100 Hp per litre?

Spi D

Spi D

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It has always been a fact that a modest hp performance per litre sets the base for longevity. Relatively.

Not that a sluggish engine will last forever, but high performance engines delivering high hp from small volume has always been pointed out at short-lifed.

So what is going on in the car industry these days? Eg. 140 hp from 1.4 liter engines in standard household vehicles? Even 250 hp from 2.0..!

100 hp/liter certainly is a lot and might never be used for marine engines but still?
 
Yes - racing engines have always been impressive. I had one 1.8 at 372 hp which was fun but now we see standard family cars going down in size yet up in performance.

Will they hold over time? Is this trend going to the marine industry?
 
Modern road car engines are generally lifed for 300,000km between major failure, using synth engine oil, and servicing every 30,000 ish km. I have generated the road load data in a previous life.

You need also to consider that the duty cycle is quite low, as we spend most of our time in cars at very light duties, cruising at 80ish mph or sitting in jams. Less powerful engines, sub 100hp actually work much harder.

Specific hp per litre has really improved with better combustion and engine management, plus forced air breathing. Synth engine oil is very durable, and modern machine tools are much more accurate these days.

Again, forced air engines, even gasloline, only rev up to circa 6000, and diesels 5000. With motorcycle and race engines, normally aspirated, you can get much higher revs, 10-12,000 and beyond. This increases wear rate dramatically.

With planing boats, where you might be using 70-80% of max power much of the time, giving a much higher duty cycle.
 
Lakesailor said:
I remember when 100 bhp per litre was a goal for rally engines.
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! that must've been mid sixties

S2000 is a good counterexample (also redlines at 8k rpm or thereabouts!), my two 2lt petrol cars demo the two other extremes, bmw n/a 150bhp (dull uninspiring, plain boring), fiat coupe 16vt originally 200bhp, now fully forged, larger turbo , racing cams, gasflowed head, larger exhaust, injectors, remapped, etc., etc. dynoed at 330wheel bhp at 1.3bar (say 350 normal bhp) Running strong 30k+ after the rebuilt. Had also done 180k in original/mildly tuned guise.

Conclusion, ok cars can be pushed and we get away with it (give or take), marine is taxinng too hard the motors so it makes absolute no sense. Would be nice to have extra low consumption motors though :rolleyes:, or extra light engines?

V
 
You can take a Reliant Robin engine to beyond 100bhp per litre pretty easily and fairly reliably. 91bhp from 850cc giving 107bhp/litre to be precise.
 
I'm aware of the fact that using a small engine, with a power reserve, allows for normal pushing of a family car - annd occasional high output.

But will a 1.4 do this as reliable as least years 2.0 fitted for the same purpose?

All else equal one would expect the larger engine to do better over time...
 
willfinch36 said:
Indeed they have about as much "torque" as Steven Hawkins though...
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not much, just like a lot of bike engines really & with a brilliant 6sp gearbox you just need to do a bit of work, keep it in vtec range and they are a crack to drive. And actually virtuvas its not 8k redline... its a bonkers 9k redline where they just scream... and as I say, bulletproof. How do they do it?!
 
Spi D said:
I'm aware of the fact that using a small engine, with a power reserve, allows for normal pushing of a family car - annd occasional high output.

But will a 1.4 do this as reliable as least years 2.0 fitted for the same purpose?

All else equal one would expect the larger engine to do better over time...
Click to expand...

I'd say it won't last as long, but that won't matter. Average mileage is circa 12k, usually a bit less with something like a 1.4. At 10 years old it'll have only done 120k, but it'll be worth next to nothing. By the time they've done enough miles for the engine to be worn out the car will be worth nothing.

The breakers yards are full of cars with perfectly good engines in them already. Most modern cars will die because of expensive electronics failures.
 
How about this then....

New BMW 550d - Tri-turbo 3 litre diesel inline 6.

375 bhp with 546 lb/ft torque.

0-62 mph in 4.7 seconds and (alleged) average mpg of 44.8.

No doubt the new M5 (4.4 Petrol twin turbo V8) is more fun to drive, but the diesels figures are mighty impressive.
 
willfinch36 said:
BHP sells cars, Torque wins races...
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+1 and to be a bit more pedantic, the torque curve shape (as in area under the curve + gearbox combo) wins races ;)

FF, on the plus side, the S2000 doesn't need heavy clutches and doesn't really give the kicks unless you're happy driving around at 5K+ rpm (which I'm not, never was even when much younger!)

cheers

V.
 
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