Dyno tests

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ir3333

ir3333

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When an engine is tested on a dyno, quite often there
is no alternator,fan,fuel pump water pump or exhaust
pipe.
... how much hp might this be?
 
ir3333 said:
When an engine is tested on a dyno, quite often there
is no alternator,fan,fuel pump water pump or exhaust
pipe.
... how much hp might this be?
Click to expand...

All depends on the parts drag on the engine...it doesn't matter really because it won't work in the car correctly or at all without those parts!
 
ir3333 said:
When an engine is tested on a dyno, quite often there
is no alternator,fan,fuel pump water pump or exhaust
pipe.
... how much hp might this be?
Click to expand...

Mine doesn't have a fan or a fuel pump run by the engine in the car.

Every engine dyno I've seen has exhaust pipe with mufflers.

A 100 amp alternator would be about 1400 watts output , or about 2hp, figure 50% efficiency that would suggest you need 4hp at maximum load.
 
A good clue to the answer is in the HP derating that occurred when the HP ratings of US engines went down, from gross HP to net HP. Similar changes in test methodology took place; gross HP, prior to the change, was without the pumps and fans, etc. (Dunno about the exhaust for gross tests, but one might resonably suspect that gross HP tests were done without normal manifolds, etc.) 10-15% HP drops were the norm when that change in HP measurement methodology was adopted.
 
It's a little bit of a loaded qustion, your not clear on what your asking. Do you mean water pump, ALT, power steering, mechanical fan, AC and even the mechanical fuel pump? For that matter we could even discuss auto verse manual trans, smog motor or not, ETC...
 
It's not a set figure. If i had to guess, 30-40 depending on what your car has vs. the dyno cell. Some cars with power steering and full exhaust with less effective headers or manifolds will be a bit more.
 
moper said:
It's not a set figure. If i had to guess, 30-40 depending on what your car has vs. the dyno cell.

...so a dyno reading 362 HP may actually be 322 - 332 w/accesories ...real world crank hp
Click to expand...
 
ir3333 said:
moper said:
It's not a set figure. If i had to guess, 30-40 depending on what your car has vs. the dyno cell.

...so a dyno reading 362 HP may actually be 322 - 332 w/accesories ...real world crank hp
Click to expand...

then you would have to factor out the correction for standard air....dyno correct the HP for 29.92 baro...60 degree....and no humidity........
Click to expand...
 
plus if you are not using your intake/carb/jetting/plugs/hdrs/fuel delivery system/timing/mufflers it could be even more off once you get it in the car and running... makes it a bit of a joke doesn't it to spend $500 or whatever. Cheapest way is to run it down the track a few times and and go by your best/average mph on the slip, get the weight of the car with you in it at the line and use the Wallace calc, that will tell you how much hp you have on the day under those conditions, much closer than dyno hp. If you run it on street tyres you'll mph higher than with slicks so try and get the car to hook as best you can.

http://www.wallaceracing.com/accel-calc.php
 
I've never had an engine dyno'd with the top goal of finding out my hp and torque.
 
70aarcuda said:
ir3333 said:
then you would have to factor out the correction for standard air....dyno correct the HP for 29.92 baro...60 degree....and no humidity........
Click to expand...


yup. Dynos are great tools. The output is fun to talk about, but the only real deal is when it's in your car and you're accelerating down a track. Chassis dynos have the same issues with correction factors and operators.
Click to expand...
 
Hanging an alternator and running a water pump are really insignificant regarding power draws.

Start running the other items, fans/clutches/ac/PS and the draw s much higher.

The linked articles are pretty good at displaying the draw each item may have. Nice post!
 
Alternator and water pump wouldn't be more than 10 hp

Breather can also be a huge power robber.
 
IMO, the biggest usurpers of honesty in terms of engine dynos are in this order: the air filter/intake, exhaust, fuel supply, and water pumping system. The others are bolt on power robbers. The ones mentioned are almost always vastly different when in a chassis and can realy reduce the real power produced.
 
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