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3 years ago

Horsepower per liter - it is serious business!

At some point or another, you have likely encountered someone chiming on about an NA engines horsepower per liter - it is inevitable whenever an engine produces 100 hp/l or more. But what is the significance of this interesting little figure?

To sum it up, there really is none. hp/l has as little significance to performance as the storage capacity of your cars boot.

hp/l is not even necessarily directly associated with engine weight. Less displacement and more revs is just one of the many ways to go after big power. Some manufacturers choose high displacement, some go with forced induction, and others opt for high revs. They can all make equal power and they can all (for the most part) be packaged to weigh the same. The choice often comes down to the manufacturers goals for the characteristics of the engine (and their chassis space constraints).

BMW has had no trouble in the past producing NA engines that make more than 100hp/l. But they have recently decided to go with forced induction. I assume, they have chosen to go this route because they feel it is the most appropriate approach to meet their goals.

At the same time, Ferrari and Porsche know that their customers expect high revving engines that rush to within an inch of their life to reach their screaming redline.

In contrast, a powerful Mercedes isn't a true Mercedes to many without displacing more than 5 litres and/or sporting the barely audible whine of a blower or a pair of turbochargers.

A small displacement NA motor can actually have its disadvantages. The power is very often much more peaky than most modern FI and large displacement engines. It can feel gutless down low and make day to day city driving a PITA.

So why do people go on and on about NA hp/l? Well, it is often viewed as an engineering marvel - a way for followers to brag about their favourite brands engineering prowess.

What some people often don't consider is how common place high hp/l in a NA engine really is. Look at most any modern bike manufacturer and you would be hard pressed to find one where their sportier versions make less than 100hp/l. I know, I know, its a bike, but the same principal stands. In fact, bikes have managed to make over 100hp/l for years even with carburettors. Fact of the matter is: Honda, BMW, Ferrari, Porsche, VW/Audi/Lamborghini, and several others have all produced production engines with more than 100hp/l.

There is no doubt that producing an NA engine that makes a lot of hp with little displacement is tricky. It takes a perfectly honed intake system and a top end setup that can squeeze every last bit out of the little displacement that is offered. But, it can be equally difficult to make a reliable high hp engine that makes use of forced induction.

Fact of the matter is, a powerful forced induction motor can actually be trickier. You have to deal with more moving parts, a significantly hotter engine bay, and everything needs to be even more stout to deal with the additional stress that FI puts on an engines internals.

Ultimately, it comes down to a manufacturers personal taste. The technology to make an engine produce a lot of power with very little displacement has been around for a while, but it is not something many manufacturers or consumers want in an engine.

I don't expect this to change anyone's opinion as many of the people that hold hp/l in high regard are not easily swayed. I mean only to present my own take on the matter, as it is commonly brought up at one time or another.

What is your take on hp/l?

Community comments (147)

  9 months ago
I like all the engines mentioned here. I used to have an RX7. Great motor. I currently have a 2.0L Turbo GTI, and a N/A 6.4L SRT Challenger. Both loads of fun. The 6.4 puts out 470 ft/lbs of Q through most of the RPM range...constant "slam you in the seat feel." My GTI is tuned ... My fun meter is pegged either way.
  11 months ago
@voice of doom.

Performance doesn't neccesarily come in the form of acceleration numbers. MPG is too. For all I know, if a long top gear allows high MPG, then so be it.

Everywhere in the world is harping on emissions. That's fact, and every manufacturer is thinking about it.

The laugh is NOT about about HP/l. It's this cheesy hybrid business of extreme hypercars claiming low emissions so that they meet certain standards when in fact most people driving those cars won't ACTUALLY meet those standards. The electric mode of the Mclaren P1 lasts only a few miles, and I don't know how much does the Laferrari. Now THATs a loophole. And no wonder everyone's using it. These cars now can claim acceleration numbers with all the max juiced up. However they don't tell you how quickly that juice is gone, another exageration of performance.
  11 months ago
If you want to see how HP is developed from each country of manufacture, i.e. big OHV V8 / small OHC VVT / Turbo, then all you need to do is look at the cost of fuel and cc tax, in the country of export. The ''laugh'' is, when Chevy build a V8 with gearing SOOOOOOO long in top, to sell on mpg. by exploiting the ''average'' MPG loophole. How can that ridiculous top gear be for performance? No, they are concealing a design shortcoming.
The law (according to physics is) OHC kicks OHV, because of less mass losses, 4 Valves per cylinder kicks 2, because although mass losses are greater, the VE improvement more than compensates. Turbo kicks all because both VE and thermal losses are reduced.
But in the end, it's all about how much your country charges at the pump that dictates the level of technology / HP.

Don't start me on secondary safety and weight gain!
Nor ''lean burn'' and efficiency vs pollution (Nox.) and public opinion. (where in the USA political agenda becomes scientific fact via the fox news network)


  2 years ago
@ Future: Back to reality, please, you're either living in the future or a fantasy world, opposing magnetron forces?, really?, maybe in another 100 years or so. Fossil fuels will be around for at least the rest of my life, and I'm only 28 years old.
  2 years ago
I judge an engine's power output by 2 standards to gauge whether it's a powerful engine for its size, the old method, horsepower per cubic inch, and the newer standard, horsepower per liter, if the engine's power output is more than, the same as, or even a little less than its displacement in cubic inches, it's a powerful engine for its size, if the horsepower is more, equal to, or even a little less than 100 horsepower per liter, it's a very powerful engine for its size.
  2 years ago
some cars are built to be push rods and others to be DOHC, but as much as people make fun of them I've seen more than one small displacement push rod take on a turbo DOCH and win, but don't judge a cars output by its 1970's era emission control system
  2 years ago
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  2 years ago
cars of the future will use opposing magnetron forces within a wave field. Clear ones mind of fossil fuels
  2 years ago, last edited 2 years ago
"engine that is the same displacement, but has dohc vtc cam gears and some form of controlling the valve timing"

Just noticed this gem from "c00l"
VTC and some form of valve timing control?
Ever heard of a thing called vvt?
Ford actually has an extremely advanced vvt system.

Also, I already own a dohc supercharged V8 Ford. I'd be willing to gamble that it's quicker than anything you've owned before too...

Speaking of my Ford (and not directed to cool). I'm really tempted to sell it come next fall and getting another LS car. The mod motors are just a PITA to work on and I kinda miss my old c5.
  2 years ago

You know somebody's an expert when they call a pushrod motor a SOHC and a F430 engine 4.6 liters....



LOL I was gonna point that out...but i thought i would let him correct himself LOL

Honestly where do these people come from? Surrey? lol
  2 years ago
You know somebody's an expert when they call a pushrod motor a SOHC and a F430 engine 4.6 liters....
  2 years ago

The fact that the ls engines from gm use pushrod sohc setups is a joke.



Pushrod SOHC?....strike 1.

I have a really hard time believing that you have an accurate weight on the f430 4.6L v8



F430 4.6L?...Strike 2.

I'd rather have the highest end inline 4 or inline 6 than a low end or average v8 regardless of which makes more power...



...and we're done.
  2 years ago, last edited 2 years ago
@ cool

What's a pushrod sohc motor?

My old c5 made ~440whp thanks to better heads, cam, and other goodies. I never had any trouble with a ferrari at the track. Not bad for old tech.

I wouldn't want dohc or vtc on an ls engine. A simple cam swap on my c5 netted 50whp and took me a little over an hour. New cams in my dohc 03 cobra would take me a whole afternoon and net me virtually nothing.

Ps, I've owned hondas and dsms in the past. Not really my cup of tea.

And please keep your angry inaccurate prepubescent insults to yourself.

Thank you
  2 years ago
@Cool

The Engine weight of a F430

F430 451Lbs
C6 LS3 432Lbs
R8 V8 492Lbs
V8 Vantage 456Lbs

As tested By Road&Track in there Exotic V8 Comparo V8 To Creston lineup.

However, i hear the Weight of the C6 ZO6 LS7 is 442Lbs from LS1Tech.

And a Stock F430 will not beat a stock ZO6 in any Acceleration type, that has been proven, fastest 1/4 mile was 11.4@128.1 by MotorTrend in there 2006 October Issue(3.4s 0-60mph, 7.4s 0-100mph, Fastest F430 time was also by MotorTrend 11.7@123.7Mph(0-60mph 3.7s, 0-100Mph 7.8s) Also fastest 0-150mph times of 17.0 Zo6, and 23.7 F430, So please, dont say the F430 will beat a ZO6 when the fact is it will not(Best For Best)Same outcome on the track.

And like E said, what is Low Tech about a Corvette engine?
  2 years ago
E

I have a really hard time believing that you have an accurate weight on the f430 4.6L v8... Not to mention I that the 505hp rating on the zo6 is an inflated number to the crank... The stock f430 will beat a new z06 in a 1/4 mile by a few tenths of a second, but that isn't really what it was built for obviously. It will really outshine the vette in a road race where power band and the ability to rev higher longer really comes into play...


Honestly though I do agree that it is important to look at hp/weight of the engine, and in that regard some of the low tech pushrod v8s are not too shabby. I look at it as a trade off though. With domestics you get an average v8 where with a lot of other cars you get a smaller less desirable engine, but it is the best of its kind. I'd rather have the highest end inline 4 or inline 6 than a low end or average v8 regardless of which makes more power...
  2 years ago
LS7, 505 hp, ~450 lbs
F430, 490 hp, ~450 lbs

What's low tech?

Don't forget that road cars don't race competitively and that makers choose how much hp they want. The Corvette has 505 hp because GM wanted 505 hp, not because they got every hp/L out of it.
  2 years ago
Another thing to keep in mind. When lambo builds an engine they don't make it 2 valves per cylinder with push rods and nothing to control the valves. Clearly hp/l is not an end all say all stat. If you really understand cars, then you realize there is no end all stat that is the final say in how fast a car/engine is. Domestic fans have their panties in a bunch because although they are right to a point, they realize their engines are low tech. The fact that the ls engines from gm use pushrod sohc setups is a joke. I would love for this Apathy domestic dick rider to seriously come on here and tell me that he wouldn't rather have an ls engine that is the same displacement, but has dohc vtc cam gears and some form of controlling the valve timing to create an engine that puts out more hp/l than the curent ls engine. Simply put, if you are designing a high performance engine hp/l does matter.

I know the new 5.0 is an exception, but most domestics could be a lot faster with some technological upgrades with head and cam design...

Not to mention the fact that building a v8 costs a shit ton more than a smaller displacement engine with high hp/l .

The extra 100-175lbs a v8 has is a bigger issue than some of you think. I say that, because this is not dead weight along for the ride. Some of this is weight from things such as more and longer rods, more and wider pistons, and a beefier crankshaft to handle the harmonic vibrations a v8 produces. This makes a big difference in
  2 years ago
displacement is definitely going to have an impact on efficiency i.e. mpg. It's not that you can't be faster with an engine with less hp/L but it does say a lot about how high performance your engine is...
  2 years ago
It all really comes down to the Manufacturer and vehicle personality. A Ferrari is not a Ferrari without a high revving engine and a Viper is not a Viper without a low revving engine. In the end it gives each car its own unique appeal and a personality. I think both are great but i mostly prefer the high-revving types.
  3 years ago
Perfect example with three engines:
All three engines are made from the same block, heads, intake, exhaust, etc. The only thing different being the internals.

1) 8.5 compression pistons, short stroke
2) 10.5 compression pistons short stroke
3) 8.5 compression pistons, long stroke crank.

Engine 3 makes the same power as 2, and engine 1 makes 3/4's the power of 2 and 3. All three use very basic technology, and there's certainly nothing advanced about higher compression pistons, at least not in comparison to a longer stroke. Even though engine 2 has a higher hp/l than the stroked engine 3, niether is more advanced than the other.
  3 years ago
Incorrect.

An engine's technolical level is measured by its efficiency. The engine that produces the most usable power with the least consumption is the most technologically advanced. Displacement is entirely irrelevant. No sense in arguing that point either.

They're all just different approaches towards the same goal. The only technological benchmark is consumption efficiency. HP/L is for the same people that think their car can go as high as the speedometer can read.
  3 years ago
hp per liter number shows how smart technical and modern the engine is. bigger hp per liter number - the engine is better, smaller - the engine declines towards those old american v8s with 5.7 liters and 113 hps, in a word - junk.
its how engines progress.
  3 years ago
IT really falls down to what you want out of a car

A 2 litre turbo is probably going to provide amazing power for the engine but stick that engine on a 2 tonne car and the block is going to fold after 15,000 miles

It's all down to ways of dealing with all the different problems in engineering
  3 years ago
I agree with the article. Hp/l is only useful for class racing. Power/weight ratios are much more important.
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