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Author Topic: Limp home RPM. Are you joking?  (Read 8227 times)

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Paul M

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Re: Limp home RPM. Are you joking?
« Reply #45 on: 08 January 2008, 18:34:51 »

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Why does the 2.5 have lower gearing than the 3.0 then? If anything, the torque peak is lower on the 2.5 -- certainly this is supported by the fact that the 2.5 produces less BHP per litre than the 3.0. Official figures for the x25xe are 227Nm at 3200 RPM, and x30xe are 270Nm at 3400 RPM.

So all else being equal (and considering only torque -- they both peak power at 6000 RPM), the 3.0 should have lower gearing than the 2.5 to get it to its higher RPM torque peak quickly, yet the 3.0 has higher gearing. I suspect it's at least partly to do with economy, but I believe the 3.0 would accelerate more quickly with the 2.5's gearing. Hence the benefit of a 6sp -- have the 2.5's existing lower gearing for 1-5, plus an additional 6th for overdrive cruising (say about 2600 RPM at 70 MPH).

Its totaly to do with economy on production cars......you seem to have some belief that 6 speed gearboxes are better on all configs.....you are wrong and particularly in the case of the V6.

You seem to be missing the fact that you will get to the torque peek in first gear almost instantly (whilst loosing traction!), if you then rev it just past the peek and change gear, in the next gear you will be just below it again......and so on.

And of course the 3.0 would in theory accelerate quicker with the 2.5 diff (gearbox ratios are actualy fairly similar)...hence why the 3.0 manuals are no quicker than the 2.5 manuals in real terms.

Remember that the number of gears required has nothing to do with the position of the torque in the rev range......its all to do with the width of the torque peek (or bhp) and on high output engines, as already mentioned, you might throw in an extra overdrive gear.

Also, forget bhp.....torque is the useable power.....if I had an engine with 1Nm torque at 100000 rpm I would have a 190Bhp engine (this is part of the principal used with small electric motors to get output up).

I don't think 6 speeds are better on all configs, just many of the ones where the best of the power is at the top of the rev range, and lasts for less than 2000 RPM, which in my experience is how the 3.0 V6 is. I'm talking about keeping it on the boil during spirited driving, not keeping it in the torque band. Power is where it's at to make good progress, I'm sure we all know the reasons why this is the case even though the engine actually produces the most output at peak torque.

For example, the 2.0 8v Audi I used to own would have been totally pointless having a 6 speed gearbox, as there was no incentive to keep the revs up or even within a specific band -- it seemed to pull much the same whether it was at 3000 RPM or 5000 RPM. Other similar "lazy" engines are likely to show no benefit with closer ratios, but I wouldn't describe the 24V V6 as lazy.

You just agreed with me that the 3.0 would be quicker with the 2.5 gearing, so much so that with the standard gearing it is barely quicker despite a 37 BHP and 43 Nm advantage. So what would be the drawback of fitting the 2.5 gearing (overall, inc diff) but add a higher 6th so you don't compromise the long distance cruising refinement and economy, but get the advantage of better acceleration when pressing on?

On your last point, torque may be what the engine actually produces, but BHP is what actually accelerates the car. I can reverse your analogy -- if you have an engine that produces 10000 Nm of torque, but could only turn once a minute (1 RPM), you'd have to gear it so high for it to actually move the car at any reasonable speed that it would be chronically slow accelerating (1.9 BHP actually) :P

As said before I like a nice blend of torque, but also some nice top end. So basically a decent torque curve throughout the rev range, that is maintained enough at high revs to give good peak power. Hence why I'm not so keen on most 2v/cyl engines -- poor top end -- let alone diesels!
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Paul M

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Re: Limp home RPM. Are you joking?
« Reply #46 on: 08 January 2008, 18:38:14 »

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I'm waiting for the argument that the Omega V6 is actually better off with four gears now  ;D
No, just better with a proper gearbox.  Why do you think the dear Lord gave you 2 feet?

Don't know about your feet, but mine can operate three pedals simultaneously just fine. I guess it's just one of those skills of driving that you only learn if you actually drive, rather than let the car do a poor job of most of the driving for you ;). Kind of like learning about the workings of a processor by writing some Java  ::).
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Jay w

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Re: Limp home RPM. Are you joking?
« Reply #47 on: 08 January 2008, 18:40:54 »

this has gone from discussing limp mode RPM to redlining and now to the finer merits of Auto V's Manual gearboxes......
 ;D

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TheBoy

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Re: Limp home RPM. Are you joking?
« Reply #48 on: 08 January 2008, 18:43:07 »

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I'm waiting for the argument that the Omega V6 is actually better off with four gears now  ;D
No, just better with a proper gearbox.  Why do you think the dear Lord gave you 2 feet?

Don't know about your feet, but mine can operate three pedals simultaneously just fine. I guess it's just one of those skills of driving that you only learn if you actually drive, rather than let the car do a poor job of most of the driving for you ;). Kind of like learning about the workings of a processor by writing some Java  ::).
You are of course forgetting that many of us 'autobox boys' have been driving manuals (often very fast) since way before you were even a smile on your Dad's face ;).  Don't worry, you'll probably learn to drive fast/quick/safe as you get older, even with an auto (which if driven properly do have control and speed (though not usually to the finite offered by traditional manuals)) :P
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amigov6

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Re: Limp home RPM. Are you joking?
« Reply #49 on: 08 January 2008, 18:48:52 »

 :oWow! I actually understood some of this:- Modern diesels, one quick punch & that's your cracker in said gear. Other than mine i've only driven early 2.0's so hard to make a comparison. I've never driven a V6 auto (mig) a 3.0 /3.2 (yet) All i know is mine must be healthy for a 2.5 as it pulls like a train up to 144mph (indicated). I do push up to the red 1st 2nd 3rd here & there but think 6.5 occasionally is enough. No smoke ever. Lots of oil/filter changes. The engine has other qualities, ie only using 3rd on light throttle in town.
    Overall from one end of the spectrum to the other you could take Granny to church, do a few trackday laps & take Granny home again!
   Not a bad all-rounder i reckon. :y
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Kevin Wood

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Re: Limp home RPM. Are you joking?
« Reply #50 on: 08 January 2008, 19:09:30 »

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So what would be the drawback of fitting the 2.5 gearing

Economy mostly. Keeping the revs low during cruising cuts down the losses in the engine. Might take a bit off the maximum speed too I suppose.

If the engine's got the grunt, it's much better to cruise with low RPM and a wider throttle opening than at a higher speed where it could potentially generate much more power than required but is being throttled back.

Production cars are about a compromise of all factors, not just fastest to 60 etc. after all.

In fact, my main moan about most manual cars is that first gear is designed to pull away with a caravan on the back, a bootful of luggage and a back seat full of kids, and a less than competent driver at the wheel, without burning the clutch out. Conditions that my car rarely ever sees (ok, maybe the incompetent driver...). I'd say the auto has the upper hand here, because first in a manual will just light up the back tyres when given full bore in first without a full load, whereas in an auto the combination of a higher first and a torque converter that will give a lower ratio for just as long as it takes to get the engine up into the torque means that the initial 30 feet might be slower, but you won't be reaching for another gear at 35 MPH.

So, replace first and second gear with one gear almost as high as second but not quite, and the aforementioned 4 speed Omega would probably do pretty much as well as a 5 speed. Wouldn't be fun with a caravan though. :-X


Kevin

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Andy B

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Re: Limp home RPM. Are you joking?
« Reply #51 on: 08 January 2008, 19:19:37 »

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...... revving to 6000+ RPM in 1st gear, quick change to 2nd ......

So ....... when do I change from 'D'?  ;)  :y  :y  :y

Once someone teaches you the art of driving, and lends you a car that is designed to be driven :P

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......You are of course forgetting that many of us 'autobox boys' have been driving manuals (often very fast) since way before you were even a smile on your Dad's face ;).  Don't worry, you'll probably learn to drive fast/quick/safe as you get older, even with an auto (which if driven properly do have control and speed (though not usually to the finite offered by traditional manuals)) :P
Thanks Jamie. I was trying to think of a nice way to say that. ;)

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Paul M

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Re: Limp home RPM. Are you joking?
« Reply #52 on: 08 January 2008, 19:32:11 »

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You are of course forgetting that many of us 'autobox boys' have been driving manuals (often very fast) since way before you were even a smile on your Dad's face ;).  Don't worry, you'll probably learn to drive fast/quick/safe as you get older, even with an auto (which if driven properly do have control and speed (though not usually to the finite offered by traditional manuals)) :P

Perhaps, but lack of practice driving proper cars, coupled with the slower reactions of an oldie can't be helping matters :P

I can drive fast/safe/quick perfectly well at the moment, although admittedly only with a real car that is actually under my control. Doubt I'll ever learn to do it with an auto though, as the things bore me to tears to the point where I just can't be bothered pushing on any more, and usually drive it like the old man it was designed to be driven by :P
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shyboy

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Re: Limp home RPM. Are you joking?
« Reply #53 on: 08 January 2008, 19:39:06 »

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Right! The penny's dropping. But surely people aren't really serious about most driving being in the 6/7k+ zone. My engine is in good nick, and it did tear away earlier today, and I think I will push it harder from time to time, but I don't envisage too much 7k stuff. I'm nervous about flying. (The real stuff anyway!)

It's designed for it, that's why there's a rev limiter at 7000 RPM -- that is a safe speed for the engine to be turning at without damaging it.

If you need to accelerate quickly, you should be using the full power of the engine, which means revving it up over 4500 RPM where it really comes on song. If, for example, you pull out from a side road onto a B-road (60 MPH speed limit), and there is a blind bend 70 metres up the road, once you decide it's safe to pull out you should be accelerating as quickly as possible up to the speed limit. That means revving to 6000+ RPM in 1st gear, quick change to 2nd and do the same. By this time you'll be at (or near) 60 MPH, so you can easily slot it into 5th and cruise happily at 2500 RPM assuming the road is straight.

There is a junction similar to that above near where my sister used to stay, and I wouldn't feel safe pulling out of that and shifting up at 3000 RPM -- it would take so much longer to get up to speed that you're in the danger zone much longer should a car come around the corner rather quickly.

Appropriate gear for the conditions -- if you need to accelerate, use the lower gears and the engine's power as it was designed. Not doing so is akin to only ever using half the travel on the brake pedal, to prevent wearing out the discs & pads too quickly ;)

Jeez.! Don't tell me you use your brakes as well!!
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Paul M

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Re: Limp home RPM. Are you joking?
« Reply #54 on: 08 January 2008, 19:43:15 »

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So what would be the drawback of fitting the 2.5 gearing

Economy mostly. Keeping the revs low during cruising cuts down the losses in the engine. Might take a bit off the maximum speed too I suppose.

If the engine's got the grunt, it's much better to cruise with low RPM and a wider throttle opening than at a higher speed where it could potentially generate much more power than required but is being throttled back.

Exactly, that was my point about the benefit of a 6 speed box. You can get the benefits of the 2.5 ratios, with the addition of a higher 6th for low RPM cruising, so you're not sacrificing that from the standard 3.0 box.

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Production cars are about a compromise of all factors, not just fastest to 60 etc. after all.

In fact, my main moan about most manual cars is that first gear is designed to pull away with a caravan on the back, a bootful of luggage and a back seat full of kids, and a less than competent driver at the wheel, without burning the clutch out. Conditions that my car rarely ever sees (ok, maybe the incompetent driver...). I'd say the auto has the upper hand here, because first in a manual will just light up the back tyres when given full bore in first without a full load, whereas in an auto the combination of a higher first and a torque converter that will give a lower ratio for just as long as it takes to get the engine up into the torque means that the initial 30 feet might be slower, but you won't be reaching for another gear at 35 MPH.

I like the relatively low first gear, in a heavy RWD car with decent tyres it won't spin the wheels much unless you dump the clutch at 4000 RPM. You can accelerate quickly up to 30 MPH, which is surprisingly useful for darting onto busy large roundabouts without causing anyone to brake. One thing I dislike about torque converter autos is that you can't rev it just before making a quick launch, unless you hold it on the brake (which will probably smoke the transmission fluid pretty quickly). I did try revving one in neutral then dropping it into gear, but there's a delay before it engages then it does so with a rather unhealthy clunk ;D

It's one of the reasons I'd like to try an SMG or DSG, I do like the interaction of a normal gearshift and clutch, but I'm prepared to accept that these systems are actually quicker than even the best human at shifting. And the key thing is they have no torque converter, so you can launch it like a manual, and drive it on the limit like a manual, with the paddle shifts being near instantaneous (unlike that steptronic rubbish you get on BMW automatics).
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shyboy

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Re: Limp home RPM. Are you joking?
« Reply #55 on: 08 January 2008, 19:51:52 »

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:oWow! I actually understood some of this:- Modern diesels, one quick punch & that's your cracker in said gear. Other than mine i've only driven early 2.0's so hard to make a comparison. I've never driven a V6 auto (mig) a 3.0 /3.2 (yet) All i know is mine must be healthy for a 2.5 as it pulls like a train up to 144mph (indicated). I do push up to the red 1st 2nd 3rd here & there but think 6.5 occasionally is enough. No smoke ever. Lots of oil/filter changes. The engine has other qualities, ie only using 3rd on light throttle in town.
    Overall from one end of the spectrum to the other you could take Granny to church, do a few trackday laps & take Granny home again!
   Not a bad all-rounder i reckon. :y

My Granny was crackers. She'd have said, 'Stuff the church! Get me to the track now!'.
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shyboy

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Re: Limp home RPM. Are you joking?
« Reply #56 on: 08 January 2008, 20:00:40 »

Seriously, fellas, I initially wanted to query the wisdom of using very high revs. on my 2.6l. The points raised are fascinating, and I realise that, as one of the oldies, my conception of modern engine capabilities was way wide of the mark. You live and you learn. I think I'm beginning to feel like the oldest swinger in town.
I'm not sure which one of you I'll home in on to blame when I blow the top off my little darling, though.  ;D ;D ;D
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TheBoy

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Re: Limp home RPM. Are you joking?
« Reply #57 on: 08 January 2008, 20:45:14 »

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Seriously, fellas, I initially wanted to query the wisdom of using very high revs. on my 2.6l. The points raised are fascinating, and I realise that, as one of the oldies, my conception of modern engine capabilities was way wide of the mark. You live and you learn. I think I'm beginning to feel like the oldest swinger in town.
I'm not sure which one of you I'll home in on to blame when I blow the top off my little darling, though.  ;D ;D ;D
Basically, occasional use of the redline does help her clear her throat ;)
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Martin_1962

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Re: Limp home RPM. Are you joking?
« Reply #58 on: 08 January 2008, 21:52:03 »

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I'm waiting for the argument that the Omega V6 is actually better off with four gears now  ;D
No, just better with a proper gearbox.  Why do you think the dear Lord gave you 2 feet?

Don't know about your feet, but mine can operate three pedals simultaneously just fine. I guess it's just one of those skills of driving that you only learn if you actually drive, rather than let the car do a poor job of most of the driving for you ;). Kind of like learning about the workings of a processor by writing some Java  ::).
You are of course forgetting that many of us 'autobox boys' have been driving manuals (often very fast) since way before you were even a smile on your Dad's face ;).  Don't worry, you'll probably learn to drive fast/quick/safe as you get older, even with an auto (which if driven properly do have control and speed (though not usually to the finite offered by traditional manuals)) :P


I've only had a car for 18 years at his age I owned a bike - not sure if it would have been a GS250T or the GSX600F, I borrowed my mums Avenger estate though
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Martin_1962

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Re: Limp home RPM. Are you joking?
« Reply #59 on: 08 January 2008, 21:54:53 »

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I'm waiting for the argument that the Omega V6 is actually better off with four gears now  ;D
No, just better with a proper gearbox.  Why do you think the dear Lord gave you 2 feet?

Don't know about your feet, but mine can operate three pedals simultaneously just fine. I guess it's just one of those skills of driving that you only learn if you actually drive, rather than let the car do a poor job of most of the driving for you ;). Kind of like learning about the workings of a processor by writing some Java  ::).
You are of course forgetting that many of us 'autobox boys' have been driving manuals (often very fast) since way before you were even a smile on your Dad's face ;).  Don't worry, you'll probably learn to drive fast/quick/safe as you get older, even with an auto (which if driven properly do have control and speed (though not usually to the finite offered by traditional manuals)) :P

Both are good in the right circumstances.

Stuck on the A30 on a bank holiday - give me an auto any time, even if I did almost overheat the 2.0s once (slow crawl up hill near Fraddon heading towards Goss Moor)
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