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Old 07-23-2005, 03:39 PM   #16 (permalink)
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Flywheel vs Rear Wheel Horsepower

It is my impression drivetrain losses are relatively "fixed" as some of the posts suggest.

I know of a very well funded team with reources sufficient to do the appropriate testing and I believe the differences between crank and wheel HP are well under 10% for them.

However, they deal with relatively high HP and very finely tuned components. I think you could interporlate that losses for a 400hp setup would be 15%-20% based on these results.


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Old 07-23-2005, 10:35 PM   #17 (permalink)
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Flywheel vs Rear Wheel Horsepower

I believe the percent losses for a stick car are going to be far more constant than that of an automatic car. The losses associated with an automatic car can change greatly due to the torque converter. The stall of the torque converter alone can change the drivetrain efficiency. This is why late model vehicles come with a lock-up converter. The locking action of the converter makes the drivetrain more efficient leading to better gas mileage/more power to the ground.
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Old 08-02-2005, 10:45 PM   #18 (permalink)
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Flywheel vs Rear Wheel Horsepower

Here is a very good website that really explains the difference between flywheet power and what gets to the rear wheels. There is an article on there from I think car craft and they took a 351 winsor that was just mildly built and put it on the engine dyno then the put it in the car. On the engine dyno it made 371hp. Then when they put it in the car with an AOD tranny and ford 9inch rear it lost 24%. The rear end makes a difference too. An 8inch will not soak up as much hp that I 9inch will. Also the AOD is most inefficient of all the automatics. I have seen time and time again stick cars lose about 15 to 17 percent and automatics always lose at least 20 percent or more. This is just the brutal truth. Here is the website that really explains it all.

http://www.superstang.com/horsepower.htm#Proof1


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<font size=-1>[ This Message was edited by: EricButler on 8/3/05 10:46am ]</font>
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Old 08-05-2005, 02:53 PM   #19 (permalink)
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Flywheel vs Rear Wheel Horsepower

I have found 20-30 percent is lost on a dyno. My Mustang made 480hp on a dyno and 388hp on a chassis dyno.
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Old 08-06-2005, 10:40 PM   #20 (permalink)
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Flywheel vs Rear Wheel Horsepower

Quote:
On 2005-08-05 14:53, 472Mach1 wrote:
I have found 20-30 percent is lost on a dyno. My Mustang made 480hp on a dyno and 388hp on a chassis dyno.
It's not correct to state that as a percentage. You probably had power steering and a fan on the engine during the RWHP test that you did not have on during the engine test.

Regardless...if you were to bump the horsepower production of your motor up your transmission is unable to resist *more* as a percentage indicates. It's lossy, yes, but fixed.

One of my engines made 455 FWHP and 392 RWHP with a C6 and the addition of the fan and P/S. With a 125 Shot, well, it made 125 more HP not 70% of 125HP.
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Old 08-22-2005, 02:27 PM   #21 (permalink)
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Flywheel vs Rear Wheel Horsepower

I'm thinking that losses are fairly constant in a given situation, but that is not to say that putting 1000 HP through the same transmission as 100HP would give you the same loss.... The 100 HP engine would indeed move the car because the 100 HP isn't gathering the amount of friction as the first because a.) it isn't accelerating the rotational assembly nearly as fast, and b.) the force generated on the meshing surfaces isn't nearly as high as a higher HP motor - the fluid can lubricate much better and you are losing much less due to metal contact.

I think that once the HP levels reach a certain point, the transmission becomes "saturated" (you're pushing all the fluid out that you can and all the metal that will touch is touching. Once you get there, in higher HP motors, you lose about a given amount of power, cause you've got the transmission losing the most that it can.

Now, in an auto tranny, you lose more because you have a torque convertor, as has been said. You have to rely on a fluid to transmit force, and since the input fins on the engine side are moving much faster than that of the transmission side, you're going to generate heat simply due to friction - any heat generated is a direct loss of power. That, in addition to the fact that the sun and planetary gears on an auto generate a lot more friction than their manual counterparts.

I'm curious to see if someone could study the loss due to friction on the main bearings as a function of horsepower.

<font size=-1>[ This Message was edited by: thekingofazle on 8/23/05 2:40am ]</font>
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Old 09-23-2005, 09:04 AM   #22 (permalink)
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Flywheel vs Rear Wheel Horsepower

The loss is a combination of frictional loss, efficiency losses, and inertia loss needed to accelerate rotational masses including the trans and rear end.

I like to think of things in extremes to help to understand them. Imagine a 4 ft diameter 250 lb flywheel. The amount of inertia required to accelerate this mass is going to be significant. The faster the flywheel is accelerated, the more power is needed to rotate the flywheel. The same principal holds for rotating the torque converter or flywheel/clutch assy, trans internals, driveshaft, ring and pinion, axles, and wheels/tires. So you end up with frictional heat losses, gear efficiency loss, and inertia loss. Inertia loss is one reason why a 9" uses more power than an 8". 100 HP loss through a drivetrain is not due to just friction. If it was, the heat generated would be tremendous.

A friend who has a built 289 with a toploader and built 8" behind it lost 15.5% from flywheel to chassis. 375 FWHP and 317 RWHP.

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<font size=-1>[ This Message was edited by: blkfrd on 10/19/05 11:31pm ]</font>
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Old 09-25-2005, 08:33 AM   #23 (permalink)
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Flywheel vs Rear Wheel Horsepower

FWIW, the below numbers are an example the differences of an engine dyno and a chassis dyno on the same engine.

Engine dyno:
415HP@6200RPM
408TQ@4500RPM


Chassis dyno:
323HP@6000RPM
299TQ@4750RPM

I'm not sure of the make of the engine dyno, but the chassis dyno was a Mustang Dyno which will typically show lower numbers than say a Dynojet chassis dyno. You can count on about 5-10% in most cases I've seen.

This particular 331 stroker engine was installed in a 1966 Shelby Mustang with a manual transmission.
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