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How can gross hp be so much higher than net?


turbogrill
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Hi,

 

How can the gross power be some much higher than the net horsepower? 

 

The difference between the Datsun L28 engine is huge:

280zx (net) : 135hp

280z (gross): 170hp

 

How on earth did they manage to squeeze out 35 more horsepower ? It's very hard to get more than 10+ HP on these engines without change a cam.

Feed it with nitro during testing?

It doesn't have that many emission stuff and besides weight there is a very minor performance degradation.

 

The only think I can think of is running without alternator, AC and fan.  But that shouldn't be to much.

 

 

 

 

 

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2 minutes ago, turbogrill said:

But the fan is only running if it's needed right?....in go stop traffic not WOT.

 

Same with the AC and alternator?

A/C kicks off @ WOT but your internal fans continue.

Alternator is always pulling something or the battery would discharge

A RWD fan never stops, may somewhat freewheel but is ultimately thermostatically controlled (random)

FWD fan runs from battery : See Alt, even if the fan is not running the battery is still catching up a little from last fan cycle

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10 minutes ago, red0 said:

 

Is it about transverse vs longitudinal not FWD vs RWD?

 

800px-1993_Saab_900T_Convertible_B202_en

Splitting unnecessary hairs, HP losses stack up no matter the config,  belt dress and mass of the components + cooling (water pump/fan) etc...

 

Most every car guy can feel hp jump when the belts throw (3 min before meltdown)

Edited by Team Infiniti
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7 minutes ago, Team Infiniti said:

Splitting unnecessary hairs, HP losses stack up no matter the config,  belt dress and mass of the components + cooling (water pump/fan) etc...

 

The HP losses are especially great if your HP has to make a 90* turn like it does on this saab. 

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14 minutes ago, Team Infiniti said:

A/C kicks off @ WOT but your internal fans continue.

Alternator is always pulling something or the battery would discharge

A RWD fan never stops, may somewhat freewheel but is ultimately thermostatically controlled (random)

FWD fan runs from battery : See Alt, even if the fan is not running the battery is still catching up a little from last fan cycle

 

Are you telling me I should connect the TPS to a relay that cuts the magnetic field on the alternator during WOT?

 

 

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48 minutes ago, okkustom said:

 If net includes drive train .   Also turning trans ,rear gears , all bearings , shafts ect , all adds up

Indeed.. You have friction in the trans, diff, inertia to overcome in the driveshaft, axles, wheels & tires.. (friction, not just gear on gear, but viscous losses of trying to spin parts through thick oil) 

If they were doing this "net" test on an automatic vehicle then you have losses from the torque converter.

 

I'm assuming the different tests which generated the OP's data were engine dyno vs. chassis dyno.

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35 minutes ago, red0 said:

 

That is the distributor, before they went with the direct ignition cassette I would assume. It looks like it might be vacuum advance too?

 

Man... when did you guys get so gullible?   :lol::lol:

 

The other real problem with that engine shown is there are NO spark plugs.  No way that's gonna work.  I say machine some spots for spark plugs into that head and it will probably develop more power.

 

Edited by Ham Sammich
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Net was before SAE net.  Before SAE hp the manufacturers could test however they wish, i.e. run everything external to get gross hp.

 

So some/everything would be driven external: fuel pump (mechanical or electric), alternator, power steering pump, oil pump, air pump, fan (mechanical or electric)... that chews up a lot of hp.

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1 hour ago, Ron_e said:

Net was before SAE net.  Before SAE hp the manufacturers could test however they wish, i.e. run everything external to get gross hp.

 

So some/everything would be driven external: fuel pump (mechanical or electric), alternator, power steering pump, oil pump, air pump, fan (mechanical or electric)... that chews up a lot of hp.

 

Maybe have two  motors synced at the exact same RPM and have the second motor drive the camshaft and take all the drive train loss :)

2 hours ago, mhr650 said:

 

Been there done that, easy to do with MS,  works great for sprint racing.

 

Do you drive the magnetic field directly from a GPIO output or do you have a relaly or transistor inbetween?

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 I run cars on the dyno a bit.   I ran a VW with a field wire hooked to the fan switch .  No charge until you turn the fan and alt on. 2-3HP loss , charging..   It was enough that I made  a  full Throttle switch that cut the alt  for one of the early SCCA cars.

     Later/now I use 3 batteries and no alternator. 4HP .  is a lot on 125.  Maybe 1.5 sec per lap  @ Sebring.    

  I learned the field wire deal withe ministock . Run non charging for the race  and turn the fan and alt on as we roll through tech. The cam rule was it had to draw 17 in vacuum . Charging hard with e fan on dropped the idle to the 1000 and the wild cam made it through tech. Won  many  of the races . 

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15 hours ago, Team Infiniti said:

yes if its worth the couple of hp and is ok with your team that you added complexity and points of failure.

 

I suppose you could generate the same result with underdrive pulleys, but depending on make/model of car could be cheap or expensive.  At least then its not an extra point of failure.

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39 minutes ago, flyinglizard said:

 I run cars on the dyno a bit.   I ran a VW with a field wire hooked to the fan switch .  No charge until you turn the fan and alt on. 2-3HP loss , charging..   It was enough that I made  a  full Throttle switch that cut the alt  for one of the early SCCA cars.

     Later/now I use 3 batteries and no alternator. 4HP .  is a lot on 125.  Maybe 1.5 sec per lap  @ Sebring.    

  I learned the field wire deal withe ministock . Run non charging for the race  and turn the fan and alt on as we roll through tech. The cam rule was it had to draw 17 in vacuum . Charging hard with e fan on dropped the idle to the 1000 and the wild cam made it through tech. Won  many  of the races . 

I'm not sure how efficient an alternator is at converting hp to amps, but the math says 4hp @ 14v is over 200 amps, that certainly seems like the upper limit of plausibility. 2hp seems easily believable though if you wait to turn it on until the battery has significantly discharged. 

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13 hours ago, turbogrill said:

 

 

Do you drive the magnetic field directly from a GPIO output or do you have a relaly or transistor inbetween?

 

The ones I have seen used a relay.

 

Don't forget the difference between the J607 and J1349 correction factor. Most race engine builders still use the old J607 factor since it gives a bigger number they can show to the customer.

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This is one of the reasons you see manufacturers trying to get all the accessories off the engine. Everything is going to electrically driven accessories (48V is coming hard). That power had to come from somewhere (engine and batteries), but once those accessories can be controlled completely independent of the engine, they can be operated much more efficiently, and also keep the engine happier.

 

example...

http://autoweek.com/article/technology/why-mercedes-new-inline-six-matters-even-if-no-one-sure-when-well-see-it

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18 minutes ago, JBgotM said:

This is one of the reasons you see manufacturers trying to get all the accessories off the engine. Everything is going to electrically driven accessories (48V is coming hard). That power had to come from somewhere (engine and batteries), but once those accessories can be controlled completely independent of the engine, they can be operated much more efficiently, and also keep the engine happier.

 

example...

http://autoweek.com/article/technology/why-mercedes-new-inline-six-matters-even-if-no-one-sure-when-well-see-it

 

Makes sense to me.  I always thought it would have been a good idea to get all the accessories to be electrically driven and then it would be much easier to shut the engine off at stoplights.  I know a lot of cars have stop/start systems now even with belt driven accessories, but its still easier to manage when they have their own drivers.

 

 

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