Specific Output (a.k.a. hp/L)

[Firebird]

Most useless measurement ever conceived.

That is all.

 

[Quick_Nick]

That's a ratio, not an output. It's also very useful.

 

[Firebird]

Oops! Meant to put quotation marks around "measurement".


And it is not useful whatsoever.

 

[inferno]

Volumetric eficiency is everything. I know its not in direct proportion but on a broad scale an engines displacement is reflective of its actual size. A big engine is a heavy engine, and a heavy engine is bad. the lighter an engine is the smaller of a vehicle it can be put in while maintaining proper weight distibution. the higher an engines specific output the more power it makes with respect to its displacement, as in its size, as in its weight. this leads us to the all important power to weight ratio. a lighter engine in a lighter car means less overall weight. and the higher that engines specific output the more power it makes. so it would seem, the higher an engines specific output the better.

 

[Firebird]

Specific output and volumetric efficiency are not the same thing.

And displacement is not directly proportional to size and weight.

 

[iceburns288]

Ricers = "it's all about hp/l br0!" rofl

It is quite handy to see how effecient your engine is, like the CS which is 118hp/l!

It does get stupid though, like saying the Enzo's engine is weak because it gets about 95hp/l I think.

 

[Quick_Nick]

I guess it depends on how you judge cars. I try to look at the efficiency of each component, instead of just reading about its overall specs & performance numbers.

BTW the Enzo gets 108.3333 HP/L.

 

[neanderthal]

Most useless measurement ever conceived.

That is all.

its a good measurement of volumetric efficiency.
id take a nice 400hp V8 over a 185hp one. wouldnt you?

thats volumetric efficiency.

 

[StevieMo]

Probably not a good example. I would have went with say a 360 C.I. engine instead of just V8. If my 200 C.I. V8 had 185hp I certainly wouldn't be dissapointed. But if my 454 was putting out low numbers like that then I would be dissapointed.

 

[///M-Spec]

Power/liter is useful to race car engineers whose design parameters include getting the most power out of whatever displacement the rules specify.

But outside of racing, power/liter is over emphisized by too many people, IMO. Especially young people in the 'tuning community'.

Firebird is right. Using displacement to gauge an engine's size and weight is NOT reliable. The basic architecture has as much to do with it as cylinder displacement. A 5.7 small block pushrod V8 may actually end up being the same weight as a 4.4 quad-overhead cam V8 or even a 3.0 liter dual cam twin turbo intercooled V6. Cams, fancy heads, turbos and intercoolers are not weightless, folks.

And just as important as weight is where it is in the car. Some engines are very tall, as in the case of quad-cam V8s, especially ones with exotic heads and race car throttle bodies. They end up raising the CG of the car, pushing out the polar moment over the front axle or both.

I'd be very curious to see a table that lists dimensions and weight for popular street performance engines, which would really help the discussion.


M

 

[Firebird]

its a good measurement of volumetric efficiency.
id take a nice 400hp V8 over a 185hp one. wouldnt you?

thats volumetric efficiency.

Volumetric efficiency is the ratio of the actual volumetric flow rate over the theoretical volumetric flow rate (displacement).

Specific output is power per unit displacement.

And I would want a 400hp V8 over a 185hp V8. Then again, the 400hp V8 could be a 10L turbodiesel designed for heavy duty applications, weighing only, oh... 3,000lbs or so.... and the 185hp V8 could be something like a Buick/Rover 215 V8, whichs weighs about 315lbs.

Or the 400hp V8 could be a GM LS6, which weighs about 500lbs w/ a Tremec T-56 attached, but it also much smaller than the Mustang Cobra's 4.6L DOHC V8 (which is absolutely enormous by the way. We're talking about the same size as an old FE block V8, and those could have displacements up to 460c.i.).

 

[Firebird]

Power/liter is useful to race car engineers whose design parameters include getting the most power out of whatever displacement the rules specify.

But it isn't particularly useful outside of racing.

 

[///M-Spec]

But it isn't particularly useful outside of racing.

You did read my post beyond the first sentance, right?

But outside of racing, power/liter is over emphisized by too many people, IMO. Especially young people in the 'tuning community'.

M

 

[Firebird]

You did read my post beyond the first sentence, right?

I did.

The point that it isn't useful cannot be overemphasized.

 

[Firebird]

Did I mention specific output is useless?

 

[Ottoman]

hahaha

ahh I remember discussin this long and hard with your firebird..

decided to dig it outta the grave huh?

 

[neanderthal]

Volumetric efficiency is the ratio of the actual volumetric flow rate over the theoretical volumetric flow rate (displacement).

Specific output is power per unit displacement.

And I would want a 400hp V8 over a 185hp V8. Then again, the 400hp V8 could be a 10L turbodiesel designed for heavy duty applications, weighing only, oh... 3,000lbs or so.... and the 185hp V8 could be something like a Buick/Rover 215 V8, whichs weighs about 315lbs.

Or the 400hp V8 could be a GM LS6, which weighs about 500lbs w/ a Tremec T-56 attached, but it also much smaller than the Mustang Cobra's 4.6L DOHC V8 (which is absolutely enormous by the way. We're talking about the same size as an old FE block V8, and those could have displacements up to 460c.i.).

considering GM had a pathetic 185 hp 5.7 liter small block back in the dark days of the early eighties, i was actually thinking about a typical chevy small block.

 

[Firebird]

hahaha

ahh I remember discussin this long and hard with your firebird..

decided to dig it outta the grave huh?

It deserves its own thread.

considering GM had a pathetic 185 hp 5.7 liter small block back in the dark days of the early eighties, i was actually thinking about a typical chevy small block.

It's all relative. A 1980 Civic 1500GL had a 67hp 1.5L four-banger. Your average modern day Civic has 115hp out 1.7L. A 1980 Porsche 911SC had 172hp, while a new Carrera has 315.

Are these newer engines better because they have higher specific output? No. They're better becase they're simply more powerful.

 

[skip0110]

Volumetric efficiency is the ratio of the actual volumetric flow rate over the theoretical volumetric flow rate (displacement).

Firebird seems to be the only person in this thread who has a clue what volumetric efficiency means. It has nothing to do with the physical size of the engine.

I think that brake specific fuel consumption and power output are good measures of an engine's "goodness." Horsepower is obvious, and BSFC measures the amount of energy that an engine is able to extract from the gasoline (or actually, the inverse--how muchg fuel is used to generate a given amount of energy, i.e. horsepower for some time period). A good BSFC (low number) means the engine is well tuned.

 

[emad]

I think power to weight is a much better ratio to work with... that at least gives you a better idea of how quick the car will be in the end

 

[neanderthal]

It deserves its own thread.




It's all relative. A 1980 Civic 1500GL had a 67hp 1.5L four-banger. Your average modern day Civic has 115hp out 1.7L. A 1980 Porsche 911SC had 172hp, while a new Carrera has 315.

Are these newer engines better because they have higher specific output? No. They're better becase they're simply more powerful.

they are more powerful because they have more hosepower per liter. displacement is nearly the same.

especially in the case of the chevy small block i mentioned. given the dumb statement in the first post of this thread, would you choose the choked 185 version or the one that gives more horsepower per liter. if you choose the more powerful engine then that shows that its not a "useless measurement" as you yourself would employ it in choosing your engine of choice.

 

[Firebird]

No, they're more powerful because they have more power. (They also have freer-flowing intake and exhaust systems, use more efficient fuel systems (SMPEFI vs. a carburetor or continuous mechanical FI), and use more fuel, period.)

Say you're living in 1987. You're in the market for a brand new '87 Chevrolet Camaro. Are you going to choose

A) The engine with 48hp/L,
B) The engine with 43hp/L, or
C) The engine with 39hp/L.

By your twisted logic you should buy A). So let's say you do.

You just bought a base model 2.8L V6 with 135hp.



Then there's me, circa 1987, who buys a Camaro with engine C) instead.




I bought the 225hp 5.7L V8.


Yay for hp/L!

 

[neanderthal]

i think i have stated that my comparisons are between two chevy small blocks. not between two sets of figures for different displacement engines.

if you have before you, two chevy small blocks, and are told that exhibit a has 56.14 hp/l and exhibit b has 32.46 which one would you choose. ill tell yuo this; one is the 320 horse LS1 and the other is the wimped out 185hp thing.

if you choose the one with the higher hp/ l figure then you have have just employed the "most useless measurement."

given a choice between two same size engines with differing power outputs, choosing the higher output engine is directly/ indirectly employing and using hp/ liter. you could call it a cost/ benefit ratio or whatever you want to call it, but a rose by any other name is still a hp/ l ratio.

 

[Firebird]

No.

Given a choice between two engines with the same displacement with differring power outputs choosing the higher output engine means choosing the one with more power. hp/L is a byproduct: some quotient. Doesn't tell you anything about the torque curve. Doesn't tell you anything about fuel economy. Doesn't tell you anything about power either, unless you know displacement.

Doesn't tell you anything useful.

 

[neanderthal]

theres a saying; theres no replacement for displacement. why dont they just make it a bigger engine? that way we could all drive 13 liter cars until someone decides that is not enough.

oh wait, fuel economy. emissions. costs. durability. and so on. things that have to be considered when deciding what engine should power a car. where in the range the car should be. these limitations require efficiency. and hp/liter is a good measure (ratio) of it. stop being dumb.

 

[skip0110]

theres a saying; theres no replacement for displacement. why dont they just make it a bigger engine? that way we could all drive 13 liter cars until someone decides that is not enough.

oh wait, fuel economy. emissions. costs. durability. and so on. things that have to be considered when deciding what engine should power a car. where in the range the car should be. these limitations require efficiency. and hp/liter is a good measure (ratio) of it. stop being dumb.

HP/L does NOT measue efficiency.
Volkswagen Jetta TDI - 60 hp/L, 50 mpg city
Dodge Ram SRT-10 - 60 hp/L, 9 MPG city

So whats up?
HP/L has NOTHING to do with fuel efficincy. That has to do with how richly the engine is running, etc. BSFC measures efficiency.

 

[Firebird]

theres a saying; theres no replacement for displacement. why dont they just make it a bigger engine? that way we could all drive 13 liter cars until someone decides that is not enough.

oh wait, fuel economy. emissions. costs. durability. and so on. things that have to be considered when deciding what engine should power a car. where in the range the car should be. these limitations require efficiency. and hp/liter is a good measure (ratio) of it.

Power (in horsepower):
Dodge Viper SRT-10: 500
Chevrolet Corvette Z06: 405
Ferrari 360 Modena: 400
Ford Mustang SVT Cobra: 390
Jaguar XKR: 390
Maserati Coupe GT: 390
Chevrolet Corvette Coupe: 350
BMW M3 Coupe: 333
Nissan 350Z: 287

hp/L:
Ferrari 360 Modena: 111.1
BMW M3 Coupe: 104.1
Jaguar XKR: 92.9
Maserati Coupe GT: 92.9
Ford Mustang SVT Cobra: 84.8
Nissan 350Z: 82.0
Chevrolet Corvette Z06: 71.1
Chevrolet Corvette Coupe: 61.4
Dodge Viper SRT-10: 60.4

Fuel economy (Transport Canada figures in miles per Imperial gallon; they'll seem inflated to American forum members because Imperial gallons are larger than US gallons. All have 6-speed transmissions. All manual, save for the Jaguar):
Chevrolet Corvette Coupe/Z06: 23 city/37 highway
Nissan 350Z: 24 city/34 highway
BMW M3 Coupe: 19 city/31 highway
Ford Mustang SVT Cobra: 20 city/29 highway
Jaguar XKR: 19 city/30 highway
Dodge Viper SRT-10: 14 city/26 highway
Maserati Coupe GT: 14 city/22 highway
Ferrari 360 Modena: 13 city/21 highway

Annual greenhouse gas emissions (in tons; from US Department of Energy):
Ferrari 360 Modena: 15.0
Maserati Coupe GT: 14.1
Dodge Viper SRT-10: 12.8
Jaguar XKR: 10.8
BMW M3: 9.9
Ford Mustang SVT Cobra: 9.8
Chevrolet Corvette Coupe: 8.5
Nissan 350Z: 8.5
Chevrolet Corvette Z06: 8.5

Environmental Protection Agency emission standard ("----" meaning not high enough for LEV certification):
Ferrari 360 Modena: LEV
Chevrolet Corvette Z06: LEV
BMW M3 Coupe: LEV
Chevrolet Corvette Coupe: LEV
Dodge Viper SRT-10: LEV
Jaguar XKR: LEV
Maserati Coupe GT: LEV
Nissan 350Z: LEV
Ford Mustang SVT Cobra: ----

stop being dumb.

You first.

 

[retsmah]

edit: nevermind

 

[neanderthal]

fuel economy is dependent on many different things, only one of which is engine size. do you care to post the top gear ratios for the ferrari and corvette?
performance is also dependent on many things. again, only one of which is engine size.
emissions and greenhouse gas emissions are dependent on many things. one of which is engine size.

your little table proves nothing. anyone with half a brain can tell you that an engine that is highly tuned will yield higher emissions and fuel consumption than one that isnt as highly tuned. the person paying hundreds of thousands of dollarrs for a ferrari doenst care for fuel economy. nothing in ferraris fleet comes close to meeting CAFE standards. thier customers gladly pay the luxury tax that comes with having such a high performance vehicle so what does that tell you about those figures?

GM has to consider fuel economy in all thier cars, and in fact implemented that long 6th gear in the corvette specifically for fuel economy purposes. most overdrives are geared about 0.80 and its 0.50. only the viper and camaro had overdrives that steep. and also, specififically to boost their corporate CAFE numbers.

what i said still stands, when all the factors are considered, efficiency is still a good "measure."

 

[Firebird]

your little table proves nothing.

Actually, it proved you wrong. The engine with the highest specific output in that little group of cars had less power than one with the lowest specific output and one with the third lowest specific output, had the worst fuel economy and had the worst emissions.

what i said still stands, when all the factors are considered, efficiency is still a good "measure."

Did you always have reading comprehension problems? Your so-called "efficiency" landed you an engine with terrible fuel mileage, worse emissions, and less power than two far less "efficient" engines.