Vernier gears

hi guys ,

has anyone spent time on the dyno to see what the effects on both advancing & retarding the intake & exhaust cam has on torque, kw , engine response , afr's & ignition timing

is there a rule of thumb when it comes to setting the gears

or is there a place where i can get more info on this ?

Yes, I've spent many hours on many dynos adjusting cam timing. There isn't a general rule you can apply to every engine though as to where the cams should be set - It will depend on the engine design and the cam specifications.

As a guide, normally advancing the cams favours low rpm torque/power, while retarding the cams favours high rpm torque/power. If you're running an aftermarket cam profile then I'd suggest starting out with the cams dialled in at the cam manufacturer's recommendation and then adjust the timing from there in 2 degree increments. You'll typically find the engine will be more sensitive to changes in intake cam than exhaust cam. Advancing or retarding the cams independently of each other will also affect the amount of overlap.

As you change the cam timing, the engine's VE will also be affected and this may mean you need to adjust the fuel and/or ignition to optimise them. It's a time consuming process manually optimising the cam timing, and it's important to understand that ultimately it will be a compromise.

how would you go about degreeing stock cams?

I know decking the head and block as well as head gasket thickness can affect cam timing (not sure on the magnitude).

so how would you degree stock cams (with adjustable cam gears). if you don't know the recommended timing?

sorry for the thread hijack, I thought it was relevant.

Degreeing cam isn't really hard. You just need a degree wheel and a dial indicator (with something to attach it, like a magnetic base)

Here is one way:

http://www.motoiq.com/MagazineArticles/ID/2284/PageID/4012/How-To-Degree-Cams.aspx

If you don't know what the cam centrelines are for a factory cam then you're a little stuck unfortunately. Often this information will be known by aftermarket cam suppliers who have measured the stock cams prior to designing and developing their aftermarket profiles. Failing all else I'd generally dial the cams in at a known centreline and start tuning them from there on the dyno to find out what the engine actually wants/needs, or alternatively where you want the engine's power band to be. You need to understand that the factory cam timing spec isn't necessarily going to be the best for your needs.

For a turbocharged engine if I didn't know any better I'd start perhaps with the intake cam at 110 degrees ATDC and the exhaust at 112-114 or thereabouts and optimise from there.

Hello guys,

Just to add to the link given by Ludo, do checkout Kelford and Webcamshafts websites.

They do have the steps given to do cam degreeing.

Cheers.

Haz