Multi-valve engines

Honest John Back Room » Technical matters
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Sat 26 Oct 2002 07:22
Multi-valve engines - L'escargot
Multi-valve engines may have a lot of advantages, but low-speed torque isn't one of them. Give me a "two valves per cylinder" engine any day. Lots of low-speed torque and flexibility. Presumably the reason that 0-60mph times have increased over the last few years is due to the proliferation of multi-valve engines. What I need is good acceleration, not an unusably high top speed. Oh for the good old days !
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Sat 26 Oct 2002 07:50
Multi-valve engines - madf
Hmm I would have agreed with you but....
Ford's 1.25/1.6 litre 16 valve Zetec engine in a Fiesta is very flexible. The 1.6 will pull happily from under 25mph in 4th.. 1200rpm.

Almost as good - but not - as a 1.9TDI Audi A4.But much smoother and far nicer to drive.



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Sat 26 Oct 2002 12:01
Multi-valve engines - RogerL
It's the camshaft profile which determines what revs maximum torque occurs at. However a multivalve engine won't improve the low-end power compared to a two-valve, because breathing isn't a problem at low revs. So the only way to take advantage of multivalves is to move the power band up the rev range to gain power, at the expense of low-end flexibility.

In the 80's and early 90's, Vauxhall made a big thing about LET (Low End Torque) engines but seems to have changed it's mind. I do miss my 8v Vauxhall 2.0 litre which had max torque at 2600rpm, was geared at nearly 30mph/1000rpm and never went above 4000rpm - this meant that 80mph was very economical. The current equivalent, 2.2 16v, has max torque at 4000rpm. It has plenty of power if you rev the b**ls of it but is not relaxing to drive.
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Sat 26 Oct 2002 18:39
Multi-valve engines - Arfur
The problem appears to be that, whilst manufacturers are still selling their engine on power output then there will be an incentive to develop power at higher and higher revs to boost the apparent power of the engine.
We have a 1.8 16v Ford focus. The engine drags the car around alright once your going but you have to feather the throttle a bit when you pull away. By comparison I had cause to borrow a 1.8 CVH engined Sierra the other week. The engine doesn't have the same top end power but the power it does have was so much more usable. Much more relaxing to drive.
If you want a good drivable engine these days you need to look at diesels or Light Pressure Turbo petrols.
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Sun 27 Oct 2002 08:34
Multi-valve engines - jc
It's not just the valves;the 1.6 zetec in the Escort had 16 valves and fuel injection but produced less power than the carburetted 1.6 CVH(8v).The reason for this was emissions-you need to control the fuel very accurately to make a catalyst work and it's not going to give the power.There are ways round this for top-end power but already the enviromentalists are trying to change the emission regulations stop it.
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Sat 26 Oct 2002 17:55
Multi-valve engines - dave18
There must be exceptions; my gran's 3yr old 1.2 Clio is crap at low revs. It does get used properly; she (don't laugh) is quite a fast driver.
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Mon 28 Oct 2002 00:04
Multi-valve engines - J Bonington Jagworth
My instincts are similar (I prefer the simplicity of two per cylinder) but our recently acquired pre-cat 1.8 Mazda 323 has 16 valves, is tuned for a decent power output (140hp) and pulls like a mule at almost any revs. Admittedly, it hasn't got much weight to drag around, but I was genuinely taken aback at the amount of torque. The later catalytic version is quite a bit less powerful, however, so the blame may lie in emissions control.
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Tue 29 Oct 2002 14:53
Multi-valve engines - Emerson Fittipaldi
Well Honda must have done alot of research on this subject, as the engine in the new Jazz is an 8 Valve chaincam engine! Will other manufacturers follow suit?
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