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Thread: RevTalk and Radiators...

  1. #16
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    Quote Originally Posted by spi-ti-tout
    OK, remembered another one. Two actually, forgot the 4th.

    3) Why do the revs go down for a second when you change gear? I know it's because torque is suddenly suspended when the firewall disengages with the clutch and connects again with the other gear. I just need to know the thing exactly.
    Are you talking auto or manual?
    And the fire wall isn't a part of the transmission.
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  2. #17
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    Quote Originally Posted by Coventrysucks
    The rev output of the engine, i.e., the maximum revs that the engine can achieve is linked to quality.

    An F1 engine can do 19,000rpm - you need very high quality materials and manufacturing techniques to do this: to stop bits of the engine hitting each other/bending/breaking etc,.

    The revs that you achieve at a particular speed & gear in a car is nothing to do with the quality of the car's engine, but is governed by the gear ratios.



    At a complete guess I'd say it was due to the flat 6 configuration.

    Useful Stuff About Configurations: http://www.e31.net/navmisc_e.html



    Depends on gearing & power.

    You need power to overcome friction & drag.

    For a certain ammount of power you can get a certain ammount of speed.

    You need to have the gearing set up so that the wheels can actually turn that fast at the correct engine revs.

    E.g., if you need 500bhp to get your car to 200mph, and it produces 500bhp at 5000rpm, your gearing needs to work out so that when the engine is at 5000rpm the wheels are turning at 200mph.

    Obviously if you have top gear set to do 250mph at 5000rpm, you probably won't get to 200mph, because the get the wheels at 200mph, the engine would have to be at 4000rpm, which might only generate 450bhp, which is only enough power for, say, 185mph; that would be your top speed.

    With the correct gearing you should be able to get a vehicle to the same top speed whether you power it with an engine that produces 500bhp@1000rpm, or 500bhp@10,000rpm.



    Depends on what the engine is.

    A big 26 tonne marine diesel producing 5000bhp at 1000rpm isn't going to be remotely "brutal" or "aggressive" as the moving parts are very large, therefore more difficult to accelerate.

    A 2.0-litre V8 weighing 75kg producing 500bhp to 10,000rpm will be more brutal because the moving parts of the engine are easy to accelerate.

    However, a 26 tonne diesel engine with a max. engine speed of 10,000rpm would be just as sluggish, and a 75kg V8 with a max. engine speed of 1000rpm would be just as fast.

    (I think...)
    F1 engines can go 19000 rpm cuz they have a really short stroke, the piston speeds in an f1 engine arnt much higher then a "regular" performance engine say s2000 or audi's v10 in the rs4

    generally a higher redline means more power and thus top speed

    and i didnt understand anything you said after that

  3. #18
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    Quote Originally Posted by spi-ti-tout
    OK, remembered another one. Two actually, forgot the 4th.

    3) Why do the revs go down for a second when you change gear? I know it's because torque is suddenly suspended when the firewall disengages with the clutch and connects again with the other gear. I just need to know the thing exactly.
    when you shift up, you're going into a longer ratio, think about it

    if your first gear is 1:1, then at 1000rpm engine speed your wheels are going 1000rpm, now lets say ur 2nd gear is 0.5:1, your engine rpm must be 500rpm for the wheels to go at 1000rpm

  4. #19
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    The revs drop because (unless you're flatshifting) you take your foot off the throttle and as the engine is disconnected from the drivetrain, there's nothing to keep the engine spinning so it loses momentum and hey presto, the revs drop
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  5. #20
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    Quote Originally Posted by KnifeEdge_2K1
    when you shift up, you're going into a longer ratio, think about it

    if your first gear is 1:1, then at 1000rpm engine speed your wheels are going 1000rpm, now lets say ur 2nd gear is 0.5:1, your engine rpm must be 500rpm for the wheels to go at 1000rpm
    Hmn, I'm a bit confused as I don't think this is what I was actually asking. Does this have anything to do with the temporary decrease of revs (down and back up again) when you shift gear (in a manual - thanks johnny)

  6. #21
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    Quote Originally Posted by spi-ti-tout
    Hmn, I'm a bit confused as I don't think this is what I was actually asking. Does this have anything to do with the temporary decrease of revs (down and back up again) when you shift gear (in a manual - thanks johnny)
    As 2ndcc said, when changing gears in a manual your foot comes off of the accelerator. (Unless you are powershifting)

  7. #22
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    Quote Originally Posted by Rockefella
    As 2ndcc said, when changing gears in a manual your foot comes off of the accelerator. (Unless you are powershifting)
    I think you misunderstood. Say you're cruising at 100 mph at 2500 rpm, when you shift the needle sticks down all the way to 0 revs and then just as you finish shifting, it goes back to about 2450 rpm and starts counting. I doubt acceleration would climb that quickly back up again, unless the power was suspended and readily available again as soon as the clutch and gear made contact, or something to that extent. Or I just may be a n00b.

  8. #23
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    You let off the gas(rpms drop), push the clutch(rpms now drop faster), change the gear, let out the clutch(the clutch grabs), and get on the gas again(rpms climb). I think I typed that right.
    "We went to Wnedy's. I had chicken nuggest." ~ Quiggs

  9. #24
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    4) Turning Circles

    I can't really explain it properly but in my mind these cars will have the bigger turning cicles in order:

    AWD/4WD
    RWD
    FWD

    Because in FWD the power and steering is one, therefore when you try to steer both are applied at the same time. With RWD, you have the steering the power at opposite ends, so basically you require space to put out the power. In AWD, the power is divided by even more space.

    Meh, I'm not thinking.

  10. #25
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    Quote Originally Posted by spi-ti-tout
    4) Turning Circles

    I can't really explain it properly but in my mind these cars will have the bigger turning cicles in order:

    AWD/4WD
    RWD
    FWD

    Because in FWD the power and steering is one, therefore when you try to steer both are applied at the same time. With RWD, you have the steering the power at opposite ends, so basically you require space to put out the power. In AWD, the power is divided by even more space.

    Meh, I'm not thinking.
    Actually RWD have smaller turning circles because the front wheels doesn't have to transmit power (can't remeber of the name of the parts that transmits the power to the wheels), and as result can have more degrees of steering lock.
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  11. #26
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    Quote Originally Posted by Ferrer
    Actually RWD have smaller turning circles because the front wheels doesn't have to transmit power (can't remeber of the name of the parts that transmits the power to the wheels), and as result can have more degrees of steering lock.
    I was also thinking of understeer when I wrote that. If you went round a corner too fast you'd have understeer which would help because the car locks and then you can continue, so it'd be a smaller line than a RWD coming in fast as a RWD has oversteer.

  12. #27
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    Well actually oversteer tends to tighten the line, while understeer opens it, as demonstarted by those rather basic drawings:


    Understeer


    Oversteer
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  13. #28
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    Just one thing I thought I
    d point out about engine speed. F1's operate at the highest rpm for cars, as Knifedge said their piston's stroke is very short. NASCAR engines, on the other hand, rev to ~10,000 rpm, and have very long strokes. Their engines piston speed are incredibly high, about twice what the accepted safe range is.

    Turning radius should not be affected by drive type, since under/oversteer only occur when traction is at the limit, and the turning radius is a a low speed. Turning radius is dependant only on the geometry of the 4 wheels on the ground and the maximum turning degrees of the front wheels. But like ferrer said it may be that due to mechanical considerations rwds generally have a greater range of steering motion, and therefore a smaller turn radius.

  14. #29
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    To clear that up, the turning circle should be the same whether the car is fwd, rwd, awd, or just pushed by someone, because at low speeds the front and rear wheels turn in unison anyway and are not close to the limits of traction.

  15. #30
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    Quote Originally Posted by Bob
    To clear that up, the turning circle should be the same whether the car is fwd, rwd, awd, or just pushed by someone, because at low speeds the front and rear wheels turn in unison anyway and are not close to the limits of traction.
    The question came to me because of how Clarkson was moaning about the turning circle of the MRFQ400. IIRC NOBODY have ever mentioned a horrible turning radius of any EVO, atleast none that I have spoken to or read from, but that turning circle was really horrible and it was based on the stock MR, which is also AWD and shares all the same technology. I was just thinking "why?", if this has been so bad why hasn't anybody ever mentioned it ebfore.

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