Another mystery to me is that why most diesels have 6 gears as having torque constant over a wider RPM range means one hardly needs so many gears!
I think it's because the rev limiter on a diesel is low and there is quite a bit of power these days. So you need the extra gear to get maximum performance. And more gears to ensure ec***my does not suffer.
Around town I would only use gears 1-3 (plus reverse) but on the motorway the other gears are all needed. When I have used a petrol car for a bit I tend to find I want to change up from 6th at 80mph indicated and I am sure the car would cope with a seventh gear.
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Does the swear filter really have a problem with the word economy?
Edited by rtj70 on 21/02/2010 at 22:20
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It does at the moment because the old list was used... they're working on it. The new swear filter is working a little differently. The old swear filter could be quick to intervene too mind.
Edited by rtj70 on 21/02/2010 at 22:22
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Most new designs with turbos (petrol and diesels) are electronically (software) limited torque wise (producing the flat characteristic). This is to protect the clutch/gearbox/transmission which have a maximum torque rating.
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Another mystery to me is that why most diesels have 6 gears as having torque constant over a wider RPM range means one hardly needs so many gears!
It is a marketing thing, drivers want it so the cars have it.
Don't really need it - I had a 5 speed Honda Diesel for four years and never felt the need for a sixth, the current cars have six.
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Another mystery to me is that why most diesels have 6 gears as having torque constant over a wider RPM range means one hardly needs so many gears!
Is it not because the power band is so narrow on diesel? So that you have a gear that gets you in the powerband for pretty much any speed you choose.
Diesel Version:
If you make 300 lbs/ft of torque at 2000rpm, you'll accelerate pretty quickly with the revs at 2000rpm, if you're torque curve is flat (variable vane turbo) up to 3500rpm, you'll continue to accelerate fast up to that point. But then you're out of puff, the diesel engine has exhausted itself, so you change up a gear to get the revs back down to 2000rpm and accelerate like a rocket ship again.
Petrol Version:
If you run a petrol turbo with the same torque from 2000rpm, the torque curve will stay flatter, longer, maybe up to say 5000rpm. So where you'd be using another gear at 3500rpm to make more meaningful progress in the diesel, the petrol just keeps going in this gear. Then you get up to 5000rpm, and you change up to drop the revs to 2000rpm, lather, rinse repeat :-P
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It was one of the reasons I did not choose an Accord 4 years ago, I would look for 6 gears in a car of this class every time.
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The 5 speed box was a reason I nearly didn't test-drive the Accord in 2005, but ended up being one of the reasons I bought one. The engine is unusually tractable and flexible for a diesel, and the 5-speed box suits its character much better.
I had a 6-speed Accord as a courtesy car, and while there were some advantages, it generally meant I was changing gear more often. I didn't grow to like it in the 2 weeks I had it.
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My two regular drives are turbodiesels of similar size and output. The Verso (2.2l, 138bhp) has six speeds, the Volvo (2.4l, 163bhp) only five. Both are strong cruisers, but the Verso has to be well above UK-legal speeds before its extra gear makes it noticeably more relaxed than the Volvo. At my typical cruising speed, the Volvo is perfectly happy at about 2500rpm (against the Verso's 2200), and has the benefit that I can back off slightly without feeling that I might drop out of the torque band and have to change down to get back to speed.
In town (1st to 3rd) the two are indistinguishable, but I sense that the Verso's 4th has been lowered to make room for 5th. This means that on a moderately twisty B road I can simply keep the Volvo in fourth while the Verso prefers me to alternate between fourth and fifth. In other words, if the six-speed box is supposed to make driving more relaxed, my experience is that it has the opposite effect.
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