards to pump fuel and additives in Aus i was told not to run BP98 as the additives would foul plugs as there wasnt enough temp in the motor to burn these completely. My running temp is 190f by the way and i run a heart shaped chamber

My carb guy told to me to drain it completely and put BP95 in it before he would even look at it! Other people have recomended I find another carb guy but he got it to run great after that.

Hysteric


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 Post subject: Re: Low comp. & fuel
 Post Posted: Sun Jan 08, 2012 7:54 am 
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Hysteric, are you asking for an opinion on the issue? BP had a problem a few months back with bad fuel, they wouldn't admit it of course but it was terrible, detonated in performance applications, gummed up the valves. That said, all the fuels now are junk, there made for these SIDI engines (which are just a detonating carbon depositing disaster).
There is substantial differences in engine response for different brand fuels.
Your carby guy may have seen a problem with the fuel you were using and recommended the change based on good reasons. I certainly would see those things too. I would say any tuner who isn't able to recognize things like that is not good enough. If your happy with the results the tuner has obtained then stick with him.


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 Post subject: Re: Low comp. & fuel
 Post Posted: Tue Jan 10, 2012 6:16 am 
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Thanks Shrinker, the question was more general but i used my situation as an example.

My Carb guy (rebuilder) would not even look at my car until i had changed the fuel over. What im really hoping you can answer is whether the higher octane pump fuels and the additives they use to increase the octane rating(my understanding) are incompatable with older engines, mainly open chamber design heads and other inefficiencies of the 60's and 70's engines.

He told me that the older engines cant run hot enough to burn the additves thoroughly so they foul plugs and other things. Yet others say they run pump premium and get good results? Is it just a question of running temp or is there more to this than what was told to me?

Thanks again

Hysteric


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