Am considering showing the kids (and so I can learn as well) how to degree a camshaft. I understand kinda how to do it, but my question is "why" to do it? I know you are basically double checking the specs of the cam, but once you do that, what remedies are there if its not quite right? This is going to be in a tame street small block chevy and this is the cam we are going to use no matter what... What advantage is there to doing this if we aren't going to change anything afterwards, or are there changes we can make without changing parts (advancing/retarding the cam? we do have a 3 keyway timing set...) thanks-
you can adjust the cam timing with the timing set, or an offset bushing or key. Sometimes parts are made wrong or tolerances add up to make the cam timing off a bit too far, but it's rare.
Some school of thought would be to put some advance in it so when your timing chain wears it will be closer to spec after the engine runs in some.
It is somewhat similar to "blueprinting" an engine. When you are after the maximum power (especially in a stock cl***) having everything as correct as possible helps. There are also times when you would want to advance or retard cam timing.
IMHA, adjusting cam timing Is a way of fine tuning a cam ... Or in some cases a band aid fix for a bad cam choice ... also what Saltflats and jseery said...
I thought when you degree a cam it gives you away to change things a bit. I have been told it can change torque specs a bit. Sometimes change if your valves are going to hit pistons ect. I have never had occasion to do it. I never did the finely tuned race motor thing. Squirrel has spoken on this thread. I am sure he will correctly say what I am saying.
Don't run gears. I ended up retarding the cam a couple degrees on my Chevy II to make sure I had enough valve clearance. Most street cams have some advance built in.
The "Why Do It" question should be answered with the reasons behind camshaft degreeing in. When building a performance engine there is an attempt to reduce all of the variables inside the engine. This includes balancing rods,pistons,maintaining a specific deck height,making sure the head chambers are all the same and more. Degreeing in the cam confirms that the cam is ground as specified and that it will be installed for the best performance as the builder sees fit. Be it straight up/advanced/retarded. By the use of advance and retard "keys" and other methods to move the cam timing around,maxium performance can be obtained and then also repeated if desired. Its just another tool to reduce the variables in engine building. Personally I check all of my cams on my Cam Dr machine as I have found some "differences" shall we say in manufactures specs. Hope this helps,Oldmics
Well said Oldmics, that's a great description as why we check cam installation with a degree wheel ... To see if we got what we asked for or what they specked for us from the cam grinder...
Generally more advanced= more low end less advance = more top end, also more advance can lower water temp Posted using the Full Custom H.A.M.B. App!
I don't think that the novice engine builder or even the more experienced engine builder such as myself has enough knowledge to select the proper cam for a given build. I know a veteran builder who spends endless time on the dino and has tried hundreds of cam combinations for the NASCAR spec late model stock car engines with 2x carb setups. I believe he has by far gotten the most hp out of this combination that I have seen in a long time. If you ask him what cam to run he probably could get you close but that last 20 to 30 hp that makes the diff can only be found on the dino. The cam degree fazing is one of the ways that it's found along with many other fine adjustments found only in the dino proses. All these things have to complement each other and one of them out of spec can diminish the end results. Most reputable cam grinders can get you close for your street application if you listen to there recommendations and give them correct info when asking for a cam recommendation. Compe***ion however is a hole nother ball game and will require the expert dino guy to get all that is available from any combo. Dino tuning is priceless in my book for compe***ion engine building...
Jim, I don't know all of your story here, but, retarding the cam may not have been the way to go. In the motor/cam/crank/piston phasing cycle, the pistons are chasing the ex valves to close/seat. The old clay spec of .10 clearance is to make sure the piston never hits the valve if it hesitates, ever. By retarding the cam, you are effectively putting the piston closer to the ex valve and taking out this clearance. Still the most effective tool to determine this clearance is clay. Not to bust you, just informative. John
There are many here that can probably figure the proper set up in their sleep. For many of the rest of us it's something rarely done. Generally speaking a cam manufacturers tech line is helpful for those that do not do this every day. Sorry for ****py pic.
Yeah, I used clay and checking springs and solid lifters to check the clearance. The intake was pretty tight...the cam has quite a bit of advance ground into it, and the pistons are stock replacement.
An old tip from Edelbrock..... Get a set of offset cam keys or bushings and try different advances. Check compression with a compression gauge. Whatever setting gives the most compression will work best for street use, by giving you the most low end torque. Advance the cam for better low speed performance, retard for high speed performance. You can actually "rock" the torque curve about its mid point this way.
Back in the early 70's I installed a Crane flat tappet cam kit in a Boss 302 Ford in my drag car. It was a duel pattern with 560 intake and 585 exhaust lift. It came with 4.5 degrees of advance ground in, we retarded it 4 degrees as I turned the engine over 7,000. It would have been instructive to have it on a dyno, to see what the change gained or lost.
My recent experience on my DD: it's a workhorse, but my policy is, as soon as something needs serious work, improve it. It was getting so valve stem seals at the very least would be needed, and if the head was to be pulled I might as well go for a gas-flowed one with a nicer cam. I ordered a reconditioned head and 272H cam from STK in Port Elizabeth. I didn't have the time or the space to do the work myself, and at that stage I hadn't yet learned exactly what kind of monkey my then-regular service guy was. The first time I got the car back it was lively enough but there were oiling problems which culminated in #5 main bearing seizing a few weeks later. I also noticed that the adjustable cam pulley was still in the box STK sent it in. When I got the car back the second time the oiling was good but it was pinking, it didn't want to spin happily past 5K or so, and it was actually slower than stock. It sounded good at idle, though: "that sounds impolite!" was what the guy at the alignment place said, with a huge grin. There was no way I was going back to the guy who did the install. A colleague recommended someone else. I knew the cam was hugely overadvanced (I got the idea the first guy had all his adjustments backwards - he actually wanted to sell me a set of 12.5:1 racing pistons when I instructed him to install a deck spacer to knock a point or so off the static CR - awful fuel.) The new guy retarded the cam roughly, but even that pretty much fixed it: it pulls, no pinking, it spins past 7.5K without complaint, and it still sounds impolite. I'm sure a bit of adjustment to the cam would release yet a bit more.
as we found out on a friends ford , sometimes even the manufacturers screw up labeling/stamping cams , the three of us though were were dummies ( all three getting the same numbers ) , till I pulled up some cam cards on the computer and found it was a cam that was 1 group lower , but labeled for the higher group on the stick .later we found we were not the only ones there were other guys who ordered ( was back ordered ) the same spec around the same time that recieved the same screw up, someone at the plant stamped or grabbed the wrong cores , the cam would have ran good at lower rpm but the car would have ran way off the mark at top end .
Usally the big variable is the keyway in the crank. As far as advance or retard unless you have tried it both ways with a given combo you really don't know if you went the right way.
There are a lot of reason to degree a cam shaft, I have one for instance that I am running just ever so slightly retarded (amount is a secrete) to achieve a better top end pull with it. You normally do it to make sure that the intake valve is chasing the piston down the hole and that it starts chasing the piston down the hole when you want it to. Ideally a new camshaft will be spot on but some are not, normally if you are not a machinist you have nominal numbers to work with as far as advance or retard of the cam timing. So more often than not you need to work a compromise, a little faster or little slower. You can adjust it with the timing chain in some cases or with offset keys. You should be able to buy keys in 1-2 degree increments. If in fact you were 1.375 degrees off you would be screwed if you couldn't machine your own key, but you could buy for example a key that was 1 degree off and only be .375 degrees away from your target or maybe you would use a 2 degree key and be .625 off in the opposite direction, maybe one or the other would be a good thing. Anyway it is a way to see how close you are from intended spec and maybe adjust accordingly or it is away to set your won target and see where you end up. Either way a degree or two in either direction is nothing unless you have an interference engine which most of us do not have.
PNB remember the old stock GM belt chain sets that were retarded from the factory for emissions ?? it was off by 3* retarded , would mess with many peoples minds if they were not told .
I do it and use the results to see if I need to do more intensive machine work. Two different crankshafts may check very different. If you degree the cam on every cyl. it will probably scare you. The crankshaft throws may not be 90 degrees apart or the lifter bores may be slightly angled . Several variables there. But although I get a lot of flack on it I use the advance and retard of the cam and compression reading to set position of the cam. If thats confusing just message me and I'll tell you my theory on it.
Yep there was more grunt to be had just by a simple crank gear change. Most of the manufacturers in the '70s detuned to emissions and "mileage." as if making an engine less efficient was a way to cure either. Hell Joe tell your theory here, most of us are interested and if it works for you who a****st us has any room to be a nay sayer.
Very simple, ( glad you ask ) .I believe that a engine will perform better the higher compression it has. I put one piston and rod in ,head installed on that side and adjust the valves.With the cam set straight up, spin it with the starter and record the compression. Advance it 2 or three degrees and spin it again. Record it and retard it two or three from straight up.You would be surprised how much the compression changes. I then figure out where it is highest and leave it there.( you can even play with valve lash and see the best setting). NOW the disclaimer, several very qualified engine builders have told me cranking compression has nothing to do with running compression.They were never able to tell me why. I have used this method for years and will continue to do so ,I am a hard headed SOB.
the difference between cranking and running is the bleed down speed ( dynamic cam timing ) the faster the motor turns the less chance of the air backing up the intake tract due to the piston rinsing on the intake cycle . the faster the motor turns hemholz effects will start to take over and can "ram " air down the intake tract thru the pulsation of the valvetrain cycling . we do this in superstock to make long durations cams work with low compression ratios , also higher the compression ratio the more torque you generate , thats been a long time known fact , and the higher the torque the better the fuel burn is ( more complete burn ) if you get some books BY Sir Harry Richardo he goes into it in more detail .
But you win right? I understand the theory of compression under load, but tuning is tuning and it gives you a baseline and something to work toward. It is like timing, I set timing by feel, I always have. I don't need numbers I need results. Your theory works and it is how you tune. it gives you results and if you can teach someone how to do it and get results then you have accomplished something aside from just going fast. I am willing to try it. Stimpy, Your theory is good and it take into account the laws of physics but it does not taker into account things like crank case pressures or ring flutter both of which are a moderating factor to consider when thinking of compression under load, all the things that effect the engine are changed with load. Once on the track a good tuner over comes them with foolishness another form of logic. Not to argue for either tuning theory just to be the devil's advocate here.
The whole thing about cams is that they need different timing to work well at different rpm. If you set it up so it makes max cylinder pressure at cranking speed, it won't work very well at 7000 rpm. Something about how air has momentum, and you have to open and close the valve at the right time to deal with the air's momentum.
There is a simple rule of thumb that I have used for years. it is not a pure science but it works for me. Take a given RPM range for a cam shaft ( you can get that from the manufacturer if you can't figure it out on your own). If you want to move the RPM range to a higher number you retard the cam timing and if you want to move it lower you advance the cam timing. How much comes with experience and if you have interference tolerances you will have to clay everything again after changes, and that is overly simplified. In a perfect world you do that with a combination of cam and ignition timing, as well as intake choice and valve sizing and etc. You in effect can render an engine useless pretty easily, and a less is more mentality is good. Modern engines do that with the ECU, it is monitoring your engine in nano-seconds and can change cam and ignition timing about that fast. As well as fuel charge and even engine temp. We unfortunately don't have that option with what we are working with, so we trade off a little here for more there. Here is something that everyone needs to understand, you cannot learn to tune from a book. Theory is only a suggestion and practice is what perfects it. Even that is not always enough, you either are a tuner or you are not. it is just the way that it is. Everyone that tunes successfully uses his own tricks, sometimes he learns something new from another tuner and if it works he uses it and if it doesn't he always goes back to what he knows works. Theory be damned, what works, works. Someone said that you can't change the laws of physics, I say that you can bend them, any law can be bent and it is real world application that is the proof. Oh I should mention this, Squirrel and Joe already know this but maybe Stimpy doesn't yet. None of what I have to say is a personal attack, you know what you know and what I have to say has nothing to do with what you know to be true. Capisce?
The Jalopy Journal
