Chech out this article on Dyno tuning....Look at the transmission loss:
"And when comparing the same type of car and engine with automatic transmissions, the losses climb too 36 to 38% of the engine-dyno tests. So the biggest loss of power in the drive train will most always be the Automatic Transmission and the Torque Converter. The automatic transmission consumes power in two ways – slippage in the torque converter and the hydraulic fluid pump that supplies pressure to the transmission."
The full article is below:
Today you can even find dyno’s set-up and operating at car shows. In the early 70’s a rear wheel dyno section would set you back up to $200 an hour and sometimes even more, that was a weeks pay for many people.
Today the average cost is around $35 more or less to find out what your machine is putting to the ground.
Yes, rear-wheel chassis-dyno-testing is becoming increasingly popular with performance enthusiasts. While the data is very useful, it can also be discouraging, or at least very humbling. When Numbers are lower then what was expected, it’s not time to give up, but time to start looking for the lost power.
Engine Dyno’s
Engine builders sell their engines rated at maximum base horsepower. This is the horsepower that is displayed on a dyno while the engine is pushed to its red line.
These engines are placed on stands and connected to the dyno at the output shaft (crankshaft) of the engine. Most engines will use an electric water pump or even be force fed with coolant, and will not have any accessories running on the engine.
Factory Engines, are Net-Rated and never see a dyno test. They are designed and mathematically calculated to the optimum horsepower at the output shaft with ALL accessories connected. Now most of us realize that Net-Rated power is only a shot in the dark for the actual engine hp, and that everything from the radiator cap all the through to the weight of the tires will require or rob horsepower from the engine.
Question: What robs horsepower from the engine?
Answer: Everything that moves, and some that don’t.
Weight is a major factor to performance. With the introduction of the LT1 engine, Corvette stopped installing carpet padding to cut down on weight and promote less pounds to the horsepower. And over the years we have seen major changes like spare tire or jacks being eliminated, lightweight composites that are stronger to replace heavier metals and even fiberglass.
Thus, the less weight, the better the performance.
The base figure for determining horsepower loss through the drivetrain has always been a round-about figure of 20% of the net rated horsepower, but nothing could be further from the truth. Thousands of rear wheel dyno tests have shown that performance cars with big block engines and no options like air-conditioning, power steering, smog (fresh air) pump, using manual transmissions and top of the line drive-lines and bearings have 21 to 26% loss when compared to the same engine tested on a engine-dyno.
And when comparing the same type of car and engine with automatic transmissions, the losses climb too 36 to 38% of the engine-dyno tests. So the biggest loss of power in the drive train will most always be the Automatic Transmission and the Torque Converter. The automatic transmission consumes power in two ways – slippage in the torque converter and the hydraulic fluid pump that supplies pressure to the transmission.
Slippage is an inherent factor of any torque converter (except locking converters) with a slippage factor of 5 to 8% after the stall point. This does not mean you lose 5 to 8% of power, but anytime the converter gets hot the fluid thins out, slippage increases and flywheel power is lost. High stall converters allow even more slippage to raise the stall rpm’s and create even higher fluid temperatures more quickly. In addition to the converter, all Automatics must drive a pump to create hydraulic pressure required to apply the clutches and bands. Heavier transmissions like the TH700R4 require additional power to spin the heavy clutch drums. Thus, the quicker you accelerate the more power the unit eats.
But let's not forget the manual transmission or the rear-end. Friction causes heat and heat eats horsepower. Gear multiplication (meshing of two or more gears) will always require horsepower to complete because of friction. High gear, as with most four speed transmissions, creates the least amount of friction because they just lock the input and output shafts together. 5 and 6 speed transmissions on the other hand, require gears again to get the over-drive efficiency of their design.
Rear-ends also eat power because of the sliding action of the hypoid gear design. Where the pinion gear is designed to meet the ring gear can also mean greater horsepower losses as well as the physical size and weight of the gear set and the quality of the gear lube used in the rear end.
These are the main sources of horsepower loss, but it does not stop there.
Steel drivelines and jack-shafts (independent axels) require more horsepower because of there weight. Every universal joint between the transmission output-shaft and the wheel requires horsepower to turn, and if those universal joints are even slightly worn or low on lubricant, the amount of loss can double, triple and even quadruple.
Brakes and wheel bearings can also be a large cause of losing horsepower before it gets to the ground. Non Vented rotors, glazed rotors and worn pads all cause excessive friction that develops excess heat. Heat causes the bearing to expand and create more drag and requires more horsepower to move. Worn wheel bearings will also have the same effect even when they are cold.
Wheel Bearings, Brakes, Rotors (preferably Cross Drilled), Universal Joints, Rear-End Bearing and Gear Lube must all be in good or better condition to have the least amount of power loss.
We have looked at most of the reasons for power loss from the back of the engine to the rear wheels, now let us explore some of the reasons in the front of the engine.
Up front we have engine driven fans, (84’s use electric), water pumps, power steering pumps, A/C compressors and some years use V-Belts.
Engine Driven Fans can eat as much as 28 hp and even flex fans and fiberglass fans can devour 15 hp at 5500 rpm. These should be changed out for a good Electric Fan that will mount to the edge of the radiator cowling for maximum airflow. In some areas with hot summer weather, small pusher fans inside the front air duct may be required to help cool down the coolant when idling with the air conditioning working.
Air Conditioning. No one wants to get rid of the air conditioner, but there are vacuum switches that can be mounted and wired into the air conditioner clutch circuit to break the power when the accelerator is pushed hard.
But the thing to really watch for is bad or worn bearings in the free wheeling electric clutch. The pump can suck up 23 hp when working properly, but the clutch, even when the pump is not being used, in good condition, robs 2 hp by itself, and those numbers can climb too 4 to 7 with bad bearings, and you may never know it.
Water Pumps have the smallest effect on horsepower, but still requires at least 12hp to operate. When water pumps become worn (not bad) those numbers can reach 20 to 24 hp before going out completely.
Power Steering Pumps will use up a whopping 22 horsepower when working well. That power loss can and will grow well past 30 if the pump is making any noise at all. Low fluid can cause internal damage to the tube vanes. If the pump is making any kind of whining or chattering noise it needs to be replaced. Some enthusiasts replace the power rack and pinion with a manual unit and remove the pump completely. Corvettes seem to loose there driving appeal without power steering though..
V-Belts also require more horsepower then serpentine belt configurations, and because some engines require more V-belts then others, more hp is lost.
The last major unit that depletes horsepower is the exhaust system. Restrictive mufflers, pipes and headers all rob horsepower from the engine. You can drill a small hole in the collector of the Y-pipe and insert a closeable hose connector. Use a low-pressure (0 – 15 lb.) pressure gauge and measure the amount of backpressure in the exhaust system. Anything over 2 pounds at maximum rpm’s should be repaired. If the Catalytic converter has over 50K miles, it should be replaced with a high flow converter. 3 inch Y-pipes and 3 inch Stinger style mufflers make the best mixture in our opinion for the least feedback noise into the cockpit while maintaining the best free flow of exhaust.
Headers are the last part of the exhaust system. The stock headers work well but do not scavenge (pull out) the exhaust. They also drop the Volumetric Efficiency of the X-Ram by 10%, but that is not all that bad. Headers do make a difference.
Long tube headers make the best hp by returning 25 to 30 horsepower (un-capped) to the rear wheels that was stolen from the stock system. Even in street form gains of 6 to 7 hp can be found with these headers. Mid length headers can find 15 to 20 hp, with Shorties coming in last at around 10. There is a couple of drawbacks to that horsepower though, when it comes time to replace the spark plugs, you will wish you never heard the word "headers", and they also destroy spark plug wires.
