We've dynoed a 4WD 6-speed manual that as a stock car had close to 24% drivetrain loss (320 crank gave 258 at the wheels...62hp gone) . With 2.5 times more whp (645) the engine alone kicked out 733 hp...that's 88 hp,i.e. a higher loss in hp ( read: friction)...but the percentage is now 12. Quite a difference...

IF that "the percentage stays solid-rule" should apply,then we should have seen 848 crank hp - 24% = 645AWHP. And,come to think of it,this example:150Kw of heat lost (200 hp)....that much heat would,in my opinion, have killed the drivetrain.

The November 2003 issue of Car Craft has a great article titled "The Brutal Truth" by Jeff Smith (page 40). In the article they place two engines on an engine dyno and then dyno the engine again once it is installed in the vehicle. One engine is a 357 cubic inch Ford Windsor engine and the other is a 455 Buick. The Ford 357 was installed in a 63 Comet using an AOD transmission and Ford 9" rearend with 3:50 gears (exact combination of drivetrain in my Mustang except my AOD is a non-lockup which means it is even less efficient or should lose even more horsepower). The 455 was installed in a 70 Buick GS with a Muncie 4-speed and a 12 bolt rearend with 2.73 gears. The point of the article was to show how things like a belt driven cooling fan or poor vehicle exhaust could affect the engine output in the vehicle but was equally as valid for showing drivetrain induced power loss.

Without reading any further it would be my assumption that the Ford combination would lose a larger percentage of power through the drivetrain. Not only is the AOD an Automatic it is also a 4 speed Automatic that has substantial weight and rotating mass. The 9" rearend is also larger and heavier than the 12 bolt Chevrolet.

The Ford 357 produced 371 horsepower on the engine dyno at 5,000 RPM. On a 1990 Mustang that came stock with an AOD and a 3.27 8" rearend (more efficient than the 9") the rear wheel horsepower is typically 180 hp. That represents a loss of 45 horsepower given the rated 225 flywheel horsepower on that vehicle. Using this 45 horsepower and even giving it another 5 for the 9" rearend the 357 would have produced 321 peak horsepower on the chassis dyno. Well, it didn't! Even after removing all the factors that could have contributed to extra power loss in the vehicle (removing the belt powered cooling fan) the chassis dyno only showed 283 hp. In fact over the entire power curve the difference between the engine dyno and the chassis dyno was 24%. This provides more evidence that the power loss through common drivetrain remains a percentage even as power is increased rather than remaining a static loss value.

The Buick 455 produced 329hp and made 280 through the drivetrain at 4,500 RPM. The average drivetrain horsepower loss in this vehicle was 18.3%. This can be accounted for by the fact that the 4 speed Muncie is more efficient (require less power to accelerate) as well as the 12 bolt rearend being more efficient than the 9".

Horsepower loss through drive train is caused by a few different things. Some have greater affect on resultant horsepower loss than others. If you can't agree with or understand these next few statements then the rest of the article will not help.

Statement 1: Frictional force increases the power required to move an object. This is the most major contributing factor to horsepower loss in drive train. Here is an example.

If you tie a board to a rope and drag it across a linoleum floor and then drag it across a carpeted floor it will be harder to pull on the carpet. If you put a stack of bricks on the board it will be even harder to pull. If you were to drag the same board for the same distance at the same speed and took a temperature measurement on the bottom of the board it would get hotter as you added weight. The heat generated would increase linearly as compared to the amount of weight you put on the board. The force required to move the board would also increase linearly.

For this same reason if you apply 10 ft-lb of torque on a gear it will produce a given amount of friction. If you change the force from 10 ft-lb to 100 ft-lb more friction will be generated by the turning gears. In a transmission or rear end (drive train) this increased friction is seen as heat generated. This is why when you add more power to a vehicle you need to install better coolers to keep everything cool.

Statement 2: It takes more power to accelerate any given object more quickly. This is probably the most obvious statement but is also very critical to understand. Second to frictional losses is acceleration power loss.

If you take a given car that can at best run the quarter mile in 14 seconds the only way to increase this acceleration (other than changing its weigh or drag - next two statements) is to increase the power. The more power you add the faster the vehicle can perform the work of traveling down the quarter mile. This is why we all build more powerful engines! If it wasn't true then we would all be driving Yugo's at the track.

Statement 3: It requires more power to accelerate a heavier object. This is one of the explanations for the difference in horsepower loss between automatics and manual transmissions and why a Turbo 400 takes more power than a Turbo 350. Here is an example:

Grab a 10lb bag of potatoes and see how long it takes you to get to a full running speed. Now grab a 100lb bag. I can think of millions of more examples but....

Now picture the rotational mass of your transmission. If it weighs more it will take more power to make it accelerate to the same speed.

Statement 4: The faster you want to move an item the more power it takes (drag). Here is an example:

If you take a stock Mustang six cylinder and try and obtain a top speed rating it will probably be around 110 mph. Now get in a V8 Mustang and it will go faster. For an average vehicle to break 200 mph it takes around 500-600 horsepower. As an item accelerates it becomes harder and harder to push it because of the drag induced by the wind. See footnotes for more detailed information.

For the same reason it will take more power to spin a transmission at 7,000 RPM than it will at 6,000 RPM. The gears moving through the fluid in the transmission will require more power at higher RPM's.

Lingenfelter Performance Engineering, Inc.

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March / April 1996
Race season is well underway and the shop is as busy as ever. The engine dynamometer has been especially busy with the drag race engines - including our own - as well as the street engines and R&D projects. Our Dynojet chassis dynamometer continues to get more and more use as well. We have now chassis dynamometer tested many stock and modified ZR-1 Corvettes along with a variety of other cars and trucks.

As part of this testing, we have been able to measure many different variables that effect rear wheel horsepower. One such variable that we have been able to quantify is the horsepower losses due to elevated vehicle operating temperatures. The LT5 engine seems especially sensitive to this. This highlights the need to cool the intake manifold and get the water temperatures down between drag runs. We have also been able to measure and quantify the losses between an engine dynamometer test run and a chassis dynamometer run of the same engine. Even when an engine is run on the engine dynamometer with all of the accessories and the catalytic converters (the way we usually run most engines), you will usually see losses of between 15% and 20% between the engine dynamometer and the chassis dynamometer. These losses are due to the additional backpressure of a complete exhaust system and the frictional losses in the transmission, differential and tires. We have even been able to measure the differences in friction due to changes in tire pressure - in one case a customer had left his rear tires roughly 15 psi low after leaving the dragstrip and then came to the shop. We chassis dynamometer tested his vehicle with the low tire pressure and then brought the tires up to proper street pressures and gained close to 15 horsepower at the rear wheels.

The Dynojet chassis dynamometer is an inertia type chassis dynamometer. This means that it calculates horsepower and torque based on how quickly a given inertia - in this case, a set of rolls of given mass and dimensions - is accelerated. The length of time it takes to accelerate from one rpm level to the next is the sweep time and the rate that you accelerate from one rpm to the next is the sweep speed or sweep rate. Because it takes more power to accelerate the mass faster, you will see lower horsepower figures when a car is tested in a lower gear (1st gear for example) then when it is tested in a higher gear (3rd gear for example). This is because at higher speeds and higher gears, it take longer to accelerate from one rpm level to another (for example, 2000 rpm to 6000 rpm). This remains true until the gains in horsepower from increased sweep time are offset by the increased frictional losses of the transmission, differential and tires. As speeds increase, the frictional losses in the transmission, differential and tires increase. The higher the horsepower of the car, the faster it will accelerate the rolls and the higher the speed (and therefore the higher the gear) will need to be to get the sweep time long enough to give an accurate reading. Because the Dynojet chassis dynamometer is an inertia type chassis dynamometer it does not allow you to perform fixed rpm or step type horsepower tests - you can not hold the vehicle at a given rpm or speed and check the horsepower level. Despite this limitation, the inertia type dynamometers give you a very accurate measurement of what the vehicle sees in real world situations. An inertia type dynamometer will show the effects of reduced driveline inertia (such as lightweight flywheels, driveshafts and wheels) while a steady state test does not show these improvements.

Because the Dynojet chassis dynamometer uses one large diameter roll per wheel, overheating the tires and the tendency of cars to try and jump off the rolls is not a concern. This design also means that the cars do not need to be loaded down against the rolls - further reducing tire heat build up and increased frictional losses through the tires. This means that the risk of tires exploding from too much heat and load is virtually nonexistent.

In our continued effort to offer more horsepower for the LT5 engine - we will soon be offering larger, lightweight stainless steel valves for the LT5 engine packages. The larger valves will offer improved airflow and the reduced mass will provide higher rpm capability to the LT5 engine. Keep an eye on this Shoptalk section to get more information on the improvements provided by the larger valves as well as from the titanium rods mentioned in the last issue. Many other improvements for the Corvette and the LT5 engine are also in the works.

For those ZR-1 owners that would like to upgrade to the newer 1994 through 1995 ZR-1 wheels or want an extra set of wheels, we have available a limited number of the GM 5-spoke ZR-1 wheels. A set of the 17 x 9.5" front and 17 x 11" rear wheels sells for $1099 while a set of four of the 17 x 9.5" wheels (for 1988 through 1996 Corvettes other than the ZR-1) sells for $1079. We also offer polishing and powder coating for $995 a set.

In our continued brake package improvements, we will soon be offering a brake package designed to bridge the gap between the stock ZR-1 brakes and our complete 13.5" Alcon brake package. The new packages will keep your stock 13" rotors but use the 4 piston Alcon calipers. These calipers offer increased stiffness over the stock PBR two piston floating calipers and should provide better heat dissipation and pad wear. You will be able to later upgrade to the 13.5" two piece rotors without having to change calipers. These Alcon caliper/13" Corvette rotor packages are also available for the Camaro, Firebird and Impala SS as well. The Alcon calipers are now also available powder coated. We now also offer the complete line of Performance Friction "-4" and "Z" compound street pads along with the Performance Friction racing compound pads.

With the weather finally starting to look better and spring already here (and summer not far away), it is time to start enjoying our cars again.