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Thread: Guesstimated power?

  1. #11
    Sorry but I'm bored.


    Torque = power x 9551/rpm.

    It is a bugbear of mine that people compare horsepower and torque when in reality torque is but a result of the POWER at given revs.

    So I can reword a statement and say a Windsor makes great horsepower at midrange rpm and very bad torque at high rpm. If someone reads that and quotes me as saying the Windsor has good horsepower and bad torque it would be wrong since they haven't mentioned the rpm that is relative in this equation...... in the same way traditionally people have been saying the Windsor makes good torque and bad power; they are also WRONG by not linking the amount of torque or power to revs.

    A car does 400 km to a tank of fuel. Is that good or bad? Naturally you would then ask how many litres of fuel does this tank hold. You need more info to understand the full picture.

    The Windsor is a "torquey" motor is what y'all should say. Meaning it has a power delivery whereby peak torque is reached earlier in the rpm range compared to other engines. For example the 185kW Windsor does not have more torque than a Gen 3 so which is "torquier"? The Windsor is, because it arrives at it's peak torque noticeably earlier than the 5.7 does. At the point where it makes it's peak torque it may or may not have more torque than the Gen 3, but let's assume it does. If it's making more torque at about 3000rpm that would automatically mean it's also making more power at those revs, therefore the 185kW Windsor is a more powerful engine than the 220kW Gen 3....... at 3000rpm.

    That is but half the story.

    If I got a 40kW, 8 pole motor and coupled it to 1000:1 industrial gearbox I would then be able to pull a train. I'm assuming 545,000Nm is enough to pull a train. So much torque but is that good for speed?????? NO!

    If you want speed from your vehicle you need horsepower. Dick Johnson even said it once; they tried to maximise the torque from their engines and found that to be a waste of time so they went back to focusing on maximising horsepower in the last band of revs up to 7500rpm.

    I do appreciate "torquey" motors for the street though.

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    4Vman (5th June 2014)

  3. #12
    Tech Admin flappist's Avatar
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    There is a reason why mechanical engineers require a degree and significant post graduate work.

    The goal is maximising the area under the torque curve.

    This is why a 270kw XR6T will demolish a 315Kw BOSS 5.4 in the same chassis.

    Lots of newtons spread out over a wide range means wider gear ratios and potentially higher top end.

    500Nm @ 5000 RPM is exactly the same power in a I6, V8, V12, T4 or any other engine. The trick is to have 500Nm at 1600 RPM and still have it at 6000RPM as opposed to 600Nm at 5000Rpm which ramps up from 250 at 1800 RPM and trails off to 400 at 6000RPM like a NA V8 does.
    A velocitatem terram

    Google-Fu, the ancient snowflake art of knowing little, understanding less but believing anything they find on Google as the word of God.

  4. #13
    Quote Originally Posted by flappist View Post
    There is a reason why mechanical engineers require a degree and significant post graduate work.

    The goal is maximising the area under the torque curve.

    This is why a 270kw XR6T will demolish a 315Kw BOSS 5.4 in the same chassis.

    Lots of newtons spread out over a wide range means wider gear ratios and potentially higher top end.

    500Nm @ 5000 RPM is exactly the same power in a I6, V8, V12, T4 or any other engine. The trick is to have 500Nm at 1600 RPM and still have it at 6000RPM as opposed to 600Nm at 5000Rpm which ramps up from 250 at 1800 RPM and trails off to 400 at 6000RPM like a NA V8 does.
    By the way 600Nm at 5000rpm is only 1146kW but I get where you're coming from

    Yes, the area beneath is the aim, and the curve is shaped to match the application. The area is important, but so is the shape. For road vehicles, maintaining the torque isn't required at high rpm unless marketing and/or high performance are a priority. In race applications where the engine revs don't drop below 4 or 5 thousand rpm it doesn't matter what the curve's like below those revs.

    No one talks about torque in F1 cars, not until these latest hybrids anyway. They're making more torque now because of the E motors and turbos than what they did in the 3.0 atmo days but would get flogged by the 3.0 V10s due to having less top end power.

    Which brings me to the next point. The comparison you gave between the I6T and the Boss 315 is a very good example to use to demonstrate the effect of power at low rpm. You called it torque. Yes, that, too. It has more power than the Boss up to 4500rpm but beyond that the 5.4 does in fact have more power (and consequently more torque). Like you said, on the street, off the lights the GT will disappear in the rear view, but in the situation where the two cars don't drop below 4500rpm the one that has the more power will come out on top. From the mph at the tracks the 314 5.4 indicates it comes home strong, almost as potent as the blown 315. On a circuit where top end power is critical a GTP would be quicker than the turbo. To simplify it, on a Nascar oval the Turbo would eventually get lapped if there were no speed limiters. The F6, however.

    In the situation where someone's looking to find the best setup for his car from the one engine - does he set his engine up for better low end, or top end power, or a compromise between the two. Which direction does he take with the manifold, heads, cams and compression? What does Xr8au1 want to do with his vehicle? I'm guessing a street monster, revving no higher than 6500rpm. He should speak to Greg (project064) in that case.

    Quote Originally Posted by 4Vman View Post
    They'd be around 140 at the crank with those mods, gains are hard earned with the early small port 5.0's
    You meant 140 at the wheels didn't you?

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