Posted 20 May 2007 - 05:57 AM
So that said:
What gauges is everyone checking their motors with?
What is everyones squish at?
What pistons are we all using when checking?
Does everyone have at least a well known tool company compression gauge?
What domes are you running in your cool heads?
Whats your compression?
Posted 20 May 2007 - 11:07 AM
Posted 20 May 2007 - 03:46 PM
I use a snap-on guage,I run 21cc domes and the bikes compression is 147#s after it was ported.Before it was ported with the 21cc domes I had about 152# of compression.Wesico prolight pistons.
OK, that makes sense. Any idea what your squish is?
Posted 20 May 2007 - 04:05 PM
your buddy is the only person i have ever heard of thats run 92 oct on comrpession of 170.... i simply dont see how... at 150-155 i start running 50/50 anything past 165 range straight race gas...
this is an on going topic but for the extra few bucks it cost to get race gas, i know its not going to detonate and fuk up my brand new motor, im not bothering with some 92.
Posted 20 May 2007 - 04:07 PM
Posted 20 May 2007 - 06:11 PM
Snap on makes the best period. Always. I found out on mine haveing different adaptors and long ends of the hose will read different. I had some autoparts special carp that read 130 someting on mine and then I used my dads snap on and it read 145-147. Mine had 2cc more space in the end before it read. Also you dont need to run race fuel with slightly higher compression, I know methanol mixes with castor oil well wich burns much more efficently and cooler and is easier to get. With a much cooler motor than stock (all aluminum) and low coolant temps help too. Sharp edges in the combustion chamber willl play a role, as well as piston material. Squish and dome shape. Pro design probley said that just because they dont want to be accused of blowing up motors because of one given dome size in a wide variety of alt, temp, stroke, ports, pipes, jetting, ect... Im not saying you dont have to use race fuel. Im saying there are alternatives to getting away with not. Oh also there are ceramic coatings that you can get your piston domes coated with to protect them from high combustion temps too.
here are some examples I found on the internet showing variables in compression ration and psi at different alts:
Here are some data on the relationship between compression ratio and compression. The Bosch Automotive Handbook gives the following formula:
Compression = (Compression Ratio minus one) to the 1.1 to 1.2 power multiplied by Atmospheric Pressure
Given Atmospheric Pressure at sea level = 14.7 psi, we have the following:
Compression Ratio Compression (psi) Range (psi)
6.5 96-114 18
6.6 98-116 18
6.7 100-119 19
6.8 102-121 19
6.9 104-124 20
7.0 106-126 20
7.1 107-129 22
7.2 109-131 22
7.3 111-134 23
7.4 113-136 23
7.5 115-139 24
7.6 117-142 25
7.7 119-144 25
7.8 121-147 26
7.9 123-149 26
8.0 125-152 27
The Engine Volume of the VW Workshop manual gives the following specifications for these specific engine types:
"Compression (with engine warm, throttle open, all plugs out, gauge in plug seat and engine turned by starter):
Engine code B, AE (up to 558 000) [Compression Ratio = 7.5]
New part: 114-142psi Wear limit: 100psi
Main difference between cylinders: --
Engine code AE, AH, AK, AM [Compression Ratio = 7.3]
New part: 107-135psi Wear limit: 85psi
Main difference between cylinders: 28psi"
Knowing the compression won't help you pinpoint the CR. However, if you are presented with an "unknown" engine that tests out well on a leak down test, and you proceed to check the compression, you can at least tell if your CR might be extreme (e.g. if the leak down is good and compression measures at 150, you can conclude you have an engine with a high CR built in). For the most part though, knowing the compression will tell you very little about CR (as the table above shows), especially if you measure a compression of 110psi (could be a CR of anywhere from 6.5-7.3:1).
All this is bookish info, for your information. In the real world we aren't all at sea level, and though standard atmospheric pressure at sea level is 760mm on the mercury barometer (1013.2 millibars), atmospheric pressure can range from 950-1050mb according to some reference book I just had lying around here. This, the fact that we all don't have access to a leakdown tester and don't know how much we are losing past our rings/valves, and the wide range of compression for a given CR makes the whole business of relating CR to compression interesting only in an academic sense.
So depending on your elevation you may have to run more or less octane to cylinder psi. a given compression ration can have a difference of say 27 psi from sea level to 5000` for example. On this chart its noted that a 8.0 CR can be from 125 to 150, I know I can run about a 9:1 on pump gas and 10:1 with about a 10% methanol addative.. What psi would that put me at? Dont know axactly, but according to the research Ive done, its well over 150psi. So its feasable to run 1601s maybe 170`s on pump gas. Here is some more info I found on octanes......
In this article, I'll try to shed some light regarding the variety of fuels available and their applications. I'm not a chemist, so I'm going to focus on fuel from a mechanic's point of view. I don't necessarily believe you have to know the composition of fuels to properly use them.
Above all else, remember rule number one: SAFETY FIRST! Your life is the most important thing here, so great care must always be observed in when handling fuel. Methanol is extremely poisonous. It's an accumulative poison, one that builds up over time, and it can oxidize to form formaldehyde. This can cause blindness, or worse. It can be absorbed through the skin and lungs by either direct exposure or inhalation of fumes. Also, inhalation of the exhaust can be very dangerous. Be careful and use your head.
Methanol and ethanol will absorb large amounts of water from exposure to air, so they must be kept in airtight containers. After burning methanol or ethanol in a two-stroke engine, it's most important to run a petroleum/oil mix through the engine. If you don't do this, the alcohol will corrode the cylinder wall, crank bearings, etc., which will lead to premature engine failure. I recommend that you run a half-quart of 16:1 petroleum/oil mixture through the engine. In most brands of fuel, higher octane ratings are achieved by adding tetra-ethyl-lead and ethylene dibromite. The decomposition of these additives may cause problems in two-stroke engines. The use of higher octane should be limited to blending additives such as acetone, methyl benzene, benzol, ethanol, or methanol. Such fuels will not cause problems in two-stroke engines, but they are more expensive.
Both methanol and ethanol have an octane rating of 140 to 160, so they can be used with very high compression ratios. This can result in an increase of up to 15 percent in horsepower. Where does the power increase come from? The two-stroke engine is a heat-type engine which burns fuel to cause expansion of gases, which propels the piston. The more heat produced by combustion fire, the more pressure will be exerted on the piston resulting in a power increase.
The fuel/air ratio for best power is 1:12.5 for petroleum, and 1:5.5 for methanol. One pound of petrol has an energy potential of 19,000 BTU; methanol has 9800 BTU. However, when these are mixed together, more heat energy is produced.
12. 5 / 5. 5 = 2. 2 7 * 9 8 0 0 = 2 2, 2 4 6
A 17 percent heat energy increase is very desirable, but there is a catch. With this mixture, you will bum 1.8 times as much fuel as with petrol alone. When using exotic fuels, make sure to increase fuel flow accordingly, or engine life will be shortened.
Also, the oil/fuel ratio needs to be changed. Start with 20:1 and work from there. An alcohol burner requires a strong ignition system, due to the much higher compression ratios, as well.
There is much confusion about what octane ratings are. Most people realize that we can get extra power with a high-octane fuel because of the higher compression ratio and spark advance. However, changing from, say, 97 octane to 110 octane will not give an increase in power. In fact, you could lose power if the engine is not modified accordingly. To combat this problem, I have developed my own method of finding the correct combination of octane and compression After the engine is built, proper carburetion is established. I begin to mix two brands of gasoline, for example, 93 octane pump and 116 octane racing fuel, in small increments. Take two gallons of 93 and add one quart of 116. Now take a speed run verified by radar gun. You should see a speed increase. Now, increase the 116 octane and make another run. Keep doing this until you notice a decrease in speed. You are now running too high an octane rating. Record the mixture that achieved the highest speed. This is the octane requirement for that particular engine setup.
The anti-knock properties of hydrocarbon fuels are related to their molecular structures. The paraffin's heptain and kerosene are long chains of carbon and hydrogen held together by weak molecular bonds which are easily broken down with heat. Iso-octane is a member of the iso-paraffin- fin family, which forms stronger bonds to resist detonation better. The cyclo-paraffin's (napthens) also have good anti-detonation properties. The aromatic fuels such as toluol also have very strong bonds. They also have good anti-knock characteristics. The chemical composition of the fuel determines just how rapidly the fuel will bum and how well it will resist detonations at high compressions and temperatures. For this reason, a high octane fuel will not increase engine power unless the engine actually needs fuel which is chemically stable at high temperature and pressure. Obviously, if the engine does not have proper compression to provide high combustion and temperature, then the octane fuel will not burn completely, resulting in power losses.
Nitromethane is not a good fuel, but it can provide two-stroke engines with a useful power burst. Nitrous contains approximately 53% oxygen by weight, so it is a chemical supercharger. In drag racing car engines, nitro is blended up to 15%, but in two-stroke engines it creates serious problems. I don't recommend its use in anything but small single-cylinder engines.
As mentioned before, an engine could waste power if it is mismatched with the octane requirement of a fuel. If the octane level is too high, only wasted energy and money are produced. However, if the octane level is too low, then we are faced with serious problems. An engine will run on one batch of bad fuel (too low octane), but it will burn holes in the pistons. Another batch of bad fuel can cause engine destruction through detonation.
So you can see how it's important to both the engine manufacturers and consumers to know the octane characteristics of each batch of fuel. To determine this, a special research engine was constructed, by the U.S. government utilizing variable compression features to evaluate and grade fuels. The test engine was a single cylinder, which was operated at standard temperature under full load at standard rpm. The compression was increased until the test fuel produced engine knock. The fuel's anti-knock quality would be specified as Highest Useable Compression Ratio (HUCR). In order to attain reliable tests, the high reference fuel chosen was iso-octane, and the lowest reference fuel was normal heptane. A series of tests were run, using various mixtures of those two fuels, until the blend was found which produced anti-knock behavior identical to that of the test fuel. So if the mixture of 75% iso-octane and 25% heptane produced the same anti-knock characteristics as the test fuel, the test fuel would receive an octane rating of 75.
Recently, a motor-test method, employing a greater engine speed and higher inlet temperature than the research test has come into use. Since the motor test is more severe, it yields ratings 6-12 octane lower than the research test. This is important, since it informs us that the Motor Octane Number (MON) is more relevant to racing engines than the Research Octane Number (RON). The number shown at the pumps is the Pump Octane Number (PON), the average of the RON and MON: (RON+ MON)/2=PON. This yields a credible rating of a fuel's performance under actual load conditions. I sincerely hope that this information will produce better racing engines and add to your enjoyment of our sport.
Posted 20 May 2007 - 06:22 PM
Posted 20 May 2007 - 07:03 PM
Posted 20 May 2007 - 09:50 PM
that depends. some places you can run only 130-155 psi on 92 pump, and some places you can run more. On 96 octain you can run in cylinder psi`s of about 147-183. there isnt one given number for everyone. It varies.
That is exactly right!! Volume of a given cylinder, squish area, velocity, clearance, and overall design all affect how a motor will respond with a given fuel. What you have to consider is you are testing "static" compression and that is no where near "running" compression numbers. As a general rule, the bigger the bore and stroke, the less static compression you can have before detonating. We are able to run a stock bore banshee at insane compression without problems but I ran my "honzilla" (250R with LT560 motor) at around 140psi on race fuel. That 560 pulls one big mouth full of fuel on the down stroke which changes everything.
This is why we tune with numbers and not gauges. Let the gauge be a testing tool and bench mark.
Posted 21 May 2007 - 12:24 AM