1991 R100 GS/PD dyno run

Discussion in 'Airheads' started by midlman, Feb 27, 2011.

  1. midlman

    midlman Adventurer

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    We had a local dyno day here in Oly, WA and along with my Duc, I figured I would run my PD just to get a baseline. Ended up with 49hp and 49 ft-lbs at the wheel. Each run it was getting better..probably clearing up since it really hadn't been run since early December. Air/fuel was slightly rich in the upper rpms..but it was also really cold..so I'm going to leave the jetting alone for now.

    It's totally stock (even has air inj still there) and has around 86XXX miles on her. I was pretty happy since stock crank hp is around 65... :D Now to resist doing any upgrades for more power as she runs really great!...

    [​IMG]

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    #1
  2. larryboy

    larryboy Chopper Rider

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    Did they leave the Dynojet extra 20% in the calculations?




    :hide
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  3. Weaverman

    Weaverman Damaged goods

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    You think that's running too fat on top? I think it looks like a pretty good power enrichment curve for a large-bore air cooled twin.

    My '94 owner's manual claims 56.1 lb/ft & 58 bhp, so even with all the mileage, etc., this test indicates only a 15% loss (including the driveline losses) from new or advertised! Pretty cool.

    Are you gonna just tease us or show us the Duc's numbers??
    #3
  4. midlman

    midlman Adventurer

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    Best the Duc did (04 998 Matrix edition) was 115 and 69 ft-lbs but I was in the process of creating a dual map (one for each cylinder). The vertical cylinder was perfectly dialed in but for some reason the A/F on the front cylinder wouldn't cooperate...way lean at low rpm and then rich at upper. No amount of playing with the PCIII would help, so I've got some underlying issue with that cylinder. Need to look at the plugs/wires to see why we were having a random miss too.

    On the PD, I figured it should be around 13ish to 13.5..but don't know...It doesn't belch black and the plugs are nice and tan so I'll leave it alone...
    #4
  5. bgoodsoil

    bgoodsoil Dare to be Stupid

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    thanks for posting that up. Manufacturer horsepower listings (and weight) are always lies. Stagehand put in a Siebenrock kit. Maybe he'll do a Dyno and we can get some honest comparisons.
    #5
  6. supershaft

    supershaft because I can

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    That's a good reading. Cold ambient, just like cold engine temp, makes them run lean.

    So I am guessing your bike still had the 135 stock mains in it? That is about the same A/F ratio my bike had with a 135 mains in my 38mm Dell's with airbox mods, port mods, sport cam, and Staintune Sport mufflers. You might crack 50hp with 130's. 130's got me another almost 1.5hp and an A/F line right around that target line on that chart. It won't rev past about 5000rpm with 125's in it. It just flat out quits running like you hit the kill switch.

    Usually the higher and higher readings are mostly a combination of the bike getting up to most efficient temp which is a LOT hotter than many think AND the dyno itself getting up to its most efficient temp. It's real common. Remember that that phenomenon and others can be used to manipulate dyno results in this or that direction. Comparing dyno runs is a tricky business and very difficult to manage in the best of conditions.

    The most efficient mix will almost always leave your plugs looking too lean but it isn't! IMO, you piston top is more accurate. White plugs, no problem. White piston top, problems. At least with pump gas. Race gas leaves everything white well before optimum mix. White just means you are getting close with race gas. It's the lead in it.
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  7. Weaverman

    Weaverman Damaged goods

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    That extra fuel keeps her tickin' on for miles and miles. A little additional fuel goes a long way towards cooling down combustion chamber components.

    Since the bike has off-road capabilities, it's reasonable to expect the cooling fins will become dirty (clogged?) and pistons/rings, heads & valves, spark plugs and oil temperatures will rise. There's no temp sensor in this baby to pull spark or add fuel when she starts heating up, no cooling fans to kick on; this calibration has to err on the side of safety.
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  8. supershaft

    supershaft because I can

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    I disagree. I think the extra fuel builds up carbon and gets her pinging when it gets hot out on the trail in the mud or whatever. 13.25 is extra fuel, just less extra than 12.5 but it makes more power on less fuel and keeps the engine cleaner. I went from 135's to 130's in my bike about 50,000 miles ago. It likes it. Just for instance, last summer I was ripping up I-5 blasting in and out of traffic between about 80 and squirting up to about 105 or so and rolling into and out of the throttle pretty hard in 108 degree heat and never heard it ping a lick. That's with the 130's in it.
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  9. Rob Farmer

    Rob Farmer Long timer

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    I'm covinced they need to run rich for road use. My last dyno run showed mine running slightly rich just off tickover and midrange. I dropped a jet size on the needle jet and it needed the choke on for several miles and even then it felt like it was straining.
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  10. Weaverman

    Weaverman Damaged goods

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    Negatory, Supershaft. Extra fuel is how you avoid detonation.

    Of course, carbon buildup can be the source of detonation. Most "carbon" (or more accurately, combustion deposits) you find in your ring grooves, on your piston crown, and on your head/valves are from the components of the oil, not the fuel.

    And remember, "Old's Cool" factory jetting will always be conservative to protect the engine from timing scatter, low-grade fuel, hot running, etc. No dispute that more power can be safely made by leaner jetting if, for example, you ride where the air is thin, never load it in the dirt or two-up, etc.

    When dyno tuning a carbureted engine for everyday use (motorcycle or otherwise), tuners often find the A/F ratio that yields LBT conditions (Lean Best Torque), then add ~ 5% fuel for safety. With an injected engine, the game is a little different because sensors can tell you a lot more about the actual operating conditions. I've seen conditions with A/F ratios as low as 8.5:1 at certain operating conditions on production cars to extend the life of pistons, converters, etc.
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  11. Lornce

    Lornce Lost In Place

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    Strapping in...


    :lurk
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  12. midlman

    midlman Adventurer

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    I don't have much experience playing with carbureted engines...but if I plug the air injection system on the PD..I suspect the air/fuel will go even richer? right?..

    So maybe go down to the 130 and then plug the air inj system would still be safe and give a bit more power?
    #12
  13. Weaverman

    Weaverman Damaged goods

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    The air injection system on your bike is a "post burn" sytem. Doesn't have any impact on what's going on in the combustion chamber, only on how bad your emissions are! It's an effort to clean up unburnt hydrocarbons in the exhaust by introducing a little oxygen to the port.

    Interesting what you're saying here though. I was assuming the system was removed. Since the system is there and working (?), what this means is that you're actually running richer than indicated by the Lambda sensor (A/F ratio sensor). The additional air injected into the gas stream after the port would be recognized by the sensor. Changed your air filter lately?
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  14. midlman

    midlman Adventurer

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    I was just typing that up..when you added to your post.. LOL..I'll take a look at the air filter and see how bad it is...but yes...I think I can comfortably go to the 130 ....
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  15. Weaverman

    Weaverman Damaged goods

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    Midlman - where are you located geographically?
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  16. anotherguy

    anotherguy unsympathetic

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    The bike has CV carbs does it not? If so the air temperature is negated by the carbs. The reason the numbers increase by the run is efficiency. The hotter it gets inside more of incoming charge is evaporated thus an increase in amount burned. If you have copies of the earlier runs watch the A/F ratio change as the runs go on.

    If it were mine I'd go down a step on the main. Then again if it ain't broke.............:evil
    #16
  17. midlman

    midlman Adventurer

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    There's the debate... she runs great..fires up everytime...no issues.. But I always strive to make it more efficient... Hmmm...

    BTW..I'm in Olympia, WA ... PacNW.. elevation of maybe 100msl. On a trip to central OR a year or so ago...had to turn up the idle a hair just to keep it running (about elevation 3500msl)
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  18. Lornce

    Lornce Lost In Place

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    None of the readings mean much at all as long as your fresh air plumbing is hooked up, no?

    :scratch
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  19. Benjava

    Benjava ?

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    Wide open AFV is only part of the story. Good dyno tuners will set the brake at cruising speed. Then check what the AFV is at 1/4, 1/2 and 3/4 throttle. As in rolling along, pulling up a hill and pulling up a really big hill against the wind. This will tell you if you're getting best gas mileage without detonation and burning down the motor.
    #19
  20. Weaverman

    Weaverman Damaged goods

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    Not aware of CV carbs negating air temp? Very interesting. Even if there were some "warming" contribution to the IAT (Inlet Air Temp) at idle or part throttle by the slides, I don't see how it would differ at all from a non-CV slide. The point is moot, however, since this test is a WOT test and the slides/needles are fully raised. Inlet air temp is definitely a factor.

    You won't change the "efficiency" at all by re-jetting. The Brake Specific Fuel Consumption (BSFC = lbs fuel/hr/HP = efficiency) is already fixed by the combustion chamber design, CR, pipes, runners, etc. You'll only change the amount of fuel thrown in the fire (and out the pipe). Of course, higher temps will better vaporize fuel, and higher temps will come with leaner operation. That's one reason why leaner operation contributes to detonation.

    BTW, your main jet doesn't contribute to your idle change at altitude; your pilots do. But understand the effect exists across the band.

    If you were really interested in making a change to your main jet, which you can probably do with just the data you have now and not worry much, it would be great to have some part throttle A/F data. It might be wiser to change the needle and leave the WOT fuel (main jet) alone. you don't run at WOT all that often, and when you do...protection is good!

    Where I live in Mid-Michigan, my GS actually runs better with the needles raised a notch (richer through the middle). Also, I ride down into the 20sº F. Lots of oxygen in the air at that point here at ~ 230 msl. The stockk jetting works pretty well.
    #20