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Bench Racing

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  • Bench Racing

    With your truck in the garage for the winter, it’s time to bench race.

    So let me post some racer math, and some explanations if you are a bit unclear.

    Performance can be measured as Power to Weight. The more power you make, the faster your truck is. But don’t forget the less your truck weighs, the faster it will be. To the balance of 100lbs of weight loss equals roughly 10hp in performance gains. So don’t overlook losing some pounds, it’s cheap and easy.

    Now for power, Horsepower is typically measured three different ways. Brake Horsepower (BHP), Wheel Horsepower (WHP), and Fuel Consumption algorithms.

    Brake Horsepower (BHP) is what you typically see from an OEM car manufacturer in magazines and TV commercials. It is the engine’s peak horsepower measured at the crankshaft. The SyTy’s were advertised at 280 BHP. To get a BHP measurement you need to remove the engine from the truck, and install it on an engine dynamometer. The engine dynamometer uses a water-brake to measure torque, then calculated horsepower. It is the closest number to the engine’s actual power output.


    Unfortunately, it is a little tough to remove your engine just to measure it’s horsepower. So another tool is a chassis dynamometer. This is a electromagnetic roller that uses resistance to measure torque, and calculate horsepower. The lets you measure your horsepower a lot easier, since you simply drive your truck on top of the dynamometer. The measurement is known as Wheel Horsepower (WHP). But don’t be fooled, Wheel Horsepower IS NOT Brake Horsepower. The chassis dyno measures power at the tires, that means that the power must run through the torque converter, automatic transmission, differentials, and finally the tires. All of those factors consume power, and reduce your final numbers by roughly 25-30%. In other cars, these losses can be reduced by using a single differential (unlike SyTys), or a manual transmission. So remember when you see a car/truck on a chassis dyno, the power numbers are 70-85% of what the engine is actually producing.


    The third type of power measurement is through calculations. Late model computers now offer the feature of calculating your engine’s power output. The ECU reads fuel flow, engine RPM, and manifold pressure to estimate how much power the engine is making. Arguably, these numbers are “abstract” since you are not mechanically measuring engine output.

    Now, onto the bench racing. Drag racing performance is a game of numbers. In a perfect world, under perfect conditions, you can calculate track times by using horsepower and weight. Here are some basic examples for SyTys.

    A stock full-weight Syclone is 3600lbs + 95lbs (15gal gas) + 200lb driver = 3900lbs
    A stock full-weight Typhoon is 3900lbs + 95lbs (15gal gas) + 200lb driver = 4200lbs

    Let’s figure an engine output (stock or modified) of 300 Wheel Horsepower.
    A Syclone would run an estimated 13.3 seconds at 102mph 1/4 mile.
    A Typhoon would run an estimated 13.6 seconds at 100mph 1/4 mile.

    If we drop some weight off of these 300WHP trucks they will be faster. Lets say -30lbs for the spare tire, -35lbs for the passenger seat, and -15lbs for the stock jack. We can drop 0.20 seconds off the 1/4 mile ET. Bringing the Syclone to a 13.1, the Typhoon to 13.4
    The disclaimer being that these calculation assume perfect conditions. A great launch with no wheelspin, keeping the RPMs in the peak powerband, etc.

    Another example, let’s take an all-wheel drive Syclone with a turbo 4.3L that makes 600 BHP at the crankshaft. By the time the power reaches the pavement, we are talking about 450 WHP. In a Syclone with minor weight loss, say 3800lbs. We get approximately 11.45 seconds at 118mph, from the 600 BHP engine.

    Remembering the drivetrain losses, if we build a truck to run 11.45 seconds, we need a turbo, fuel system, heads and cam rated at 600 BHP, not the 450 WHP that it takes to run 11.45.

    Let’s push a Typhoon to a 10.99 pass. Shedding some serious weight (200lbs) we drop down to 4000lbs with driver. The truck needs to put down 540 WHP on a chassis dyno. Taking into account the driveline loss, that puts the engine at 740 BHP.

    My purpose for this post was just to remind everyone that there is a performance difference between seeing Engine Dyno numbers, and Chassis Dyno numbers.
    Also, never underestimate the performance gains from weight loss. Your truck will accelerate quicker, brake shorter, and corner better as you shed the pounds. Many weight loss mods are free. For example, have you removed the ABS module from your truck, did you remove the wiring harness as well? That harness has copper wires, plugs, and clips that run all along your frame. You’d be surprise how much it weighs.
    Last edited by Aeroking; 12-07-2017, 01:55 PM.

    jabroni beating, pie eating, trail blazing, eyebrow raising, heart stopping, elbow dropping, step off the brake put your foot on the gas, always ready to whoop some ass.