Before we go any further, it’ s important to take a few things into consideration. Remember, we monitor driveshaft rpm, not actual“ wheelspeed”, so we are basically counting pinion rpm. So different rear gears will generate different driveshaft numbers even though the car may be going the same speed. If someone tells you that you need to be at 3,000 rpm by 1 second, for that to be an apples-to-apples comparison, that person would need to have the same rear gear as you( and tire size).

If you are trying to compare two different gear ratios, you need to convert to“ axle speed.” This can be calculated by dividing driveshaft rpm by the rear gear ratio. For example, if you have 1,000 rpm of driveshaft and a 4.29 gear, you have 233 rpm of axle speed( 1000 / 4.29 = 233). Once you have axle speed, you can convert that to any gear ratio. So if I wanted to reference driveshaft numbers from a Top Alcohol Funny Car with a 4.29 gear( with the above 1,000 driveshaft / 233 axle rpm) to a Pro Mod with a 5.0 rear gear, I would take the axle speed and multiply it times the comparison gear to get the comparison driveshaft rpm. In the above example, I would multiply 233 times 5.0 to equal 1,165. So 1,000 driveshaft rpm with a Top Alcohol Funny Car with a 4.29 would equal 1,165 driveshaft rpm in a Pro Mod with a 5.0 gear.

I will point out I was recently looking at some runs on a friend’ s car, and the wheelspeed numbers just seemed really high for the ET and speed he was running. Come to find out he had programmed a conversion into his config file, which was converting the raw data to a

number that compared with the gear he used to have. So make sure your data logger software is configured to read 1 input equals 1 output.

Any curve must start at zero. Where you“ zero” your run is important for a number of reasons, but it’ s especially important if you are comparing driveshaft rpm numbers. Some data loggers will automatically zero off of the first turn of the driveshaft, while others go off the G-meter. Most experienced tuners do not zero their runs this way; they will zero the run off whatever starts the“ timers” for the run. On almost all converter cars, this would be the transbrake. Clutch cars will either

use a clutch switch or wide-openthrottle switch. This is done so that the events on the data graph correspond with the time-based tools we use to tune the car, such as timing curves, leanouts, boost controllers, stages of nitrous, etc. If you zero your runs differently than someone who may be giving you numbers, your time vs. rpm will be different.

Now that we have the disclaimers out of the way, let’ s start a curve. The first key is that you start a curve and not a“ step.” This is the part of getting the car“ on the tire” and moving. It is very hard to see much here on the graph unless you have 8 magnets or more on your driveshaft collar.

The more magnets or teeth to count, the more“ resolution” you will have seeing the driveshaft curve. The difference in a one- or two-magnet pick-up and 8 magnets and higher is like the difference in an old TV and a new HDTV.

Until I get a car’ s initial driveshaft curve looking right, I don’ t spend a lot of time looking at target numbers inside of. 5 seconds. By“ looking right”, I mean no dips from a hook or too steep of a slope( which usually comes from bouncing off wheelie bar). Once I get the“ hit” right and get the curve looking manageable, I will start looking at a. 25 target. If you have a big hook in your driveshaft coming off the line, you don’ t want to target whatever driveshaft number that is going to give you at. 25.

From there you can start establishing target numbers for. 5,. 75 and 1.0. For most cars north of 2,000 horsepower, 650-700 axle rpm( convert by multiplying times your rear gear) is a safe starting point for a 1.0 target. If it makes it very far past 1.0 without shaking, the slope of your curve is generally set. I typically reference off my 1.0 number, then record in my notes where it crossed 4,000 and 5,000 driveshaft rpm. As you make more runs, you can look at your good runs and know that you need to cross 4,000 and 5,000 by certain points in the run.

If you don’ t have enough driveshaft early in the run, it is difficult to reach your target numbers without too steep of an acceleration rate, which leads to spin and / or shake. You pay a price for any hooks or spins in the driveshaft. Hook the tire and your numbers will be slow and you may have to fight recoil spin from the wheelie bar and sidewall. Even with a controlled spin, at some point the tire has to hook back up, and usually that hurts your acceleration rate pretty hard. A“ perfect”- looking curve spreads the acceleration rate out over a longer period of time, making higher numbers 1.0 attainable without shake.

The more“ controlled” driveshaft you can achieve, the quicker and faster you can go. DI