Looking at my cam card, couple of questions

R

redterror302

Founding Member
Jun 29, 2002
895
0
0
Mertztown, PA or State College, PA
#1
I am just trying to figure out whether I am understanding some of these numbers correctly. This is something it says:

Valve timing at .006:
open/close
int 27 BTDC 63 ABDC
exh 74 BBDC 22 ATDC

The cam has 270/276 degrees of duration to it, and it has .544" lift. So doing some simple algebra, I came to the conclusion that at TDC, the intake valve will be opened .1088" and the exhaust will be opened .0867". Simple math really, since the intake valve is opened for 27 degrees before TDC, and it reaches peak lift halfway through its total duration(270/2=135), you would do 27/135 then multiply that by .544. Same type of equation for the exhaust.

Now for the questions. Can I assume that the way I did it, or does it open and close at a different rate, not uniformly? If it isn't uniform trhoughout, there is no way for me to find that out is there?

Also, if I would happen to be right, is there a way to tell how far the valve would be from the piston? Say the valve were not moving, does anyone know how close the piston gets to the valve at TDC, or at different times throughout its stroke?

I am still going to use clay to check my piston/valve clearance, but I want to get some sort of idea now(stock valves/pistons). I am trying to figure out if I can run 1.7's or not.

Also, it says the specs are for the cam installed at 108 intake center line. What does that mean? That is the only thing I really have no clue about.

Thanks for the help, I appreciate it. Sorry it's so long.
Chris
 
#2
You've got some considerable misunderstanding about the dynamics - the good news is that you're asking about it.

First off - the lift. All of your assumptions about the math are incorrect. Peak lift is just what it says - peak lift. The lobes don't necessarily ramp linearly which your math assumes. The peak valve lift is probably calculated with 1.6 rockers - that means that at peak (which is usually, but not always, halfway between the opening and closing numbers; some lobes are assymetrical) the valve will open .544" - a little over half an inch. The lift at the cam lobe is .544" divided by the rocker ratio. So, at 27 degrees before top dead center at the end of the exhaust stroke (piston's still on its way up), the intake lobe will be open .006". The valve will be open your rocker ratio X .006". 270 crank degrees later, the intake will be almost closed again - it will have returned to .006" lobe lift. If your lobes are symetrical, the peak lift will occur halfway between those points - (270/2) - 27 = 108 degrees ATDC. When they tell you to install it on a "108 Centerline" that's what they're talking about. However, I always use the .050" intake lift numbers to do the install because some lobes are asymetrical and it's hard to determine the centerline or peak lift point. The same dynamics are at work on the exhaust side (it opens to .006" 74 crank degrees before the piston reaches bottom dead center), and it closes to .006" lobe lift 22 crank degrees after tdc. That's during the overlap period - since the intake started opening 27 btdc, this cam has 27+22=49 degrees of overlap at .006" lift. You can work out the same math/relationships with the .050" lift numbers. The reason those are presented is that as a practical matter, significant flow past the valve begins to occur around .050" lift. Hope that helps.

Go here and read -- look at the chart. It's a great graphic that will help you understand what's happening. http://www.wighat.com/fcr3/timing.htm
 
#4
Lastly, the 1.6 vs. 1.7's won't much difference on p to v clearance. Look at your cam card - it should tell you at what degree the .050" lift occurs. For that cam it's probably gonna be with 5 degrees of tdc. It's right around there that your minimum p to v clearance will occur. So, .050", which is about .080" at the valve -- if that's the lift at minimum valve clearance with 1.6's, it's only .085" with 1.7's. 5 thousandths of an inch difference. Unless you're right on the edge of clearance, the rocker won't affect you much. You're looking for .080" intake and .100" exhaust minimum clearances.
 
#6
Mike, wow man, thanks for all of the info. I was just playing with numbers since I was bored, but I had the feeling it wasn't going to work that way. The lift numbers I gave you are with the 1.7's calculated in. According to comp, the cam is technically designed to work with the 1.7's. With the 1.6's, it would be .512" lift. Yeah, I found the overlap when I was doing my mathematics, but don't really know what to compare that too. The overlap is for the exhaust scavenging right? Is that a lot of overlap or not much?

When you say that their should be a degree for when the .050" lift occurs, do you mean the 218/224 duration that it has? Also, for the 108 intake center line, is that what it is at if I install the cam with the dots on the timing chain being straight in line, or straight up or whatever it is called? I will be checking the p/v clearance for sure, I was just running some numbers through my head, seeing if I can theoretically figure out anything.

Just trying to teach myself a bit. Thanks for the help.
 
#7
5.0GT - happy to try and help. Yes - installing it at the 108 centerline is what should happen if you install dot to dot - but that's in a perfect world. Unless all the bits and pieces are completely accurate (cam grind, cam pin hole, cam gear pin hole, crank keyway, crank gear keyway, etc.), installing dot to dot can result in them being as much as 4-6 degrees off. That's why using an indexed timing set (adjustable) and degreeing the cam is so important. That way you can move it around to whatever is needed to assure that the intake valve "opens" (.006" lobe lift) at 27 degrees btdc.

Yes again - the 218/224 duration numbers correspond to the .050" lift duration. There should be intake/exhaust open/close numbers that correspond to that lift on the card too. I'd expect that the intake open .050" number would be somewhere between 5 degrees before, and right at tdc. As I mentioned before, unless you're absolutely certain the lobes are symmetrical, I wouldn't use the centerline to degree the cam. I'd degree it so the .050" intake opening occurs when the cam card says it should.

As for comparing overlaps, it's better to compare it at .050" - tells you a bit more about what's going on. But for example, the stock HO cam (89-95) has 39 degrees of overlap at .006"; the Cobra cam has 32.5; yours has 49 degrees. It's complex (read more at the cam site above to learn about it; I'm a novice at best), but at lower rpm there's more reversion - where the exhaust pressure/flow in the cylinder either limits flow into the cylinder from the intake, or even 'reverts' slightly into the intake manifold. It's what reduces idle vacuum on 'cammed' engines; and it contributes to the lopey idle. At higher rpm the effect is different; more mixing of the incoming intake stream with the outgoing exhaust stream; or more intake port velocity allowing greater cylinder filling/pressures. So you begin to see why, very generally, if everything else is equal (and it never is!) with more cam, the power band shift higher in the rpm range. The engine makes more power higher, and less power lower. I've way oversimplified to illustrate the point. People who know much more than me have written volumes on this -- read all of Buddy's site (above). There's a wealth of info about how complex it is and how it actually works.
 
#9
I've found if you're patient, and go slow, with a degree wheel, the cam card and a dial indicator you can learn a bunch about what actually goes on with all this. I just read up on it a bit, and then sat down and degreed my first one by myself. Actually, I think you'll find that the toughest part is stuff like getting the dial indicator lined up the way you want, and where do you put the magnetic stand when you've got aluminum heads. And they don't teach squat about degreeing cams, cam timing or 'intake reversion' in engineering school - at least not the one I went to. :)
 
#10
Michael Yount said:
Unless all the bits and pieces are completely accurate (cam grind, cam pin hole, cam gear pin hole, crank keyway, crank gear keyway, etc.), installing dot to dot can result in them being as much as 4-6 degrees off.

Yes again - the 218/224 duration numbers correspond to the .050" lift duration. There should be intake/exhaust open/close numbers that correspond to that lift on the card too. I'd expect that the intake open .050" number would be somewhere between 5 degrees before, and right at tdc.
Click to expand...

That's the thing though, the cam card has no mention of what the numbers are at that lift. The only numbers it shows is the duration at .006, the duration at .050, and the stuff that I previously mentioned. So how do I degree it to what is the "ideal" degree for the cam?
 
#11
You can simply set it up at the .006 numbers; however, contact the cam manufacturer or their website. The valve event timing at .050" lift is certainly available even if it's not on your cam card. And remember, there's a coorelation between the event timing at .006" and .050" -- it's not like you're gonna get a completely different result if you use one rather than the other. I just like to use the .050" numbers since that's where signficant flow practically begins. And I usually check all the other numbers (.006" open/close intake/exhaust, .050" close intake/.050" open-close exhaust, and peak lift measurement and where it occurs) just to be sure that the cam grind is what it's supposed to be. You have 8 events to choose from - 10 if you include the centerline points (C/L intake and exhaust, .006" int/exh open, .006" int/exh close, .050" int/exh open, .050" int/exh close). Theoretically you can degree to any one of those, and all the rest are set by the cam grind; in other words, change your install relative to any one of those 10 points, and the other 9 change accordingly.

The specs look familiar - is that the CompCams XE270? If so and you go to their website (www.compcams.com) you can probably download a more complete cam card.
 
#12
I just did this on my car and I have some suggestions. As far as degreeing goes - do it with the heads off the car and you can use the block deck for the magnetic base of the dial indicator. To make a long story short, use the lifter body flat area at the top of the lifter next to the plunger to set your dial indicator on. I tried the "solid lifter" deal and it was not reliable/repeatable - take my advice and use the lifter body flat next to the lifter plunger - when I used that I got good repeatable results. I took vavle events at 3 places - .0005", .005" and .050" of lift. The dial indicator should have .001" between the dial face markings, so finding .0005" is rather easy. I took that value just to see absolute total lift values.

once you see that .0005" of lift, then go .005" more lift as read on the dial face and mark your valve event, continue to .050" lift and take the value again. When comming down the other side to the cam, go all the way down to where the lifter is on the base circle and the dial does not go any lower and reverse your ratchet and mark the .0005", .005" and .050" events again. Do this for intake and exhaust.

Edit: BEfore you clay, you must measure deck height. Do this by using the dial indicator to find TDC and then lay a good stell ruler edge across the piston and use a set of feeler guages to measure the gap if there is any. Most Ford 5.0 cars have zero deck (piston even with block) or negative deck (deck below piston top). Measure your P-V clearance on the piston with the most negative deck - end edit. When you do the claying, go to an art supplier store and find modeling clay that can be set by baking in the oven. I bought Sculpey brand "oven bake clay" in a two ounce size for $1.50. I used this clay and when I was done, I gingerly removed the clay pieces from the piston and set them on a piece of aluminum foil which I put in the oven for 15 minutes at 275°. When the clay comes out of the oven, it has the consistancy of a light rubber and will not distort when you cut it into section to measure - VERY important! You need to check the cross section at several places and the thinnest is likely to be at the edges ot the valve relief eyebrows. I am thinking of doing a write up on this with pictures for posting on the veryuseful.com web site.

I'm posting my final valve info here for you to see the measurements I took. My can is one of the early 87-88 high ramp rate cams, so your may not come out with as much duration. When I put this in an Excel spreadsheet i did for comparing cams, I found my stock cam is VERY close to the Crower 15510 cam with the eexception being mine has a little more intake duration............
 
#13
Wow, tons of info right there. Mike, yes it is the XE270HR, I didn't know if I should come out and say it right away, in case some of these specs were supposed to be hidden from other peoples view. I went to the website and still cannot find the valve event timing at .050". It had even less info about the cam then the cam card has. Perhaps I should call comp and see what they say. Is there a way to find out by just using the dial indicator?

The heads will be off the car when I do this, because I will be throwing on some ported stockers. Tmoss, when you say I should measure the most negative deck height, do you want me to leave the crank in that position, and move the cam by itself? I always just planned on applying the clay, and rotating the crank several times so that it presses it to where it should be.

I won't be using solid lifters, but I have some of the dummy springs that you can compress easily with your fingers. Comp said they will compress so easy that there is no way the hydraulic lifter will compress at all. WIll that be ok, or should I still go with solid lifters? Good idea on the oven baking, I never thought of that. I was just going to use model clay like you said, and see if I could get an accurate reading.

Thanks again guys.
 
#14
You won't ever go wrong with tmoss' advice - nice paragraph Tom.

With stock valves and reliefs, there's little need to measure valve edge to edge of relief clearance; that can only be done with clay - unless I need that measurement (.06 - .08 min for our revs), I prefer the drop valve technique because it gets me out of the vagueries of the clay business. The downside is the valve springs have to come off.

Be careful on CompCams advice regarding test spring rates vs. the plunger on the lifter. YOU MUST WATCH the plunger carefully on all these measurements. I've seen new heads/new valve seals that had enough stiction in them to compress the plunger even with a light test spring. So there is no one-size-fits-all answer to the issue of lifter plunger compression - whatever technique you use you must watch to be certain you're not depressing the plunger during measurements.
 
#15
I can help you out with the .050" lift events possibly - if your cam is one of the cams in this illustration. I wrote a simple Excel program to calculate the events. My cam is in there too...........
 
#18
No need to start another thread. I was reading up on the methods of checking p/v clearance. The drop valve seems so easy, so why would I bother with having to take off the heads and having to retorque them multiple times to do the clay method? I figure the main reason why the drop valve method would be effective is because I am sticking with the stock valves and pistons, so there is already reliefs that are the right size for me. I was thinking of just installing the cam in there and then checking the clearance before even touching the heads(except for installing the 1.7's to check that).

Questions though, because of stock valves and stock pistons, does that mean there is no reason for me to check the clearance between the edge of the valve head and the side of the valve relief? I want to absolutely make sure this cam will fit right. Also, is there any difference in checking them with the stock single valve springs, as opposed to the double valve springs I am going to get?

Just one more question, with the drop valve method, do I have to worry about the hydraulic lifter compressing at all? It doesn't seem as if there will be much pressure on it, but I just want to find out for sure.

Thanks again for the help.
 
#19
You always have to be sure that you're not compressing the plunger in the lifter. As I mentioned earlier, I've seen seals that create enough friction on the stem that when you rotate the engine with light test springs it will still depress the plunger. So, when I check I take the springs completely off, and when I'm mapping the valve seat to piston top clearance, I simply move the valve up and down by hand (fingers on the stem) - the rocker isn't in place at all. 5 degree increments starting at about 20 btdc and going to 20 after. Once that's done for both intake and exhaust, then set you dial indicator up on the lobe or pushrod, and map the lift at the same 5 degree increments. Multiply by the rocker ratio, and subtract that resulting valve lift from the piston seat to top measurement at each 5 degree increment. The result is your p to v clearance. The plunger stays up the whole time.

I believe with stock valves and reliefs your edge clearance will be fine.
 
#20
I am not sure if I follow exactly what you are saying Michael. Where exactly are you measuring then if you don't have the rockers on? I planned on doing it just like Mouse's page shows where you take the spring off, keep the rocker on, and use a feeler guage to see what my clearance is. With the valve spring off, there should not be any compression of the lifter right? Then I lightly press on the back of the rocker to mate it with the pushrod, to get an accurate measurement of the clearance. I will go throughout 30 degrees BTDC to 30 degrees ATDC to see what is my minimum clearance. Sound good?

Also, do you check every cylinder when you do it, or which ones should I check?

Thanks
 
You must log in or register to reply here.

Similar threads

mustang matt 1993
Engine Valve and or rocker noise .....new to this but dont mind getting my hands dirty.
Replies
16
Views
2K
Fox 5.0 Mustang Tech
rednotch
rednotch
6
Hey all,I’m putting together a 302 for my 1968 Mustang and wanted to post the combo + some questions to make sure I’m not missing crucial
Replies
4
Views
938
1965 - 1973 Classic Mustangs -General/Talk-
gray owl
G
Boydster
SOLD SOLD!!!! 1993 Notchback Roadracer For Sale. She's a beast!
Replies
0
Views
1K
Fox Body Mustangs For Sale (1979-93)
Boydster
Boydster
A
Fox Planning on building my foxbody and was wondering if I can get any tips or anything to watch out for!
Replies
76
Views
5K
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Robman8028
R
ChillPhatCat
Specific Cam Questions that Google can't seem to answer...
Replies
3
Views
803
2.3L (N/A & Turbo) Tech
ChillPhatCat
ChillPhatCat
Top Bottom
Back
Forums
Menu