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Discussion Starter · #1 ·
Hey,

I am kinda new to all this, and i saw a MG ZR 105+ that said Twin Cams, what are they? and how does it improve preforamce? Also if u get any 16v engine will it always have Twin cams with it?

thanx

tom

p.s try and explian it so a notice would understand :bgrin:
 

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Twin cam refers to the cylinder head (the bit with valves) have 16 valves * inlet and 8 exhaust valves.What makes them better than just 8 valves alone it each cylinder has 4 valves rather than 2 (2inlet 2exhaust) o with more valves we also have a greater capacity to move more air either in as fuel/air mixture or exhaust gases.Generally a 16v will allow the engine to 'breath better and hence more air in and a bigger bang.Here we are talking a 4 cylinder but you can have v6 engines which usually have 24 valve 12 inlet 12 exhaust same for v8 they have 32valves.

Anyone remeber audi's 5cylinder?that had 20v
 

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griffmonster said:
Twin cam refers to the cylinder head (the bit with valves) have 16 valves * inlet and 8 exhaust valves.What makes them better than just 8 valves alone it each cylinder has 4 valves rather than 2 (2inlet 2exhaust) o with more valves we also have a greater capacity to move more air either in as fuel/air mixture or exhaust gases.Generally a 16v will allow the engine to 'breath better and hence more air in and a bigger bang.Here we are talking a 4 cylinder but you can have v6 engines which usually have 24 valve 12 inlet 12 exhaust same for v8 they have 32valves.

Anyone remeber audi's 5cylinder?that had 20v
Bravo for giving an explanation the guy will never understand!
 

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alright then....

Normally a basic engine has 1 camshaft the job of thats shaft is to open the inlet valves (the fuel/air mixture) and also the exhaust valves to let the waste gasses out. each cylinder has 2 valves 1 inlet and 1 exhaust the camshaft of a single cam rngine has two lodes for each cylinder an inlet lobe and an exhaust lobe they look egg shaped and either push directly on the valve to open it or operate a push rod and rockers like a fiesta engine, but due to the limited area of the valves less inlet charge goes in.After that things get complicated with respect to formulas, valve timmings ect..

heres my twin cam, the rear shaft with egg shaped lobes is the one that open the inlet valves and the shaft closer to you is the exhaust shaft.



and these are the valves.top ones inlet and bottom ones white as they get hotter due to the exhaust gasses flowing over them.This is the clyinder head and it goes on top of the engine and is driven by a belt of the crank shaft (that has the pistons on it)
 

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Discussion Starter · #6 · (Edited)
okay then so correct me if i am wrong. a twin cam engine basically means that you have two fuel and two exhuats valves in the cyclinder head? And say if u have twin cam will it run on both, okay wot i am saying is, my mate in a convo said his second cam came in after 5k so does this mean he is running only a single cam until he hits 5k (therefore he is only running the equivelent to an 8v up until 5k?)

if so does

16v = twin cam

8v = single cam
 

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Not necessarily. There are plenty of older vehicles with twin cams that only have two valves per cylinder (i.e. 8v for a four cylinder car). One cam controlled the inlet valves and the other controlled the exhaust valves. The main advantage was that it enabled engineers to tune the engine by independently adjusting the inlet/exhaust valve timings without needing to install different camshafts.

Modern four valve per cylinder engines though are now almost invariably twin cam units for the simple reason that it would be difficult to squeeze enough cam lobes on a single shaft without encountering serious durability and reliability issues. A secondary reason is that it allows manufacturers to more easily make engines with automatic variable valve timing (the very thing that engineers and mechanics had to do manually in the old days).
 

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tom_k said:
okay then so correct me if i am wrong. a twin cam engine basically means that you have two fuel and two exhuats valves in the cyclinder head? And say if u have twin cam will it run on both, okay wot i am saying is, my mate in a convo said his second cam came in after 5k so does this mean he is running only a single cam until he hits 5k (therefore he is only running the equivelent to an 8v up until 5k?)

if so does

16v = twin cam

8v = single cam
Depending what car hes got (and it sounds like it could be a Honda) it might have a VTEC system.

This has different Lobes on the shaft which a computer switches in and out (god knows how) depending on the revs.

Each set of two valves (inlet or exhaust) has three lobes on the shaft, two of one profile and one of a higher profile

The two similar profiled lobes are used below 5k and only opens the valves a small amount, allowing for docile driving and economy. Above 5k a pin is placed through all the lobes, locking them together (the computer does this bit). The locked together lobes now follow the profile of the high lift lobe, which opens the valves more, allowing more gases to flow more quickly and hence you get more power and imporved performance.

I think...!
 

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shakenNstirred said:
also dont honda do a 16v single cam
Yeah, they did a few of them and they were installed in R8 200/400 in 1.6 form.

Also, another one was installed in 600 in 1.8 and 2.0 form.
 

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More valves were used in an engine to help volumetric flow.

Volumetric flows refers to the amount of air that flows ino the engine
Look at it this way:

An engine which is 1000cc capacity, if the engine was able to fill with 1000cc of air this is said to be 100% volumetric efficiency right?

Ok, so.... an engine is 100% volumetric effiecient.........no.

As the engine speed increases, the amount of time the valve is open, governes how much air can flow into the combustion chamber. The valve opening time is now the dimishing factor (time) as its controling the amount of air entering the engine Via the camshaft (its the lobes that actually control this, they push the valve downwards, opening the valve, air gets dragged passed it)

Now, volumetric effieiceny can be easily increased (he says) by either using more valves, forced induction, or head work. All you are trying to do is to allow more air into the engine hence more power (as long as the fuelling is matched)

Ok, now to really get down to it: The volumetric effieicey will be at its greatest when the cam timing and pulses of air match eachother (or work in harmony) to produce a high volumetric effiencey, say 85%. VE can easily be 110% maybe even more because, as turbos do, allow more air into the cylinder filling our engine of over 1000cc of air to 1100cc of air. This is the whole point to forced induction, to pressursie the air above 14.7psi (1bar) which is...atmospherice pressure.

Some people are forgetting that although 16v engines allow it to be revved higher and still produce power at the top of the rev range, 8v engines often had more torque at the bottom end. We could get into square and over square engines, but thats way off the subject.

Also, i believe (not that i know how it works) but hondas VVTi single camshaft system worked off oil pressure. The high oil pressure allowed it to alter the cam duration.

Sorry, but i think i went way off there.

Ben.
 

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No, thats a really easy to understand explantion of what valves do and how the camshaft and its control over the valves can affect the characterisitics of an engine.
 

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tom_k said:
thanx for that explanation nebburns, thats what i was looking for. Mike200SEi the car that i was on about was a Metro twin cam 1.4 16v.

thanx for all your help
The Metro does have 2 cams, but they work together all the time.

I dont know what engine is in the metro, i assume a K series (think the A series was 8V), but the only K series to have a trick valve system was the 1.8VVC and this was never fitted to a metro (not standard anyway).

The 1.4 K series is just a standard twin cam engine, that works as discussed earlier in this thread.
 

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sph060977 said:
so i take it the the kv6 which is a quad cam has 2 cam shafts on each bank of the v one doing inlet one doing outlet?
Thats correct, two cam shafts on each side of the V and 6 pistons operating on a common crankshaft.
 

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Discussion Starter · #17 ·
okay so in essence, a cam shaft is a rod that has these lobes that push down the valves to open them causing fuel to enter the cyclinder and then once the explosion has happened the exhaust valves opens again to let the exhaust fumes out. Twin cam mean that there is two of these shafts which means that the valve timing can be changed to allow more air into the cyclinder therefore more power as there is more air and fuel in the cyclinder? Okay so if there is four valves the two are fuel and the other two are exhaust so where does the air cum in from?

 

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The air is entered via a manifold (not present in my picture) For the k series it is cast in two halves *(well the early ones like mine) and its alloy.Ill do a pic later.If you look at my pic above the rear cam is where the manifold bolts onto it has large expansion chamber which feed into four tubes which goto each one of the cylinders.part of the inlet manifold has a fuel rail attached the rail feeds a common supply to the four injectors which spray a fine mist into the bores.the injectors have an electrically operated solenoid which pulls a needle (or pintel) of its seat which allow pressurised fuel to be squirted in the bore, the ecu determines when to open the injector on the induction cycle as the piston moves down the bore sucking in air as well then when piston has moved almost to top dead centre of the bore the spark plug ignited the compressed fuel/air mixture it fires before TDC as the explosion is not instant.The old days this timing was altered by a diaphragm pushing an armature in the distributor to adjust the ignition timing and that was altered by the crank case vacuum, but now all that is controlled by the ECU.
 

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Discussion Starter · #20 ·
sorry about all the questions.

so the fuel and air vapour is mixed in the cyclinders or is it mixed before then?

tom
 
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