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  1. Join Date
    Apr 2009
    Posts
    1,902
    #1
    What value does it really give? What do I get out of it?

    What's so special if I have a high specific output for my engine?

    Why did Honda brag about the 100 hp/li B16A engine when it first came out?

    * * * * *

    High horsepower rating = engine is more powerful on top-end, has faster top-end speed

    High torque rating = engine is more responsive

    High specific output rating = ??????

    * * * * *

    Take this case between a 1.3 and 1.6 engine where the 1.3 gets more specific output:

    Mazda B3 (Gen 2.5)
    73 hp / 1.3 liters = 56.15 horsepower per liter

    Mazda B6 (Astina)
    88 hp / 1.6 liters = 55 horsepower per liter

    Does that mean I can almost "feel the same power" when I downgrade to the 1300 engine?


  2. Join Date
    Dec 2007
    Posts
    1,906
    #2
    It's an engineering feat more than anything else.

    The usual ways of making more power from an engine are
    1) increasing displacement
    2) adding boost
    3) increasing compression

    Imagine your engine is an air pump. The more air that it takes and expels, the more powerful it is. That's the whole point of an engine really.

    Engine makers have moved the engineering game by making more power out of small engines (hence higher specific output). For Honda it was via sky-high RPM and the valve lift/timing trickery called VTEC. For other carmakers, it was via better-controlled fuelling (carburetors vs. mechanical injection vs. electronic injection).

    Specific output is power developed per unit of engine displacement. It's got more to do with HP than torque, which your post explains well.

  3. Join Date
    Dec 2007
    Posts
    1,906
    #3
    To add to my post above.

    High specific output is also beneficial from a taxation point of view. Many countries tax vehicles by engine displacement: the larger your engine the more tax you pay. If your small engine can make just as much power as a big one, you can skip out on the tax.

    Larger engines are also usually heavier like-per-like vs. small ones, unless engine builders resort to exotic materials and/or construction techniques. More weight means more fuel burned.

    It can be argued that in many situations drivers don't really need all that much power...but when you do need it it's nice to know it's there. Supposedly that's the allure of an engine with two characteristics - quiet, docile, idles nice and saves gas at low RPM but punchy and powerful at high RPM.

  4. Join Date
    Apr 2009
    Posts
    1,902
    #4
    Thanks for the reply.

    Now here's my dilemma, assuming both engines bolt on the same vehicle, say a Sentra GX:

    Nissan SR20DE (JDM) = 140 hp/2.0 li = 70 hp/li
    Nissan QG13DE (PHDM)* = 95 hp/1.3 li = 73 hp/li

    [SIZE=1]*NMPI claims 95 hp as per brochure for the Sentra GX[/SIZE]

    It's a given that the SR20DE has much more hp and torque rating.
    But based on computation, the QG13DE gives more specific output.

    Is it safe to say that the QG engine makes power more efficiently because it can give 3 more horses per liter?

    Although I know that in the end, the SR will yield much more because it's got 700 cc more, hence more volume to accomodate fuel to burn.


  5. Join Date
    Aug 2004
    Posts
    22,705
    #5
    More efficient in terms of peak power per liter.

    But it doesn't tell you how much power the engine has "under the curve".

    The Engine Masters series in the US uses both peak and average horsepower to grade their engines.

    To get the average (for performance purposes), you'll need a dyno chart and you'll need to know where the 1st-2nd gear shift (typically the longest) lands you. Usually at 4k rpm in 2nd gear for a gasoline engine and 2k rpm in 2nd gear in a diesel engine.

    Measure out the average to redline. That's your useable power band.

    I did one before to compare the Lynx RS to the Focus TDCi. The Lynx averaged around 118 whp (from 4000 - 6500, measurements every 500 rpm). The Focus averaged around 125 whp (from 2000-4500 rpm). So, despite my Lynx making 148 whp at peak (around 178 bhp) and the Focus making only 135 wp at peak (around 150 bhp), the Focus diesel engine still made more power in real life. Which is why they're just as fast as each other in terms of pure acceleration, despite the Focus being heavier.

    ---

    Still, comparing average hp to liters will still give you a hp/liter metric... but what's more useful to performance builders and tuners is the hp/kg metric. How much power does an engine make compared to how much it weighs? Considering the TDCi motor weighs about 100 kilograms more than a gasoline 2.0 motor (typically weigh around 150 kgs)... the power per weight density really isn't very good... but it makes up for it by being very, very, very fuel efficient.
    Last edited by niky; August 6th, 2010 at 04:11 PM.

    Ang pagbalik ng comeback...

  6. Join Date
    Mar 2010
    Posts
    143
    #6
    i hope we can continue with this thread. i too have questions, maybe similar to thread starter but too techie for my layman mind to comprehend.

    am comparing two engines: Urvan and Starex TCI and they have different measures thus can't easily compare like apple-to-apple .

    Output 100ps/3800rpm 84hp/4300rpm
    Torque 23kg/2000rpm 178nm/2200rpm

    The second column are values for TCI and the last column values are for Urvan.

    What do these mean in real world? Maybe it's safe to assume that Starex TCI can run faster (top end speed), has more hauling power and even accelarate faster. If all those are true, by how much (%)? salamat.

  7. Join Date
    Aug 2004
    Posts
    22,705
    #7
    Not having driven the Urvan lately, I can't really say by how much the TCI is faster (if it is).

    There are other factors at play. The weights of the two vans (the Starex is heavier), the transmissions and gear ratios, drivetrain losses and etcetera.

    A car can have more power on paper, but if it's heavier and has higher drivetrain losses, a "weaker" car can actually be faster.

    Ang pagbalik ng comeback...

  8. Join Date
    Mar 2010
    Posts
    143
    #8
    I wish Life if simpler, little of variables, unknowns and IFs ;). Thanks

  9. Join Date
    May 2009
    Posts
    1,990
    #9
    Quote Originally Posted by 14myXUV View Post
    am comparing two engines: Urvan and Starex TCI and they have different measures thus can't easily compare like apple-to-apple .

    Output 100ps/3800rpm 84hp/4300rpm
    Torque 23kg/2000rpm 178nm/2200rpm

    The second column are values for TCI and the last column values are for Urvan.

    What do these mean in real world? Maybe it's safe to assume that Starex TCI can run faster (top end speed), has more hauling power and even accelarate faster. If all those are true, by how much (%)? salamat.
    i suspect these are usually brake hp not wheel hp, i.e. that's the hp you can get at the crankshaft not on the drive wheels. say a 20% drivetrain loss, bhp x 80% = whp.

    much better if you can see the performance curve...you can analyze the characteristic of an engine with the shape of the curve.
    say 1 hp = 1.01 ps and 1 Newton = 0.1020 kg force
    the resulting table will be:

    Starex: 98.6 hp * 3800 rpm, 225 Nm * 2000 rpm
    VS
    Urvan: 84 hp * 4300, 178 Nm * 2200 rpm

    For the meantime let's say power is related to speed while torque is to pulling force
    Power: Starex achieves the rated hp at a lower rpm than the Urvan (so it can propel and accelerate itself faster than the urvan)
    Torque: Starex achieves a higher torque at a lower rpm again than the Urvan (you can haul more comfortably with the starex than the urvan)

    Say they have the same drivetrain gear ratios, the starex requires lesser driver effort (changing gears) and it can go faster at a much lower fuel consumption.

    actually, i'm more concerned with the torque curve. i prefer an engine that is easier to handle and has lugging abilities (maybe nasanay lang siguro kasi ako sa mga light trucks, tractors, )para lesser effort in changing gears, etc.....kaya i'm not that "fast and the furious" guy.

  10. Join Date
    Mar 2010
    Posts
    143
    #10
    thanks for the illustration. i wish our regulating bodies can do something like this even on paper specs for the benefit of the buying public ;).

    if i can't have it all, it'd take one with greater power (for ease in overtaking). my driving style will benefit from this and perhaps more fuel-efficient too. seldom do i see either van fully loaded anyway.

    i checked the gross weight of the two vehicles and quite a difference: starex 12-seater 3120kg and urvan escapade 2750kg.

    am actually leaning towards starex with the engine in the nose and not under the driver's seat. my one hesitation is the long-term maintenance. read many threads about high maintenance cost for this. on the other hand, urvan seems to outdo the starex in terms durability, rugged driving (given the number of them used in public transport). i hope to get the chance to drive both soon. ;)

SPECIFIC OUTPUT in layman's term