BHP/Litre and BHP at the crank - Irrelevant now?

[-Z-]

This topic is nothing more than a rant at how irrelevant these statistics seem to be.

BHP/Litre- I HATE this. What is it actually a measure of? Wouldn't BHP/Kg (weight of engine + ancillaries) be a much better measure of the effectiveness of an engine?

For example on another thread someone argued that the e46 M3's S54 engine is better than the e9x M3's V8 because its BHP/Litre was higher. What benefit is that when the V8 weighs LESS than the straight 6 and develops more power (as well as revving higher).


BHP at the flywheel/crank: Will manufacturers ever publish BHP at the wheels or hub? Would make it far easier to compare 2WD and 4WD cars and how much power 4WD (or a crap gearbox) saps. Also makes tuning your car more accurate and would also make it far easier to work out if your car is not making it's published figures (probably why they don't publish this )

[kambites]

-Z- said:

This topic is nothing more than a rant at how irrelevant these statistics seem to be.

BHP at the crank isn't as bad as torque at the crank in the "pointless stats that people seem to care about" stakes.

One could argue that power at the wheels is also pretty useless, mind. Power to weight and power to drag ratios are the important thing.

[TheAngryDog]

who cares?

BHP is for impressing your chav mates down the pub.

[alock]

-Z- said:

BHP/Litre- I HATE this. What is it actually a measure of?

It's in no way scientific, but I reckon if you surveyed people for the most exciting engines, there would be a fairly good correlation to BHP/Litre. I know there are exceptions, but generally the higher this figure, the more exciting the engine is to use.

[rigga]

Cast iron engine versus aluminum engine both making the same power is just pointless comparison as its just the difference in casting material weight, the efficiency of the engine would have more affect on how it performs, so how much horsepower it makes from its capacity is relevent .....more so bmep.

[vtecyo]

I've only heard people crying about bhp/litre in the Honda circles, spouting drivel about the EK9.

Pointless.

[RizzoTheRat]

BHP per litre only really makes sense for bike where there do tend to be specific classes of bike, ie 600, 1000 and 12-1400cc

[mikeveal]

Well actually bhp/litre gives you a fairly good idea of how highly strung the engine is.

[aka_kerrly]

vtecyo said:

I've only heard people crying about bhp/litre in the Honda circles, spouting drivel about the EK9.

Pointless.

Much the same way only diesel owners seem obsessed with quoting torque figures but have no idea if its foot pound or newton metres just that higher must mean better with no context as to where all this torque is available.

I have also found that 0-60 is a largely useless and demonstrates grip & gearing more so than outright power so I find myself looking at 30-70, 50-70 times now.

[TheEnd]

mikeveal said:

Well actually bhp/litre gives you a fairly good idea of how highly strung the engine is.

Yep, I take it is a guide to how much capability the engine is using.
75bhp/litre is decent, but wouldn't be really classed as sporty, 80-90 is good going and pretty well advanced, and 100+ is sporty, and 120+ is a race engine (or an S2000!)

[92JWS]

TheEnd said:

Yep, I take it is a guide to how much capability the engine is using.
75bhp/litre is decent, but wouldn't be really classed as sporty, 80-90 is good going and pretty well advanced, and 100+ is sporty, and 120+ is a race engine (or an S2000!)

Or anything with forced induction these days

S2000 is an astonishing engine for its time though. I read it held the highest specific HP output of a NA production engine until the 458 came out!

Edited by 92JWS on Friday 21st February 16:30

[aka_kerrly]

TheEnd said:

Yep, I take it is a guide to how much capability the engine is using.
75bhp/litre is decent, but wouldn't be really classed as sporty, 80-90 is good going and pretty well advanced, and 100+ is sporty, and 120+ is a race engine (or an S2000!)

Interesting assessment but there are other factors that would need assessing before writing off a engine with relatively low HP/l eg a 60hp/L large capacity engine with long gearing could well be considerably faster (more sporty?) than a 100hp/l small engine with short gears.

[anonymous-user]

bhp/g/km Co2 is were it is at these days..........

[McWigglebum4th]

Do i have to get my scaffolding pole out?

[skyrover]

TheEnd said:

Yep, I take it is a guide to how much capability the engine is using.
75bhp/litre is decent, but wouldn't be really classed as sporty, 80-90 is good going and pretty well advanced, and 100+ is sporty, and 120+ is a race engine (or an S2000!)

Not at all.. plenty of large capacity american V8's out there with low output per litre, yet still plenty exciting and with a more usable torque curve.

[sgtbash]

You do realise there is a difference between HP and BHP????

[crazy about cars]

sgtbash said:

You do realise there is a difference between HP and BHP????

Yup, HP is where all the action is :P

There is a different but just in how they are measured. Same argument as Flywheel vs Wheel HP.

[aka_kerrly]

skyrover said:

TheEnd said:

Yep, I take it is a guide to how much capability the engine is using.
75bhp/litre is decent, but wouldn't be really classed as sporty, 80-90 is good going and pretty well advanced, and 100+ is sporty, and 120+ is a race engine (or an S2000!)

Not at all.. plenty of large capacity american V8's out there with low output per litre, yet still plenty exciting and with a more usable torque curve.

which is a better explanation than what I gave.. I was thinking V8 200hp that would spank many a highly strung 200hp 1.4 16v

[lincsls2]

skyrover said:

Not at all.. plenty of large capacity american V8's out there with low output per litre, yet still plenty exciting and with a more usable torque curve.

^^^ This.

My 6 litre V8 Monaro makes only ~66bhp/litre, but its plenty exciting using all 400bhp and such a good noise too!
But, its the useable bottom end torque that is most remarkable. You need to run one for a while to understand. I'm talking about 800/1000rpm pulling power that even diesels can't muster (no boost at that rpm).
I'm currently at the Lakes and the car is making easy work of all the inclines, hauling its ~1650kg body around at just 1k rpm in 5th with no complaining or hesitation at adding speed. Very little need to stir the box, 5th gear will go as low as 20mph and pull cleanly if required.
ETA: The gearing of 5th is such that it could achieve 175mph.

Edited by lincsls2 on Friday 21st February 18:50

[Hol]

mikeveal said:

Well actually bhp/litre gives you a fairly good idea of how highly strung the engine is.

Every petrol head should have been taught this???


I