i have been goin thru hell tryin to get my fresh 406 dialed in (see thread still cant get it) just talked to the engine builder(short block only) he said the cam was advanced 4 deg what does this mean in relation to my problem?
was it advanced by him, or did it have 4 degrees advance "built in" to the cam? most hydraulic street cams are ground with 4 to 5 degrees advance.
i'm not sure what your problem is , but advancing the cam 4 degrees would tend to move the power band of the engine down....retarding would put the power at a higher RPM
i am in process of finding out if he did it or if it was "built" in. would this effect my innital timing settings? and all in?
did he actually degree the cam in , or did he put a multple keway crank gear at 4 advanced? if he degreed it and its at 4 advanced its not going to have the problems you are having..... I did just pull one apart that a guy was having trouble with....when we put a degree wheel on it, it had an intake centerline of 122 instead of the 106 the cam card said...the cam is on its way back to the manufacture to see what happened. i have been following your other thread, and I think Scotch has it diagnosed as best that can be done on a messageboard.. the only other thing is you say this is a brand new mill.......did you break in the cam....and have you checked the lift at the rocker arms to see if you have any lobes going flat? Fred
Like the other guys said some cams have 4deg. built in and some cams I have found older ginds you have to get a timing gear set with the 4 deg built in to the key ways on the crank timing gear. Happy hunting John
I've been following your other thread. Advancing the cam would have no bearing on your problem which I'm 99% certain is a va***n leak somewhere. Camshafts are advanced to get more bottom end torque. Doing this also takes away from your top end RPMs a bit also also. I believe that the formula is for every drgree of cam advance, 100 RPMs are lost from the top end of the powerband. In general, it's a worthwhile tradeoff.
Did you check it with a dial indicater and a degree wheel yet? Generally Lobe centers are around 106 to 110 degrees and are fine tuned with offset keys or an adjustable cam gear.
Crane hydraulic cam .516 .525 lift 244 252 dur at .050. 110 lobe sep. i dont have a degree wheel. im definatly a novice to engine builds. im trying to find some help but i live so far in the boonies there is no help around and the cows aint much friggin help.....how much varience will there be in the diffrernce in the lift of the rockers if the cam is gone or going? will the diff be visible with the naked eye? builder said the advance was done at the timing chain. what does this mean? i bought it on e bay and the guy is 700 miles away so im talking to him with e mail. i just resealed intake etc vac at 11 on idle@1000 rpm. vac dies off on full rev of engine and will steady climb to 20 with constant slow acceleration will idle smooth for 3-4 min then starts to die rpm dies to about 500 she struggles and sometimes comes back slowly then does it again. whal its dying if i just barley touch the gas she catches right up. as soon as i put it in gear it dies. modulator and brakes disconected.... **** i just dont know.. i know i'll know at least this engine inside and out by the time its done. its been like paying to go to engine builders school.but tuition money is runnin low.. anyone know someone in southern virginia... thanks for the imput guys.. at least yall have kept me busy!!! lol lol
Pull the plugs if you have wet or oil fouled ones then with a new engine you have a dead cam. I know you probably ran it for 20 min. above or at 2000 rpm but, I have seen it first hand. The timing seems like it will not stay a few small back fires. You can't quite get the carb in tune. This all leads to cam failure. Who's stahl are you using some of the supposed 3000 are not what they say. Do yourself a favor and get some rocker arm clips so, you can run the engine without the valve covers and if you have a dead stick you will know right away. I have seen comp cams die in 8 min. after start up. If you had any problems getting it to fire the fist time and had to screw with it a lot then I would almost guarantee a dead cam. I know not what you wanted to hear but, someone had to tell ya.
YOu didnt recurve the distributor and at idle the advance isjust barely able tokeep theengie running . You need full advanceat 3000 with total timing set at least 38 degres at 3000 RPM. You should have lots of in***ialbut still haveit low enough to start without fighting the starter. More Hp in a proper distributor recurve than most would ever believe. If you have nagging questions about the cam and it placement take a physical comression test. Tat will tell you right away quick if all is ok. I dont know about the chevy stuff but the fancy timing chain set ups for opars. (you know the ones withthe shiny grearsand the fancy holes drilled in them and multple postions on the crank gear for cam dialing inare absolute Junk. One set a guy broughtto my shop was off 7 degress and another was 11 degrees out. I refuse touse them anymore Dont have thetme to fool with that gofy stuff. I stick to Melling or sealed power replacement double rollers . They ae always right onthe moeny. and if I want to move the cam I go fromthere. Hopefully yours is ok. the compression test will tell immediately. (Like if you get 90 psi you know you are in trouble. if you get anything over 135 depending on your compression ratio you are probably ok, at least it will run ok. Nobody actually explained the theory to you. Did you want that or just want to get it running.
i will do a comp test tomorow. i pull all plugs disconect power to the dizzy conect comp tester and turn it over 3 or 4 times right? and repeat for each cylinder. is there anything else i can do?i did not recurve dizzy it has both heavy springs with vac disconnected it 1dols at 18 with all in at 36 when i go to 3000 does this mean my mech is at least working? at 18 if i connect the vac adv it jumps to 30 at idle no wet plugs slight dry black foul readjusted af mix today. using an ACI 28-3200 stall. i tried the rocker clips they worked like **** so i just stand a piece of cardboard up to keep the oil from going everywhere. is there a diff i should be able to see pertaining to the valves and rocker movement in relation to a frigged up cam? any theory would help i find it easier if i actuallly understand something. im not a mechanical dumb***. i have built and rebuilt a ton of old harleys and trumpets. but this engine is kickin my ***. thanks guys....
I haven't seen your other post about your engine tuning difficulties. But, with that large cam and if you are running a single plane intake(without any vac leaks) it sounds like you need a carb with a tuneable idle circuit. 54chop
sounds like the distributor timing is set up close enough that it should run ok. see if any of the rocker arms don't move as far as the rest of them, if so that cam lobe is wiped out.
always use a degree wheel to check your cam timing. They make gears with different degrees of advance or retard but you have to know what youre starting with. Sometimes a cam is not straight up out of the box and you can make problems by moving cam timing. You need to know what you have before you make changes. also timing chains are a poor way to turn your cam. They stretch and cam timing is effected. Gear drive is more accurate and holds the setting.
Ok here goes. of all the cam timing events the most important one is intake valve closing. That is because no compression will take place in the cylinder until that happens. When we advance the cam we move it forward so the intake valve closed earlier which raises cylinder pessure in the cylinder and improves bottom end perfromance, to a point. The reason the intake valve is open into the beginning of the compression stroke is because once we have the column of air and fuel moving it has a tendency or interia to keep moving even though the piston has started back up the bore on compression and there is a point at which the piston is not yet moving fast enough to upset the incoming flow generated bythe natural inertia and other factors including ram tuning etc. At some point the benafit cancels out and we might as well close the intake and get on with the compression stroke. Advancing the cam 4 degrees closes the intake valve earlier and the compression begins earlier. Cams are usually designed to run with some advance and 4 would be typical. Occasionally cams are retarded and that adds slighly to top end but very slightly although it is sometimes used (by me) at least to kill of bottom end torque when it is excessive. The holding of the intake valve open into the compression stroke is also why we often need to increase the compression ratio when we install a big cam. If we could measure (and we can ) where the intake valve actually closes and exactly where the piston is on the compression stroke at that moment we would discover very quickly that say in a 4 inch stroke motor we really only have for example 3 7/8 inches of stroke actually being used in the compression stroke so even though the engine might be a 10 to1 engine using conventional calculations the effective compression ratio is much less because the intake valve was not closed until the piston was 1/8 up the bore on compression . Instinctively right away we think we could add a 1/8 inch bump on the dome of the piston to get back the squeeze we just lost from the intake valve being open for an 1/8 inch of the compression stroke and while it is not quite that simple it is certainly thinking on the right track. We dont raise compression to get more power by compression alone, we raise it to get back what we lost from the longer intake valve timing. Or we could advance the cam which moves the position of the closing side of the ramp further along than it would be if the cam was installed straight up as in a stock motor and that wil close the intake valve earlier and help build more cylinder pressure. 4 degrees is pretty typical. Your ingnition advance is not bad. try another 2 dergrees total (38, i have run chevys as high as 42 but not long stroke like your 406.)and get some weaker advance springs. Let me know in the morning what the compression test is. Engine should be warm and throttle must be open during cranking. We will know a lot more then Don Dolmetsch Engine Development
that was an awsome post don, super informative. i will try the comp test today.throttle open? meaning wot? so i just tie the carb open?ill let u know how it works out. thanks again all of yall have been super helpful......
242/252@50 duration is a rowdy cam. I think you are not going to get much more than 12 inches of va***n at idle with this cam. The larger displacement of the engine will tame is some, but it will still idle rough with low va***n. It sounds like you might be running real lean at idle due to the low va***n. With a big single plane intake, your idle screws will loose their sensitivity. Try this test. With the engine idling, take your hand and cover the air corn, restricting air flow. If it dies, you are real rich. If it picks up some, you are lean. You should be able to smell it if it is real rich. The exhaust will stink like fuel. What carb are you using?
had a holley 670 street avenger i put on an old edelbrock i had and it seem to have helped alot. i can get the timing down now and dosent die under load. gonna go test now ill let yall know.... oh also switched to a diff plug
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