I know a lot of people always have the curious question and the question is asked a lot:
1: What are the benefits of running advanced timing?
a: Do I lose top end
B: Do I gain bottom end
2: What are the benefits of running a larger carb?
a: Do I lose top end
B: Do I gain bottom end
While searching for some timing/plug related posts on bansheehq, I came across a GREAT post that illustrates this change perfectly so you can PHYSICALLY see what kind of changes you will see with both modifications. Keep in mind this is a Banshee being dynoed and not a Blaster, but specifically, the curves and how they are effected are what you are interested in.
"Advancing the timing isn't all that straight-forward. It's like compression. If you raise the compression, you'll gain more low end torque, but too much compression, and it will kill your top-end performance. The same is true with timing. Here's a plot of my old 4mm cub motor on racing gas. The lowest HP curve is 4 degrees of timing. The middle curve is 8 degrees, I believe. You can see that significant gains were made everywhere except after the peak. If I had the HP vs Time curve, it's a better view to see how much faster the motor accelerates with respect to time. You can clearly see though, that once the HP peaks, the power just falls off, whereas with the 4 degrees of timing, it held on for longer. The largest curve is 8 degrees with 39mm carbs rather than 36mm, so you can see the effects of going to a larger carb as well."
Green: 39mm carbs, +8 advanced timing
Red: 36mm carbs, +8 advanced timing
Blue: 36mm carbs, +4 advanced timing
-Now for my take. Advancing the timing doesn't necessarily "kill your top end". What it will ultimately do is increase your peak power BUT at a lower RPM, so it's not like your top end no longer exists.....you have simply decreased the RPMs at which the peak power is reached. You still have a bottom, mid, top end power, but you have changed the range within the engine puts out the power.....this is why some say after they top end that they have "lost" top end power and you gain "bottom end"....no....you are simply just achieving peak power(a greater peak power) at lower peak RPMs.....two ENTIRELY different things from "losing top end". In fact, many cars, advance timing more via ECM at higher RPMs to ignite the air/fuel mixture earlier to compensate for the increase speed the piston is traveling. "Top end" is commonly referring to the power you generate in the "top end" of your total power curve.....the same applies to bottom end. This is why you always...errantly....hear people say "It decreased my top end"....no....it decreased the RPMs at which you achieve a GREATER peak power. The feeling of "more bottom end" is pretty close to correct, because you do gain bottom end power just like you gain top end power, and the reason you feel "more bottom end" is because of the phase shift principle. The power has moved "Northwest", therefore comes on SOONER and at a HIGHER peak power FOR THAT GIVEN RPM. You have changed the characteristics of the engine AS A WHOLE as you can see from the dyno graph where it is constantly at a high power output at all RPMs....for those that are familiar with basic math, this is closely resembling nothing more than a "phase shift" in which you have moved the entire curve "Northwest" on the dyno graph as I said....the curves are close to identical, but one has increased power throughout. While he doesn't show the dyno with the stock timing, guaging from the difference from the +4 advance and +8 advance, it's easy to tell what the trend is for the stock timing....lower peak output across the board, but will hit peak power at 10,300RPM(for the banshee mind you)....slightly higher than the advanced timing setups. Does this mean you should run as much timing as humanly possible?......NO!!! There are things such as reliability and heat that play an important factor in power production....in this case, being mostly a drag shee, it goes on a short, hard run and then it's done......it doesn't tear around trails for an hour....this is where advanced timing is quite dangerous in that you have to find the RIGHT setup for YOUR engine and YOUR riding type(and YOUR fuel).
-The carb setup is pretty accurate in power gains and losses. Note the dyno is a bit different since it's a Banshee(a drag Banshee at that). Looking at the +8/dual 39mm setup, you would think, "Well that's dumb, he lost all bottom end except at midrange/peak power", which is true.......but it's a drag shee.....they just want peak output for the most part.....note dual 39mm carbs is a large setup for a shee, except for when you are dragging. Also note where the peak power is reached. With the larger carbs, it increased the peak power RPMs around the same point where the +4 advance was running with the smaller carbs setup.
This is where you riding style comes into mind. Does bottom end mean that much to you that you are willing stay with a smaller carb and miss out on some midrange or top end? Does top end mean that much to you that you are willing to sacrifice some bottom end for the same mid range power and increased top end power(at a higher RPM)? That's comes down to you.
Anyways, I thought I would share this info which is common sensical for the builders that have seen it hundreds of times, but for those that are always "wondering", this is a great illustration of what you keep hearing from most all of us. I:I
1: What are the benefits of running advanced timing?
a: Do I lose top end
B: Do I gain bottom end
2: What are the benefits of running a larger carb?
a: Do I lose top end
B: Do I gain bottom end
While searching for some timing/plug related posts on bansheehq, I came across a GREAT post that illustrates this change perfectly so you can PHYSICALLY see what kind of changes you will see with both modifications. Keep in mind this is a Banshee being dynoed and not a Blaster, but specifically, the curves and how they are effected are what you are interested in.
"Advancing the timing isn't all that straight-forward. It's like compression. If you raise the compression, you'll gain more low end torque, but too much compression, and it will kill your top-end performance. The same is true with timing. Here's a plot of my old 4mm cub motor on racing gas. The lowest HP curve is 4 degrees of timing. The middle curve is 8 degrees, I believe. You can see that significant gains were made everywhere except after the peak. If I had the HP vs Time curve, it's a better view to see how much faster the motor accelerates with respect to time. You can clearly see though, that once the HP peaks, the power just falls off, whereas with the 4 degrees of timing, it held on for longer. The largest curve is 8 degrees with 39mm carbs rather than 36mm, so you can see the effects of going to a larger carb as well."
Green: 39mm carbs, +8 advanced timing
Red: 36mm carbs, +8 advanced timing
Blue: 36mm carbs, +4 advanced timing
-Now for my take. Advancing the timing doesn't necessarily "kill your top end". What it will ultimately do is increase your peak power BUT at a lower RPM, so it's not like your top end no longer exists.....you have simply decreased the RPMs at which the peak power is reached. You still have a bottom, mid, top end power, but you have changed the range within the engine puts out the power.....this is why some say after they top end that they have "lost" top end power and you gain "bottom end"....no....you are simply just achieving peak power(a greater peak power) at lower peak RPMs.....two ENTIRELY different things from "losing top end". In fact, many cars, advance timing more via ECM at higher RPMs to ignite the air/fuel mixture earlier to compensate for the increase speed the piston is traveling. "Top end" is commonly referring to the power you generate in the "top end" of your total power curve.....the same applies to bottom end. This is why you always...errantly....hear people say "It decreased my top end"....no....it decreased the RPMs at which you achieve a GREATER peak power. The feeling of "more bottom end" is pretty close to correct, because you do gain bottom end power just like you gain top end power, and the reason you feel "more bottom end" is because of the phase shift principle. The power has moved "Northwest", therefore comes on SOONER and at a HIGHER peak power FOR THAT GIVEN RPM. You have changed the characteristics of the engine AS A WHOLE as you can see from the dyno graph where it is constantly at a high power output at all RPMs....for those that are familiar with basic math, this is closely resembling nothing more than a "phase shift" in which you have moved the entire curve "Northwest" on the dyno graph as I said....the curves are close to identical, but one has increased power throughout. While he doesn't show the dyno with the stock timing, guaging from the difference from the +4 advance and +8 advance, it's easy to tell what the trend is for the stock timing....lower peak output across the board, but will hit peak power at 10,300RPM(for the banshee mind you)....slightly higher than the advanced timing setups. Does this mean you should run as much timing as humanly possible?......NO!!! There are things such as reliability and heat that play an important factor in power production....in this case, being mostly a drag shee, it goes on a short, hard run and then it's done......it doesn't tear around trails for an hour....this is where advanced timing is quite dangerous in that you have to find the RIGHT setup for YOUR engine and YOUR riding type(and YOUR fuel).
-The carb setup is pretty accurate in power gains and losses. Note the dyno is a bit different since it's a Banshee(a drag Banshee at that). Looking at the +8/dual 39mm setup, you would think, "Well that's dumb, he lost all bottom end except at midrange/peak power", which is true.......but it's a drag shee.....they just want peak output for the most part.....note dual 39mm carbs is a large setup for a shee, except for when you are dragging. Also note where the peak power is reached. With the larger carbs, it increased the peak power RPMs around the same point where the +4 advance was running with the smaller carbs setup.
This is where you riding style comes into mind. Does bottom end mean that much to you that you are willing stay with a smaller carb and miss out on some midrange or top end? Does top end mean that much to you that you are willing to sacrifice some bottom end for the same mid range power and increased top end power(at a higher RPM)? That's comes down to you. Anyways, I thought I would share this info which is common sensical for the builders that have seen it hundreds of times, but for those that are always "wondering", this is a great illustration of what you keep hearing from most all of us. I:I
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