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