Is it possible to degree an unknown cam? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 03-14-2006, 08:48 PM
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Is it possible to degree an unknown cam?

well here's my qestion. I have a 350 chev that is basically stock far as I can tell. Stock intake, rochester 4 barrel carb, stock heads, headers. It was rebuilt at one time before I owned it and it runs pretty well but their are a few problems.

It pulls 14 inch of vacuum at about 900 rpm but it the needle on my gauge vibrates pretty good. It will vibrarate between 14 and 15 inch making it hard to tune the carb and I have found no vacuum leaks. the timing mark will also wander slightly by about 3 degrees totol on the damper at 900 rpm Timing is all set up at 12-13 initial advance, 10 at the vacuum can, and 12 mechanical. mechanical starts at 1500rpm and all in at about 2800 rpm. The vacuum can pulls full at 12 inch of vaccuum so it is not interfearing. I did a cold compression test and all of the cylinders were at 119-121 PSI. I did the test with all the plugs in but the throttle was opened fully.

When I rev the motor up the vacuum and the timing become more stable but it's not rock solid like I understand that it should be. It will also float the valves at about 5100 RPM.

Other than that the motor is soundless with great oil PSI and will drag my 3700 LBS truck with 2600 sall converter and a 373 rear end through the quarter mile in about 15.5 seconds .

My plan: I want to replace my timing set and possibly advance the cam because i believe that the cam is slightly big for the compression i have. I do not know what the cam specs are so can i still use the intake center line method to find where the cam is at based in the intake valve lobe max lift. The method for cam degree is the same as recommended by comp cams. Is this of no use to me because i do not know the LSA of the cam or where the Intake Center Line is of the cam is supposed to be? I also have a set of valve springs i plan on installing hopefully to help cure the shakey vacuum gauge and the valve float.

Thanks to anyone that reads this

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Last edited by Scrumgees; 03-14-2006 at 09:18 PM.
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Old 03-15-2006, 05:38 AM
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cam

Well lets see.... where to start???

You can move the cam in relation to the crank with-out having any info on the cam...But i think with 120lbs of cranking compression you have other issues... Unless the builder really got the cam installed way retarded...When you did the test was that a one hit reading or did you hit the gauge 4 or 5 times?????? advancing the cam 4 degrees will only get you 5 or maybe 7 cranking psi...

Let me see if i can typ this...

You will need to find the valve events @.050 lift. So install your degree wheel. Find true TDC, put the indicator on the intake lifter and turn the engine over untill you have the lifter on the heal of the cam.Then set indicator to zero. Turn the engine in it's normal running direction untill the lifter rises .050" record that number..continue untill the lifter goes past peak lift and back down to .050" and record that number.... Add those 2 numbers +180 and that will be your duration @.050 of the cam...


Then turn the engine untill the lifter is at max lift and reset the indicator to zero. Rotate in the oppisite direction untill you go past .050 then reverse and stop at .050 below max lift. record that number. rotate in the normal direction ,go past zero untill you get to .050" below max lift, record that number... add the 2 numbers,and divide by 2 and thats your installed centerline..

get those numbers to us and we will go from there....


Keith
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Old 03-15-2006, 01:48 PM
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if you are going to replace the timing set (timing gear and chain?) then you can simply take the cam out and get the info off of it.you'll probably have to get all the numbers and have it in front of you when you call the cam companies but they will get you the info you need.then you will know everything about the motor and leave nothing to chance.its hardly any more work.you can try emailing the cam co's. but i have found that you get better results by talking directly to them.
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Old 03-15-2006, 07:30 PM
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The compression was on the 4th hit on the gauge and i'm sure that their are no leaks. It burns no oil and all the compressoin numbers were 120 + or - 1 PSI I never did think to just check the cam for numbers though.

I may just replace the cam it but i'm not sure what pistons i have. They could be a set of rebuilers pistons at 1.540 compression height with 10cc valve reliefs or 1.560 compression height at 5cc valve reliefs. I do know they are federal mogul though.

The heads are 76cc and i do not know if they block has been decked or not. I can Ballpark the static compression so i could put in a new cam but this is more fun, at least for now.

Measuring the cam seems like an entertaining idea though. I'll mess around with it this weekend when i have time and see what i get for numbers
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Old 03-18-2006, 11:50 AM
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Quote:
Originally Posted by GoneNova/406
if you are going to replace the timing set (timing gear and chain?) then you can simply take the cam out and get the info off of it.you'll probably have to get all the numbers and have it in front of you when you call the cam companies but they will get you the info you need.then you will know everything about the motor and leave nothing to chance.its hardly any more work.you can try emailing the cam co's. but i have found that you get better results by talking directly to them.

There is a big differnce between replacing a timing set and pulling a cam..... isn't there?

*******************

14 in vacuum at 900 rpm? That is not a radical cam that would make 120 psi. Your static compression is probably very low.

What is your ignition timing at 900 rpm? Are you running ported or manifold vacuum to the can?

Sounds like your distributor is worn out, and you need new valve springs too. If you are floating the valves at 5100, there must be harmonic valve bounce at ridiculously low rpms.
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