yamil_787 Posted June 17, 2015 Report Share Posted June 17, 2015 I checked compression on my banshee the other day has 175+ on both sides and i do have a 4mm crank with basic porting on the cylinders, i was wondering what fuel i should be running ? Im in Texas btw Quote Link to comment Share on other sites More sharing options...
BANSHEE HP Posted June 17, 2015 Report Share Posted June 17, 2015 110 octane Quote Link to comment Share on other sites More sharing options...
yamil_787 Posted June 18, 2015 Author Report Share Posted June 18, 2015 VP? Quote Link to comment Share on other sites More sharing options...
lil Doobie420 Posted June 18, 2015 Report Share Posted June 18, 2015 Doesnt have to be.ur gonna want to advance the timing to 5 or 6 too Quote Link to comment Share on other sites More sharing options...
wv redneck banshee Posted June 23, 2015 Report Share Posted June 23, 2015 I am new as well, 21cc domes, trail port, vforce4 reeds, racefuel? also does 340main 27.5pilots sound accurate for 500ft obove sea? Quote Link to comment Share on other sites More sharing options...
lil Doobie420 Posted June 23, 2015 Report Share Posted June 23, 2015 Sounds like 93octane motor. Check compression report back... Quote Link to comment Share on other sites More sharing options...
wv redneck banshee Posted June 23, 2015 Report Share Posted June 23, 2015 ken oconnor??? anyone can chime in,gimme a honest answer plz.. thanx Quote Link to comment Share on other sites More sharing options...
sheerider1026 Posted June 23, 2015 Report Share Posted June 23, 2015 Keep it under 160 and you can run 93 pump. Id aim for 150-155 1 Quote Link to comment Share on other sites More sharing options...
sheerider11 Posted June 23, 2015 Report Share Posted June 23, 2015 ken oconnor??? anyone can chime in,gimme a honest answer plz.. thanx what do you want to know? a simple search on here and you will see what people think about him. Quote Link to comment Share on other sites More sharing options...
registered user Posted June 23, 2015 Report Share Posted June 23, 2015 Keep it under 160 and you can run 93 pump. Id aim for 150-155 THE TRUTH ABOUT COMPRESSION TESTING by Mull Engineering We would like to take the chance to answer some general questions and myths about compression testing an engine. Compression testing is a method of using a pressure testing device to measure the “cranking” pressure developed in the combustion chamber during cranking speeds of kick or electric starting. These engine speeds are generally between 100 and 400 rpm. This is usually accomplished by removing the spark plug and installing a pressure tester in place of the park plug and cranking the engine over. This pressure can be somewhat indicative of the condition of an engine and is often used to trouble shoot an engine. We get a lot of questions about what the pressure should be for a given engine and especially, what is safe for certain fuels. Well, hate to break the news but if you are going to rely on compression testing to determine your fuel selection, you are asking for trouble. The reason is that cranking compression numbers can vary greatly from actual running compression due to many variables such as volumetric efficiency or air fill into the cylinder at cranking speeds, and the wet fuel that is added by the carburetor as rpms come up to operating speeds which does not compress as easily as air. These do not even consider the high pressures of burning fuel in the combustion chamber. The only way to correctly determine the right fuel for an engine is by comparing the swept volumes of an engine when the piston is at top dead center and bottom dead center. This is expressed as the compression ratio or CR. There are also other considerations like head design, piston design, squish clearance, etc, but we will keep it simple for this discussion. Checking compression is a great way to check the condition of an engine and determine if an engine is in need of service providing additional tests are performed. This is only applicable if there is a base line measurement to refer to, either from a manual, or from testing a given engine when it is new and considered a valid value. Regarding four strokes, this form of testing is also a great way to determine if valves are seating properly and at the right time. This form of testing, however, may not give accurate data as to the piston ring seal, wear on the piston rings, or piston condition itself. Bottom line is that many other things can be going wrong in the engine and the compression test will not show it! This is why experienced technicians use this form of testing only as a guide and usually along with other tests. This testing might be compared to testing a child’s temperature to determine illness, it is simply not enough data to give the full picture. However, by compression testing, one can easily determine, if an engine has lost substantial compression and if an engine is in need of service. Many people will look to perform a compression test at home and this can be done with just as much accuracy as any service shop, given the right equipment and knowledge. Contrary to popular myth, an actual pressure gauge bought about anywhere, can be rather accurate. This, however, is only looking at the dial gauge portion though. There is also a hose extension and the adaptor component that will screw into the head in place of the spark plug. One of the most common mistakes is selecting a tester in which the head adaptor does not screw into the cylinder head with the same amount of thread as the spark plug that came out. This lack of thread can be compared directly to adding extra volume in the cylinder head and will not represent the same pressure numbers as if the spark plug were reinstalled. Obviously selecting a tester with the correct length of threads will eliminate this problem. You must also be careful not to use too long of an adaptor as well because of the opposite effects as well as potentially causing internal engine damage from mechanical contact from moving parts in the engine and the tester adaptor. The next and most common problem we see is when a tester is selected, it should have a “Schrader valve” in the very tip of each adaptor. A Schrader valve is the same valve used in the valve stem of a tire and is a one way or check valve device. What this does is isolate the volume in the cylinder head from the volume in the tester adaptor and extension hose. Without this valve in place at the very tip of the adapter, the extra volumes in the hose and adaptor will act to increase the cylinder head volume and give a false (low) reading. The Schrader valve must be in good condition and work correctly and it is common to replace them regularly. The method for compression testing an engine is rather elementary but certain things must be considered. First, you want to turn the ignition switch off so you don’t get surprised. Install the tester adaptor in place of the spark plug and either hold the throttle wide open to allow the most air to the engine or you can simply remove the carburetor entirely. Then either kick or electrically crank the engine over until the compression gauge will not go any higher. This process generally takes around 50-200 revolutions of the engine to complete the test. Excessive cranking while the gauge is still climbing is sign of leakage somewhere in the engine. When the test is complete, the gauge should hold the tested pressure at the gauge indefinitely. If not, there is certain leakage of the tester, either the mentioned Schrader valve, or other unions should be inspected. It is NOT a requirement to purchase an expensive compression tester but one should certainly be selected of decent quality and include the considerations listed above. Regarding four strokes, it should be mentioned many engines use a form of compression release to lower cranking compression to make an engine easier to turn over and start. This compression release is usually turned of by mechanical means right after starting. This mechanism will directly affect accurate compression testing. You may need to refer to your manual for an estimated compression value with the compression release in use, or you may need to render the release mechanism ineffective for testing. If the engine uses electric start, it may be impossible to turn over without the compression release so derated numbers from a service manual will be required. Quote Link to comment Share on other sites More sharing options...
sheerider1026 Posted June 24, 2015 Report Share Posted June 24, 2015 I was " generally speaking" RU. I do know a few things about tuning engines. Boosted and N/A. Have a good day Quote Link to comment Share on other sites More sharing options...
#1JUANstunna Posted June 24, 2015 Report Share Posted June 24, 2015 I was " generally speaking" RU. I do know a few things about tuning engines. Boosted and N/A. Have a good day You dumb! you can't give Tyler a boost let alone figure out an engine. Sent by me FFS from Tapacrap Quote Link to comment Share on other sites More sharing options...
sheerider1026 Posted June 24, 2015 Report Share Posted June 24, 2015 Maybe 1 Quote Link to comment Share on other sites More sharing options...
registered user Posted June 24, 2015 Report Share Posted June 24, 2015 generally speaking CRANKING COMPRESSION VS OCTANE REQUIREMENT Generally, when you increase compression past a certain level, you need to increase the fuel octane requirement in order to combat detonation. Detonation occurs when the cylinder pressure is high enough to ignite the end gases without the aid of the spark plug. This usually occurs in the combustion chamber end zones (near the bore edge of the dome). This ignition of the end zone gases will create a shock wave that will travel and collide with the on-coming flame front. It is this collision that will do the damage to your engine. So, think about it..if you increase the fuel's resistance to auto ignition by raising its octane level then it MAY not self ignite before the flame front reaches it. So, what does this have to do with compression? It stands to reason that higher compression RATIOS will yield higher cylinder pressures (given that nothing else has changed before the compression ratio was raised) Well.. we just determined that the higher pressures are a major player in causing the fuel to auto ignite (not good) hence, the need for higher octane with higher compression RATIOS. OK, we have been talking about compression ratios NOT cranking compression. What about the cylinder's cranking compression? Continuing along the above lines: What about cranking PSI vs Octane requirements?? My opinion is that they are not very closely related. In other words.. knowing what PSI your engine "cranks" out will NOT tell you whether or not you need a higher octane fuel, unless, of course, the PSI number is extremely large (like 200). Then, it may carry more weight and tell you , "yes", you do need some high octane fuel BUT it will NOT tell you which octane you need. OK, "WHY?" Let's do some deductive reasoning here: Take an engine with an exhaust duration of 182 degrees ATDC and install some domes (any domes) that yield.. say 170 PSI cranking compression. OK, take another engine, exactly the same, except the exhaust duration is at 198 degrees ATDC (ie higher exhaust port) Now, install the SAME domes that the other engines has. Now, the cranking compression reads only 150 PSI. Hmmm.... so does this engine require a different octane of fuel than the other one? Probably, but not what you think.. It , most likely, requires, a HIGHER octane fuel NOT a lower octane. I know that the general conception among riders is that the higher the PSI .. the higher the octane needed.. Well, I just told you completely the opposite. With the general consensus.. it would stand to reason that when ever you raise the exhaust port... you need to run a lower octane fuel because the cranking compression will, indeed, get lower with higher exhaust heights. Does this seem right?? What if you lowered the exhaust height? Would you then need a higher octane fuel because the cranking PSI would surely go UP? Let's look a few of the determining factors behind the above statements: Please realize that I will be over simplifying the processes but it should get the point across. 1: With an increase in exhaust height or area.. the probability of having more escaped fuel/air charge "stuffed" back into the cylinder just prior to exhaust port closing increases. This will raise your dynamic cylinder pressures and combustion temps. 2: Along those same lines... during the peak scavenging phase the larger exhaust CAN effectively pull more F/A charge in the cylinder and out the exhaust which then leads us back to #1. 3: Crown temps are higher with a raised exhaust. Anytime you have elevated crown temps, you increase your chances for detonation. IMHO, there is no direct relation between cranking PSI and octane required. I wish there were. For example.. one of my race engines (snowmobile) cranks only 140 PSI but I know that if I don't run at least 110 octane , the engine will not live for very long. As we are beginning to realize... these PSI charts really give no relative information unless your engine is stock ported (and even then, I find that they are not useful) This all relates to information needed when choosing a dome for your engine. I know that when you call up the head shop or go to the counter and ask the parts guy the conversation goes something like this: YOU: "So, if I want to stay with premium pump gas, which size domes should I purchase?" THEM: "Well, if you want to stay with premium fuel your cranking compression needs to stay below 160 PSI. These XXcc domes will put you right at that correct PSI for premium fuel" I DO NOT AGREE WITH THIS LINE OF REASONING! We see that the porting arrangement plays a MAJOR role in the resultant cranking compression. It is NOT only about the head!!! Then.. You factor in the bore size in the equation and you REALLY can get into a pickle!! So, you have to be very careful in choosing domes for your engine. The head (dome) design itself, plays a large role in determining octane requirements of an engine. If the dome is not correct for the engine, you could be forced to run race fuel in order to avoid engine failure. OR on the other extreme, you may THINK your engine requires race fuel, when, in fact, it would live just fine on pump fuel. So, you could be throwing money and convenience right out the window. © Copyright 2006. 2StrokeHeads.com Disclaimer Website updated by Urban Plains Web Design 1 Quote Link to comment Share on other sites More sharing options...
trickedcarbine Posted June 24, 2015 Report Share Posted June 24, 2015 Ok, this gets to I depth every time this topic comes up. While everything RU posted is legit, people need to remember this is not just some new combo that needs to be figured out. The Banshee platform has already been subjected to just about any combo that can be dreamt up. Meaning that all the foot work has been done. At this point, if you stay up to date, it's pretty common knowledge that a stock cylinder banshee is on edge at about 150-160 psi depending on machine work. Now start throwing variables at it like porting and dome changes and that number may be lower but still need race fuel. Or vice versa. However, in OP's case whether he did a calculated compression ratio or not at this point I don't think it matters because no way no how, will any stock cyl motor cranking 175psi be ok on pump fuel. Remember it's making that even with a little exhaust work. 1 Quote Link to comment Share on other sites More sharing options...
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