Piston to valve clearance problems

[fst65mustang]

Is there some rule of thumb with comp cams master lobes as to how much lift will be lost by decreasing the duration @.200 lift? Like say loose .006 lift for every degree of duration lost or gained @.200 lift. Am using a comp cam solid roller and need to gain approx .030 in piston to valve clearance, but don't want to give up much total lift and not much duration as this motor lives at higher rpm. Am hoping just a custom grind and a more agressive lobe will do the trick.

[amick]

There is no general rule of thumb as it is completley dependant on the lobe profile. I will say lift is not really going to be your issue as PTV clearance issues typically take place at or near TDC and not at full lift. Duration, Lobe Seperation Angle, and Centerline typically play much more of a role in determining PTV clearance. If you can provide the serial/part/grind number on your current camshaft and let me know what it is degreed in at I may be able to suggest something for you that can gain the extra clearance you need.

[fst65mustang]

The cam I am running now is comp #35-781-9 and it is degreed in at 108. Best I can calculate with the .081 headgaskets and cutting the pistons and valves to get the clearance, only have around 11 or maybe 11.2 compression. Know that cam needs more compression than that. If I can get another .030 clearance, will put .051 headgaskets on and it should get the compression up over 12.

[fst65mustang]

Ok, must be too hard of a question, how about this one, can anyone out there tell me what lobe profiles are used to make the cam previously mentioned? Thanks

[amick]

You could roughly come down to something like a 269/276 on a 111 LSA to pick up the clearance. That is about where the math works out to get it clear. You could use our 4311F/4268F lobes to get there. The lobes on your current cam are numbers 4238F/4117B. This is also hypothetical and I could not guarantee it. I will mention the camshaft sounds a little large for a 12:1 motor also. If you would like us to give you a recommendation you could send me the run down on your motor via PM or my e-mail at amick@compcams.com. I wanted to say I am sorry for the length of time on the response. I was out of the office for a couple days after my initial response and when I came back I just forgot this question was here.

[fst65mustang]

Thanks for all the help with this cam. What is the current lead time to order a custom cam like Matt recommended? Do you have billet cores in stock? Thanks again, looking forward to trying this cam out!

[amick]

No problem at all. Current grind time is about 3 days.

[fst65mustang]

So I could have it in hand in maybe 7 to 10 days? How do I go about ordering it, can you take the order?

[amick]

You can place the order over the tech line (800-999-0853) or you can call Matt direct at 901-795-2400 ext. 596 or you can place the order over e-mail with me. Just however you would like to do it.