View Full Version : Piston to Valve Issues and Valve Events, Everyone please read.

11-14-2004, 06:53 PM
First off, people piston to valve contact is not effected by the peak lift of the camshaft. When the peak lift of the camshaft occurs the piston is way down in the bore. The RAMP RATE (how agressive the camshaft is from .006" all the way up to its peak lift), INTAKE CENTERLINE (advanced, retarded, or straight up), VALVE SIZE, and HEAD DECK (stock or milled) are what effects the piston to valve clearence.

Now that that is out of the way I have some concerns and comments about this issue. Thunder racing has tested their TREX camshaft (242/248 duration at .050" lift, .60x"/.61x" lift, 108 intake centerline (advanced 2 degrees), 110 lobe separation angle and posted piston to valve clearence of ~.080" (80 thousanths) on a stock headed car ( I don't remember what gaskets were used but you are not looking at more then 10-20 thousanths difference between gaskets). My concern is in the fact that I have seen people report piston to valve clearance smaller then the TREX with stock heads and much smaller cams. Are these cams on a completely different intake centerline?

I think it is relevent the people post the complete information about a cam when asking about piston to valve clearance. Companies like LG Motorsports do not help out by not giving specs so it can be made difficult to have an aware consumer (not flaming LG Motorsports although I think it is silly to buy a cam without knowing the specs so please don't retaliate as such).

I am putting a 239/246 duration at .050", .649"/.61x" lift, Comp LSK/Comp XE-R lobed, 106 intake centerline (straight up), 106 lobe separation angel (lsa) cam in my car and will be milling my 5.3 litre heads an undetermined amount at this point and installing 2.02/1.60 valves in them. I will also be flycutting the pistons .080". What this cam yields is slightly less piston to valve clearance as the intake valve opens .5 degrees sooner and the exhaust valve closes five degrees later (an increase of 5.5 degrees of overlap at .050" over the TREX). As you know the intake opening and exhaust closing are your overlap and conern points of piston to valve contact.

The reason I am posting this is I am trying to find out some good examples of piston to valve contact of stock, milled, large valved, or any combination of the above heads and a cam of whatever spec. This way I can determine how much I can mill my heads for added compression.

This post is not meant to flame, only to start a thread for examples of piston to valve clearence with intelligently and completely listed information for my own and others use.

11-14-2004, 08:20 PM
I don't know if this is what you are asking for but here is my response. I just put a set of AFR 205's milled .010" mounted on cometic .040" gaskets. The heads have 2.02" and 1.6" valves. The deck height was measured ~-.005". The cam is a Comp with X-ER lobes. 224/228 .581"/.588" 112lsa +2, installed on a 110 ICL. P/V was measured .110" intake, .148" exhaust.
What I am planning on doing now that I have all this info is to pull the heads and mill them another.020" and to install the cam on a 112 ICL. I am going to install the cam on the 112 ICL first and measure before I do the milling because as you stated the P/V will change do to different valve events. I hope to pick up another 15hp this way. Hope this helps.

11-15-2004, 06:54 AM
That is exactly the kind of information I am looking for.