Horsepower loss between crank and tires? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 09-25-2003, 11:55 AM
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Horsepower loss between crank and tires?

How much horsepower is lost between the engine and the rear wheels? Based on a percentage if possible.

If there is a website with this info please point me in the right direction because I have looked everywhere and can't find it.

I will be running a Mopar 360 with a 727 tranny and an 8 3/4" rearend. If you need more info please let me know

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Old 09-25-2003, 12:29 PM
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November Car Craft has an article on power loss,just gives you a general idea.
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Old 09-25-2003, 01:11 PM
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Most calculators for like "ET from HP and weight"etc...Say to figure in a 18-20% loss from your flywheel figure.Usually when I play with these I figure in a 25% loss.(this way if I run faster I create the delusion of having more HP LOL) I guess allot of race drive lines can be as efficiat as to give you like 5% loss(as told by one of those hotrod TV guys once)
Really though the only true way I can see that will tell is to put it on a chassis dyno.Cause if you and me got the same motor right down to exhuast system but you got a Lenco and I got a parts america liquidation sale automatic with no **** kit,there will be a day and night differance at the rear wheels.Evan tranny type will make a differance,I now in chevys it takes more HP to run a TH400 than a TH350.
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Old 09-25-2003, 01:23 PM
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General rule is 20% for auto, 15% for manual.

Aluminum flywheel, carbon fiber driveshafts, aluminum wheels also make a significant difference.

Especially everything that is BEFORE any gear reduction. Such as flywheel weight.

In a 4.11 car, a 1 lb lighter driveshaft is equal to taking 2 pounds off of each rear wheel. And depending on your transmission, lightweight pistons and a light rotating assembly can be worth more than 10 times their weight in rear wheel torque.
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Old 09-25-2003, 04:12 PM
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Only 5% difference between Manual and standard transmissions? Are you sure? I have been told that a automatic tranny can suck up between 15-60HP. Quite a few people have told me that. And a manual tranny takes up near nothing. I wanna know now, just 5% diff sounds pretty low.


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Old 09-25-2003, 04:33 PM
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Guys old car drive trains 30% to 60% loss stick or auto very little difference. The stick is usually faster because of more gears like 5 speed vs 4 for an auto.

Now the moder drive train like the Vette or the porshe 8% to 10% loss that is why a newer car will blow any old car away with same size engines.
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Old 09-25-2003, 05:35 PM
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Actually newer car have more drivline loss/Any automatic overdrive trans takes more power to turn then a th400,and a th350 or powerglide take even less then the th400.Newer cars are faster in box stock form then hteir older counterparts because tires are better today.Newer engines are making more horsepower then theri older counterparts too.Dont buy into the horsepower numbers either.A box stock LS1 camaro is rated at 300 hp,but ill usually make that at the wheels,the engine is making closer to 400 hp in stock form.
An automatic trans skews the horsepower and torque curves on a dyno because to some xtent convertor slippage cost horsepower,but increases torque.when running a high stall drag car on a chassis dyno,you would be surprised at some of the torque readings that are built as the convertor approaches stall speed.The slippage tends to scrub some horsepower off though.
an automatic tans suffers the most loss because it has more rotating mass in high gear then a manual trans.Most automatics have all or most of the internal parts required to make all three gears working in motion when the car is in high gear.Conversely,a stick trans has only the required parts moving in any gear.A planetary trans like a lenco is more like an automatic since the gears are aligned sequentially from front to back,every time the car upshifts it is spinning all the parts that made the lower gear{S} work and the parts that are needed for the driving gear.Lencos consume a lot of horsepower,but make up for it with the lack of a torque convertor and clutchless shifting.In reality,if you can make a real stick trnas work in your application it will be faster then a lenco,but a clutchless shiftng conventional stick trans doesnt really exist,but rather such transmissions are really standard transmissions that have ben modifed to shift as effortlessly as possible,and through loose clearances and trick sliders they can make a tans that can be forced to change gears without using the clutch,but is very hard on components and doesnt last long.The only way to calculate driveline loss is with both chassis dyno and engine dyno testing under exactly the same conditions.In reality,in car engine testing also takes into account cooling system and air intake shortcomings which also hurt performance,which means it isnt just about the moving parts.I figure that even the best auto trans race car looses about 20% in the driveline,an that would be in a typical 7000 rpm bracket car with a glide,lightweight convertor,light driveshaft and a 12 bolt.Anything bigger of heavier will add to the loss.There is no way of knowing where you are at power wise,but I have done a lot of testing in my car and have backed it up with some deskdop software.My engine came off the dyno making 680 hp and went into the car and put 490 to the rear wheels.It ran 10.60's at 126.5mph in a 3550# car.My desktop software puts it down as 515 rear wheel horsepower and 730 at the crank,which is similar percentage wise to what I have as actual numbers.This is in a very efficeint stocker style drivline including a lightweight stocker style convertor,and low pressure powerglide,a steel driveshaft,as well as a 12 bolt with a drilled spool and 33 spline axles and with centerline wheels.As a point of interest,my desktop software also said my engine would be spinning 7400 at the shift and in the lights,but the engine runs best when shifted at about 7100 and in the lights at about 7200,so I saved a miniscule amount of power by not spinning 200 rpm more then I had to.It all adds up.So get it on a chassis dyno and make some pulls.


Another thing to remember is that power adder cars loose less power in the driveline since the rpm range is the same as an N?A car,but the power is much higher.Since the driveline loss is dependent on component speed as it relates to ineria as well as to frictional loss,both efects are less percentage wise when the power goes up and the rpm stays the same.
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Old 09-25-2003, 05:54 PM
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HP loss

When we ran trucks on a chassis dyno we always locked for 80% of engine horse power. We always tried to run in direct drive and the bigest hp drain was the engine fan. Hp would come up as engine temp came up and max out just before the clutch fan engaged.
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Old 09-25-2003, 07:02 PM
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30 to 60% is an insanly high number you lose around 15% in the drive train new cars run faster because they are set up better
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Old 09-25-2003, 07:40 PM
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About 20-25%. With angles and the distance, that's what it comes to. Depending on the setup, but that's about average.
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