Specific Output (HP/L)

[landyacht]

Hi, I'm new to these forums and I thought I would ask a technical question.

I see in magazines, and even on Top Gear, etc, people talk about how much power an engine makes for its displacement. I am wondering how that can be used to show how good or bad an engine is, because it seems like there are a lot of engines that are light, good on gas, and very powerful that have low hp/L figures. I tend to believe that hp/L is actually not very useful, because it does not necessarily reveal things like power to weight, mileage, average power, or similar engine characteristics directly.

Can anyone talk me out of it? I would like to know if I am on the right track here. Should someone shop for hp/L when they get a car?

I know that sometimes these types of threads can get out of hand (kind of like hp vs tq threads), so I'm hoping everyone can be nice. I certainly don't want to cause trouble. Thanks for any responses. I will probably not reply to this thread, but rather just watch and digest.

[fbc]

You're definitely on the right track.

HP/L has no relevance whatsoever when it comes to the actual performance of the motor - the motor's weight, fuel consumption, and power / torque curves are what matters.

HP/L is only useful as a measure of how much the engineers have managed to squeeze out of a given capacity - which can make impressive reading, but it's meaningless in terms of the motor's performance.

So in short, no, HP/L is meaningless when shopping for a car.

[FATMOUSE]

A meaningful comparison could be between the engine in a BMW M5 vs, say a Z06 Corvette. Compare the following between the two:
1. HP/L
2. HP/weight of the engine
3. Fuel Efficiency

All data readily found on the web.

[Hidden_Hunter]

HP/L is just something for most honda owners (excluding me obviously) to circle jerk over

[the Interceptor]

Originally Posted by fbc

So in short, no, HP/L is meaningless when shopping for a car.

Generally correct, but it does play a role if you plan to keep the car for a long time. From an engine with a low HP/L mark, you can expect a longer life than from an engine with HP/L. Actually, the statement I just made is too general and not always correct (such as in the case of a Honda), but the figure does mean something sometimes when buying a car.

Regards
the Interceptor

[thedguy]

Originally Posted by landyacht

Can anyone talk me out of it? I would like to know if I am on the right track here. Should someone shop for hp/L when they get a car?

I know that sometimes these types of threads can get out of hand (kind of like hp vs tq threads), so I'm hoping everyone can be nice. I certainly don't want to cause trouble. Thanks for any responses. I will probably not reply to this thread, but rather just watch and digest.

Like anywhere else, bringing up HP/Liter will usually get create a huge argument that leads to a thread lock.

The only real use of the argument is for racing classes and governments. Racing will obviously limit displacement, and some governments tax the shit out of you based on displacement.

Otherwise it's usually what you hear after someone driving a Honda or some other small engined car that can't outrun the big stuff.

[tigger]

Originally Posted by Hidden_Hunter

HP/L is just something for most honda owners (excluding me obviously) to circle jerk over

Exactly. I've heard people basically argue that the Honda K-series engines are better than GM's LS7 because they make so much more hp/L. Nevermind that the LS7 still has 500hp, and the K20 200 or so. They may both be great engines, but in that case it's a stupid point. Personally I normally disregard hp/L as the last argument of a fanboy. Kind of the "Well ....you're stupid!" retort of the automotive world lol.

[MXM]

hp/l means everything in everyday cars. When you are taxed by displacement, your insurance depends on displacement, and fuel consumption is determined mostly by displacement (I mean with same hp smaller engine is more fuel efficient usually).

However in performance car this is a lot less useful then some people think. hp/weight ratio and flatter power curve always beats hp/l in my book.

[bone]

Originally Posted by fbc

HP/L is only useful as a measure of how much the engineers have managed to squeeze out of a given capacity - which can make impressive reading, but it's meaningless in terms of the motor's performance.

+ in a lot of european countries (like belgium) you have to pay taxes based on hp/l, the lower the number, the more you have to pay, so hardly any corvettes over here

or any V8 for that matter, a turbo 4 banger is waaaaay cheaper

but votes are rising to change this to a tax based on CO2 emissions...

[ArosaMike]

Oh dear. Not this one AGAIN!

[Ottobon]

one thing that always changes with a higher hp per litel is the rev-range, you have to rev the car higher to get more power out of the same displacement (without adding a turbo/supercharger) , this mainly means the camshafts are setup differently, longer duration, and usually larger lift, as well everything on the engine goes through a little bit of tuning, exhaust primary collectors are shortened a little, as well as a slight change in intake length, valvetrain is stiffened, i could go on forever....

the main thing is that some cars with high hp/liter have great torque curves, some don't, its not really something to pay attention to unless you have a thing for either Forced induction or high revving engines, otherwise, just get the best car you can :p

just read up and see what reviewers say feels good and or performs well, that usually is a good starting place


i generally would go for the largest displacement motor with the lightest weight possible, since i can just do a engine build up if it has a low hp/liter and get much much more hp in the end, although usually size is relative to weight with engines

[BerserkerCatSplat]

Originally Posted by ArosaMike

Oh dear. Not this one AGAIN!

"Oh, no, not this shit again!"