Dude, im having a dilema with a cam choice,and I wanted to run it by you.
I currently cannot get more than 7psi boost from my turbo, I think the cam has too much overlap [26*]and the boost is blowing through the motor. Is it feasable to have a cam with NO overlap,where both valves are closed,to let the boost stay in the intake?
If you need more info,let me know,I know this is vauge,I just wanted a general idea of what I should be looking for in a grind.
Thank you in advance, John Bonasera.

 

What is your setup again (turbos, intake, heads, exhaust?)? If you have a restrictive air filter, that will kill boost too... Try a run down the street w the turbos' intakes open (no air filter ducting) and not running the catback. Just run an open down tube and see if that helps.

If you get a chance, pick up a copy of David Vizard's book on small block chevy valvetrains. He's got a section on turbo cams, not to mention the rest of the book is good. If the boost is blowing through, the easiest solution is to rev it higher so it doesn't have time to blow through! Turbos have 1-2x the exhaust backpressure compared to the intake side, so usually reversion is the problem. The turbo cams usually close the exhaust earlier to prevent it from blowing backwards into the intake during the overlap period.

With big backpressure setups (i.e. old style turbos with a log manifold), you'll have negative overlap. The cylinder pressure can only get as low as the exhaust pressure, and if its 2x the intake pressure, you need to keep the exhaust and intake valve closed until the piston moves down a little, creating a pressure drop enough to suck in the lower pressure intake charge. Obviously intakes, heads, and rpms will have a lot do do with what overlap you can run, but in short, yes.

Andris

 

Its a single 60mm turbo, 1-3/4 equal length headers w/18" primarys, Brodix track 1 heads, 3-1/2 exhaust from turbo outlet to rear of car w/2 bullet[straight through]mufflers.
I heard that mustang cams have 0* overlap,thats why they take to turbocharging so easily. What I think is happening with my car is the valves never close, and the boost is getting into the header,because my exhaust pressure is way more than 2-1.
Thanks for the quick response, John Bonasera.