Another Method: I prefer to do the intake centerline methods based on the peak lift of the lobe. This tends to be the most accurate and what you'll see from many cam manufacturers. 1) Find TDC as noted in the video and set your degree wheel to '0'. This sets up your degree wheel to the proper orientation/reading with the crank. You can use the "hard-stop method" to obtain TDC - is one of the most accurate. 2) Rotate the engine in the normal direction of rotation (usually clockwise) until you reach maximum lift on the cam intake lobe. Set the dial indicator to '0'. Again, this is MAX lift of the lobe. 3) Rotate the crankshaft counterclockwise in the direction of BEFORE peak lift. Go PAST where we will take readings ---> so since we're going to do readings at .050 off of max lift, rotate the crankshaft to where the indicator is .100 before max lift. Now, rotate it again in the normal rotation (clockwise) back to .050 before peak lift. The reason we go PAST .050 in the first place is to account for slack in the timing system (chain). 4) Record the degrees at .050 before peak lobe lift. 5) Now, continue to rotate the crankshaft clockwise - past peak lift - to .050 on the downside of the lobe. 6) Record the timing degrees at .050 past the peak. 7) Add both numbers together and divide by 2 - this is your intake centerline. Notes on advancing or retarding the cam: 1) Let's say your final reading was 112 degrees and the cam card specifies that the cam should be installed at 108 degrees using the intake centerline method. Your 112 reading means the cam is retarded at the moment. 2) You need to advance the cam in order to bring the intake centerline down to the recommended 108. The method you use depends on whether or not you have an adjustable timing set (typical aftermarket OHV timing set with multiple key slots on the crank gear), or maybe a Donovan gear drive (with a vernier cam gear - where the bolt hole rotation changes the timing), or maybe a flathead Ford where you need to redrill the cam gear to set the timing). You'll use one of these methods to change the cam timing. 3) To get to the 108-degree centerline, you need to advance the cam 4 degrees. 4) If your measured centerline is LESS than the cam manufacturers recommendations, then you need to retard the cam to achieve the correct centerline. Note: Intake Centerline numbers are NOT the same as lobe separation numbers - many folks get confused by the two.
Pay attention to what Dale above wrote and the video. When the cam includes the words check the cam timing its important to do it. Here's one example of why its kind of important to check the cam timing upon checking a new cast cam from Isky for a Ford flathead the cam timing card read C/L 112 degrees. Checking this new cam from Isky the cam C/L was 119 degrees. If the cam was left this way when installed the engine would be a dog. Cam timing is pretty important just because its new its not always correct. Ronnieroadster
Another thing to note is that many cam manufacturers specify an installed intake centerline that advances the cam a bit (like 2 - 4 degrees). This is typically done for 2 reasons: 1) For most street applications, having the cam advanced a bit tends to improve performance in the low-to-mid RPM range 2) Having the cam advanced a bit also makes up for the valve lash, which effectively retards the cam a bit as the valve does not start to move until the lash is taken up.
I'm going to pretend that my trusty little mill is a 312, i.l.o a 351W, but the outcome is the same. I was tired of erratic numbers on the track, so I tore my 351 down to the short block. I knew the bottom was good, as in all **** and balanced. Had alum heads with no markings. So I bought a good set of heads, and a good Isky cam. The biggie was when Ken Smith at HRW suggested we degree the cam. Okay, says I the dum****. I now have a book on degreeing the cam. I took the mill to Frank the Fabulous over at The Dyno Shop in Nampa, Idaho, and after a number of pulls, managed 470HP and 6K and an almost straight line 455 torque from 2500 up. He wanted to go to 6500, but I said no, even though the graph was going up at a 45 degree angle.... This dropped over a full second of my ET and it's extremely consistent.... I'm convinced the degree work did it, as we changed the pully adjustment by several degrees. I would rather have a Y-Block, but got a good deal on the W.....
When you degree a cam thats what you are doing. Check timing straight up to start ,and then move it to where you want it. Its important to remember no one knows more about your engine than you do. All the components have an affect on centerline timing gear key slots, key slot in the camshaft, balancing of the core during grinding process, key slot cut in the crankshaft especially if its an aftermarket piece.
This I havent seen. Doing lash loops on the dyno, adding lash makes the cam smaller or act advanced. Whenever we tighten up or take lash away the engine loses small amount of bottom acting retarded.
Obviously, it depends on all the components in the build, but tightening up the lash makes the cam "bigger" (both lift and duration) - and depending on the profile (and the rest of the engine), you might lose some bottom-end HP due to the overlap bleeding off more of the compression. Question: Do you use any software like the "CAM Doctor" to map profiles, lift, jerk, etc? I've used it a lot - is very interesting to plot a lot of different cams and then compare profiles, events, etc.. It can give you a lot of insight and a basis for comparing different grinds and engine combinations. This is especially true when you're trying to compare flat-tappet grinds to hyd/mech rollers, radius grinds, etc..
Overlap happens at the beginning of the intake stroke or the end of the exhaust stroke so we can't bleed any compression off there. I have see low cylinder pressure scenarios from over scavenging during overlap. Typically any compression bleeding comes from a late intake valve closing ABDC.
I think we're both trying to say the same thing. With more lash the intake opens later and closes sooner - same with the exhaust. There is less effective overlap, less scavenging, less potential bleed off with earlier intake valve closing. Here we are pondering lash - though it really isn't much of a factor as compared to the overall profile/timing of the cam, rocker ratios, etc. What have you seen in experimenting with tighter lobe centers versus wider lobe centers on your heads and 312's in general? Have you done much with boosted applications? BTW: Love your work on the Y-blocks . . . just fun to see folks really making a difference in an engine that most folks have not invested any new R&D and built great new products for - in many years. You're not quite as nuts as us guys building Flathead Cadillac engines for BVille! LOL
Lobe centers are strange thing for sure, when idle quality and emissions are important wide lobe centers seem to be the trick. As you start adding a little duration and looking for street performance narrowing up the lobe centers seems to help, but then you start adding a bunch of duration for drag racing and you have to start widening them out to keep the overlap window from getting too big. There seems to be some talk about newer deep bowl heads having a more natural flow path and more prone to over scavenging so guy are widening out the lobe centers. Our Aluminum heads is a deeper bowl design than the original iron heads and seem to be happy with a little wider lobe center than OEM heads. I haven't done any real work with Flatheads but guys have told me they were pretty happy with narrow lobe centers. It seems logical to me, but have no testing to back it up.
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