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Can anyone pls care to tell me the difference between 8 valve and 16 valve engines. Which one is more fuel efficient and runs better? I know that the insurance premium/group is cheaper for an 8V. Common sense dictates that the 16V has more power and leaner. Is this correct?
 

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As far as I'm aware a 16v job reduces the reciprocating mass and increases the valve port area. Reduced reciprocating mass enables the valves to open and close slightly sooner or quicker and together with larger area improves gas flow.

Insurance companies think this means more risk and therefore up the premium.
 

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when it comes down to it, most 16v engines are more powerful than their 8v equivalent, and insurance companies like to charge more for more powerful cars.

If you look at the astra G, the 1.4 16v is more powerful than the 1.6 8v offered for sale at the same time
 

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Aren't MOST 4-pots 16v these days?

Do they make many 8v's?
 

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Pretty much in a nutshell already. 8V where phased out due to the valve bounce that occurs when you make the valve bigger and thus heavier to accomodate more air, 4 valves per cylinder means they are smaller and don't bounce so are not releasing pressure and fuel.
 

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Four valves per cylinder have a bigger flow area than two valves per cylinder which is why they're used - four valves per cylinder are heavier than two valves, not the other way round as jasp asserts.
 

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Four valves per cylinder have a bigger flow area than two valves per cylinder which is why they're used - four valves per cylinder are heavier than two valves, not the other way round as jasp asserts.
Correct but a single valve in a 16v is lighter then a single valve in a 8v that has to cover the same area and do the job of 2 valves.
 

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bassicaly valve bounce is due to the weight of the single valve, and what jasp is quite correct in what said
not only do two valves not bounce but also help in other ways in how the gas flows into the bores and how well the fuel air mixture is mixed
 

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Valve bounce ???

Every engine I've used has valve springs of the correct rating to prevent valve bounce up to, and slightly beyond, the engines' rev limit.

I understand the problem with modified engines, ie camshaft, but for standard specification engines, or comprehensively modified engines, valve bounce isn't an issue.
 

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Can anyone pls care to tell me the difference between 8 valve and 16 valve engines. Which one is more fuel efficient and runs better? I know that the insurance premium/group is cheaper for an 8V. Common sense dictates that the 16V has more power and leaner. Is this correct?
Generally speaking you get less torque low down on a 16 valve engine, but a lot more top end power with a 16v. If looked after Eco engines are good, same can be said for the 8v's. Regarding fuel efficiency, I'd say that the 1.6 16v & 1.6 8v are probably about the same. All depends what your after?
If your after extra power, then the 16v engine is your choice.
If your after a reliable plod along engine & performance is not your main issue, then the 8v is good for general use. Not good for continuous short journeys.
Don't think Vauxhall now make an Astra H (petrol) 8v engine. I may stand corrected?
If you pick an 8v engine, then go for the mpi version, slightly more bhp.

If Vauxhall did a 8v petrol engine within their Astra H petrol range then I'd go for an 8v. As they don't when I renew I'll prob go for the 1.6 sxi (115), not 103.
Bring back the 8v c16se engine :)
 

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Can anyone pls care to tell me the difference between 8 valve and 16 valve engines. Which one is more fuel efficient and runs better? I know that the insurance premium/group is cheaper for an 8V. Common sense dictates that the 16V has more power and leaner. Is this correct?
an 8v engine is not as efficient as a 16v engine,if you compare a meriva the 16v engine is more economical than the 8v

Aren't MOST 4-pots 16v these days?

Do they make many 8v's?
there are a few 8v engines around

Pretty much in a nutshell already. 8V where phased out due to the valve bounce that occurs when you make the valve bigger and thus heavier to accomodate more air, 4 valves per cylinder means they are smaller and don't bounce so are not releasing pressure and fuel.
a load of crap,valve bounce used to be a problem back in the 1960s and early 1970s.a modern 8v engine revs just as high as a 16v engine in standard form,a 16v engine can be made to rev higher,not due to valve bounce but due to the superior breathing of a 16v head
 

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Generally speaking you get less torque low down on a 16 valve engine ...............................
That's not totally true - a 16v develops more torque than an 8v but it is higher up the rev range.

Torque figures for '98-'00 Astra 1.6s:-
8v - 94.4lbft @2800rpm
16v - 110.6lbft @ 3600rpm

The 8v may have more torque below 2000rpm but who drives at full throttle at such low revs - that's what the gearbox is for !
 

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if a valve is fully open and the distance from the valve to the valve seat is messured and multiplied by the circumfrance of the valve it will give you the open skirt size . a single valve with 1 inch skirt will have less flow rate than two valves with half inch skirts . more air = more fuel = more power .
 

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You can impart more swirl on the airflow going into an engine by using smaller valves. This helps you allow the engine to run more lean and at a higher compression ratio, though the latter doesn't seem to be an issue these days.

8v engines only have their torque peak at lower rpm than 16v because they are tuned that way. 16v can rev higher owing to the greater airflow and so they are tuned to have a higher peak torque output. Therefore the shape of the torque curve is more to do with valve/ignition timing rather than the number of valves, at least at relatively slow (<4000rpm) speeds.
 

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Valve bounce my ass ... 16v are quicker but cost more ... SIMPLE
Cost more to repair, cost more to buy and cost more to insure. And if you're inclined to use the extra performance you'll probably wear the engine out quicker and might also get a speeding ticket - not to mention an accident!

Having seen one or two results of a thrashed engine, if you go about it the right way you can destroy an engine very quickly. One simply way is to engage in regular heavy acceleration. This'll increase piston blow-by stripping lubricant from the piston rings and accelerating bore wear. One chap I recall destroyed his engine in about five miles! In my experience very heavy acceleration can turn piston bores into looking like a tram or railway depot!

For the average motorist I'd suggest 16v are a waste of money and time.
 
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