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Using EFI to make a larger engine perform like a smaller one

  1. Feb 21, 2014 #1
    So I was having a discussion with a fellow motorcycle racer and he stated that The bike I'm riding has too much horsepower for my skill level. I currently ride a 1000cc gsxr1000. He suggested I sell the bike and get a 600cc gsxr600. Well I love my liter bike and even though he's probably right about it being to much bike I don't want to get rid of it.

    I had the idea of de-tuning the engine to produce the same acceleration as a 600 cc bike. He stated that is not physically possible. I disagree with this. The bike has a mode selector switch that has 3 different fuel maps for the EFI system. It's a speed/density system so you can edit the ECU for any 1 of the 3 maps and control when and how much fuel is injected into the throttle bodies. There are also 2 sets of butterfly valves in each throttle body. The top one is connected directly to the throttle cable and the one below that is actuated via a servo controlled by the ECU. The original intent of the system is to offer 3 different HP curves to the rider for road riding, race, and riding in the rain.

    The gsxr600 hp curve: http://www.holeshot.com/dynocharts/images/dyno_2004_gsxr600.jpg [Broken]

    The The gsxr1000 hp curve: http://forums.13x.com/attachment.php?attachmentid=18299&d=1173117627 [Broken]

    gsxr 600 gear ratios:

    Primary reduction ratio 1.974 (77/39)
    Final reduction ratio 2.687 (43/16)

    Gear ratios Low 2.785 (39/14)
    2nd 2.052 (39/19)
    3rd 1.714 (36/21)
    4th 1.500 (36/24)
    5th 1.347 (31/23)
    Top 1.208 (29/24)

    gsxr 1000 gear ratios:
    Primary Drive Gear Teeth (Ratio) 73/ 47 (1.553:1)
    Final Drive Sprocket Teeth (Ratio) 42/17 (2.470:1)
    Transmission Gear Teeth (Ratios)
    33/26 (1.269:1)
    34/25 (1.360:1)
    36/24 (1.500:1)
    36/21 (1.714:1)
    39/19 (2.052:1)
    41/16 (2.562:1)
    Transmission Overall Ratios

    Now you can clearly see that the GSXR1000 has a totally different HP depending on what drive mode (fuel map) is selected. My question is this:

    What prevents one from attaining the same acceleration and throttle response to the rear tire as the gsxr600 on the gsxr1000 by editing the setting on the "low" fuel map? I realize it's not as simple as just matching the HP curves engine to engine because the 2 bikes have different RPM limits and gear ratios. I still don't see why editing the edu values for fuel and air intake can't compensate for that. Especially considering they can be edited for each gear and even each cylinder in each gear.

    His claim is that " it would be a crappy running bike with crap throttle response and crap acceleration and all. It won't be "like a 600" "

    and "If you had any clue about how fuel injection and internal combustion work, and how horsepower is calculated you'd see you're wasting your time"

    What do you guys think? Possible to make the 1000 perform the same as the 600 or no?
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Feb 21, 2014 #2
    do you want to exactly match the torque curve? that would be probably hard. and yes, throttle response and similar stuff may suffer.

    I don't really know about bikes, but if it is similar to cars, it should be no big problem.

    tuner can do lots of complicated stuff with mixture and advance, but do you really need that? it will cost lots of money, it will take time and there are always some risks involved.
    just let him set the rev limiter to (lets say) 9000 rpm. less revs, less power. yes you will reach lower speed on gears, but do you really need to go 80mph on first??
    and after some time, just increase the rev limiter and you are at full power.
  4. Feb 21, 2014 #3
    Isn't making throttle response worse what we want though? If I slap the throttle open mid corner on the 1000 I'm going to get a heck of a lot more torque going to the rear tire than if I was on the 600cc bike. Bad throttle response is the goal. Just only as bad as the 600s.

    Tuning is pretty cheap. It costs me $20 bucks to do a pull on a dyno where I'm at. I have software that edits the fuel tables down to each cylinder in each gear at any rpm. Even if I spent all day tuning on the dyno it would be cheaper than buying a whole other bike and setting it up for the track.

    I guess what I'm, saying is this: I see no reason I can't get my 1000 to act VERY close to a 600 by simply tuning air and fuel going to the engine. Close enough that if my coach or riding buddy is on a 600 I shouldn't be able to pull away from them use just acceleration in the low setting.

    HP is a function of torque, and torque is a function of how much air/fuel ratio and volume as well as ignition timing. All of those are controllable with my efi system is. I can even control the degree of engine braking on closed throttle.
  5. Feb 21, 2014 #4
    So you've bought a powerful bike, and now spend time effort and money to ruin the performance of it.

    You can mess with the maps, but at the end of the day its still a 1000cc bike. Its designed to breathe a certain amount of air, and therefore burn a certain amount of fuel. Maps and timing can really only do so much. Reduce the fuel too much and it'll run hot and melt something.

    Also less power is not the same thing as poor throttle response. What you are proposing is likely to make the bike unridable.

    Sell the bike, buy a less powerful one.

    Easiest, cheapest and more importantly safest option.
    Last edited: Feb 21, 2014
  6. Feb 21, 2014 #5

    I appreciate your concern for my saftey. However my question was on engine Engineering not on motorcycle purchasing.

    what specifically about having less air and fuel in the cylinder will make the bike unridable as that is exactly what went on with much older liter bikes that were carbureted?

    the air fuel ratio will still be correct as the incoming air is regulated the secondary butterfly that are controlled by the ECU. there would be just less fuel and air.

    the engine wiil not lean out and start burning valves as both air intake and fuel intake are being controlled.

    there really is no down side to tuning one of the lower maps as I never use them anyway. if I don't like the results I simply leave the bike on the main map. they are switchable on the fly via the mode selector switch.
  7. Feb 21, 2014 #6
    Why detune the engine? Tune up the rider! Spend your time and money on the track. Your fuel map is in your right hand. Throttle control is a wonderful thing...just reconnect your brain to your wrist and enjoy your bike. Don't let your friend talk you out of a very capable bike.
  8. Feb 21, 2014 #7
    only by tuning mixture you cant do that much. at WOT it will still suck certain amount of air. you can make leaner mixture, but without ignition tuning it will knock and you will possibly destroy the engine. or melt something.

    can you do something to limit opening of the electronically controlled throttle body? limit it to 60%, less air will be going into engine, and that is what you want. or put restrictor plate into the intake.

    honestly, if you don't have experience with reprogramming ECU, you will almost surely destroy the engine. this is specialized highly tuned engine and I don't think it is good one for somebody to learn how to tune fuel and ignition tables. but yes, it is possible to make it go like 600.
  9. Feb 21, 2014 #8
    Yes i can tune the secondary throttle plates to do what ever i want. The factory programming allows for this as that is exactly what they do when you switch to the medium or low maps on the power selector switch. All i would doing is retuning the low power map on a dyno with a commercially made ecu editor. Its done all the time. Its just usually done to make MORE power, not less.
  10. Feb 21, 2014 #9

    I tend to agree but several more experoanced racers have all said having too much power is slowing my progresdion due to my survival reactions to the power of the 1000.
  11. Feb 21, 2014 #10


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    Perhaps you should listen to them. Sell off the liter bike and get one more suited to your skill level. 600s can be really scary too, so you'll have your hands full for a while. Good luck.
  12. Feb 21, 2014 #11

    Why get a different bike when i can have both in the package i already own? Cheaper and no relearning andre-equiping a new bike.
  13. Feb 21, 2014 #12
    I'm a drag racer, not a road racer, but I understand what they are talking about. I went from a Honda 650 to a GSXR1100, and there is no way to prepare yourself for that change. It took me a while to adjust, but the only way to adjust is by doing it. You'll lose the fear factor, just stay within your limits. Race yourself, not the others. Quickest way to the sand is to follow the ego ahead of you!
  14. Feb 21, 2014 #13

    True stuff
  15. Feb 22, 2014 #14
    So now comes the engineering part.

    If in 1st gear the 600cc bike has an overall gear ratio of 14.257 and a peak HP of 101 at 13500rpm(946 rpm at the wheel), and the 1000cc bike has an overall gear ratio of 8.195 in 1st gear (7752 rpm to achieve the same road speed), How much engine HP does the 1000cc bike need to be tuned for to be the same power? Shooting from the hip looking at dyne charts, it looks like the 1000cc could just be rev limited to 7752rpm and would only need about an 8% reduction in power to be equivalent.

    Does that make sense?
  16. Feb 22, 2014 #15
    if you want to match 100hp, then you need 100hp. and from what you say, that is almost exactly what you have at 7750rpm.
    from your dyno graph, you already have that. it is the reduced power map (the red line on graph) just don't rev it over 9000rpm

    if you want to exactly match the acceleration at each moment (and I don't know why would you do that), you would need to match the torque transferred to the wheel/tarmac (and compensate for the weight difference)

    if booth bikes goes same speed and one is reving 13500rpm and second 7750rpm, that that is the difference in gear ratios (and wheels sizes). divide them and you have 1.74

    so go trough 600cc table, look at hp figure (not torque!) at certain revs, divide the revs by 1.74 and look at the 1000cc graph. if the hp figure would be the same, you have same performance
    you can (should) also do the same for bikes weights. heavier bike need obviously more power.

    but that all is THEORETICAL
    you can use it for comparison but reality would be much more complicated.
  17. Feb 24, 2014 #16
    If you're looking to simply lower the acceleration of the bike, you could numerically lower the final drive through sprocket changes. Most likely your 'skill level' limits are either accelerating out of corners, riding through the corners or braking for the corners. Lowering the rev limiter will not help any of the cornering situations. You will still have the same torque at lower rpms, or very close, despite tuning. You'll have to limit airflow to reduce horsepower and torque at less than rev limiter rpms. Changing the rev limiter drastically will also force shifting changes that will drop your rpms to a less than ideal point. You may find yourself reving too low at each shift and then as the engine comes into it's tuned power range (as some would say - getting on the cam) there will be a sudden surge of power making the bike even more difficult to ride fast and smooth. Adding a front sprocket tooth may be all you need to take a little power out of your rocket. 8)
  18. Feb 25, 2014 #17
    Why not just put a rubber stop behind the throttle so you can only open it to eg 75%?

    On my car the throttle map just has demanded torque values for each RPM/throttle position combination. Although I haven't tried it, I imagine just scaling down those values would have the effect of making the engine behave like a smaller one.
  19. Feb 26, 2014 #18

    Protech, at the cost of potentially upsetting quite a few guys floating around here, I would definitely tune your existing bike! It sounds like you have access to tune all the parameters you need. Traction control in road cars with fly by wire is enacted the same way you are thinking. The throttle body is closed to limit torque, creating the effect of a smaller engine stopping wheel spin.
    If you have access to a 2d VE map of the secondary throttle opening, you can set up a vac line to post 2nd throttle bodies and tune the throttles to provide something like 10inhg of vac across the rev range. This will give the engine the illusion of dropping 1/6 the displacement without having to touch fueling or timing. And no nasty throttle stops!

  20. Feb 26, 2014 #19


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    Homework Helper

    For the past few years, some motorcycles have selectable engine mapping configurations to allow for reduced power / torque output, such as the Suzuki GSXR 1000, which has 3 settings as explained in this wiki article section:


    Since you're talking about racing motorcycles, I doubt there's much difference in safety factor betwen a 600cc and 1000cc race bike, if you're actually racing. A co-worker from a former company started with a 1000cc bike as his very first bike, and got into club level racing within a few months of getting the bike. He put in a lot of track time and got his "experts" racing license in about 2 years, which is pretty quick. The point here is that skill level progress is probably not going to be hampered by running a 1000cc bike versus a 600cc bike.
  21. Feb 27, 2014 #20

    Ranger Mike

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    Science Advisor
    Gold Member

    Detune?? wtf is that ..no racer ever does that! To do so means you are racing to the REAR! you can either ride and admit you got no hair.. or RACE it...you do not win races by being timid..get up on it and drive it like you stole it. Tune the hell out of it to get the absolute max Horsepower and ride to WINNNN..because I garunteee you some one else is doing this!
    And there is a very good possibility that you will wreck, and probably DIE..
    Its called racing...Accept this or get off the track..everything else is secondary...screw what the pit gobblins say..you are at a RACE TRACK to RACE...AND WIN! end of conversation...
    Last edited: Feb 27, 2014
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