URLACHER54

what is it that can cause the issue? i want to use the F-Cam in my 88 GT and the tech support says that i should check the pisto to valve clearance. but alot of people say its not the cam that causes the issues, so what is the real issue. i want to install my GT-40 cast iron heads and my F-Cam and Cobra intake, shouldnt these all bolt right up with out issue?

67mustang302

Piston comes to the top of the exhaust stroke and both the intake and exhaust valve are open, too much duration for the size of the valve relief in the piston and the piston can smash into either or both valves and bend them.

URLACHER54

yea but what is the issue does the cam cause this, the valve springs etc, what is the main cause?

67mustang302

Cam and valve size without enough valve relief in the piston. It's not any 1 thing, it's a combination of things.

URLACHER54

is there a chart with the specs on what would work and what would not?

Joel5.0

All setups (including ones with the same components) are different...... reason why you ALWAYS need to check. The "cause" is the cam dictated events during the overlap + valves distance from the head plane + head gasket thickness + deck height of the piston + camshaft timing (degreeing) + piston crown design + head valves size + heads valve positioning in the heads (angle) +.........

mjr46

Joel is right..anyway as for the f-cam...you'll be fine..I have put numerous f-cams in stock bottom end blocks and some have had 1.90/1.60 valves and others have had stock heads like my 92..and ptv has not been an issue..but irregardless I did check ptv and so should you to be safe..a quick trip to the toy store to grab some play dough can go a long way

URLACHER54

im not sure of my valves i know the set of GT-40s have valve springsfor up to a .550 lift. how can i find out what size the valves are?

mjr46

gt-40's came with 1.84/1.54 valves stock..you'll still be okay but check it when setting it all up

5spd GT

Peak lift has nothing to do with piston to valve clearance. A Trickflow Stage 1 camshaft is 2.156" down the bore at peak lift.

Anyways, advancing or retarding the camshaft can gain you a bit...although it compromises your performance and powerband.

Advancing the timing opens the intake sooner and closes the exhaust sooner. That will gain you some clearance on the exhaust valve, but you will lose clearance on the intake valve. Retarding the cam causes the timing to open the intake valve later, and closes the exhaust later. You'll gain clearance on the intake, and lose clearance on the exhaust. So changing the cam timing won't result in increasing clearance on both valves.

You need to see which one you need most...

Adjusting either way can shift the powerband +/- 200 rpm that direction...

The general rule of thumb is .080" on the intake side, and .100" on the exhaust side.

The exhaust side needs a little more clearance due to a couple reasons:

- Piston chasing the exhaust valve as it is closing (spring has less control).
- Heatexpansion
- Chain stretch (retards the camshaft)