496 BBC Build

[Fastvette94]

I checked on et effects of the +2 lbs on the rotating assembly on my simulator and the results were surprisingly varied. If I used a tight stall then the lighter crank would edge out by a nose, with a loose stall flashing to 4000rpm the heavier crank was .01 seconds faster due to energy from the shift inertia (during stall period it basically makes no difference as RPMs are constant). So results change on configuration.

I captured a video of one test but looking back it's not a good sample as the launch RPM was higher for the Camaro.

Link http://youtu.be/Hc7Oagkm4g8

The run was a 3000lb Camaro vs a 3002lb chevy (+0.25 lbm ft^2 rotating assembly), both sporting a David V. modified 572 (800hp) w/ a TH-400 brake, 4.11 gears, 30" tire. (Aerodynamics same for the comparison)

I'm on the clock now so I can't record a better sample.

[vortecpro]

If I was to run this 496 @ 3000 pounds, this is my thought process: average power from 6000-7500 RPM where the car would be run, around 780 average HP, 780 HP @ 3000 pounds = 149.5 MPH, 1320 divided by 149.5 = 8.82 ET, this is what I would expect in sea level conditions, 29.92 baro, 60 degree air. I can tell you the crank weight is noticable on the dyno, I've built two now with that crank and you can tell the difference.

[Fastvette94]

If I was to run this 496 @ 3000 pounds, this is my thought process: average power from 6000-7500 RPM where the car would be run, around 780 average HP, 780 HP @ 3000 pounds = 149.5 MPH, 1320 divided by 149.5 = 8.82 ET, this is what I would expect in sea level conditions, 29.92 baro, 60 degree air. I can tell you the crank weight is noticable on the dyno, I've built two now with that crank and you can tell the difference.

I agree on a dyno you will see a difference with a set acceleration rate, not brake horsepower though.

There are a lot of energy transfers going on during a pass at the track. My simulation calculates every 1ms the current accelerations of the motor, tranny, reared, wheel speed with a dynamic tire radius based on the force on the tires and tire expansion, etc. When you throw the complexity of converters in the mix which holds the RPM constant the crank weight doesn't come into play at that moment. The heavier crank slows you down more during the early part of the run when engine acceleration is the highest and is dependent on the square of the rearend , tranny gearing, and tire radius. Depending on stall speed and shift rpm the motor might not accelerate much during a pass which mitigates some of that weight gain.

During the shift the stored inertia in the assembly is used to accelerate the vehicle. I include this effect in my simulation. Not all of it is converted into motion due to heat loss but I don't account for that currently as there are a lot of other effects I'm in the middle of modeling.

I will enter the motor data posted earlier and see how close I get to your number. I used a different motor I already modeled for this simulation. I only have 45mins in the morning to work on this stuff before I start work.