after market cam 4 G60

[supercharged_devil 0]

am considering an aftermarket cam, but after being at the gti last weekend, there was discusions of people using mk3 golf or very early mk2 ones depending where the car had a Cat or not, these both have a greater profile than the standard G60, can anyone shed some light on this.........

[G60Jet 1]

Aftermarket Cams for the G60 are a big talking point a cam that allows the valves to be open to long will blow the boost right through.

 

Ask Paul1 im sure he'' be able to tell you!

[G60 0]

i'm going to cut and paste a big ol' chunk of text that Gerry posted to the US list. hope this isn't a problem... cross-posting or whatever. its good info...

 

-----------------------------------------------------------------------

 

Let's see if we can start a camshaft discussion here :-)

 

So, the basic function of the camshaft (hereafter called cam, because

I'm lassy) is to time the opening and closing of the valves with respect

to the position of the crankshaft. The cam determines when each valve

opens and closes, how fast the open and closes (assuming the valve springs

have enough force to prevent valve float), and how much each valve opens

when it's fully open. Why is this important? All these factors affect

how much air goes in and out of the cylinder, when the air goes in and out,

and how fast it can go in and out. This, in turn, determines the shape

of the power curve of the engine.

 

OK, there are two meassurements that are used generally used to identify

cams, 100% open duration and lift. Duration is meassured from the point

when the valve completes closing to the point when the valve starts to open,

and determines how long the valve is open. Lift is the difference between

the height of the lobe and the base circle of the cam, and tells you how much

the valve opens. Now, these numbers can be deceiving, particularly duration,

because it tells you a very small part of the performance characteristic of

the cam. More important than duration are overlap, the time between the

exhaust valve being fully open and the intake valve being fully open, and lobe

profile. Some performace people actually refer to "valve overlap" as duration,

because it's more significant figure to drivability and power band

than actual duration of each valve.

 

So, what to look for in a cam? Well, lets touch on some more basics. At low

RPM the cylinder wants to see air moving at high speed to generate

torque. That means that you want the valves to be open for a long time (small

duration). Also, because there is a large amount of time between the cylinder

being at full exhaust and it being at full intake, the engine likes small

overlaps. As the RPMs increase the time between full exhaust and full intake

is reduced, so the engine can tolerate more overlap. Also, the time it takes

the piston to travel from the top of the travel (TDC) and the bottom of the

travel (BDC) is reduced, which means there is less time to fill the cylinder

with air, and less time to clean it of exhaust.

 

OK, with that information, how does cam duration, overlap, and lift, affect

the power band? At low RPM you don't want too much overlap, because there

is too much time for the intake gases to escape through the exhaust valve.

You also want a mild lobe profile, because this allows less volume of air

to come into the cylinder as the piston starts to move into the intake cycle,

increases the air capacity as the piston speeds through the middle of the

stroke, and then reduces it again as the piston slows down when it gets closer

to the bottom of the stroke. A fat profile (small duration), with a nice slope,

matched to the dynamic volume of the cylinder, and low overlap, gives the

engine a nice and fat torque curve at low RPM. Now, as the RPMs increase,

and the time for the cylinder to fill up decreases, this low overlap cam

doesn't give enought time for the cylinder to fill up or clean up, so the

power is decreased in the high end. As you approach higher RPMs, say 4500+,

the cam starts to limit the amount of air that the cylinder can move, and it

the power drops off rapidly.

 

At high RPM the engine wants lots of air. Since there is less

time for the cylinder to fill up, it also likes the valve to open faster and

earlier in the cycle. So, the engine wants the cam profile to get more

aggressive, which opens and closes the valve faster. A more aggressive

profile requires shorter duration. The engine also likes high lift, because

it wants lots of air. Also, since it wants the intake valve to open earlier

in the cycle, it likes more overlap.

 

As you can see, increasing overlap will increase high RPM horsepower, it will

also increase how high in the RPM band you have power at. It also degrades

low RPM torque. In high overlap cams it affects the low end so much that idle

degrades and gets bumpy. This is where the variable valve timing systems

(VVTi, Vtec, etc) come into play. They change cam overlap with RPM, which

is doable when the intake and exhaust valves are controlled by separate cams.

 

Lets summarize a bit. A high overlap, low duration, and high lift cam, will

give you better top end horse power higher in the RPM range. This will be

at the expense of low end torque, some idle degradation, and in extreme cases

drivability issues. A low overlap, high duration cam will give you better

low end torque, and the engine will run out of air at a lower RPM.

 

There are essentially four options for the G60. Neuspeed 260, Autotech

assymetric 260/256, Techtonics assymetric 268, and BBM assymetric 268. BTW,

an assymetric cam has a different duration for intake and exhaust. I don't

know much about the Neuspeed 260, but the Autotech is quite a bit cheapper,

and I like the assymetric nature. The Autotech is a very good all-around cam.

It gives you improved high end HP, enough air flow to run around 6800 RPM,

and only a trained ear would notice the difference at idle. I haven't tested

the 268 myself (it's on the list of upgrades), but here are my expectations,

which include information I've heard on the list. The 268 should give you

enough flow to run up to 7000 or 7200 RPM. It will give you a bit more HP,

probably a couple ponies, with a corresponding reduction of low end torque.

It will also be quite a bit bumpier at idle, although still barely noticeable.

As a reference, I had a 276 on my old GTI, and it sputtered a bit at idle, but

if you didn't know what a cam sounds like you'd attribute it to dirty injectors

or something like that. If you have a stock engine, with a stock head, you

might not get the full advantage of the 268. With a P&P head you'll probably

notice a bigger difference.

 

OK, this is becoming a book...sorry about the lenght.

 

Gerry

90 G60-GT

 

-----------------------------------------------------------------------

 

:)

[Dubcharged 0]

Interesting!

 

I use a Schrick 268, great for mid and top. Idle is nice too! :D

[LowG 0]

i have seen many people runing mk3 gti cams on g60,thats good if you ona budged but for max performance id go for a 268 or 271 assymentric