Quote from RasmusL :

I'd rather an MX-5 than an S2000. It's nice to brag about HP/L, it's just not very relevant when you're driving it

I had an mx-5 before i got the S2000. A friend of mine still has an mx-5, 1.8l 146hp. We've been to the track together and the mx-5 can't keep up (it's just as much fun tho). In slower corners it can be as quick as the s2000, or in other words, manage to keep up, but that's about it. The S2000, even on a slow track, will gradually pull away and eventually lap the mx-5 given enough time.

IMO, the S2000 is a step up from the mx-5 in every aspect. Especially when you're driving it.

Anyway, i'm obsessed with my car... i better get out of here.

Quote from S14 DRIFT :

It was launched in 2002/2003 and had 125bhp/l way back then so perhaps 160bhp/l is possible from a naturally aspirated engine.

Well a lot more than 160bhp/l is possible, e.g. the BMW S1000RR which makes 190bhp from a 999cc inline four...

The top MX-5 model from 2009 has 167 hp from a 2.0L. Of course the S2000 will pull away, having around 100 hp more. I guess that's my fault for stating an opinion about a car when we're after facts

I always thought the mx-5 would be quicker in slow corners tho, because of the weight difference of the two cars. Maybe it was just the driver however, and the mx-5 would really be quicker than the s2000 in such corners... i remember how i would annoy porsche drivers in my mx-5 at trackdays in the slow corners, because i was always on their ass and they couldn't pull away (until there were faster corners or straights).

Quote from RasmusL :

I'd rather an MX-5 than an S2000....it's just not very relevant when you're driving it

S2000 is said to be the best car in the "Kakeyoro" test

(That test is about driving pleasure, driving position, driver/machine integration and overall driving feeling)

Quote from J@mes :

Well a lot more than 160bhp/l is possible, e.g. the BMW S1000RR which makes 190bhp from a 999cc inline four...

Indeed. If it's naturally-aspirated road-going bone-stock HP/L you're looking for, look no further than a race-replica motorbike engine.

600cc 4-cylinders are making around 105-110HP at the rear wheel, bone stock. Figure about 85% drivetrain losses. That makes 130HP at the crank.

216HP/L

Quote from Forbin :

Figure about 85% drivetrain losses.

Quote from Forbin :

about 85% drivetrain losses.

Quote from Forbin :

85%

:uglyhamme

Quote from J@mes :

Well a lot more than 160bhp/l is possible, e.g. the BMW S1000RR which makes 190bhp from a 999cc inline four...

It's a bike. Being a motorcyclist myself I know better than anyone to try to compare output per litre to that of a car.

My Triumph 675 makes about 105bhp from it's 3 cylinders, and it sure as heck sounds nicer than the 185bhp (with full Akra system) from a BMW S1000R.

The 2011 ZX10r is going to make around 205-210bhp apparently...

Sound is subjective, and I've never heard of an S1000RR with 185 bhp. It seems the official number is 193@13k, but enthusiasts claim that this number is conservative and it's more along the lines of 200 +/- 10. At the crank, mind.

Performance Bikes magazine tested the same bike, middle of winter, 194bhp @ wheel, and around 3 months ago (so warm air, not good for peak power) at around 185. Both with the full Akra. Still, it did 203mph, so either way can't complain.

Thomas the tank

Quote from RasmusL :

:uglyhamme

Agreed. Transmission loss on a chain driven bike should be substantially less than a car (for which the 15% figure is often said to be typical for a 2WD).

Mostly I was making fun at him for what I assume is a typo Yeah, the losses in a chain driven bike should be minimal.

Well yeah, I'm assuming he meant efficieny rather than loss, or 85% would be abysmal.

If you'r going on power per litre, how about VW's 1.4tsi?
Its got 115.10 hp per liter... at 160hp for a 1390 cubic cms....

No wonder it won engine of the year.

(and if you simply chip(retune engine timings) it, it goes to 200+hp.. from a 1.4 engine.)

Good to see this actually turned into a discussion when this was just a quick question.


Carry on..

Quote from Bob Smith :

Agreed. Transmission loss on a chain driven bike should be substantially less than a car (for which the 15% figure is often said to be typical for a 2WD).

Yes, I meant 85% efficiency, 15% losses.

Anyway, tell me where I'm wrong here.

2008 Yamaha R6
Crank: 127.3 HP (see link below)
Wheel: 109.7 HP (see pic below)
Efficiency: 86%

http://en.wikipedia.org/wiki/Yamaha_YZF-R6

Quote from Stigpt :

If you'r going on power per litre, how about VW's 1.4tsi?
Its got 115.10 hp per liter... at 160hp for a 1390 cubic cms....

No wonder it won engine of the year.

We're talking about naturally aspirated engines, not forced induction. The 1.4 TSI in this Golf is both turbo- and supercharged. If we were to include forced induction cars there would be quite a few that were better than this engine with respect to specific output.

Quote from Forbin :

Yes, I meant 85% efficiency, 15% losses.

Anyway, tell me where I'm wrong here.

2008 Yamaha R6
Crank: 127.3 HP (see link below)
Wheel: 109.7 HP (see pic below)
Efficiency: 86%

http://en.wikipedia.org/wiki/Yamaha_YZF-R6

Ahh, looking at that graph makes me feel warm about the 675's good spread of power that is compartively straight compared to those of the Jap bikes. Ducati's are special so they're allowed to have lumpy power deliverys.

Talking of R6's, when it was first released (the what we call current shape circa 2006), Yamaha made a big hoo-ha about how it revved to 17,500 or something. Then someone found it the rev counter over reads (HOW DARE THEY) by about 1500-2000rpm!!

Look at the R6's power delivery, there's NOTHING in the midrange. BUT HEY THIS IS OFF TOPIC.

Tbh considering the compactness of a bike engine/gearbox and the fact most are chain (power sapping) driven, 86% efficient is very good.

Quote from S14 DRIFT :

Tbh considering the compactness of a bike engine/gearbox and the fact most are chain (power sapping) driven, 86% efficient is very good.

Chains are power sapping relative to what?
A shaft drive is much less efficient. Maybe a teethed rubber belt is more efficient, but go on and transmit 200 hp through it and you might have trouble making the rubber last long.

Really though, who cares about BHP/liter? As long as the engine's overall weight is low, I don't see why it matters.

Quote from wheel4hummer :

Really though, who cares about BHP/liter? As long as the engine's overall weight is low, I don't see why it matters.

If the overall power/torque/weight is the same, having a smaller capacity engine results in lower mpg and lower emissions, which is nice.

Depends much more on the way it's driven than the size of the engine.. And loads of other parameters than engine size matter - I don't think you'd get very far on a liter of gas in a 1.5 liter turbo F1 engine

Quote from freddyalek90 :

If the overall power/torque/weight is the same, having a smaller capacity engine results in lower mpg and lower emissions

Assuming you meant "higher mpg," not "lower mpg." Does it? Even if the whole rotating mass (piston(s), crank, flywheel, rod(s), cam(s), etc) has the same amount of inertia, and all the resistance inside the engine is the same? Though this isn't really a realistic situation. Obviously a smaller displacement engine will almost always have a rotating mass with lower inertia in real life.

Quote from RasmusL :

Chains are power sapping relative to what?
A shaft drive is much less efficient. Maybe a teethed rubber belt is more efficient, but go on and transmit 200 hp through it and you might have trouble making the rubber last long.

Chain drive is normally quite ineffecient. I think belt is more effecient as you said. Many Harleys and Buells have belts and they last quite a long time I think. A few problems with adjusters here and there but that's about it..