Gas

Discussion in '1st & 2nd Generation 1983-1989' started by smalls408, Feb 18, 2009.

  1. masonv45

    masonv45 New Member

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    Sorry, but 10.5.1 is a "low" compression engine.

    The '95 VFR has a compression ratio of 11.0:1 and Honda recommends any gas higher than 86.

    By comparison, the 2009 cbr1000rr has a compression ratio of 12.31.

    BUT - If you do have pinging, then yes, you do need to run higher octane gas.
     
  2. jaimev34

    jaimev34 New Member

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    Wow, that was a Redneck Rant. I didn't know Rush Limbaugh had a VFR. Welcome to the site.
     
  3. drewl

    drewl Insider

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    Yes, by all means, use gas. I find my bike will not run without it. Your results may vary.
    If you are talking about the other type of gas, I get it frequently. And it is HIGH octane, if you know what I mean.
     
  4. reg71

    reg71 Poser Staff Member

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    I actuall find that the bike runs better with fuel (or petrol as those on the other side of the blue thing say). everytime I try to get gas in it it floats away. there must be a trick. maybe you should hold the tank upside down then shut the cap real fast...

    :mwtf:
     
  5. leftcoast

    leftcoast New Member

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    Geeeeeeeeeeeeessssuuuussss.....
    :eek:
    A guy w/ a dozen posts asks a simple question about using Regular gas & gets a lecture about the communist bail-out in the United States of KFC....KCF10....whatever....:rolleyes:

    He'll probably never post again! poor bastard.....

    :pound::laugh:

    I use Regular.
     
  6. H.C.D.

    H.C.D. New Member

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    What about some of my corn-squeezin's?
     
  7. dogman

    dogman New Member

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    The Australian version calls for 91 octane minimum and has a compression ratio of 11.6:1.
     
  8. H.C.D.

    H.C.D. New Member

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    Speaking of high-compression, nice avatar!
     
  9. KC-10 FE

    KC-10 FE New Member

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    Since when are people from suburban NJ considered rednecks?

    KC-10 FE out...
    :plane: :usa2:
     
  10. vfourbear

    vfourbear New Member

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    That's right , cause that's how we roll around here..........heeheeehee

    Hell, how do you even know if the clowns at the gas station didnt just go ahead and fill the "premium" tank up with whatever they had left over from the "regular " tanker truck?

    "oh no, they cant't do that, that would be illegal"

    put regular in it and worry about other things, like how some folks have to tell you their political views every chance they get whether you asked or not
     
  11. leftcoast

    leftcoast New Member

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    I was reading..........I found an article.....I'm gonna post this....prolly 2 morrow, now...

    It basically talks about the "PUNDANTS" - all those talking heads guys & gals that are the News channels.....and FOX too.......

    It says that there is an inverse relationship between how loud & adement they are and how accurate they are.

    Louder & boisterous= wronger
    Quieter & less "in yer face" = right more often.

    I know...nobody will be able to sleep tonite in anticiaption........:rolleyes:
     
  12. vfrcapn

    vfrcapn Member

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    The sticker on my '85 1000R says minimum 94 RON rating. What does that work out to (r+m)/2? Around 89 or 90 octane?
     
  13. GreyVF750F

    GreyVF750F Member

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    Your PON (pump octane number R+M) would equal about 90-91. see link for more. Fuel ratings, RON, MON or PON?

    In all actuality whether a motor has 10.5:1 or 12:1 SCR (static compression ration) is irrelevant. It has very little to do with what octane is needed for a specific motor. What does have more is the DCR (Dynamic Compression ratio). This is basically set by the cam shaft, actually intake valve closing point when the motor is designed. You can have a high SCR (12:1) and a low DCR (7.5) and need a lower octane. Conversely you can have SCR 12:1 and a DCR 8.5 and need a higher octane.

    I was going to compare the two motors,83 750 (10.5:1)and 09 CBR1000 (12:1) to see the DCR numbers. I'll bet they are close if they run the same octane,most likely less on the CBR. But I can't find the rod lengths for either and that's part of the calculation. Both are still considered high compression in the gasoline ICE world.

    I went back in to some of my files on this and found a very good explanation of DCR. Sorry about the long cut and past below. But this gentleman has written a very good article about it and can explain it better than I can. Also there are some links at the end that has more discussions about octane needs and DCR/SCR and basic cam specs to look at. Octane is only one of the several things to consider when discussing when/how detonation occurs.

    Here's the article:

    Dynamic Compression Ratio
    (Will my engine run on pump gas?)
    Home

    Dynamic Compression Ratio (DCR) is an important concept in high performance engines. Determining what the compression ratio is after the intake valve closes provides valuable information about how the engine will perform with a particular cam and octane.


    Definition: The Compression Ratio (CR) of an engine is the ratio of the cylinder volume compared to the combustion chamber volume. A cylinder with 10 units of volume (called the sweep volume) and a chamber with a volume of 1 has a 10:1 compression ratio. Static Compression Ratio (SCR) is the ratio most commonly referred to. It is derived from the sweep volume of the cylinder using the full crank stroke (BDC to TDC). Dynamic Compression Ratio, on the other hand, uses the position of the piston at intake valve closing rather than BDC of the crank stroke to determine the sweep volume of the cylinder.

    The difference between the two can be substantial. For example, with a cam that closes the intake valve at 70º ABDC, the piston has risen 0.9053" from BDC in a stock rod 350 at the intake closing point. This decreases the sweep volume of the cylinder considerably, reducing the stroke length by almost an inch. Thereby reducing the compression ratio. This is the only difference between calculating the SCR and the DCR. All other values used in calculating the CR are the same. Note that the DCR is always lower than the SCR.

    Dynamic compression ratio should not to be confused with cylinder pressure. Cylinder pressures change almost continuously due to many factors including RPM, intake manifold design, head port volume and efficiency, overlap, exhaust design, valve timing, throttle position, and a number of other factors. DCR is derived from measured or calculated values that are the actual dimensions of the engine. Therefore, unless variable cam timing is used, just like the static compression ratio, the Dynamic Compression Ratio, is fixed when the engine is built and never changes during the operation of the engine.

    Two important points to remember:

    * The DCR is always lower than the SCR
    * The DCR does not change at any time during the operation of the engine


    Determining seat timing: Since the early days of the internal combustion gasoline engine, engineers have known that the Otto four stroke engine is compression limited and that the quality of the fuel used determines the CR at which the engine could operate. However, it is not the Static CR but the actual running CR of the engine that is important. Compression of the air/fuel mixture cannot start while the intake valve is open. It may start slightly before the intake valve is fully seated. However, there is no easy way to determine this point so using the advertised duration number provided by the cam manufacture is the next best thing. Most cam grinders use .006" of tappet lift (hydraulic cam), although some use other values, with .004" being a common one. This duration is often referred to as the "seat timing". We will used advertised duration for calculating the DCR.

    The special case of solid lifter cams. Solid cams are usually speced at an abitrary lift value (often .015" or .020") determined by the designer to be a good approximation of the cam's profile. This lift spec is not always correct for a particular cam. The correct lift point to determine the seat to seat timing of the cam is: Lash / rocker ratio + .004". This accounts for the lash. A cam with a .026" lash (given 1.5 rockers) should be measured at .02133" (.026/1.5+.004= .02133>"). This cam lash, with seat timing speced at .020", is actually a bit smaller than advertised since the valve has yet to actually lift off the seat. How much is the question (.024" lash is the only lash that is correct at .020" with 1.5 rockers). Without knowing the ramp rate, and doing some calculations, or measuring with a degree wheel, it is impossible to know. Again, we have to use the mfg's numbers. Here is some Chevy factory cam help.


    Why it matters: A 355 engine with a 9:1 static CR using a 252 cam (110 LSA, 106 ICL) has an intake closing point of 52º ABDC and produces a running CR (DCR) of 7.93. The same 9:1 355 engine with a 292 cam (having an intake closing point of 72º ABDC) has a DCR of 6.87, over a full ratio lower. It appears that most gas engines make the best power with a DCR between 7.5 and 8.5 on 91 or better octane. The larger cam's DCR falls outside this range. It would have markedly less torque at lower RPM primarily due to low cylinder pressures, and a substantial amount of reversion back into the intake track. Higher RPM power would be down also since the engine would not be able to fully utilize the extra A/F mixture provided by the ramming effect of the late intake closing. To bring the 292 cam's DCR up to the 7.5 to 8.5:1 desirable for a street engine, the static CR needs to be raised to around 10:1 to 11.25:1. Race engines, using high octane race gas, can tolerate higher DCR's with 8.8:1 to 9:1 a good DCR to shoot for. The static CR needed to reach 9:1 DCR, for the 292 cam mentioned above, is around 12:1.
    This lowering of the compression ratio, due to the late closing of the intake valve, is the primary reason cam manufactures specify a higher static compression ratio for their larger cams: to get the running or dynamic CR into the proper range.


    Caveats: Running an engine at the upper limit of the DCR range requires that the engine be well built, with the correct quench distance, and kept cool (170º). Hot intake air and hot coolant are an inducement to detonation. If you anticipate hot conditions, pulling some timing out might be needed. A good cooling system is wise. Staying below 8.25 DCR is probably best for trouble free motoring.

    >>Unless you have actually measured the engine (CCed the chambers and pistons in the bores), these calculations are estimations, at best. Treat them as such. The published volumes for heads and pistons can, and do, vary (crankshafts and rods, too). It is best to err on the low side. When contemplating an engine of around 8.4 DCR or higher, measurments are essential, or you could be building another motor.<<


    Details: Long duration cams delay the closing of the intake valve and substantially reduce the running compression ratio of an engine compared to the SCR. The cam spec we are interested in to determine the DCR is the intake closing time (or angle) in degrees. This is determined by the duration of the intake lobe, and the installed Intake CenterLine (ICL) (and indirectly by the Lobe Separation Angle (LSA)). Of these, the builder has direct control of the ICL. The others are ground into the camshaft by the grinder (custom grinds are available so the builder could specify the duration and LSA). Changing the ICL changes the DCR. Retarding the cam delays intake closing and decreases the DCR. Advancing the cam causes the intake valve to close earlier (while the pistons is lower in the cylinder, increasing the sweep volume) which increases the DCR. This can be used to manipulate the DCR as well as moving the torque peak up or down the rpm range.

    It is necessary to determine the position of the piston at intake valve closing to calculate the DCR. This can be calculated or measured (using a dial indicator and degree wheel). Since compression cannot start until the intake valve is closed, it is necessary to use seat times when calculating the DCR. Using .050" timing will give an incorrect answer since the cylinder is not sealed. At .050" tappet lift, using 1.5 rockers, the valve is still off the seat .075" and .085" with 1.7 rockers. While the flow is nearing zero at this point, compression cannot start until the cylinder is sealed.

    Another factor that influences DCR is rod length. It's length determines the piston location at intake closing, different rod lengths change the DCR. Longer rods position the piston slightly higher in the cylinder at intake closing. This decreases the DCR, possibility necessitating a different cam profile than a shorter rod would require. However, the effect is slight and might only be a major factor if the rod is substantially different than stock. Still it needs to be taken into account when calculating the DCR.


    Calculating DCR: Calculating the DCR requires some basic information and several calculations. First off, the remaining stroke after the intake closes must be determined. This takes three inputs: intake valve closing point, rod length, and the actual crank stroke, plus a little trig. Here are the formulas: (See the bottom of the page for a way around doing all this math.)

    Variables used:

    * RD = Rod horizontal Displacement in inches
    * ICA = advertised Intake Closing timing (Angle) in degrees ABDC
    * RR = Rod Distance in inches below crank CL
    * RL = Rod Length
    * PR1 = Piston Rise from RR in inches on crank CL.
    * PR2 = Piston Rise from crank CL
    * ST = STroke
    * 1/2ST = one half the STroke
    * DST = Dynamic STroke length to use for DCR calcs

    What's going on: First we need to find some of the above variables. We need to calculate RD and RR. Then, using these number, we find PR1 and PR2. Finally, we plug these number into a formula to find the Dynamic Stroke (DST).

    Calcs:

    * RD = 1/2ST * (sine ICA)
    * RR = 1/2ST * (cosine ICA)
    * PR1 = sq root of ((RL*RL) - (RD*RD))
    * PR2 = PR1 - RR
    * DST = ST - ((PR2 + 1/2ST) - RL)

    This result is what I call the Dynamic Stroke (DST), the distance remaining to TDC after the intake valve closes. This is the critical dimension needed to determine the Dynamic Compression Ratio. After calculating the DST, this dimension is used in place of the crankshaft stroke length for calculating the DCR. Most any CR calculator will work. Just enter the DST as the stroke and the result is the Dynamic CR. Of course, the more accurate the entries are the more accurate the results will be.

    Using this information: DCR is only a tool, among others, that a builder has available. It is not the "end all" in cam or CR selection. However, the information provided is very useful for helping to match a cam to an engine or an engine to a cam. It is still necessary to match all the components in an engine and chassis for the best performance possible. Pairing a 305º cam with milled 882 heads just won't cut it even if the DCR is correct. The heads will never support the RPM capabilities of the cam.

    A good approach when building an engine is to determine the duration and LSA needed for the desired RPM range. Once this is know, manipulate the chamber size and piston valve reliefs (and sometimes the cam advance) to provide a DCR around 8.2:1. Now that the correct piston volume and chamber size is know, enter the actual crankshaft stroke in your CR calculator to see what static CR to build to. Often the needed SCR is higher that you would expect. Note: The quench distance (piston/head clearance) should always be set between .035" and .045" with the lower limit giving the best performance and detonation resistance.

    Alternatively, with the SCR known, manipulate the cam specs until a desirable DCR is found. When the best intake closing time is derived, look for a cam with that intake closing timing, that provides the other attributes desired (LSA and duration). Often times the best cam is smaller than one might expect. Sometimes a CR change is needed to run a cam with the desired attributes.

    The information given here should be used as a guideline only. There are no hard and fast rules. It is up to you, the engine builder, to determine the correct build of your engine. And remember, unless accurate measurements are taken, these calculations are approximations.

    Here is a link to a discussion in which Jim McFarland discusses some issues regarding compression ratios and combustion problems.

    Here is an article on High Compression by David Vizard

    I hope you find this information helpful and useful,

    Pat Kelley

    *******************************************************************************************
    Some Links:

    Discussions- 8th reply dynamic compression ideas - Speed Talk

    See reply #15- DCR question/confusion - CamaroZ28.Com Message Board

    Calculators -DCR and everything else engine wise. 1/2 way down on left.
    Wallace Racing - Automotive Calculators

    So if your motor runs fine on 87 there is no need to run higher octane.....unless some of the other variables like engine temp, air intake temp are just a couple of things that constantly change and can put you over the edge at times in to detonation or just down on power. No matter how slight the detonation is, it still takes a toll on the top rod bearing and it's crush value. I'll pay the extra .50 cents to make sure it won't.
     
    Last edited: Feb 26, 2009
  14. GILL

    GILL New Member

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    Yikes! I'm squirrly eyed after that long read..... I often wondered about filling up at the pumps that have only one nozzle. If the last customer using the pump used 86 octane and you pull up and start pumping 91, would their be a few liters of the 86 still left in the hose that you are putting in your tank?

    Also, it sure is nice to see Bush gone from up here......:thumbsup:
     
  15. havcar

    havcar New Member

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    I've often considered that. Wink, Wink!!
     
  16. Nungboy

    Nungboy New Member

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    Yaoooow! That very long technical reply makes me recall an old bicyclist friend. While a dedicated cyclist, he was not a gear head at all. During a tech discussion, if asked something, he'd scrunch his shoulders and say "I pedal it and it goes..."
    So, to paraphrase Mark, "I put in fuel and it goes..."
    :thumbsup:
     
  17. vfrcapn

    vfrcapn Member

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    Thanks Grey, I'll stick to 89 or 91, the only premium grades available here in CA.
     
    Last edited: Feb 27, 2009
  18. yoda6669

    yoda6669 New Member

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    yodasmile Nooooooooo! another gas thread! I use regular unleaded, cheapest available around the area. I do put some Techron fuel system treatment every oil change just to be safe.
     
  19. mjrfd99

    mjrfd99 New Member

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    I think when we're south of 195.

    Oh yeah, my 86 owners manual says 91.
     
  20. smalls408

    smalls408 New Member

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    Thanks everyone for all the info. It's just that I heard that bikes have a higher cr than cars so that it is better for your engine to run higher octane. But you guys have cleared that up for me. I'l double check my manual and stick to what is recommended. Thanks for everyone's two cents.
     
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