Crank vs. rear wheel

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67yelodart

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What is the amount (percentage wise) of horsepower loss from crank to rear wheel.I heard it was about 40%,with a 727 trans.,,,less than that with a 904.and even less loss with a manual.
So with a 400 horse motor,would i be getting about 240 horses at the rear wheels with a 727 trans?
 
I don't think there is any set percentage for this, it could vary from vehicle to vehicle even if it's equipped with the same trans and differential. It's all going to be in how it was setup and what modifications were done. For instance if you up the line pressure in an auto trans it's going to eat more horsepower. The torque converter is going to factor into this as well, pinion turning torque is going to be a factor as well as the lubricant used in the differential and/or manual trans.
 
The figures I use are 15% for manual trans, 18% for autos. The rears are almost no difference in loss so it's basically the trans type.
 
There is also two methods of ratng crank HP, gross and net. Prior to 72 or so the engines were rated gross at the crank, that is, they were tested without alternators, water pumps, air cleaners, exhaust. Then the government step in and made they use a uniform rating system that was net at the crank where the engine was tested with all the accessories that would be on the engine in the car and with stock exhaust. The big drop you saw in rated HP for the same engine in the 72 time frame was mostly due to this testing method change not the often blamed reducion in compression for emissions.

So, if you are looking at factory ratings prior to 72 and then measuring actual rear wheel HP you could see a difference approaching 40%. The net number rating to rear wheel is in the range that has been mentioned.
 
My GTX low deck made 830 hp on the pump and 700 hp to the rear wheels on the rollers with a 4 spd and full ex with tail pipes.
 
dgc333 said:
There is also two methods of ratng crank HP, gross and net. Prior to 72 or so the engines were rated gross at the crank, that is, they were tested without alternators, water pumps, air cleaners, exhaust. Then the government step in and made they use a uniform rating system that was net at the crank where the engine was tested with all the accessories that would be on the engine in the car and with stock exhaust. The big drop you saw in rated HP for the same engine in the 72 time frame was mostly due to this testing method change not the often blamed reducion in compression for emissions.

So, if you are looking at factory ratings prior to 72 and then measuring actual rear wheel HP you could see a difference approaching 40%. The net number rating to rear wheel is in the range that has been mentioned.
Click to expand...

Learn something every day, thanks for that info.
 
dgc333 said:
There is also two methods of ratng crank HP, gross and net. Prior to 72 or so the engines were rated gross at the crank, that is, they were tested without alternators, water pumps, air cleaners, exhaust. Then the government step in and made they use a uniform rating system that was net at the crank where the engine was tested with all the accessories that would be on the engine in the car and with stock exhaust. The big drop you saw in rated HP for the same engine in the 72 time frame was mostly due to this testing method change not the often blamed reducion in compression for emissions.

So, if you are looking at factory ratings prior to 72 and then measuring actual rear wheel HP you could see a difference approaching 40%. The net number rating to rear wheel is in the range that has been mentioned.
Click to expand...
in 1972 compression ration went down to 8:1 for most engines. thats a BIG hit from 9.5:1/ 10:1 engines. the difference in HP on a 1970 340 compared to a 1973 for example is 16%. how much of that is becouse of the lower cr. then the difference would be from parasitic loss from the engine accessories.. that would be what? 5% at most. so i don't see how prior to 72 you'd get a 40% drop to the rear wheels. 5% difference at most prior to 1972. ie: instead of they typical 18% drivetrain loss factor in the 5% NET hp loss and it would be a 23% total hp loss.
 
Completely agree with A-Bomb on this one.

I know two things for a fact -

1/ - Ford use 18% drivetrain losses for their new cars fitted with factory built modular V8 OHC engines. A Ford production engineeer told me this.

2/ - A well known builder down here uses a rule of thumb of 120 HP losses for a 500HP engine through a Ford 9" and 727 with a 4000 stall. He says he's seen it many times on the chassis dyno against the engine dyno figures.

This works to around 22%, which is the figure I've always used.
 
A-BOMB360 said:
in 1972 compression ration went down to 8:1 for most engines. thats a BIG hit from 9.5:1/ 10:1 engines. the difference in HP on a 1970 340 compared to a 1973 for example is 16%. how much of that is becouse of the lower cr. then the difference would be from parasitic loss from the engine accessories.. that would be what? 5% at most. so i don't see how prior to 72 you'd get a 40% drop to the rear wheels. 5% difference at most prior to 1972. ie: instead of they typical 18% drivetrain loss factor in the 5% NET hp loss and it would be a 23% total hp loss.
Click to expand...

The performance difference between a 70 340 A-body car and a 73 340 A-body car is minimal which suggests the engine are putting close to the same amount of power to the ground. There is certainly not a 35 HP difference in performance (the difference between a 73 340 and a 70 340) which suggests that the change in the measurement system accounts for the bulk of the difference. You have to remember back in the late 60's horsepower wars the HP number in the sales brochure would make or break a sale but the vast majority of folks would never know the difference so the motivation to test engines in a way that gives the marketing types the number they wanted was great. If this was not so the government would not have stepped in and madated a standard testing method.

It's easy to accept that an engine with open headers, no engine driven accessories no air cleaner (and possibly a non stock carb) could make 16% more power on a dyno compared to the same engine with factory manifolds (and exhaust), all the factory engine driven accessories and air cleaner.

So you add the loss due to engine configuration changes (16%) and the 18% most have been stating for drive train loss you arrive at 34% difference. I previously stated you could approach 40% and there is quite likely some engine configuration that would support that.
 
soooo your saying an engine prior to 1972 that makes 300hp is only putting 180 to the ground? bullshivic. 231hp to the ground is in the reality realm.
 
I kind of get where DGC is coming from - so I'll ask a question.....

Are the "gross to SAE " losses of 16% reasonable?
 
Moparmal said:
I kind of get where DGC is coming from - so I'll ask a question.....

Are the "gross to SAE " losses of 16% reasonable?
Click to expand...
not sure what you mean but the diference between NET and GROSS hp is around 5% for any engine prior to 1972. if your using it as a bases for comparison is 5% loss for accesories + 16-18% loss for powertrain. 21-23% loss total when comparing pre- 1972 horsepower to the ground figures.
 
67yelodart said:
What is the amount (percentage wise) of horsepower loss from crank to rear wheel.I heard it was about 40%,with a 727 trans.,,,less than that with a 904.and even less loss with a manual.
So with a 400 horse motor,would i be getting about 240 horses at the rear wheels with a 727 trans?
Click to expand...

Are you lost? I am almost. There are two discussions here, both are relevant to your question.

1. How was the 400 hp on the motor determined? From 1972 on SAE Net figures are published in manufacturer's literature. Prior to '72, there was not a standard method for measurement. Manufacturers were known to have overstated and understated horsepower ratings for a variety of reasons. Ratings, both pre and post 72 were taken at the crank.

2. How much power loss can be attributed to the drivetrain? This figure is always going to be a net figure, since it is taken with the engine in the car and all accessories attached. There is a slight correction applied for altitude that can be made to the number off of the dynomometer.

If the 400 engine hp is a net figure, the 15-22% power loss figures seem reasonable. If the 400 engine hp is obtained with headers, accessories removed, outrageous timing and carburetion, etc., or worse yet a SWAG number, then a 40% loss may be possible.
:read2:
 
not sure what you mean but the diference between NET and GROSS hp is around 5% for any engine prior to 1972.
Click to expand...

I guess this gest tp the point - A-Bomb seems to think that losses through accesories to achieve an SAE rating is only around 5%

2Darts and DGC seem to think its closer to 16% ?

(Correct me if I'm reading anyone wrong - I'd hate to attract another "stalker" ! LOL!)
 
how about just dyno an engine, record what power you have made at the crank..install the engine in your car, take note of what tranny and rear end your using, then have the car chassis dyno'd and see what ur numbers are...then calculate the percentage loss...i think it varies car by car...
 
Moparmal said:
I guess this gest tp the point - A-Bomb seems to think that losses through accesories to achieve an SAE rating is only around 5%

2Darts and DGC seem to think its closer to 16% ?

(Correct me if I'm reading anyone wrong - I'd hate to attract another "stalker" ! LOL!)
Click to expand...

A-bomb is missing the point, they put headers, no exhaust, didn't use the carb that shipped with the car and didn't have any engine driven accessories attached. when they did the gross measurements prior to 72 which can easily account for 16%. As far as 5% for an alternator, water pump, fan and power steering that is awful low. I have seen tests where factory fans absorbed 5% all by themselves.

Considering STOCK 340 A-bodies back in the late 60's would run mid 14 sec in the mid 90's for mph 180 rear wheel HP is right in the ball park to produce those times.
 
k. i don't wanna seem like a complete a-hole here, but with a 180 RWHP will only
get you around 15.30's @ 90-92mph in a 3300lb car (lighter then average A-body).
 
A-BOMB360 said:
k. i don't wanna seem like a complete a-hole here, but with a 180 RWHP will only
get you around 15.30's @ 90-92mph in a 3300lb car (lighter then average A-body).
Click to expand...

Gee! I had an 89 Shelby Daytona that weighted 3400 with me in it and had approx 190 net at the crank that would 15.1 to 15.2 in the low 90's all day.
 
1979 cordoba factory 318 four barrel orange box better valve springs good tune up on thermoquad == 17.80 @ 84 mph. Removed a/c pump and brackets. 4.56 gears, cheep headman headers. early non lockup 904 with 2800 stall.==15.40's @ 90+ mph. 3905 lbs with driver. Apples to Oranges? Remember show room stock 66-67 383 B bodies only ran 16.10's.
 
A-BOMB360 said:
k. i don't wanna seem like a complete a-hole here, but with a 180 RWHP will only
get you around 15.30's @ 90-92mph in a 3300lb car (lighter then average A-body).
Click to expand...


Not far off on your claim there a bomb!

My a body charger came in on a weighbridge, at 1480 kilos or
3262 pounds.
Its a manual 318,an on the dyno *every dyno reads different
an should be only used as a tuning tool,not bragging rights*
but on this dyno,it made 200 RWHP.
An my best time on the quarter mile is 14.5, at 93 mph...
So does 280 odd crank hp sound right to you?
Gears were 3.23's.

An ive seen a manual 307 killowatt car,make 262kw at the wheels...
So a loss of around 70 odd hp...

Theres alot of factors that can contribute...

Big converters on an automatic car
(obviously)
can make a quick car look average
on a dyno,as in not produce as much hp as one would think.

Just my 2 pennies haha.
 
A few thoughts and observations...
The poster was curious about crank vs rear wheel. Using teh most common slang definitions, he means gross crank, and rear wheel is always somewhere in the middle. That's because "net" for any given vehicle will be different wif the car has been modified. Factory net horsepower is all accessories on and functioning. That means AC, PS, smog pumps, alternator, mech fuel pumps, factory manifolding and exhaust, and factory air cleaner in place) So a modified car "Net" could mean nothing but alternator, or everything but AC, etc. So trying to compare Net and Gross is just confusing an not warranted.
Now in regard to factory ratings... Nothing is iron-clad correct. Not mechanical specs, not horsepower, compression ratios, or option packages. "10.5:1 383 HPs" are really about 9.2:1. "10.5:1 340s" are really 9.4:1. "8.5:1 340s" are closer to 7.5:1. All because the specs are all way off in execution. During the 60s and early 70s all manufacturers went with gross ratings. But there's more. They didnt use a single pull for the rating. They took the engine and modified the jetting, timing, and advances to maximize the horsepower for each level. So a 440 would be set up and tested for highest possiblt power at 1K, 2K, 3K, 4K rpm, and the top reading for each rpm point was used. Not to mention the "dyno mule" blueprinted and supertuning that went into them... Plus the fact that as the horsepower wars went on... they all under-rated the highest engines. First for race rules, then later for insurance. So really... nothing in print is really accurrate for a variety of reasons. Personally I think the differences between Net and Gross crankshaft output ratings is a moving number. It's not a percentage. A non-CA emissions 318 2bbl, with AC and PS will have much greater difference percentage wise than a 440 4bbl non-CA emissions package will. Compare the losses for a single engine Gross to Net and I'd bet it's somewhere around 30-40 horsepower. Less for a factory performance engine that had a better air cleaner and manifolding.
 
I used to work at a dyno shop years ago, we had a brand new Mustang MD250 chassis dyno. Mustang was VERY proud of the accuracy of their machines. But, our customers were always questioning the 'low' numbers. We never seemed to match the 'magazine horsepower' numbers, go figure.
What would happen, is you'd run the customer's car, print a report, explain what it all meant, and the first question would be.
"What's that at the flywheel, then?"
The tech who set up our dyno said it best. Why go to the trouble to measure the hp at the wheels just to estimate what the crank hp would be? At that point you might as well just make up a number.
The reality is, there's no fixed percentage. There's lots of variables. A 727 will cost more power than a 904 (rotating assembly is heavier). Auto more than manual (slippage). High stall more than a tight/stock convertor. And gear ratio too, a numerically higher gear set will take more power to turn that a numerically lower set.
I could go on for days, but really should get back to work.
 
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