# HMMMMMM! A POTENTIALLY CONFUSING REVIST OF TIMING AND CAMS



## armyadarkness (Dec 7, 2020)

So, I was going to figure this out on my own, but my head exploded, so I figured I'd let you experts chime in on it.

I've really been wrestling with performance since December of 2020. Power is lower than I want it to be and it WAS better before I started tweaking the timing. Man I have tweaked this timing to beyond the realms of what mortal man was meant to do... I've had more than 30 American cars and all I ever did with any of them was to set the timing to the emissions label... Which worked well.

I also hate my cam... So I ordered a new one from Butler. And as I was comparing the specs today, I noticed that my old cam was degreed to 106, giving it four degrees of advance. So...

I have my base timing at 15 degrees, 10 degrees of vac advance, and 21 degrees of mechanical... So does this mean that my base timing is actually 19 degrees and my total is now 40 degrees? Or is my timing light compensating for this?

Seems to me that I would need to make a new timing mark. Thought's on this?









And here's the new cam...
BP/COMP Custom Cam- 3316-3317-HR112
(HR) (Std Firing Order/ Std Journals) 288/294, 236/242, .521/.540, 112+4 LS
Same as the Comp 433 with wide lobe separation


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## armyadarkness (Dec 7, 2020)

Degreeing a Camshaft - Bang, Suck, Blow...Sooner Or Later - Mopar Muscle Magazine


We answer an important question: is degreeing a camshaft worth the time? we find out. Click here for more details or check out the December 2012 issue of Mopar Muscle Magazine.




www.motortrend.com


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## PontiacJim (Dec 29, 2012)

armyadarkness said:


> Degreeing a Camshaft - Bang, Suck, Blow...Sooner Or Later - Mopar Muscle Magazine
> 
> 
> We answer an important question: is degreeing a camshaft worth the time? we find out. Click here for more details or check out the December 2012 issue of Mopar Muscle Magazine.
> ...


DO NOT ADVANCE THE CAM 4 DEGREES! The 4 degrees is already built into the cam - UNLESS the cam supplier/grinder says otherwise. Set the cam at what the manufacturer states - which should be "straight up" lining your timing marks dot-to-dot.

The "+4" is added to give you 112. If you degree the cam, and it degrees in at 108, but the Intake Centerline is shown as 112, then this means the cam has 4 degrees ground into it. The cam card will tell you what to set the Intake Lobe Centerline (ILC) when degreeing the cam - my bet is 108. The 112 LSA is the average of the Intake LC (ILC) and Exhaust LC (ELC). The average centerline between both lobes and expressed in degrees ranging from 95 on the extremely narrow/tight side to upward of 120 on the wide end.

108 ILC + 116 ELC = 224 degrees divided by 2 = the 112 LSA.

Your old cam shows ICL of 106 - this is for degreeing. But your LSA shows 110. So the cam had 4 degrees ground into it. If you advanced it 4 degrees, (if I am correct this gets divided by half), you moved the ICL to 104 and the LSA to 108. Should equal plenty of bottom end power, but dies at upper end - my guess.

The crank should be at TDC which is what the balancer reflects - that does not change. You changed the crank gear in relationship to the cam, ie altered it. You did not change the crank position as related to TDC. From my understanding - What has changed is the ignition timing up at the rotor/distributor. So you should now re-adjust for that with the Initial timing at the crank, your timing curve, and your Total mechanical.

Read this from Summit:






Advancing / Retarding a Camshaft







help.summitracing.com


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## BearGFR (Aug 25, 2008)

You probably already know this, but just in case: Cam timing and ignition timing are two completely separate animals/concepts. The only thing they have in common is the word "timing". Changing neither one has any effect at all on the other.

When the information on a cam card say something like "degree intake lobe to 106", like your cam card does, it means for you to use a degree wheel to verify that the point of maximum intake lobe lift occurs at 106 degrees ATDC (After Top Dead Center). It's not easy to "eyeball" the point of peak lobe lift, so it's better to use a dial indicator in conjunction with the degree wheel and find the two degree readings that result in .050 lift UNDER peak on both sides of the lobe, then use the degree point "in the middle" of those two as the point where peak lift occurs. When you're doing that, don't turn the engine backwards - always turn it in the same direction it does when it's running so as to negate any slack that might be present in the timing chain.

Lunati has a pretty good explanation of the process here: Lunati Cam Degreeing Process 

Why do you need to degree a cam at all instead of just lining up the timing marks? Because of the possible variances in manufacturing of all the parts involved including the timing gears themselves, the cam itself, the marks on the balancer, etc. It's not uncommon to have to use a timing set with several possible adjustment points in order to get the cam intake centerline lined up exactly where the vendor says it should be.

Bear


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## armyadarkness (Dec 7, 2020)

PontiacJim said:


> DO NOT ADVANCE THE CAM 4 DEGREES! The 4 degrees is already built into the cam - UNLESS the cam supplier/grinder says otherwise. Set the cam at what the manufacturer states - which should be "straight up" lining your timing marks dot-to-dot.
> 
> The "+4" is added to give you 112. If you degree the cam, and it degrees in at 108, but the Intake Centerline is shown as 112, then this means the cam has 4 degrees ground into it. The cam card will tell you what to set the Intake Lobe Centerline (ILC) when degreeing the cam - my bet is 108. The 112 LSA is the average of the Intake LC (ILC) and Exhaust LC (ELC). The average centerline between both lobes and expressed in degrees ranging from 95 on the extremely narrow/tight side to upward of 120 on the wide end.
> 
> ...


Thanks Jim. LOT"S to soak in. As ya'll know, Ive only recently delved into the world of timing. I understand how it works and what each component is made for, but I don't yet understand how the different settings affect performance.

So... yes I understand advance, retard, overlap, las, lift, etc., but still trying to learn why one helps or hurts performance at different times. 

As I look at the above cam card, it would lead me to believe that they want the installer to advance the cam.


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## armyadarkness (Dec 7, 2020)

BearGFR said:


> You probably already know this, but just in case: Cam timing and ignition timing are two completely separate animals/concepts. The only thing they have in common is the word "timing". Changing neither one has any effect at all on the other


I just found that out yesterday!


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## armyadarkness (Dec 7, 2020)

Confused or not, I will be installing the new cam with the gears exactly as the old ones are, dots at 12 and 6.


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## PontiacJim (Dec 29, 2012)

armyadarkness said:


> Thanks Jim. LOT"S to soak in. As ya'll know, Ive only recently delved into the world of timing. I understand how it works and what each component is made for, but I don't yet understand how the different settings affect performance.
> 
> So... yes I understand advance, retard, overlap, las, lift, etc., but still trying to learn why one helps or hurts performance at different times.
> 
> As I look at the above cam card, it would lead me to believe that they want the installer to advance the cam.


By advancing or retarding the cam, you are changing the valve events - advancing opens the intake and exhaust sooner; retarding opens the valves later.

By changing the advance/retard you are building or dropping cylinder pressure. Advancing can make the cam *seem more* aggressive and the engine responds better at the bottom end, but falls off on the top end. Retarding the cam can "soften" the bottom end ( an attempt to keep from breaking tires loose) and pics up at the top end to stretch the RPM's a little.

Read this:






Does Cam Timing Affect Ignition Timing?


Bad-Ass Racing Engines specializes in building some of the baddest street and race engines around!



www.badasscars.com


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## BearGFR (Aug 25, 2008)

armyadarkness said:


> As I look at the above cam card, it would lead me to believe that they want the installer to advance the cam.


No, they want you to install it so that peak lift on the intake lobe "lines up" with 106 degrees ATDC on the crank. 
Watch these videos









Bear


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## armyadarkness (Dec 7, 2020)

BearGFR said:


> No, they want you to install it so that peak lift on the intake lobe "lines up" with 106 degrees ATDC on the crank.


I've been reading some of your old posts and although I have installed the timing gears at 12 and 6 in the past, I see that I can do 12 and 12 as well... depending on whether I want the dizzy on compression or exhaust. Seems like 12 and 6, and then rotating 180 is the easiest?

In any event, okay, so Im not advancing my cam upon install, but since Comp ground 4 degrees into the cam, Im still not clear about if I should be considering that in my total timing adjustments. From what Jim said previously, I thought that maybe I should?


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## armyadarkness (Dec 7, 2020)

PontiacJim said:


> By advancing or retarding the cam, you are changing the valve events - advancing opens the intake and exhaust sooner; retarding opens the valves later.
> 
> By changing the advance/retard you are building or dropping cylinder pressure. Advancing can make the cam *seem more* aggressive and the engine responds better at the bottom end, but falls off on the top end. Retarding the cam can "soften" the bottom end ( an attempt to keep from breaking tires loose) and pics up at the top end to stretch the RPM's a little.
> 
> ...


Jim,

The new cam has less intake lift, but more exhaust lift... More duration, a bigger LSA, and no 4/7 swap! I hope that performance is substantially improved... and that that it finally SOUNDS like a GTO. It's embarrassing to have a car that's such an attention magnet, sound like a Chevy v6 with a california turbo.


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## armyadarkness (Dec 7, 2020)

So what are they referring to when they say "These specs are for a cam installed @108 Intake Center Line", on the card?


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## armyadarkness (Dec 7, 2020)

PontiacJim said:


> By advancing or retarding the cam, you are changing the valve events - advancing opens the intake and exhaust sooner; retarding opens the valves later.
> 
> By changing the advance/retard you are building or dropping cylinder pressure. Advancing can make the cam *seem more* aggressive and the engine responds better at the bottom end, but falls off on the top end. Retarding the cam can "soften" the bottom end ( an attempt to keep from breaking tires loose) and pics up at the top end to stretch the RPM's a little.
> 
> ...


That was a good article. 

So if I understand correctly... Ignition timing at 36 degrees BTDC means that the plug will fire then, however, cam timing merely dictates what position the vales will be in at that point?

If so, then Comp grinding in 4 degrees of advance, means that my intake valve will open 4 degrees ahead of TDC?


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## BearGFR (Aug 25, 2008)

armyadarkness said:


> So what are they referring to when they say "These specs are for a cam installed @108 Intake Center Line", on the card?


It means that all the other event timings on the cam card, such as when the valves open and close (the specs listed under the heading: *VALVE TIMING OPEN CLOSE*) will be correct _ONLY_ if the cam is installed with the intake lobe centerline at 108 BTDC. If you were to install it, say with the ICL (intake lobe centerline) at 106 instead of 108, then all of the specs listed under VALVE TIMING OPEN CLOSE would be changed by the difference - 108-106=2, so they'd all likewise "move" by 2 degrees.



> So if I understand correctly... Ignition timing at 36 degrees BTDC means that the plug will fire then, however, cam timing merely dictates what position the vales will be in at that point?


Correct. The two "measurements" refer to completely different things. Changing one of them _does not change the other one._



> If so, then Comp grinding in 4 degrees of advance, means that my intake valve will open 4 degrees ahead of TDC?


No. Look at the specs on the cam card. They say that _IF _you install the cam with the intake center line at 108, then the intake valve will _begin_ to open at 57 degrees BBDC (_Before Bottom Dead Center)_ and will have reached 0.050 tappet lift at 10 degrees BTDC (_Before Top Dead Center)_

Why are there two specs? Because for a long time, there was no standard with regard to what "valve open" meant. This refers to what's called "advertised duration". The situation was that every different manufacturer had a different definition for "valve open" and "valve closed". Summit has a good explanation here.

For example, take the famous Pontiac factory Ram Air IV cam. "Advertised Duration" on that cam was 308 degrees intake, 320 degrees exhaust. That's a ton. But what they didn't tell you about that cam was where, as in at how much tappet lift, those numbers came from. It got really confusing and made it hard to compare cams based on duration, because everyone had different begin and end measuring points for the numbers. 

Finally, some many years ago, someone called a stop to the madness and got everyone to agree to a standard. Duration measurements will be taken beginning at the point where the tappet/lifter has be "lifted" off the cam base circle by 0.050 and will end on the closing side at the point where the lifter reaches 0.050 lift during closing, ostly because by some miracle everyone was able to agree that no _significant _ flow happens at less than 0.050 tappet lift. 

Using the 0.050 standard, that same Ram Air IV cam has a duration of 231 degrees intake, 240 degrees exhaust. Not nearly as radical as it first appears. (However that's still quite a bit for a _flat tappet_ cam because of the overlap period that results from having to deal with the geometry imposed by using flat tappets, and that's what makes that cam pretty radical. The opening and closing ramps can only be "so steep" before the edges of the lifter start digging into the cam lobes. That also explains why there's such a big difference between the _advertised _ duration numbers and the 0.050 tappet lift numbers and the Ram Air IV cam. 

By way of comparison, the first solid roller I ran in my engine had 0.050 duration numbers of 236/242 and advertised duration numbers of only 273/279, made possible because it was a roller. It had a good idle and made 15" of idle vacuum in my 461. The cam I'm running now, also a solid roller, has 251/257 at 0.050 and an advertised duration of only 281/287. Significantly "rowdier" than the Ram Air IV but still doesn't have as much advertised duration or overlap as it did. 

Had it been a roller, they could have gotten the same 0.050 duration numbers with much steeper ramps, which would have made the advertised duration numbers a lot smaller.

Back to "what does 4 degrees advanced "ground in" mean?
My opinion is that the "ground in" advance/retard numbers have only one purpose, and that's to confuse people. As if things weren't confusing enough already.

How do you even know what that is, since Comp didn't show that on the cam card? It's computed from two numbers that ARE provided on the cam card: Lobe Separation Angle (aka "LSA") and recommended installed Intake Center Line (aka ICL). What's LSA really? Again, Summit has a good explanation here. Why do we care about LSA? Because the LSA combined with the "steepness" of the opening/closing ramps on the cam determine the overlap period - the period of time that both intake and exhaust valves are open. Why do we care about overlap? Because that is the primary factor that affects how well the engine runs at idle and very low RPM, and also determines how efficient the engine is going to be at high RPM. More overlap gives you more of that lopey/rumpity-rump idle that people associated with a 'hot' cam, but what it also does is kill low RPM torque. That rough idle really means that the engine is having such a problem with reversion that it can barely stay running. Lot's of overlap is good, even _required,_ for making torque and horsepower at high RPM - but it comes at the expense of low RPM drivability. 

To compute if the cam is ground "straight up", "advanced", or "retarded" --- is simple. If the recommended install ICL is _the same as_ LSA, then the cam is ground straight up - the intake and exhaust valves both open at the same number of crank degrees. If the recommended install ICL is _less than_ the LSA, then the cam is ground advanced by whatever the difference is. (112-108=4, in your case) - . If the recommended ICL is _greater than_ the LSA, then the cam is ground retarded by the difference. All these measurements _*assume* _that the recommended ICL will *"happen"* if you install the cam with the crank and cam gear timing marks in their original, factory specified orientation. (But like I said in an earlier post, sometimes that doesn't happen for various reasons.) So, all the "ground in" number really means is how the cam _SHOULD_ end up if you install it "stock" - as in "timing mark to timing mark", but it's just an assumption.

So, the only way to be certain that your ICL ends up where the cam grinder recommends, is to use a degree wheel and measure it yourself using the process described in the videos.

Sometimes, _but only on very rare occasions, _ it can be an advantage to deviate from what the cam grinder recommends as far as installed ICL. However, you have to have a very good reason for doing it and also have a full understanding of what you're trying to achieve by doing it. "Advancing" means that the valve events, both opening and closing, will be happening earlier than what the cam grinder thought was the optimum for the application, "retarding" means they happen later. Again, not to be done unless you really know what you're doing.

Cheers,
Bear


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## Baaad65 (Aug 29, 2019)

BearGFR said:


> It means that all the other event timings on the cam card, such as when the valves open and close (the specs listed under the heading: *VALVE TIMING OPEN CLOSE*) will be correct _ONLY_ if the cam is installed with the intake lobe centerline at 108 BTDC. If you were to install it, say with the ICL (intake lobe centerline) at 106 instead of 108, then all of the specs listed under VALVE TIMING OPEN CLOSE would be changed by the difference - 108-106=2, so they'd all likewise "move" by 2 degrees.
> 
> 
> 
> ...


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## BearGFR (Aug 25, 2008)

Baaad65 said:


>


LOL - read through it slowly, take your time, follow the links. Once you understand it, it's not nearly as complicated as it looks at first glance.


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## armyadarkness (Dec 7, 2020)

Thanks Bear. It's all starting to sink in and make sense, although I do agree that it's made a little more complicated than it needs to be. This cam in particular is a custom Comp Cam grind, made specifically for Butler... I still can't tell if it's a good cam or better than the one that I have now... I merely told them my issues and that's what they told me to use.


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## armyadarkness (Dec 7, 2020)

Ive spent a year of my life and a ton of money, trying to make this car act like a GTO... I hope this cam helps


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## Baaad65 (Aug 29, 2019)

BearGFR said:


> LOL - read through it slowly, take your time, follow the links. Once you understand it, it's not nearly as complicated as it looks at first glance.


Always wondered why there were two duration numbers, makes it so unnecessarily confusing


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## armyadarkness (Dec 7, 2020)

Yeah... I feel like Im some dumb ass when I have to keep asking people on the internet what the numbers mean... yet look at Butlers description for it:

BP/COMP Custom Cam- 3316-3317-HR112
(HR) (Std Firing Order/ Std Journals) 288/294, 236/242, .521/.540, 112+4 LS 

My feeling is that I should be able to look at the specs for this cam and my old cam, and know which is more radical. I'm a little worried that this new cam, which is supposed to be more radical, has less lift than my old cam.


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## Baaad65 (Aug 29, 2019)

armyadarkness said:


> Yeah... I feel like Im some dumb ass when I have to keep asking people on the internet what the numbers mean... yet look at Butlers description for it:
> 
> BP/COMP Custom Cam- 3316-3317-HR112
> (HR) (Std Firing Order/ Std Journals) 288/294, 236/242, .521/.540, 112+4 LS
> ...


Then there's always 1.65 rockers


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## BearGFR (Aug 25, 2008)

armyadarkness said:


> Yeah... I feel like Im some dumb ass when I have to keep asking people on the internet what the numbers mean... yet look at Butlers description for it:
> 
> BP/COMP Custom Cam- 3316-3317-HR112
> (HR) (Std Firing Order/ Std Journals) 288/294, 236/242, .521/.540, 112+4 LS
> ...


Do you still have your old cam card? Post it up and we'll have a look. 

There's more to it than just raw lift. This concept called "area under the curve" matters too. You can compensate for lift, up to a point, by adding more duration - instead of holding the valve open more, you just hold it open longer. Plus the advantage of not increasing (or even decreasing) lift is that it can help avoid having to change valve springs and/or machine the heads to allow for more valve travel without driving the springs into coil bind - up to a point. That point being if you change from a flat tappet cam to a roller that has really aggressive (steep) ramps and there's a lot of mass in the lifter/pushrod/rocker/spring/retainer/valve assembly, those steep ramps can accelerate the lifter so quickly that they "throw" the lifter off the lobe even though they have the same net lift, requiring stiffer/heavier springs to keep that from happening. That's a bad thing. Engines usually don't live long when that happens.

As far as performance, what you're getting is very similar to the specs on the solid roller I ran previously, and my car turned an 11.86 @113 mph quarter mile with that cam.
I've attached the card from it. Those gross valve lift numbers are with 1.5:1 rockers, and I ran 1.65's with it which both added a taste more duration and also netted slightly over .600 lift at the valves after compensating for lash. 










After I had a problem with rockers on the 2016 Power Tour, I decided that I didn't like 1) 1.65 rockers on the street or 2) aluminum rockers. So I replaced it with a new cam from Bullet that actually makes MORE lift and duration than the one above did, and does it with 1.5:1 rockers. I also went with Crower stainless steel full roller rockers.

Bear


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## armyadarkness (Dec 7, 2020)

BearGFR said:


> Do you still have your old cam card? Post it up and we'll have a look.
> 
> There's more to it than just raw lift. This concept called "area under the curve" matters too. You can compensate for lift, up to a point, by adding more duration - instead of holding the valve open more, you just hold it open longer. Plus the advantage of not increasing (or even decreasing) lift is that it can help avoid having to change valve springs and/or machine the heads to allow for more valve travel without driving the springs into coil bind - up to a point. That point being if you change from a flat tappet cam to a roller that has really aggressive (steep) ramps and there's a lot of mass in the lifter/pushrod/rocker/spring/retainer/valve assembly, those steep ramps can accelerate the lifter so quickly that they "throw" the lifter off the lobe even though they have the same net lift, requiring stiffer/heavier springs to keep that from happening. That's a bad thing. Engines usually don't live long when that happens.
> 
> Bear


My old/ existing cam card was posted at the beginning of this thread!


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## armyadarkness (Dec 7, 2020)

Butler did mention that their cam didn't have a ton of extra lift, but it did have much better duration.


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## armyadarkness (Dec 7, 2020)

Baaad65 said:


> Then there's always 1.65 rockers


I was under the impression that everyone here swore against 1.6 ratio rockers on my engine?


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## Baaad65 (Aug 29, 2019)

armyadarkness said:


> I was under the impression that everyone here swore against 1.6 ratio rockers on my engine?


Right, you have to have the right prep first, I wouldn't just throw them on anything stock motor. My heads were prepped by Butler for them and said so in the head build sheet and I have a full roller setup, I'm no expert by any stretch I was just throwing it out there but I've learned you need elongated pushrod openings, the right springs to avoid coil bind, screw in studs and then it still puts more stress on the valve train. Probably better to just get a bigger cam.


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## Jared (Apr 19, 2013)

armyadarkness said:


> I've been reading some of your old posts and although I have installed the timing gears at 12 and 6 in the past, I see that I can do 12 and 12 as well... depending on whether I want the dizzy on compression or exhaust. Seems like 12 and 6, and then rotating 180 is the easiest?
> 
> In any event, okay, so Im not advancing my cam upon install, but since Comp ground 4 degrees into the cam, Im still not clear about if I should be considering that in my total timing adjustments. From what Jim said previously, I thought that maybe I should?
> View attachment 147157


You can install the cam in either orientation. You install the distributer to point at whichever terminal you want to be #1 after the fact. Advantage of installing the cam in the 12 and 6 position is the marks are easier to line up. Also, make sure you turn the engine over a few times by hand after you install the timing set to make sure the marks keep lining up. I didn't degree my cam on mine and installed it straight up as Jim described. You probably already know this but pick all your other components first and order the pushrods last. Mine ended up being way longer than the stock size from the old engine. You want the contact point of the rocker to be dead center on the valve stem. I colored the top of the stems with Sharpy, installed one of the new lifters, used the test valve springs and an adjustable pushrod and rotated the engine over a few times. While this is the first one I've ever done, this is what it should look like This was on mine after cam break in, the Sharpy was still n there).


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## PontiacJim (Dec 29, 2012)

armyadarkness said:


> Yeah... I feel like Im some dumb ass when I have to keep asking people on the internet what the numbers mean... yet look at Butlers description for it:
> 
> BP/COMP Custom Cam- 3316-3317-HR112
> (HR) (Std Firing Order/ Std Journals) 288/294, 236/242, .521/.540, 112+4 LS
> ...


Just compare the advertised duration numbers 288/294, the lift numbers .521/.540, and the LSA between this cam and your old cam. Don't get bogged down with the second number, 236/242. This is the cam's duration at .050" lift. The 288/294 is no lift. If you use the .050" lift number, then you want to compare it to another cam that also provides the cam lift at .050". Only then can you see which cam is more aggressive based on the intake/exhaust duration numbers at .050" lift.

The standard spec used for factory cams across the board during the 1960's was set by the AMA organization which set the standards for car manufacturers. If you look at a factory cam spec, it will show duration at .006" cam lift. Why? Because it was decided that at .006" of lift that all the slack was taken out of the lifters/pushrods/rocker arms. This was the point at which all parts no longer had any play and the valve was now being physically pushed open and lifted off its seat.

So the aftermarket cam guys would offer assorted cam grinds and you did not know if they were advertising cam duration numbers at a cam lift of .006", .018", .037" etc.. So they could make their cam look bigger or more aggressive on paper for advertising purposes and you, the guy looking for the best grind, would select a cam with what you saw as the best specs. BUT, it did not really mean it was the "best" specs because those advertised numbers could be moved all over to "sucker" you in to buy "their" camshaft.

So most all of the cam manufacturers and cam grinders agreed to use cam duration numbers at .050" lift so you the consumer could make a better decision when comparing cams for your build. HOWEVER, this is still not 100% BECAUSE the ramp of the lobe can be contoured in an assortment of shapes/profiles.

I think most of us know what the shape of a flat tappet cam lobe looks like, it is rounded/tear drop in shape. A roller cam lobe has a more straight contour that lifts the roller lifter almost straight up rapidly. You could compare the cam duration at .050" lift on a flat tappet cam and then look at the cam duration of a roller cam at .050". They could actually be the same number, or slightly different. But after that .050" duration number which cam do you think is the more aggressive cam? You would be correct if you picked the roller cam due to its cam lobe profiling that you cannot get out of a flat tappet cam lobe. Grinders like Comp Cams has what is called "steep" ramps which open/close the valve quickly so it stays open longer. The problem is that the valve slams open & slams shut and a number of users complain about the noise - like ticking lifters. You want strong valve springs because if not, the valve can bounce off the seat when it is slammed shut - not a good thing.

So if you compare a flat tappet cam to a roller cam, you are comparing apples to oranges.


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## Baaad65 (Aug 29, 2019)

Man PJ and Bear must have master's degrees in camology, never knew there was that much to a cam...so to compare it to a human if the pistons are the heart and the heads are the lungs then the cam has to be the brains of a motor, and you need the right brain telling how and when to do things or it's not going to work right 👍


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## PontiacJim (Dec 29, 2012)

Baaad65 said:


> Man PJ and Bear must have master's degrees in camology, never knew there was that much to a cam...so to compare it to a human if the pistons are the heart and the heads are the lungs then the cam has to be the brains of a motor, and you need the right brain telling how and when to do things or it's not going to work right 👍


Never knew squat about cams, anymore than most. You just read the cam power band, picked a big duration number, and got a good lift. They sounded good, pulled hard, and I wonder how many times per second a valve kisses a piston or is valve spring clearance really that important? I just selected a cam by what I read or from others recommendations and installed it. And I did not install/swap a lot of cams throughout my lifetime of working on these cars. Back in my day, I used the JC Whitney catalog to look at cam specs (which were basics) and even bought them. Never any issues and they worked just fine. Did not know that speed shops/engine rebuilding shops could get you a cam. There was a lot I did not know back then. LOL

When I assembled by past 400CI, first engine rebuild in 30 years because life had other ideas as to what I could/could not afford, I did research. I had to learn/understand more about cam specs and the terminology than I ever knew existed. Yep, it sure was confusing and so many people have their point of view and explanations as to what makes a cam work and how. But I got a pretty good handle on it. So selecting a cam* IS* the brains of the engine, but it is useless if you do not match all your parts to go with the cam. So in my book, select a cam first, then build your engine around it using matching parts and you are less likely to be disappointed when you nail the gas pedal for the first time.

Did a lot more research putting together a build plan for my present 455 build. The most important thing I have taken away during my 455 build is: PONTIAC ENGINES ARE F'N EXPENSIVE TO REBUILD!


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## BearGFR (Aug 25, 2008)

PontiacJim said:


> Did a lot more research putting together a build plan for my present 455 build. The most important thing I have taken away during my 455 build is: PONTIAC ENGINES ARE F'N EXPENSIVE TO REBUILD!


Indeed they are. One of these days, I swear I'm going to build some bowtie, maybe a 69 camaro, and put a big Pontiac in it just to p*ss people off


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## Jared (Apr 19, 2013)

Expensive is an understatement.


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## BearGFR (Aug 25, 2008)

In case anyone is interested, I just finished degreeing my cam today and I documented the process as a sticky in this section.

Cheers,
Bear


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## armyadarkness (Dec 7, 2020)

Im chomping at the bit to hear the new cam, but Im taking the opportunity to clean and paint the intake, brackets, pulleys, timing cover, and water pump. Found a stripped hole on the PS bracket, o rocker arm installed wrong, and the cam retainer was on upside down, so the the old cam wasnt getting oil! Fixing all of this.

Praying that the new cam makes my car sound like a GTO


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