Piston to valve clearance question?
 

Guys,

Currently I have an original Cam Dynamics stock eliminator cam in my car. Specs are 519/525 lift and the .050 duration numbers are 250 int and 266 exhaust. The combo runs good, especially for the low lift however I want to run faster.

I have two options for camshafts, they are listed below:

Lunati Solid Roller: 785/785 lift duration @ .050 is 273 int and 283 exh

Ultra Dyne Solid Roller: 722/722 lift, duration @ .050 is 264 int and 271 exh

What I didn't do when I built the engine was write down what my valve clearance numbers where with the hydraulic cam. I know we had a good amount but not sure how much. Basically what I am asking is what matters more in this equation, duration or lift?

Engine is a 351C with closed chambered heads, 61cc's, .450 dome piston, block has not been zero decked.

Any good advice would be appreciated, thanks!

Smitty

Re: Piston to valve clearance question?
 

Gross lift has very little to do with it.
Duration @ .050" and the rate of lift on the cam lobe is what will cause concern. Also, lobe center separation ( under 110 starts to hang the valves off the seats pretty good at TDC )... and advancing or retarding the cam during installation, will get a valve closer ( advance = intake closer / retard = exhaust closer ).

No way would I do a cam change of that magnitude, without actually checking clearance.

Re: Piston to valve clearance question?
 

x2

Re: Piston to valve clearance question?
 

Highly unlikely either of those cams will clear, the lift and duration are both significant in the equation. To achieve higher lift lobe needs to be "longer", definately have to check PtoV clearance. Joe

Re: Piston to valve clearance question?
 

Thanks for the advice guys, pretty much what I was told before. The small cam is installed at 4 degree's advance so it's 104/111 and the the Lunati was installed my old engine at 100.5 degrees, not sure where the Ultra Dyne was installed.

I really didn't want to remove the engine but I guess I should have wrote better notes while building this engine. It runs good for what it is, I just wanted a little more umph. Altitude is pretty high out here in West Texas so if I was back home on the east coast it should run a little quicker. On the night the car had it's best pass here we were at around 4400 ft on the barometer.

Pretty nasty sounding hydraulic though, really suprised me with how it performs. I ran this same combo before with a Crane Solid that was about .050 bigger on intake and .070 on the exhaust and the difference in et was only .35 hundrenths. This engine does have more compression (first engine had same heads but they were 66cc chambers versus being 61cc chamber now) and it has a C-4 instead of a C-6. I think if I change the gear ratio it will help it out (5.67 from a 4.86). I will probably save the two solids for my new engine.

Once again, thanks for the inputs.