Snrub wrote: Yes it's a bit of of a stroker engine, compared to over bore engines in the first cars, but it's also making peak torque thousands of RPMs lower. I can't help but wonder if it is just too good to be true. Thoughts?
Stroke shouldn't affect the torque/displacement to any significant degree. In theory a long stroke engine has higher thermal efficiency but, at THESE levels, cylinder filling gets to take precedence, and that is cam timing and port shape/size.
Snrub wrote: Earlier in their development cycle I was amazed at the gains they were getting. Now I'm starting to wonder if there isn't a dyno-related issue. The Ferrari 458 Special is the production record holder for naturally aspirated torque/liter and makes 88ftlbs/liter. Apparently the last naturally aspirated F1 2.4L V8s made ~89lbs/liter. Goodwin's Miata is making 95ftlbs/liter at the WHEELS. Yes it's a bit of of a stroker engine, compared to over bore engines in the first cars, but it's also making peak torque thousands of RPMs lower. I can't help but wonder if it is just too good to be true. Thoughts?
1st thought is that looking at TQ/liter leaves out the most important variable, RPM. HP/liter, coincidentally, includes RPM.
But I agree with your point - something seems fishy.
In reply to z31maniac:
Point me in the direction of the miata forums you recommend
Robbie wrote: 1st thought is that looking at TQ/liter leaves out the most important variable, RPM. HP/liter, coincidentally, includes RPM. But I agree with your point - something seems fishy.
Torque/liter is an indicator of thermal efficiency and BMEP. It's a good metric for how efficiently an engine is breathing and putting its airflow and fuel into crankshaft rotation. Horsepower is only a concern if you're trying to do something with that.
HP/l is easy to "cheat" (just rev higher). Torque/liter has some pretty difficult engineering hurdles to overcome if you want to increase it (assuming natural aspiration, of course) and as such it's a pretty good calibration figure for the BS-o-meter.
Normally aspirated K20s can make 180 ft/lbs peak, and they're not 13:1 or direct injected.
Knurled wrote: Torque/liter is BMEP.
FYP.
One of the many dimensionless measurements that are used across engines as comparisons.
(and I wouldn't exactly call HP/L using RPM as a cheat- for RPM to really matter, that costs a lot of money, too- see Ferrari and Honda's S2000 motor)
Increasing RPM by 50% is a lot easier than increasing BMEP by 50% 
Knurled wrote: Increasing RPM by 50% is a lot easier than increasing BMEP by 50%
Only if you discount snails... 
alfadriver wrote:Knurled wrote: Torque/liter is BMEP.FYP. One of the many dimensionless measurements that are used across engines as comparisons. (and I wouldn't exactly call HP/L using RPM as a cheat- for RPM to really matter, that costs a lot of money, too- see Ferrari and Honda's S2000 motor)
It's worth noting that if you're comparing torque/L at the wheels, then a lower friction drivetrain (which is something that supposedly Mazda has implemented in the ND) will give a higher number for the same engine.
codrus wrote: It's worth noting that if you're comparing torque/L at the wheels, then a lower friction drivetrain (which is something that supposedly Mazda has implemented in the ND) will give a higher number for the same engine.
I don't doubt the ND does has a low friction drivetrain, but surely it's only a small amount better than other contemporary comparables, there are few 50-90% gains to be found in the auto industry. I've read drivetrain losses are a combination of fixed amount and percent of output. Thus higher output vehicles (eg. 458 or F1) have a bit of an advantage vs. the ND in calculating torque/L.
Snrub wrote: I've read drivetrain losses are a combination of fixed amount and percent of output. Thus higher output vehicles (eg. 458 or F1) have a bit of an advantage vs. the ND in calculating torque/L.
Drivetrain losses don't enter into manufacturer's published figures. They measure real power, not wheel power.
That said, there is something to be said for higher RPM in increasing torque/displacement. You can get more inertial filling/scavenging at higher engine speeds, and detonation is less likely at higher piston speeds so you can get away with more compression.
One of my favorite bits of engine trivia is that in a Cup engine in the meat of its powerband, the intake port is moving at over 80mph during the overlap period, while the piston is still at TDC. Good exhaust scavenging! You're not going to get that kind of scavenging at low RPM in any engine. That kind of scavenging (and the inertial filling at the other end of the intake cycle) gives very high volumetric efficiency, which is directly related to how much torque the engine makes.
Cliff's notes: Engines that make peak torque at high RPM generally make more torque than the same displacement engine that makes peak torque at a lower RPM.
fireball123 wrote: Will you be able to do the same thing with the fiat 124 spider
Of course. It has the same engine as the Fiat 500 which you can get good power out of.
Kreb wrote: So does this mean that Mazdas are finally reaching the output levels of a twelve-year-old K-series Honda?
lolol.
Not really though, as those hondas were sold like that from the factory.
Those old Hondas had very different emissions requirements, too. Honda makes killer naturally aspirated engines, but you have to compare like to like.
The 124 Spider should be much easier to get power out of, as turbo engines usually are.
Snrub wrote:codrus wrote: It's worth noting that if you're comparing torque/L at the wheels, then a lower friction drivetrain (which is something that supposedly Mazda has implemented in the ND) will give a higher number for the same engine.I don't doubt the ND does has a low friction drivetrain, but surely it's only a small amount better than other contemporary comparables, there are few 50-90% gains to be found in the auto industry. I've read drivetrain losses are a combination of fixed amount and percent of output. Thus higher output vehicles (eg. 458 or F1) have a bit of an advantage vs. the ND in calculating torque/L.
It's a combination of fixed and variable, but the fixed amount is only fixed for a given transmission. Higher-output vehicles likely have heavier-duty transmissions, which are likely to have a higher level of fixed losses.
Reduced drivetrain losses are something Mazda was touting in the marketing info about the ND, how significant it actually is I don't know. If it was achieved at the expense of longevity, perhaps we know why it's got fewer losses than contemporaries...
Given the measured wheel hp numbers of the ND in stock form, I think it's proving to be a more efficient drivetrain than earlier Miatas. It still won't be as good as a transverse FWD setup, so the numbers claimed for the Fiat 500 should be slightly higher than the numbers claimed for the 124 Spider.
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