adjustable cam pully yes or no?

[avants2turbo]

Keith, id be careful with that one on ebay, unless anyone has experience with one, as they car shere key ways etc and destroy your brand newly built motor!

[Error404]

http://www.rosten-performance.com/

[Acidburn]

http://www.rosten-performance.com/

interesting link

[Error404]

These are the bits that Thuppu posted above I believe

[Thuppu]

Yes, Rosten it is.

[JP]

Rosten and 034 do them, I believe Repo supplies them aswell? As do Kent cams on the cam chain verniers. If changing the cambelt pulley for a vernier and you run coilpack ignition system i.e. not 3B make sure you have one with the hall sender window on it or your car won't start.

Any cam can be adjusted in timing to gain power for a desired part of the rev range or make a bit more aggressive by not being overly concerned about emissions. General rule of thumb is 112-114degrees lobe separation gives a good torque curve with quicker boost response and nice idle. Whereas 108-110 lobe separation gives better top end at the sacrifice of low end and idle quality when playing with the chain verniers. You can then shift the shape of the curve and it's location on the rpm band using the main vernier. It's not golden set in stone but it is a general guideline. Getting the most out of a set of cams comes down to experience more than anything.

For example to achieve a power curve which demonstrates maximum area under the torque curve throughout the rev range of an engine on a small to medium turbo. I've ran many a simulation and ironically every time I use an engine simulator to achieve this phenomena it comes up with an identical cam profile to that of the RS2 cams. So obviously when Porsche fettled with the I5 this was their intention.

I'm currently running 2 7A exhausts clocked to ******y with very satisfying results on a head ported to suit the extra lift. In a stock head they fall flat on their face and are rubbish.

[Thuppu]

...very satisfying results on a head ported to suit the extra lift. In a stock head they fall flat on their face and are rubbish.

What do you mean with this?

[Billman]

I got mine from Rosten also.

[JP]

What do you mean with this?

Cylinderheads will flow different amounts of air at different levels of camlift. Depending on which seat angles you use, port dimensions, valve size and design you can get a cylinderhead to flow very good figures in low to middle range but then choke at high lift. Or you can configure a head that flows maximum at high lift but then looses flow in low and middle range. Much the same as a power curve.

So if you take a high lift cam and fit it to a head optimised for low to medium then you will find the combination will flow less air than when using a milder medium lift cam.

If you take a head optimised for high lift flow then you fit a medium lift cam again you may find that the cam doesn't lift high enough to benefit the port design and potentially not make a lot more power than a stockhead.
Take a high lift cam and fit it to the same ported head and the engine suddenly comes alive with big power gains as everything is correctly matched.

So when choosing a cam profile it is important to think what everything else is doing in the engine especially the flow capability of the cylinderhead. This is why any good cylinderhead porter will always ask the customer what the end plan is of the engine in respect to capacity, cam profile and driveability as small changes in the port design can make significant impact on the combinations used.

It's for this very reason that it is difficult to retail a cnc cylinderhead to the mass public as you are stuck wit one design, likewise it is difficult to specify specific stages. Lastly it also a major reason that so many people think that headwork doesn't make good gains for the financial costs as 99% of the time it comes down to incorrectly matched components.

hth JP

[Error404]

Good info as usual JP

[Thuppu]

Ok, now I'm getting it. Thanks for the info. Hmm, now I have 7A cams and adjustable camgears waiting for assembly in a stock head and it seems like a bad idea. I probably need some porting...damn this project goes bigger and bigger.

[JP]

Not necessarily what power bracket are you aiming for with which turbo inlet and exhaust manifold? Also what is the primary use of the car?

[Thuppu]

Hope for 500-550hp... Turbo CTBB comp.56mm ex.58mm/AR.84, DIY tubular exhaust manifold, 3,5"DP and 3" exhaust, AAN stock intake manifold, dual intercoolers, 450x300mm + stock. The car is a daily user, but hope for some ice track- and trackday driving also.

[JP]

Well you would benefit from improved throttle response and torque delivery by doing appropriate headwork if using a 7A exhaust cam with stock intake cam with no real need for verniers. If using both 7a cams you would benefit from having the chain vernier setup if you have the ability to dial them in correctly. The main vernier would not be considered a necessity for either application more a luxury. If building an out and out track car the vernier would allow you to fine tune the power curve to your gear ratios to give best in and out of corner response at a possible (not necessarily) sacrifice of the daily driveabilty part of the rev range.