NW94Z

I decided awhile ago to pull my heads and upgrade them to mitigate the whole exhaust valve issue. The sticking point for me has been the cam. I've been trying to decide on and off for months and I've gotten close but ran into tech issue recently and wanted to run it past some of you more experienced modders/ builders.

The Z06 has 1.8 rockers and as such when picking a cam it's important to identify one designed for 1.8 rockers. That way the lift numbers published for the cam represent what the application will experience.

Now if I were to find a cam that is designed for a 1.7 rocker setup what exactly is the impact? In other words how are the lift numbers affected when using a cam designed for 1.7 rockers in a car with 1.8 rockers?

I've done some research and wanted to know if my conclusions are correct.

Here is the scenario:

The cam has published lift numbers of .610/ .620 with 1.7 rockers.
If I were to run this with 1.8 rockers I can do some math and find out what the revised lift numbers are. The equation I found is very simple.

(lift/1.7)1.8 so (.610/1.7)1.8 = .6458 or .650 lift
(.620/1.7)1.8 = .6564 or .660 lift

Am I correct? Is this equation correct? The published lift numbers are well within the range I'm looking at for my application but if the rockers raise lift as indicated then I should steer clear of this cam since I want to stay at or below .640. Unless of course I change the rockers out for 1.7's.

Comments welcome.

v8sten

Yes your math is correct. another way is to look at the cam card and it will give you lobe lift, multiply the lobe lift times 1.8

NW94Z

Thanks for the quick reply. Is it possible or even worth it to grind the cam down to maintain the 1.7 lift numbers with the 1.8 setup. When I type that out it sounds like a bad idea.

encasedmetal

that's just more work and more complicated than it needs to be, especially since you'll have to shim the valve lash due to grinding the cam.

RedZ4me

sounds like a disaster waiting to happen - instead, get a custom grind to what you want

v8sten

Kip Fabre

If you have 1.8 rockers you want a cam lobes designed for 1.8 not 1.7 most companies just use the same lobes for 1.8 which make more lift. With the stock rockers keep the lift down to the .600 range just add a few more degrees of duration. Going from .600 to .650 lift on the exhaust will help very little but take away some valve guide & spring lift it not worth it unless you go with a roller tip rocker. You don't need to lift the exhaust more than the intake anyway the valve is smaller and its opened under presser it get to its max flow at an lower lift. We make lobe for the rocker ratio 1.8 or 1.7 even if we made a .650 lobe for a 1.7 or a 1.8 the lobe design would be different for each.

NW94Z

Thanks for the feedback guys. I've learned how to calculate lift if applying a 1.7 rocker cam in a 1.8 application and I've learned to make sure I spec a cam designed for a 1.8 rocker set up.