Rev gain is the ability of an engine to accelerate overcoming its own internal rotating mass and producing usable power. With out this ability an engine will not achieve maximum potential as a drag racing engine. It’s not needed in sled pulling why? a Sled puller starts at maximum RPM and as it moves down the track , it pulls then motor backwards down the rpm scale
Take a given engine combination, and do compressive dyno testing. We always start with a baseline slow pull using a stair step ramp leveling out at each rpm; the results will produce a given amount of power. This is usually to check oil pressure and look for any problems. Now the testing really begin , set the dyno accelerate to 300 RPMs per second , the engine will lose a good percentage of power , this because a bigger part of the total power the engine makes is used to accelerate the engine .
Now really make things interesting turn the knob to 600 rpm’s per second ramp, almost the rate a light weight diesel race vehicle will experience in first gear pull. Why is this important? The first foot is the best chance to improve the ET of any drag racing vehicle, the next foot is the next best chance to continue the quest to turn in a lower ET. If the engine has to experience an acceleration rate of 600 RPMs per second then you have to do everything possible to make then engine produce more power under those condition.
One thing to conceder is that the higher the rate of acceleration the power is less, and so is the cylinder pressure , this is the time to toss the kitchen sink at the tune, meaning you can turn up the tuning parameters that if present at a steady state rpm or a lesser rpm gain would become descriptive . This can gain you back some of this power. In Pro Stock and other maximum effort engine programs, the tune is set to a particular rate of acceleration for each gear .
Many on here have advocated that if any of the fast trucks were to lose weight down the weight I ran at, they would have easily eclipsed my performances, the problem with that, and I’m sure some will be finding out soon is it doesn’t work that way, as you ask these engines to accelerate the amount of power at that accelerate rate goes down considerably . What was a 1000 hp becomes significantly less. The diesel already doesn’t like being asked to do this, so there are ways to mask this,