1991 R100 GS/PD dyno run

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

  1. supershaft

    supershaft because I can

    Joined:
    Sep 9, 2010
    Oddometer:
    9,116
    Location:
    San Francisco Bay area
    Who would call best torque a torque reading that can not be sustained under normal operating conditions? Perhaps to see how quick you can lunch an engine? Why even consider a torque that isn't doable? It seems pointless to me other than see just what will destroy the engine. I have no interest in that. My point is that best torque can be found for any particular situation. Regular OR premium. My above 13 A/F ratio has plenty enough room to cover both because, even above 13, it is still not close enough to rule one out. That's my main point.

    The fact that our bikes run just fine with 10% ethanol demonstrates that our jetting is indeed a bit fat. If it wasn't already, the stuff would be melting engines right and left which it isn't. Maybe 15% will get our bike leaned out about right without rejetting?

    Thanks EPA? I think you mean the corporate farming lobby. Talk about corporate welfare. Ethanol mixed gas is a double whammy!
    #41
  2. RecycledRS

    RecycledRS Along for the ride

    Joined:
    Nov 2, 2008
    Oddometer:
    1,048
    Location:
    Vancouver Island
    :lurk
    I love this site!
    #42
  3. SCQTT

    SCQTT Zwei Kolben

    Joined:
    May 16, 2005
    Oddometer:
    5,626
    Location:
    Mike's Sky Rancho
    I have one & I'll probably never sell it, but what a waste of 1,000ccs!

    Talk about understressed.......with that HP to displacement ratio they should run forever without a rebuild.
    #43
  4. Stagehand

    Stagehand Imperfectionist

    Joined:
    Oct 6, 2004
    Oddometer:
    31,934
    Location:
    Shawangunks
    Yeah me too, even if I dont understand a thing and just like the way the words sound :D

    I would be curious to get mine on a dyno too, but I assume it would be pretty anticlimactic.
    #44
  5. bgoodsoil

    bgoodsoil Dare to be Stupid

    Joined:
    Jul 9, 2008
    Oddometer:
    4,674
    Location:
    Washington, DC, USA
    It's going to take me an hour of research on the internet to even understand what ya'll are talking about but I'm sure it'll be worth it! And I thought that short piston/long rod thread was enlightening.
    #45
  6. Lornce

    Lornce Lost In Place

    Joined:
    Aug 17, 2003
    Oddometer:
    19,727
    Location:
    Way Out There.
    Science and business/politics. :huh

    Reality is so complicated. :evil


    Just to recap: SS you're saying 13.5 is the target, right?


    :ear
    #46
  7. anotherguy

    anotherguy unsympathetic

    Joined:
    Jun 18, 2009
    Oddometer:
    9,090
    Location:
    the hills
    Most bikes make the most power at 13:1 or thereabout. The only way to know is test.

    Honestly A/F R is the worst way to tune. A good exhaust system pulls some fresh air into the system giving an erroneous reading. A very rich mixture will give a lean reading through the sensor. I've had guys come in saying their bike is rich beacuse they can smell fuel in the exhaust when they are lean. A lean mixture is very hard to light and leaves a good bit of unburnt fuel in the exhaust.

    Most carbed emission controlled bikes are lean off idle and way rich on the mains. The EPA testing concentrates on highway speed emissions (well used to) and that left the main circuit to be jetted fat. Why do you think DynoJet jet kit mains have their own numbering system? They got too many complaints about leaning the bike being the wrong way to go.

    Having been a dyno operator/tuner for 25 years I've learned a few things about these bikes. I've had guys bitterly disappointed about only gaining 2 HP after a couple hours of dyno time. I'd tell 'em go ride the bike and come back and pay if you're happy. They only see the peak output and miss the 7HP/15FT-LB gain in the middle.

    You can watch the efficiency go up as combustion chamber temps increase. I found out the hard way landspeed racing that fuel demand increases as time at WFO goes up. Someone whom I respect a great deal helped me on that one.

    Oh and the reason you see ethanol in gas isn't because of farm lobbyists or politics. Economics alone. Lawsuits and costs. It's because MTBE (methyl tertiary butyl ether) seeps through steel and pollutes. No other reason.
    #47
  8. midlman

    midlman Adventurer

    Joined:
    Nov 20, 2007
    Oddometer:
    26
    Location:
    PacNW
    Not sure on the seeping through the steel, but, MTBE is a possible carcinogen and also doesn't have an affinity to be sorbed onto organics in the groundwater/soils (eg. carbon/clays). This means it will hit the groundwater and just head downgradient until it hits your water well. You can tell how far a gasoline spill will travel on the groundwater just by tracking the MTBE as it will get there first (conservative tracer)....
    #48
  9. supershaft

    supershaft because I can

    Joined:
    Sep 9, 2010
    Oddometer:
    9,116
    Location:
    San Francisco Bay area
    A big +1 except for the very last part anotherguy! Thanks for the excellent input.

    My main point I am trying to get past is that so many people think they need to be richer when in fact they need to be leaner. On the mains that is. As you said too, just off idle often is where it really needs richening up.
    #49
  10. Weaverman

    Weaverman Damaged goods

    Joined:
    Jul 27, 2009
    Oddometer:
    60
    Location:
    Mid-Michigan USA
    Supershaft - I think I need to further or better define MBT. The term has been around forever in GM, and many people say "Mean Best Torque". We looked it up today in the GM Test Code, and the acronym is defined as "Minimum Timing for Best Torque". Simply defined, what's the minimum spark advance required to achieve maximum torque - MAXIMUM being the key term.

    This is why I say MBT often cannot be achieved. Many engine designs are limited by knock before you can add enough spark advance to achieve max torque output. I've seen production engines reach the knock limit with the torque curve still rising as you add spark even with 100+ octane fuel. That's what I mean when I say many times MBT timing cannot be achieved.

    I agree with Anotherguy on most points...I guess everything, it's just that I don't know anything about MTBE penetrating steel. I do caution peoplae who are looking at A/F ratios and shooting for a lean number, especially with the fuel we're using now. I don't think 13.0:1 is viable with 10%+ ethanol. It does bring with it some evaporative cooling, which helps to stave off detonation with bikes like the airhead.

    Seat of the pants feel is all about torque, not the peak HP numbers on the sheet. That's (part of) why we like these airheads; they feel good in the range they run, and we're not usually redlining any bike with each gear change. The torque of an R100GS v. the torque of the F800GS is very similar. It's just that the R100 has a lower RPM ceiling and thus less HP. Quirky old POS, but out of the 30+ bikes I've owned I think it's my all-time favorite. Funny.
    #50
  11. Lornce

    Lornce Lost In Place

    Joined:
    Aug 17, 2003
    Oddometer:
    19,727
    Location:
    Way Out There.
    Absolutely.

    Had a similar discussion with a friend over the weekend as we made plans to increase compression in his '88 RS. Done right it'll improve torque throughout the rev-range, which equates to more manageable power where it's useful to have it.

    And better efficiency, too.

    :thumb
    #51
  12. supershaft

    supershaft because I can

    Joined:
    Sep 9, 2010
    Oddometer:
    9,116
    Location:
    San Francisco Bay area
    I still don't understand what good a torque figure is going to do you when you achieve it while the engine is self destructing via pinging. Supercharged engines for instance, if it were not for pinging their torque would be amost unlimited. Why go there? It isn't doable.

    I caution everybody shooting for best power too. It's real close to trouble. But best power, however close to trouble, is not trouble. It is GOOD for an engine. It is efficient for an engine.

    I know that 13.1 IS viable. My bike is there and a bit above that with 10% ethanol fuel. It has been for 50,000 miles now. More power, better mileage, cleaner running engine. Like I said earlier, there are reasons why people that actually tune bikes on a regular basis set their target lines where they do. What works works.
    #52
  13. Weaverman

    Weaverman Damaged goods

    Joined:
    Jul 27, 2009
    Oddometer:
    60
    Location:
    Mid-Michigan USA
    What bike is running 13+:1 reliably?

    In research or development of an engine design, MBT is a crucial study. Maybe it can't be reached intially...that's why you continue development. Dick with the factors until you need less advance to achieve the torque (mod the chamber to increase burn rate, swirl, tumble, etc.). If you don't know what's possible, you'll never find a way to get there.
    #53
  14. anotherguy

    anotherguy unsympathetic

    Joined:
    Jun 18, 2009
    Oddometer:
    9,090
    Location:
    the hills
    I have found that an engine with a great pull from early in the rev range that sacrifices a couple ponies up top will out accelerate an engine that makes more peak. Which means it will likely have a higher top speed and better economy as well. It's all about the highest average power. That was a real eye opener.

    Oh and 14.7:1 is great if you wanna heat the house cheaply. :D
    #54
  15. Weaverman

    Weaverman Damaged goods

    Joined:
    Jul 27, 2009
    Oddometer:
    60
    Location:
    Mid-Michigan USA
    Anotherguy - yes! It's about the area under the curve (in the horizontal axis range you use...RPM). A nice peak is good if you run right up there and then stay there for the duration...like a drag car with a high-stall converter, or a racing snowmobile with the variable drive dialed in correctly. If you're roadracing on a hilly course, you'll probably want a fatter torque curve since you'll be pulling long and hard. Consider a 2-stroke with light-switch powerband port timing...goes like a bitch in the narrow range where it makes power (which you often can't use). Ask King Kenny about it after he rode the TZ-based flat track bike at Indy way back when...never again he said! Actually, if I remember correctly, he said "they don't pay me enough to ride this".

    Supershaft, I'm not saying you can't run 13.1:1 A/F. But my money says if you can, you've left power on the table because the spark advance curve is not optimum. First you develop the timing curve for MBT, then you fuel it. HP is a function of torque, so more is better anytime and anywhere. You make torque by optimizing spark advance. What kind of EGT readings are you getting? I bet they're way up there.

    MBT is an acronym where "best" means "the most"...maximum. Your definition of "best power" seems to be best for your application. In my mind, you always want the most torque you can get with the fuel you use (octane). Period. If you need a different powerband, then you mess with valve timing.
    #55
  16. Lornce

    Lornce Lost In Place

    Joined:
    Aug 17, 2003
    Oddometer:
    19,727
    Location:
    Way Out There.
    What do you knowledgeable fellows think about this?


    :ear
    #56
  17. supershaft

    supershaft because I can

    Joined:
    Sep 9, 2010
    Oddometer:
    9,116
    Location:
    San Francisco Bay area
    I completely agree with anotherguy his time. My main tuning slogan has always been, "High rpm hp? First you have to get there!"

    Weaverman, MY bike is running 13.1 plus reliably. That is what it sniffed with pump 10% ethanol. I had it around 12.5 for about 15,000 miles but about 50,000 miles ago I leaned it out to a bit to above 13. I knew it made the most power there from the seat of my pant dyno but I had gone back one step richer just to be safe. Then I dynoed it and saw I had plenty of room to go back to what I thought felt the best. The Highly experienced dyno operateor thought the same thing. It's not an exception, it's the norm according to him and others I talk to including anotherguy. I like to think my seat of the pants dyno is fine tuned some since I have been test riding just dynoed bikes since I was a little kid. My dad wasn't really into getting some of our race bikes up on the pipe when they were between his legs!

    IMO, developing the ignition curve beyond accepted norms takes some serious dyno time that I don't have. I learned that back in junior high helping my dad run his dyno and have had that notion reinforced workin with a couple of other dyno tuners since then. One being Chris from San Jose. I am running absolutely stock timing. I know all about the benifits of being able to achieve more power with less advanced ignition. I preach it all the time on this forum. Long rodding airheads is a perfect example of that. It's not just the combustion chamber! I also know all about adjusting the curve for best power. I advocate that all the time here on advr when dual plugging airheads and have done it myself numerous times for a real gains on and off the dyno. Single plug, the factory got it close enough for me. I fine tuned my advance to the factory specs. They very often are not even close. Mine wasn't.
    #57
  18. Weaverman

    Weaverman Damaged goods

    Joined:
    Jul 27, 2009
    Oddometer:
    60
    Location:
    Mid-Michigan USA
    Fair enough. I don't now all about anything!

    But since you do, tell us how rod length impacts spark timing?
    #58
  19. Weaverman

    Weaverman Damaged goods

    Joined:
    Jul 27, 2009
    Oddometer:
    60
    Location:
    Mid-Michigan USA
    No Googling now...explain it in your own words!
    #59
  20. supershaft

    supershaft because I can

    Joined:
    Sep 9, 2010
    Oddometer:
    9,116
    Location:
    San Francisco Bay area
    I don't know all about this but I have actually been there and done it some. I know people that have TONS more experience and knowledge about it than I do. Chris at San Jose would be one among others. My dad would be another.

    I hope you are not suggesting I am a googler? :rofl I go way back before the net! I have read a bunch of Smokey Yunick though. Now there is someone with some dyno time! He contracted R+D for GM out of his own shop down in Florida! I have seen a lot of his advise WORK.

    I have already tried to explain that many times on this forum. Yunick can do it better than I can. In a nut shell, it changes TDC (and BTC) piston dwell. Longer rods increase TDC piston dwell. The piston hangs around TDC longer for the flame front so you can light it later. I have helped set up and dyno tune long rod beemers. I am not claiming that I have done it near as much as some but I have done it and I tried to learn while I was doing it!

    I am just sharing what I have seen work. I hope it might help someone out there. It's just that you are telling me that 13+ shouldn't work and I know that it does and I am not the only one. Not even on this thread!
    #60