What size cam will fit in a 86 H.O.?

[1bad92lx]

My friend has a 86 gt and people are telling him that he can't put a cam in it larger than stock because of the heads and pistons in the 86's. I was wondering what the maximum lift cam he can install without fear of having pv clearance problems? Thanks for any help.

Matt

 

[Michael Yount]

As much lift as his valve springs will allow Matt - because peak lift doesn't impact p to v clearance at all; when the valves are at peak lift the pistons are well down the cylinder so there's plenty of clearance then. The clearance issue occurs during overlap when the piston is passing through tdc and the exhaust valve is about to close/intake valve is just opening. So you see, the valves are barely open when clearance is tight. Others may tell you what they ran, but most folks don't actually measure p to v. They just install something someone else says 'worked in mine' and hope for the best. Ultimately, you'll have to make your best guess based on what others tell you, then install and measure to be sure. It's the increased duration that causes the problem (actually earlier opening intake timing, and later closing exhaust timing). But, if you're still running speed density, then there are only a few cams that will work anyway because most off the shelf cams give the speed density system problems. Go to this link and read -- it'll explain the dynamics. Post a thread aimed at the speed density guys and they'll tell you what works and what doesn't in terms of cams. http://www.diyporting.com/PVC.html