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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
I'm setting up my Comp Nitrous-HP cam. It's the 08-301-8. Complete K-kit so I'm also using the Comp double-roller timing set. This is on a factory 99 Vortec crank.
I'm supposed to set it on a 108 degree intake center-line. It has a 113 degree lobe separation.
I set it on the O marks and triple check the center-line, and I get 113. So I set it on the "Square" mark for 4 degrees of retard, and now I'm at 109 - so I'm within the magic 1 degree. Great.
Then I read that Comp "grinds the cam with 4 degrees of advance built in"..... so now I'm second guessing. If I had't retarded the cam it would be at 113 which matches the LSA..... but comp says to set it on 108.... but I had to retard it to get it there so what's the point of them grinding it 4 degrees advanced if I have to take that back out anyway?!???
I'm too confused by all the numbers and the way they add up so perfectly in multiple ways.
Can someone please tell me which way is correct?
Why don't they just grind is "Straight up" and let the engine builder decide if it should be advanced or retarded?
Thank you!
GD
Last edited by GeneralDisorder; 10-12-2018 at 10:35 AM.
Why don't they just grind is "Straight up" and let the engine builder decide if it should be advanced or retarded?
what i always heard was most cams come with advance built in because people tend to pick a cam bigger than they need. They install it on a regular timing chain “dot to dot” aka straight up. But because it has 4 feg built in its advanced not straight up
the advance helps bring power in sooner and build low end some. Thus making over cammed engines run a bit better than if it was straight up
so on your timing set whatever marks call for “straight up” no retard no advance, set it there and check centerlines. It should be close to 108 or 109 (comp usually has 4 deg) plus or minus a deg generally
Crap - now that you mention it - perhaps the first time I checked it I was at 105. It was late. I remember now - the total before dividing by 2 was too low at first.... so yes it was 105 (ish). But it did come out to 109 after I retarded it. I've checked it about 6 times now in two sessions and it's definitely at 108.75 (ish) now with the timing set on the square keyway.
I just wanted to make sure that's correct, and it sounds like it is correct if I want to use the factory 4 degree advanced position
Do I want to do that? LoL.
Comp's Camquest software says this thing is going to put down 442 TQ..... which is honestly probably too much anyway. Of course I don't have the option to retard it any further without a different timing set since I had to use the 4 degrees I have just to get it straight up.
Last edited by GeneralDisorder; 10-12-2018 at 12:29 PM.
If its at 109 then leave it, it should be good to go
i would then verify intake valve opening event at .050. Make sure its opening at the right deg value at .050 inch lift at lifter or whatever the cam card states
If its at 109 then leave it, it should be good to go
i would then verify intake valve opening event at .050. Make sure its opening at the right deg value at .050 inch lift at lifter or whatever the cam card states
I checked that and of course the cam card has the intake open and close specs @ .006" (which is .004" at the lifter correct?)...... supposed to be 30 BTDC on the open, and 66 ABDC on the close. I get about 26 on the open, and I did get 66 on the close. It is admittedly a little hard to get those readings. I'll try harder. My assumption was that since I got the correct value of 66 on the close it's probably a testing error with the 26 reading on the open. Why they couldn't just do it @ .050 like everyone else I don't know.
The cam will retard ALL BY ITSELF over time, as the chain wears.
Best to leave it in a little advanced. Better than to start out retarded, or even straight-up, unless that's what you're specifically shooting for.
About the numbers: cam timing is AFTER TDC. Remember, the valve starts opening close to TDC, continues to open as the piston descends, and reaches peak at about 90° of crank rotation (Ľ turn) after TDC. Advancing it brings its peak closer to - i.e. a lesser # of ° after - TDC. Its specs are given in CRANK degrees.
Lobe separation and intake centerline are TOTALLY UNRELATED. Lobe sep is the # of ° that the exh peak occurs BEFORE the intake, while the piston is heading back up toward TDC. It is measured in CAM degrees. Therefore all of that about lobe sep minus whatever, is WRONG. Doesn't work that way. Lobe sep is ground into the cam and cannot be changed during installation; int CL is what the installer can do, and doesn't change lobe sep. The 2 #s are not related to each other, mathematically or otherwise, in any manner way shape form or fashion. If you add and subtract them from each other you get GARBAGE... "correct" garbage, if you do it right, but meaningless GARBAGE just the same.
If Comp says set it to 108° ICL, then set it to as close to 108° ICL as you can get it.
Cam card specs are given at the lobe (.006" and .050"). The valve lift is only provided as an approximate reference, since rockers and other things vary so much.
It's ground 5 degrees advanced (113-108=5, so if you retard it 4 degrees, you'll be at 1 degree advanced...
Yeah I wondered about that. They say 4 degrees built in, but the specs say that if you set it to 108 that would actually be 5 degrees total advance..... what makes my brain hurt is..... if they ground it for 4 degrees advance, and then they want you to install it 5 degrees advanced..... wouldn't that be 9 degrees of total advance?
I dont know what was said above but its not complicated lol
lobe sep is intake centerline plus exhaust centerline divided by 2.
a cam installed staight up is an intake centerline thats the same as the lsa. Advance and retard shift the centerline and is what was discussed here
5 deg advance ground in means the intake centerline is 108 when installed dot to dot. 113 minus 5.
Ok I think I've made the mistake of measuring the intake center line using .050" at the valve retainer...... but I swear that's what the instructions on the degreeing kit said (I am using 1.5 rockers). AHRG! I'll check it at the lifter if that's what I need to do? Or just redo the test with .075" at the retainer? I'll do both! Hhhhmmm that's probably going to mean I will be putting it back to straight up installation....... aaaaannnnddd that's why I ask these questions.
Last edited by GeneralDisorder; 10-12-2018 at 01:30 PM.
GD, you probably already know this, but make sure that when ALL readings are taken that you are rotating the crankshaft clockwise ONLY - never backwards. Especially true when determining true TDC. If you do rotate backwards, you MUST go past where you want and approach your target from the CW direction.
Now forget about all the numbers on the cam card except the 108 degree intake centerline you are trying to achieve.
Whether you position the dial indicator on the lifter side, or the valve side, all you need to do is get to max lift and pick your own distance for either side of that, let's say .100". For example, let's NOT use the valve side because the rocker introduces another variable, so use the lobe side.
Read on the dial indicator what the max lobe lift is. Then rotate the crank backwards more than .100 on the indicator. Then slowly rotate CW and stop when you read .100 and note the degree wheel reading. Rotate CW, past max lift and stop at .100 on the other side. Again note the reading on the degree wheel.
Add the two degree wheel numbers together, and divide that by 2. You should be within 1 degree of 108. Good luck.
For sure - I always make sure to go past the point I'm aiming and then creep up on it CW to insure the chain slack isn't a factor. As an amateur machinist and owner of very old and clapped out machine tools, one has to be very aware of the gear lash and the thread lash. My lathe was built in 1950 and formerly owned by an Alfalfa farmer that regularly turned up new table and chair legs for the wife I'm pretty sure. That dead tree carcass does nothing useful to a metal cutting lathe I can assure you.
I will try your method this evening.
Comp does recommend the intake center-line method, but I've since read other treatise on the subject claiming it's not all that accurate for a lot of modern cams with asymmetrical lobe ramps..... I have no idea if this even applies to my cam. But I don't have the data to say it doesn't either.
After reading more on the subject - I also see what Sofa means about the LSA and ICL being completely unrelated. Although it is interesting that the LSA (minus) - ICL is approximately equal to the advance ground into the cam (it's actually not - it's off by 1 degree). I don't see what the angle in between the intake and exhaust center lines has to do with the angle of the intake center line. Indeed they seem entirely unrelated to me.
As mentioned somewhere up above, moving the cam timing around can change the powerband. Advancing the cam moves the powerband down in the rpm range which is good for the majority of street cars so that's why advance is ground into a camshaft. Retarding a cam moves the powerband upward which is good for race cars needing top end power but even the camshaft in my car is only installed straight up.
LSA as mentioned above is ground into the cam lobes and can't be changed. A typical factory street cam is around 112-114* which makes for a very smooth idle. Performance cams are normally in the 108-110 range. A small block race cam can be at 106 and I don't think I've ever seen one ground at 104. Maybe in a Stock Eliminator car. Now when you get into big engines like mine, the LSA goes back up. My cam has an LSA of 114* but the intake centerline is at 110. Even with 0.833/0.809 lift and 282/290 @ 0.050 duration, the engine idles smooth without a large lopyness. Of course it also idles at 1200 rpm. I've never tried advancing or retarding the cam to see if moving the powerband around would help. I also use a fixed idler timing gear set. No chain to stretch to change valve timing and the timing light is rock solid.
When you advance or retard a camshaft, you are changing the valve timing. Depending on piston design, duration and lobe lift, changing cam timing may cause piston to valve clearance issues. When an intake valve is opening, it's chasing the piston down into the cylinder. As the exhaust valve is closing, the piston is chasing the valve up into the head. Changing valve timing will increase or decrease the amount of space between the valve and piston. A camshaft with 4* of advance ground into it and is advanced another 4* means it now has 8*. Without doing a modeling clay test on top of the piston, you won't know how much piston to valve space you have to play with. Exhaust valves need more clearance than intake valves.
It's good that you're degreeing your camshaft. Cam cards are to check to make sure the cam timing is set properly but other clearances need to be checked as well when you start changing things. It takes time to build an engine properly compared to getting a bunch of parts and just assembling it.
I triple checked - this time directly at the lifter - and am still between 108 and 109 degrees for the ICL with the timing set 4 degrees retarded.
When I check the intake opening and closing @ .006", which should be 30 open, and 66 close.... I am at 28 open, and 68 close. However Comp's instructions do not expressly say to check this. It only says to check ICL. Other sources say it needs to be within 1 degree..... I retarded the crank 4 degrees which is 2 degrees on the cam so this makes sense to me.
Obviously I can't change one but not the other. They all change in unison. But the ICL is pretty much spot on. So what do I do? Leave it the way it is? What more important ICL or open/close timing? Was this cam ground wrong?
Last edited by GeneralDisorder; 10-12-2018 at 10:06 PM.
My opinion is to run it the way you have it right now. I have never had a cam agree exactly with the cam card - never.
You just have to get as close as you can and call it good. That is where you are right now. Measuring at .006" lift is really splitting hairs. That's why I suggested the ICL method. And as to the 30/66 vs 28/68, you are correct in that you can't adjust both in opposite directions.
My camshaft degreed in exactly like yours in that respect. It is unusual that your stacked tolerances add up to 4 or 5 degrees, especially since you have Comp's complete kit. I would expect that to happen if you were using parts from all different manufacturers.
But that is exactly the reason we do this check. If the square symbol is giving you the setting you are looking for, then go with it.
Last edited by NoEmissions84TA; 10-12-2018 at 10:39 PM.
And yeah this would be an excellent case for why you need to check and not just throw parts together. Which of course I would never do...... I was just thinking that it would be more likely to be an easy straight up installation because I'm running stock block, crank, and packaged Comp K kit that is supposed to have matched parts from what I understand to be a very reputable high end manufacturer. In my mind this should result in near perfect circumstances for everything to fit correctly.
If this collection of ideal parts results in stacked tolerances this badly in 2018 with CNC controlled cam grinding..... well then manufacturing tolerances on the old Vortec block must have been just unbelievably loose..... I guess I'm not that surprised - the bearing inserts I pulled out from GM were not at all consistent. Had a mish-mash of different sizes in there. Had to line hone it and cut the crank to get them all consistent.
Factory tolerances are no where close to being exact. There's always a high and low acceptable range and as long as it falls into that range, they'll let it run. Now, when we build engines, we expect tolerances to be much closer. 100% exact is always nice but there's always something to make it a little out of perfect spec.
I don't know about SBC but it's pretty rare for a stock GM crank to be keyed wrong in the LS engine. Not so rare for an aftermarket crank to be keyed wrong.
Proform 66838 is a handy tool for measuring cam lobe lift. The tool sits on the rim of the lifter so you don't have to worry about the lifter cup compressing. And the micrometer is set perpendicular to the lifter without hassles of setting up a magnetic base and rods.
My opinion is to run it the way you have it right now. I have never had a cam agree exactly with the cam card - never.
You just have to get as close as you can and call it good. That is where you are right now. Measuring at .006" lift is really splitting hairs. That's why I suggested the ICL method. And as to the 30/66 vs 28/68, you are correct in that you can't adjust both in opposite directions.
My camshaft degreed in exactly like yours in that respect. It is unusual that your stacked tolerances add up to 4 or 5 degrees, especially since you have Comp's complete kit. I would expect that to happen if you were using parts from all different manufacturers.
But that is exactly the reason we do this check. If the square symbol is giving you the setting you are looking for, then go with it.
That's what I use for determining ICL. But I only go 0.050" over the lobe nose. Finding the IVO And IVC at 0.006" is way too difficult for me at least and keep in mind most lobes are assymetric where the exh ramp maybe longer than the intake lobe ramp.
Do it as many times as needed because the more you try it and think it over the better to sort it out for you when working by yourself and don't have someone to double check your work.
Well as far as having advance ground into any cam that's really the reason to degree the cam in the first place. I've had cams retarded 4* and my last one was advanced 2 1/2*. Most published advice says 4* ICL advance is optimum for the sbc but I have also read of others using as much as 12* ICL advance for the performance they want. The only reason to retard the cam ICL as that would reduce power but it does allow a lower dynamic compression if the engine was built with a to high static compression.
I generally only worry about ivo and ivc events as thats what the engine sees. A deg or 2 off generally is ok. They make 9 keyway sprockets to really dial things in and cloyes hex adjust is nice too
So seeing as I'm within 1 degree of ICL, and about 2 degrees on the IVO, IVC..... should I get a more adjustable timing set and dial it in closer? Maybe get the IVO and IVC spot on and let the ICL remain advanced? That might give me like 6 or 7 degrees total advance but with correct IVO/IVC. I'm in no rush here. Still waiting on plenty of other parts so there's no reason to slap it together.
I think I'm right in that the align hone would have resulted in the cam being retarded, not advanced, if the machine shop had removed a lot of material and shortened the distance from cam to crank centerlines? The chain is not at all loose.
My reading on the subject suggests that the poor tolerances with respect to cam-to-crank centerline distance at the block factory may be the underlying reason for so much variation in degreeing.
I think I'm right in that the align hone would have resulted in the cam being retarded, not advanced, if the machine shop had removed a lot of material and shortened the distance from cam to crank centerlines? The chain is not at all loose.
My reading on the subject suggests that the poor tolerances with respect to cam-to-crank centerline distance at the block factory may be the underlying reason for so much variation in degreeing.
Ahhh! I read all my preaching has done some good.
Now you can buy tighter timing chain sets by the 0.001" increments and I think Summit makes it easy to find them. But the difficulty is measuring the crank to cam distance to compare with a stock motor measurement. And I don't think a calipers will cut it. I believe it takes a large micrometer.
Cloyes hex adjust would make it real easy to adjust cam timing without worryig about length
But since this block is align honed (and the mains clearance turned out amazing with just a single set of .010 bearings), the stock Comp chain may be too short? I have about 1/4" of deflection on the slack side. But it also seems about the same on the tight side. I'm sure some slack is normal. It's probably fine but....
I'm heavily eyeballing the Comp belt drives. Yeah I know I'm crazy. But this car/engine is also an advertising piece for my shop. We just bought a 2000 HP DynoJet so....
Last edited by GeneralDisorder; 10-14-2018 at 12:55 PM.
So with the hex-adjust Cloyes set, I dialed it in as carefully as I could, triple checked everything, and got it right on 108 ICL with the timing set retarded by about 2.25 degrees. And this time it was ~105 with it straight up. The hex-adjust is a beautiful thing. That shouldn't even be optional. Appearance and quality - especially on the billet gear and the chain itself - was much nicer than the Comp unit. And the chain deflection is about half what it was with the Comp set. It was maybe 1/4" before and now it's closer to 1/8"
I also measured for pushrod length last night. Came up with the stock 7.200's being .150 too long. I'm struggling to understand where 150 thou went. The heads and block were surfaced to clean them up and I'm using a .015" shim head gasket. Is this a result of the reduced camshaft base circle with the high lift camshaft, in conjunction with the slimmer head gasket and the surfacing? How typical is it to need 7.050" pushrods?
I try to search for this stuff but the discussions are sparse.
Last edited by GeneralDisorder; 10-17-2018 at 10:20 AM.
How come you're not using the real rocker arms for pushrod measurement? Or are those caps just protecting things while in storage?
Did you measure the length of the check rod with a caliper? I have 4 of the Comp Cams length checkers and none are the same length. The "count turns" method is junk because they don't control the length of the rod well enough.
This is a 99 Vortec block so the cam was always roller. But the pushrods came in a Comp K kit for 87+ factory roller motors. They came with the 08-301-8 camshaft. They are the 7.192 "stock" length roller cam pushrods from what I have researched. The length checker measures in at 7.050" to get the Proform tool touching the valve stem.
What I find most displeasing here is that the cam, lifters, timing set and pushrods all came in the same box from Comp. In what universe could you throw all that together and it would work correctly? Now I see why the amateur's out there with basic tools and little engine building experience fail so frequently. I have never had this many problems with parts even from different manufactures, let alone all from the same kit. What a crock. Almost makes me want to send it all back and look into some other cam manufacturer.
Live and you learn. All builds vary, they dont specify deck height and gasket thickness and how thick your head decks are. Variances can be found and change things
its not like camming an ls1, where known dimensions are there with shaft rockers, you can buy a kit and drop it in
General, I have a question for you. When using that tool will you use the exact measured length pushrod or will you go down the .050 that is often recommended with other methods? It’s discussed in this thread, https://www.thirdgen.org/forums/tech...lve-train.html.
Live and you learn. All builds vary, they dont specify deck height and gasket thickness and how thick your head decks are. Variances can be found and change things
its not like camming an ls1, where known dimensions are there with shaft rockers, you can buy a kit and drop it in
i always buy separately
For sure - not having custom built an engine that was designed in the 1950's before (all my previous engine building has been 1990's and up), I am seeing this first hand for the first time. Doing a lot of reading.
I find it somewhat sinister that Comp even sells complete kits for applications that require this level of customization. And the pushrod length issue is that the rods *they included* are too long because of the lifters *they included*. The parts in their kit don't work together. For that matter their timing set didn't work with their own cam - it was not capable of dialing in the required ~2.25 retard - it could only do 0 or 4. That's two completely separate compatibility issues with the same "kit" of parts ostensibly designed to work together. It is VERY clear from this and the packaging that no measurement of individual components took place at Comp. They just grabbed part numbers off the shelf and threw them in a box. They have to know this couldn't work and thus I conclude their tactic is to get double purchases out of customers who they have tricked into buying a ready-to-go "package"
General, I have a question for you. When using that tool will you use the exact measured length pushrod or will you go down the .050 that is often recommended with other methods? It’s discussed in this thread, https://www.thirdgen.org/forums/tech...lve-train.html.
I haven't determined the answer the that yet. I have some Comp documents to read through that detail the three methods of measurement, etc. I will review that thread and offer my conclusion. Thank you!
How does this look? That Proform plastic rocker tool is useless. Did not yield anything close to a reasonable geometry. This is actually the pattern from the stock length 7.200 pushrods. Seems centered and relatively narrow. Looks like a win to me.
After reading more on the subject - including the PDF linked above - I conclude that the Proform tool is correct and is positioning the rocker such that it will be at 90 degrees to the valve axis at half the total valve lift. Which will yield correct geometry. So I do need 7.050" pushrods. The Comp pushrods are .150" too long.
And this is why everything gets triple checked. Using multiple techniques.
GD
Last edited by GeneralDisorder; 10-19-2018 at 10:35 AM.
How does this look? That Proform plastic rocker tool is useless. Did not yield anything close to a reasonable geometry. This is actually the pattern from the stock length 7.200 pushrods. Seems centered and relatively narrow. Looks like a win to me.
Originally Posted by GeneralDisorder
After reading more on the subject - including the PDF linked above - I conclude that the Proform tool is correct and is positioning the rocker such that it will be at 90 degrees to the valve axis at half the total valve lift. Which will yield correct geometry. So I do need 7.050" pushrods. The Comp pushrods are .150" too long.
And this is why everything gets triple checked. Using multiple techniques.
GD
So now I'm confused. What was wrong with the ProForm tool measurement yesterday that is better today?
The Proform tool actually puts the rockers to a position such that at half total valve lift the rocker is at 90 degree's to the valve axis. You can read the PDF linked through the post link above, or you can just visualize that the rocker tip swings in an arc (portion of a circle) and since the valve has to move linearly along it's axis, you want the portion of the rocker's arc that is the most linear for best efficiency and lowest side load. That portion is the one where halfway through the total valve lift the rocker makes a 90 degree angle between the line's containing the valve's axis, and the line through the rocker trunion axis and the roller tip axis.
So regardless of contact location, you want the most linear motion with respect to the valve stem axis. This should also result in the smallest contact patch - but measuring that by guessing and checking is not the efficient way to go about setting it up.
I've read the PDF before and agree with what that man explains. It's just i don't know what you didn't like about the ProForm checker tool in the earlier post #50 saying it was worthless. Not trying to flame you but thought I had missed some kinda flaw with using the checker tool. My self I a advocate of using checker tools for moderate/modest lift cam. I own 2, one from MOROSO and one from ProForm and FYI they will measure a little different but close is good enough I have learned. My personal opinion is the checker tools are well engineered to make engine building a street motor much easier. To bad they create so much contriversey. Having tried to use the adjustable p-rod method with the block in the car i would only recommend that method for those that enjoy pain.
My experience is you can only buy p-rods in like 0.050" increments unless you are willing to spend for custom made. I measured my TrickFlow p-rods and found them a few/several thousand off the ordered size which was also lazer etched into the p-rod.
The checker tool put the pushrod at the location that makes sense from the engineering aspect. I had initially got all youtube certified and tried running a pattern test like virtually every youtube video (even Summit's own video on pushrod length), and got what looked to be a great centered pattern using the 7.200" stock length pushrods included in the cam kit.
Then after reading more on the subject, and taking the approach of measuring the tip to trunion distance and aiming for half the valve lift, I also discovered that the Proform tool was aiming for that same point.
I ran the pattern test again and realized that with the hydraulic lifter you actually want the pattern to be slightly toward the intake side of the valve stem as there is a delay in the valve motion while the lifter compresses.....
Ultimately there are a TON of videos and articles full of the wrong method. Turns out you just buy a $7 plastic tool and it takes care of it. Not that it's so hard to measure half the valve lift and use a straightedge to put the trunion that far below the valve tip.....
I ordered the TrickFlow 7.050" pushrods. I'm not too worried about a couple thou. Hell the lifter pre-load differences will likely be more than that..... But 150 thou isn't going to do it for me.
10-12-2018, 10:20 AM
