This could have been added to the thread about R&P but that one was getting stale and I thought this might be of interest to others. If you haven't read that one, Nsxtasy posted some excellent insight relevant to this.
I went out this afternoon and did a few runs in my bone-stock (drive train) '93 with a mild launch in first and an early shift to second so I could record the acceleration at wide open throttle from well below VTEC range on up. This link takes you to the graphs:
http://i1b.yimg.com/1b/78396e8f/h/15358750/2ndearly.JPG
Because the G readings are a bit erratic during and just after a shift, on this run I shifted very early so I could get a clean reading at relatively low RPM in second. Keep in mind that the elapsed time is badly skewed due to a mild launch and very early shift. Both graphs are from the same run but the first displays acceleration and speed at the point where things settle down after the shift and the car is accelerating at WOT. The second shows acceleration and speed at the point where it hits max Gs for second gear. I have scaled the graphs so you can clearly see the steps as torque increases, rising from 0.37 to 0.40 Gs during a period of 1 second.. The ripple further down may have been the result of the bumpy stretch of road I was on (tough to find a flat empty strip on a sunny Saturday afternoon), or I may have been hovering right on the edge between 0.39 and 0.40. I've noticed similar bumps in dyno torque graphs from stock engines, so that may be part of it as well. I'll repeat these runs soon with double the sample rate and see if it looks any different. I also can't specifically account for the fact that the Gs do not increase slightly at higher RPM as does torque, but I'm guessing that it is offset by increased air and rolling resistance.
How does this translate in terms of speed and times? Working from the fact that 1G = 32.17405 ft/sec^2, each 0.01G increase in acceleration will yield an additional 0.2194 MPH per second. So in the example graphs, the car is moving at approximately 0.33 MPH slower by mid 2nd gear than if it had pulled 0.40 Gs throughout that three seconds. Of course, you would never shift that early in a race, and by the time you do shift you are already in the range of maximum acceleration even though still on the first cams.
So, it appears that the second gear hole is indeed almost entirely a result of the tall gear ratio as a torque multiplier and not from falling beneath the torque curve. (Kudos to Nsxtasy) By contrast, with a proper hole-shot 1st gear peaks at 0.77G and tapers off to 0.57 by 8000 RPM, still well above the 0.40G maximum in 2nd. Third gear drops to a dismal 0.26 but manages to sustain most of it to well over 100 MPH before physics take a noticeable toll. That gives you a good idea just how direct the torque multiplying impact of gearing is.
These graphs also further illustrate what dynos and our seat of the pants have always known, that the real beauty of the VTEC design is a VERY wide power band. It reminds me that the "VTEC range" is just as much about the low RPM cams as the high ones, possibly more so.
[This message has been edited by sjs (edited 25 March 2001).]
I went out this afternoon and did a few runs in my bone-stock (drive train) '93 with a mild launch in first and an early shift to second so I could record the acceleration at wide open throttle from well below VTEC range on up. This link takes you to the graphs:
http://i1b.yimg.com/1b/78396e8f/h/15358750/2ndearly.JPG
Because the G readings are a bit erratic during and just after a shift, on this run I shifted very early so I could get a clean reading at relatively low RPM in second. Keep in mind that the elapsed time is badly skewed due to a mild launch and very early shift. Both graphs are from the same run but the first displays acceleration and speed at the point where things settle down after the shift and the car is accelerating at WOT. The second shows acceleration and speed at the point where it hits max Gs for second gear. I have scaled the graphs so you can clearly see the steps as torque increases, rising from 0.37 to 0.40 Gs during a period of 1 second.. The ripple further down may have been the result of the bumpy stretch of road I was on (tough to find a flat empty strip on a sunny Saturday afternoon), or I may have been hovering right on the edge between 0.39 and 0.40. I've noticed similar bumps in dyno torque graphs from stock engines, so that may be part of it as well. I'll repeat these runs soon with double the sample rate and see if it looks any different. I also can't specifically account for the fact that the Gs do not increase slightly at higher RPM as does torque, but I'm guessing that it is offset by increased air and rolling resistance.
How does this translate in terms of speed and times? Working from the fact that 1G = 32.17405 ft/sec^2, each 0.01G increase in acceleration will yield an additional 0.2194 MPH per second. So in the example graphs, the car is moving at approximately 0.33 MPH slower by mid 2nd gear than if it had pulled 0.40 Gs throughout that three seconds. Of course, you would never shift that early in a race, and by the time you do shift you are already in the range of maximum acceleration even though still on the first cams.
So, it appears that the second gear hole is indeed almost entirely a result of the tall gear ratio as a torque multiplier and not from falling beneath the torque curve. (Kudos to Nsxtasy) By contrast, with a proper hole-shot 1st gear peaks at 0.77G and tapers off to 0.57 by 8000 RPM, still well above the 0.40G maximum in 2nd. Third gear drops to a dismal 0.26 but manages to sustain most of it to well over 100 MPH before physics take a noticeable toll. That gives you a good idea just how direct the torque multiplying impact of gearing is.
These graphs also further illustrate what dynos and our seat of the pants have always known, that the real beauty of the VTEC design is a VERY wide power band. It reminds me that the "VTEC range" is just as much about the low RPM cams as the high ones, possibly more so.
[This message has been edited by sjs (edited 25 March 2001).]
