8 valve vs 16 valve.

[barefoot]

Here’s a bit of a ramble/diatribe/rant about 8v vs 16v inspired by a couple of you mentioning stuff along the lines of ‘aren’t 2.0 8v Cavaliers relaxed’ & ‘BX seems quick until you try to drive it quick’.

 

Since ’94, the barefoot dailys have been a Porsche 944S & a VWT2.

I’m not going to involve the T2 in this, since it doesn’t really make any sense.

 

But the 944 is the 2.5 16v effort with 190bhp @ 6000rpm & bog all torque until 4000rpm when there’s about 170’s worth there all of a sudden.

It accelerates with much spectacularity & has on occasion surprised me when it has hit its soft limiter at 6800rpm for there is no drama & I am led to believe that this engine was tested up to 13000rpm.

Interesting, but not a deal of use around the Safeway parabolica.

It’s not happy at 30mph in 5th & really prefers 3rd @ 2,200rpm

To be honest it’s crap at low revs, the balancer shafts don’t work below 1800rpm.

Porsche addressed this with the S2, which was bored out to 3.0 litres and is, I have to admit, a much better car.

 

On to the Scirocco, this is 1.6 8v and 75bhp @ 5000rpm but a peak torque of 125 at just 2500rpm. All this in a car that weighs just 875kg.

When I first bought it, I tried to drive it in the same manner & was amazed at it’s breathlessness & inability to rev. There really is no point trying to take it much above 4000rpm.

It wasn’t until I took it to a specialist for a bit of a tune up & he drove me home in his, never exceeding 2500rpm!

He did 30 mph in 5th at diesel type engine revs – 1200ish.

 

I have learnt over the past year to drive in a similar fashion and am amazed how it can cover distance so easily.

I often enter empty roundabouts in 5th, dropping to 4th to exit them.

It’s all about keeping up momentum.

 

I appreciate it’s really all about reducing emissions and being able to claim higher & higher power outputs in brochures and the like but as per the Honda S2000, what’s the point of 10,000bhp if its only available between 15 & 16,000rpm or whatever it was?

 

So, new fangled 16v vs old-fashioned 8v provides quite a different driving experience and I’ll finish with the question;

Is it still possible to buy a new car with an 8-valve petrol engine?

[Cheggers]

Hi Barefoot - I used to have a 944 S2 and now drive an 8v 2.5 Lux. The S2 was certainly quick and, as you say, not quite so "all or nothing" as the S but still happier higher up the rev range. The Lux is completely different - it's quick enough (it was never going to be a ball of fire with 165bhp when new), but is far nicer than the S2 for everyday driving. It's quite happy bumbling along at low speeds in 5th gear and when you do want to make faster progress, the power delivery is very smooth & free of drama. I've only had the Lux since Saturday, but right now I think I prefer it as an everyday car to the S2

 

Mrs_Chegg much prefers driving the 8v and finds it far easier to drive smoothly.

[dollywobbler]

It's interesting to compare a BX GTi 8v with a BX16v. One is quick, the other is lunacy - but only above 4000rpm.

 

I don't believe the complete and utter lack of torque you find with modern engines is just down to the valves, but it is a big part of it. Mix in tiny flywheels and short strokes and you'll never have the low down grunt that even my wife's Mini displays.

[fiatdaft]

Interesting, this debate i think started with the mk2 golf gti,the 8v and 16v, the 16v felt peakier and less grunty than the 8v but the torque curve was always higher than the 8 valve anywhere in the range,dolly not all moderns are lacking in torque! my 1.4 punto has 200 torques at 2750 revs !

[Barry Cade]

Interesting, this debate i think started with the mk2 golf gti,the 8v and 16v, the 16v felt peakier and less grunty than the 8v but the torque curve was always higher than the 8 valve anywhere in the range,dolly not all moderns are lacking in torque! my 1.4 punto has 200 torques at 2750 revs !

 

I had 8 and 16v VW's back to back, and far far preferred the 8v. Maybe i was my driving style, but the 8v felt much faster.. Same with my bikes- had a Boxer engined BMW 1100 with 95 bhp, and could cover ground efortlessly for hundreds of miles at quite impressive speeds, now have a 600 Kwak, with 100bhp, and after a while I get fed up going up and down the box, and find I go everywhere at 68.2 mph in 4th.

 

Torque is better than POWAHHH.

 

Modern cars have lots of torques, but they seem to have a rev range of 7RPM. Your Punto may have 200 torques at 2750, but if its anything like most new cars it has about 18 at 2000, and 46 at 3000.

[CreepingJesus]

Interesting, this debate i think started with the mk2 golf gti,the 8v and 16v, the 16v felt peakier and less grunty than the 8v but the torque curve was always higher than the 8 valve anywhere in the range,dolly not all moderns are lacking in torque! my 1.4 punto has 200 torques at 2750 revs !

 

'Twas the same with Mk2/3 Astras and Mk3 Cav 2.0L's in 8- and 16-valve flavours. I had them all regularly thro' work at the time, and I'm firmly of the belief that the 16-valvers were much more fun, when the chance arose to work the box and use the revs. But for everyday, real world 'quick' driving, the 8-valvers were easier to use. One of the managers had a Mk3 Cav 2.0Li 4x4 saloon, which had the 130 horse chip dropped in its' ECU. That was fun...

What I will ask is this: is it just me, or did it not matter that much in bigger cars? At that time I had goes in 12- and 24-valve Sennys and Carltons, and only the manual box Carly GSi could make any real use of the 30 extra horse, and easier revving. But it always felt like it lost more than it gained, to me.

I had the chance to drive (I think) all the engines of the Frogeye Scorp. The 2.0L's were both hopeless, the 2.3L was surprisingly wheezy, the 2.5 TD wasn't so bad; but again, I got the feeling that the 24-valve V6 just had too many revs, and not as much bottom end as the 12-valve. Even in a hearse it was better; but I did have to turn my Slayer tape down to hear it...

[Luxobarges_Are_Us]

What I will ask is this: is it just me, or did it not matter that much in bigger cars?

 

It's not just you. A well-designed engine that also happens to be reasonably big will enjoy a decent amount of power and plenty of torque throughout the rev range. As you say, the 2.3 Scorpio is a good example of that (although I also used to own a 2.0 facelift Granny Scorpio DOHC for a short while, which I didn't find too bad...well, at least not until it cooked the headgasket). More recently, the advent of variable valve timing has allowed some carmakers, especially Japanese ones, to get GR9 results out of some small engines, too. The VTEC in me old 2.2 Accord was nothing short of amazing- bags of power delivered in an ultra-smooth way, but even a modern 1.3 Yaris/Sirion is a bit of a marvel compared to the late 80s/early 90s 16v EFI stuff that went into Corollas and such, and which was totally gutless below 3500rpm.

 

Has anyone driven the 8v 1.8 Xantia? On paper, it looks much slower than the 16v, which is the only Xantia I've ever driven and which seemed to perform more than adequately.

[Ross_K]

Has anyone driven the 8v 1.8 Xantia? On paper, it looks much slower than the 16v, which is the only Xantia I've ever driven and which seemed to perform more than adequately.

 

Funny you should say that, I've had both the 8v and 16v and much preferred the the 8v even though it was down about 20bhp.

 

The 16v had a bit more power but it felt like you had to drive the arse off it everywhere you went.

[mk2_craig]

Torque is better than POWAHHH.

 

100% agree. I have gone from a 2004 Focus ST170, with its 16 valves and variable timing trickery, to a lower mileage 2.0 Sierra with the DOHC motor but only 8 valves. I found the Focus sluggish during 'normal' driving i.e. usually changing gear no higher than 3000 revs. The Sierra has plenty of oomph in comparison.

 

Dad's 850 estate (20v turbo) is much the same - great at higher speeds, bit of an effort to row along round town.

[carlo]

This thread echoes my sentiments entirely.

 

A big reason I gave up on my 406 2.0 automatic was the total unsuitability of the 16v engine to the car and gearbox. I think it developed about 130 lb/ft of torque at well over 4000 RPM, in a car weighing nearly 1400kg. I love to drive with cruise control on the motorway and, guess what, every time the thing met even a slight incline the box would shift down to third, frightening me to death with the sudden racket, because the top gear couldn't pull at 70mph. Automatics really need torquey engines and now I'm back to a 405 the difference is immediate. The car weighs only 1160kg, a similar torque figure of 132 lb/ft is developed at only 2800 RPM so you can do the maths. The thing flies up hills in top gear, 2800 RPM just happens to be 68mph! The fact is that it's more fun to drive on the motorway and country roads, because of the engine (but also it has better steering feel and lighter weight.) So what it it's a bit noisier to rev.

 

I really don't get the obsession with 16 valves, perhaps they're more sensible in sports cars with close ratios but for a heavy automatic it's a dead loss. Seems a bit like the modern obsession with handling at the total expense of any sort of ride quality.

[Pillock]

I found driving my 1.8 Scirocco 8v very lazy..... once you're moving around town it's 3rd and 4th, and once you're on a 40mph limit you leave it in 5th.

Yet on the few occasions I had a point to make, it would take off like a scalded squirrel as long as you are quick with the changes.

[Barry Cade]

I really don't get the obsession with 16 valves

 

Its for teh performance, no its for teh environment, no its for teh cheap tax. or whatevah is fashionable that year.

[Pillock]

It's so you can claim peak BHP figures.

1984cc 8v Golf GTI engine - 112bhp.

Slam a 16v head on it, leave pretty much the rest of the engine untouched (same bore, same stroke, same fuel injection system) and you see 150bhp. And in the world of advertising or blokes down pubs, 150bhp is approximately fourty-seven times better than 112bhp.

[Cavcraft]

My Golf GTi loving mate swears that the 8V is a much better and more 'driveable' engine.

[cobblers]

Right. Mk3 golf 8v engine has 122 lb·ft peak torque, at 3200 rpm.

 

Here's the rolling road printout that came with my old golf (16v mk3 GTi engine)

 

The torque figure is pretty flat throughout the measured rev range, and at no point below 6500rpm is it lower than the 122lb/ft PEAK figure that the 8v achieves.

 

I've driven 8v mk2s and mk3s and neither were especially quick. OK round the houses, but no amount of "driving everywhere in 4th gear" made them fast. The Mk2 felt a lot more sporty than the mk3, but neither are an engine I'd personally associate with a "Hot hatch" - Both flat as farts and something more at home in a van. In fact,I put Pillocks old golf engine in a mates van, and it is right at home! I'm doing the same to mine soon.

 

This 16v on the other hand was an absolute monster if you wanted it to be, and even at 1500rpm it pulled MUCH harder than either 8v engine.

 

The WHOLE IDEA behind a modern 16v head is to allow the engine to have a better torque curve. You can have massive peak power from an 8v engine by putting 2 big valves and a wild cam in it. But it'll have sod all torque and be a nightmare to drive, so they have to find a happy medium, which is why the 8v version of the engine has 40 less BHP - it's a compromise.

4 more valves allows a lot more airflow at peak without sacrificing torque, which is why everything is going that way - They can get "peak" power per CC, without sacrificing driveability.

[CreepingJesus]

^The whole idea behind a 4v head, is to allow faster and more complete cylinder filling and exhausting. Given that you've got, typically, 30% more total surface area in two pairs of smaller valves, than two larger singletons, that isn't hard to see. It's also what all the other factors that play into how the combusting mixture is used, that determine the characteristics of the engine. By that I mean not only camshaft profile (lift, ramps and duration), but combustion chamber shape, squish band (if there is one), piston acceleration and all the little details in the valves and tracts which help determine how vacuum and backpressure are used. Niggly, technical stuff I know, but...

...typically a 2v camshaft profile will have to have more lift and duration, with a 'faster' ramp in the opening side of the inlet, and a 'faster' closing ramp on the exhaust (and breathe), to do the same job as a 4v design. These factors render it useless at high revs, because the valves start floating earlier than the 4v. This was well known about for years before it got properly into road engines, but it's ok in a racing engine, 'cos you only really set it up for 'maximum'! Fuel injection, and electronic ignition came along, and helped smooth out the flatspots, so the 4v became truly viable.

In fact, 115 horse from an injected 8v 2.0L is hardly pushing it, as is 150-odd horse from the same bottom end with a 16v head on it. The Vauxhalls of the same period had very similar figures, from similar origins; but the 16v definitely felt peakier (at least subjectively), and it was probly due to it flowing better at high revs, where the resonances could be harnessed to make it act in a certain way.

So in other words, market research suggested how it ought to be to drive it, the engineers made it so. VW felt their customers would want it that way, VX thought differently.

Besides, there's an elephant in the room here: the 12v four pot. Anyone ever driven a great 12v? I haven't. They always felt as if they were neither beast nor fowl.

Now an 8v turbo with a big fat midrange, I'll have any day

Or an F2 hot rod Pinto; Cossie crank, diesel rods, single 40 and a full-race cam. That's violent power delivery! Fuck all up to about 4k, then you're away.

[John F]

Besides, there's an elephant in the room here: the 12v four pot. Anyone ever driven a great 12v? I haven't. They always felt as if they were neither beast nor fowl.

 

My Maserati Biturbo is an 18v six-pot, and I like the way that develops power. That being said, the car is about the size of an Escort and comparatively light by modern standards, so with a fuel-injected 2.8 it's not going to hang about even before the turbos kick in

[Guest]

OK, so if the point of 4 valves per cylinder is to improve the torque curve, why the fuck is my C4 HDi a 16v? I thought diesels were all about bottom end \ mids, rather then screaming top end. It still gets breathless if you rev it past 3500 (and that's way out of the powerband anyway).

 

Also, how torque 'feels' \ is perceived is a weird one for me. Bald figures just confuse the siuation. Is having the same figure in BHP and lb \ft desirable? The 460 is almost there with that. It feels like it has way more than 125 lb \ ft when you're belting it.

[Pete-M]

OK, so if the point of 4 valves per cylinder is to improve the torque curve, why the fuck is my C4 HDi a 16v? I thought diesels were all about bottom end \ mids, rather then screaming top end. It still gets breathless if you rev it past 3500 (and that's way out of the powerband anyway).

 

4 valves per cylinder isn't just about torque. It's about gas flow. It's easier to accurately control four small valves than two whopping big ones. 4 smaller valves will weigh less, have less inertia and more surface area than a pair of whopping big ones. Your C4 will be a 16v because it's easier to get better emissions results if you can keep the valve timing as accurate as possible, as well as to optimise torque over as wide a rev range as possible. The breathlessness at high revs will be down to the burn characteristics of diesel fuel as much as anything else, there aren't many diesels that do anything much above 4000 rpm.

 

Also, how torque 'feels' \ is perceived is a weird one for me. Bald figures just confuse the siuation. Is having the same figure in BHP and lb \ft desirable? The 460 is almost there with that. It feels like it has way more than 125 lb \ ft when you're belting it.

 

Having the same figure in BHP and lb ft is a good thing to aim for more often than not. 'They'* used to say that if you can have say 150 bhp at 5500 rpm and 150 lb ft at 2750 rpm then that is about right for something to drive well, but that has changed a bit with so many people driving and being used to turbo diseasels now. Turbo diseasel stuff tends to use a fat wedge of torque and very carefully optimised long gearing to hide the lack of power, and to be honest, in some good stuff it works quite well. It's no substitute for a decent petrol engine, but there are too many tightwads out there determined to squeeze every last mpg out of something rather than enjoy 7000 rpm on occasion.

[forddeliveryboy]

I remember the hoo-haa when VW introduced its 16v engine into the Golf GTI, a car which was the journalists' darling at the time. Once they got used to adding a litre of oil every few hundred miles (harder piston rings, engine working less hard in a given situation) many of them complained about the flaccid power delivery until the tacho swung past 5000rpm. VW pointed out that the power and torque figures up to 5000 were about the same as for the 8v car, but it never felt like it due to the mind knowing what there was beyond that.

 

Multi-valve engines seem to have improved quite a bit in their delivery, but there never will be a substitute for shed loads of low down torque. Once drove a Series 2 Land Rover round a ring road dotted with loads of slow roundabouts, the cars behind took half a mile to catch up after each one. Gave me a new perspective of what 'fast' meant, given the thing was all out at 55-60mph.

[forddeliveryboy]

Seems a bit like the modern obsession with handling at the total expense of any sort of ride quality.

 

Many cars seem to ride so harshly that they end up bouncing and skitting about at British speeds on British roads. 50-section tyres don't help. Give me taller tyres with much less rubber in the suspension for a much better handling car in the real world. Coupled to sensible spring and damper rates with plenty of suspension travel (the old bugbear of Japanese stuff) you can have a comfy car which holds the road better than one set up for the Nurburgring.

[e287yba]

OK, so if the point of 4 valves per cylinder is to improve the torque curve, why the fuck is my C4 HDi a 16v? I thought diesels were all about bottom end \ mids, rather then screaming top end. It still gets breathless if you rev it past 3500 (and that's way out of the powerband anyway).

 

Also, how torque 'feels' \ is perceived is a weird one for me. Bald figures just confuse the siuation. Is having the same figure in BHP and lb \ft desirable? The 460 is almost there with that. It feels like it has way more than 125 lb \ ft when you're belting it.

 

Don't forget that Diesel engines are - generally - unthrottled, so the cylinders usually get their full whack of air when they are on their induction stroke at slower engine speeds, and 'your' engine with 16 valves has a better chance of managing this than an 8 valve engine at higher revs too. But it's the amount of diesel fuel injected that dictates how fast the engine runs at a given moment.

 

Petrol engines - again, generally - take their petrol/air mixture through the valves, and the mixture can't be allowed to vary much so they have a throttle on the air supply to control the engine's speed.

 

It's like comparing apples and oranges - the end result is the same, but they're just different ..

 

Pete-M is on the money when he refers to emissions and why Diesel engines don't rev as fast.

 

 

And how does torque 'feel'? Maybe think of it as giving you the push in your back when you accelerate - especially in a high gear .

[M'coli]

The other thing to remember about diesels is their rev range isn't limited by breathing but by the time it takes to burn the fuel - even the Le Mans diesels don't rev fast.

[Barry Cade]

I'm out of this arguement... all I will say is my old RD350 had no valves at all, but was very very fast.

[406V6]

Well mine has 24 valves and manages to have its cake and eat it too - great torque at low revs and excellent power & breathing at high revs. Plus the fuel economy is excellent for a big engine (better than 30 mpg most of the time). The engine is well suited to the auto box due to the high torque. Much of the time at town speeds the engine is barely turning over at 1200 rpm and still pulls away nicely. Some thanks are allegedly due to Porsche who engineered the later 210 hp variant as well as modern electronics & fuel injection.

[mk1_4dr]

Well mine has 24 valves and manages to have its cake and eat it too - great torque at low revs and excellent power & breathing at high revs. Plus the fuel economy is excellent for a big engine (better than 30 mpg most of the time). The engine is well suited to the auto box due to the high torque. Much of the time at town speeds the engine is barely turning over at 1200 rpm and still pulls away nicely. Some thanks are allegedly due to Porsche who engineered the later 210 hp variant as well as modern electronics & fuel injection.

 

Big displacements will always have fat lumps of torque.

The 24v bit just means it will sing and give you a decent thump in the back when floored over 4k too.

 

Like you say, cake and eat it.

[oman5]

I've had Volvo 740 8 valves and now have a 740 16 valve. Both engines are torquey buggers low down, the main difference is the 16 valve has lots of high up power as well, get it over 3000 rpm and it flies (for an old brick volvo, anyway)

It does feel somehow "wrong" to have a revvy engine in such a barge.

[M'coli]

I'm out of this arguement... all I will say is my old RD350 had no valves at all, but was very very fast.

Elsie?

[Barry Cade]

I'm out of this arguement... all I will say is my old RD350 had no valves at all, but was very very fast.

Elsie?

 

Yup was an F2 though.

[Cavcraft]

Not the same (sor of valves) I know but you could powervalves for them though I think! Those LCs were mental and the choice of every two wheeled hooligan back in the day, especially when Stan Stevens and Terry Beckett weaved their magic.