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Message: <blockquote data-quote="Addicted" data-source="post: 1463349" data-attributes="member: 24638">I understand completely if I confuse everyone, I change my mind to much when doing something I care about.  Since day one ive been what everyone calls a "NPI Guy". I love the 'Ole mistreated and bashed NPI heads, and it shows in my decision making. What ive been trying to accomplish is an higher lift aftermarket N/A PI camshaft installed in a NPI head, .556" intake lift to be exact. This has been a debate from the late '90's, and as you see it still is today but .ost people just switch the heads out to PI's. I want to make it work because I know the capabilities of the NPI head in naturally aspirated form, I would almost go out on a limb and say that if your staying under 400rwhp that it is<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite9" alt=":eek:" title="Eek!    :eek:" loading="lazy" data-shortname=":eek:" />. Yes I said that! Lol. Now in forced induction builds I say go ahead with the PI heads instead, but I'm not FI yet nor will I be for a while.   Many big named people has made our NPI heads dip well into the 11's on a setup that can be street driven decently. Yes, the PI's have had that success also, but when a NPI does it, heads turn. Its a challenge, kinda lime the girl you try to date and she dont give you the time of day, eventually you take her out.  The big debate is true .550" lift, and I mean a true .550" lift lobe, not like Comps "OTS" cams that are listed as a .550" lift, but they measure in at a true .540" lift. My Cams are ground by Comp, but there MHS cam #'s which is a true intake lift at .556", correct .556". Many people have run the Comp cams w/ the .540" lift in their NPI heads w/ +.060" retainers installed so the valve springs won't have coil bind or what some call coil stack. Here's the thing, it's not the coil stack thats going to hurt me, it's the valve keeper/retainer to valve seal clearance. Its been said that keeper/retainer to seal clearance is limited to a camshaft w/ .560" lift, some others have said .570" lift. There lies what you see me doing, im pushing the limits to these #'s. Now here's the question, "Do I think I will clear?" Yes I do, but I want to know for sure how much clearance I actually have left. I want to be able to say w/o doubt what I have, so I can feel comfortable on my decision, and to give others confidence in theirs also.  Was the .560" clearance figured out on a bone stock totally untouched head? Was the .570" clearance figured out on a head w/ a valve job? Was the measurements done with factory valve or aftermarket valve seals? ECT.... I don't know yet TBC. Every alteration you make to the valve or seat changes all the measurements, and must be accounted for. I do have a valve job on my heads now, so it gives me some teeny tiny room.  Here's something to think about, Jim Cushman of Cushman Motorsports told me the other day that his .550" NPI cams are actually a true .547" lift, that's .007" bigger than Comps OTS cams, but  it's .009" smaller than my MHS cams. Yep, I'm talking .009" lift more, but that's me and how I make decisions. I dont say the heck with it, I know for sure. TBC.......</blockquote>