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Old 10-27-2012, 11:55 AM
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Cam Lobe Lift Numbers

I need some advise/opinion regarding whether or not you think there would be any noticeable loss of power due to the lobe lift on the #2 cylinder exhaust lobe?

The cam is in the motor which is in the car.

All measurements done with a magnetic dial indicator with the rocker arms off and the dial set up in the oiling hole at the pushrod end.

Cylinder # Intake Lift Exhaust Lift
1 .301 .323
2 .310 .285 (possible problem)
3 .308 .324
4 .314 .325
5 .308 .323
6 .308 .327
7 .308 .324
8 .311 .324

I am getting ready to swap a set of Vortec's onto this 350 and I was trying to get the lift numbers off of the cam. The car is a '74 Nova, 3 speed Saginaw trans (manual), 3.08 rear gear.

If you guys don't think the low lift reading on #2 is a big issue then I will button it up with the vortec heads and intake and see how she runs. If I don't like it then I will swap the cam later. The car is just a weekend street cruiser that will never see the track but will see spirited driving from time to time.

Thanks

Jon

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Old 10-27-2012, 12:22 PM
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You might want to check that lobe very carefully as it could be on it's way out meaning it's going flat. The lift on that lobe is quite a bit lower than the rest which indicates something's amiss and If I were you I'd want to find out why as if you swap heads then the cam goes flat you'll wish you'd changed it when you had the intake off for the head swap.
While it is true most of the run of mill cast in bulk cams have wrinkles in them, meaning the duration maybe slightly higher on a couple of lobes as well as the lift however it shouldn't vary by that much. If the cam is in fact going flat on that lobe then feel fortunate you caught it this early, as if you hadn't it would fill the engine with steel and cast iron particles which wipes out bearings and rings rather quickly and you'd be looking at a rebuild.
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Old 10-27-2012, 12:36 PM
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I agree with DoubleVision's advice. Check that lobe carefully again with the indicator ...if it is indeed coming up short then now would be the time to change out the cam/lifters before the real damage happens.

If it is bad, and you caught it like this ... head to the local Casino and win some cash...your luck is very up right now
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Old 10-27-2012, 03:08 PM
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I appreciate the advice guys. I checked and re-checked that lobe and it always came up short. I will replace the cam now versus later.
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Old 10-27-2012, 03:09 PM
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Either the cam is worn or the hyd lifter is collapsing.
Stock oem vortec heads need to use a cam with less than .460" lift or
modify for additional lift clearance at the guide boss.
Hand verify valvetrain clearance @ full lift with all cams over .450" valve lift , on stock vortecs.

The GM bowtie vortecs already have all the valvetrain upgrades for high valve lift
and true hi perf cams, and high lift they flow more and are much better castings too.

When you change the cam be sure to deglaze/deburr the lifter bores to ensure lifter rotation.
Pulling worn lifters out up thru the lifter bores is enough to burr the bottom edge of the lifter bore and scratch the lifter bore.
If the lifter faces/face edge is rolled. ( cannot get the lifter out without force) do not force. Lift up all lifters and pull the cam out. with the cam out, push all lifters down out the the bores into the oil pan. remove the oil pan and remove lifters.
Inspect all lifter bores ,especially the bottom edge of the bore.
Your new cam + lifters will fail if the lifters cannot rotate.

For flat tappet hyd or solid cams:

Consider a high quality new Isky flat tappet Cam and lifter set. If you don't see exactly what you want in the catalog
or want a custom version of a catalog cam....or need selection advice , call them and custom order.
Lots of cool stock vortec head compatable .450" lift cams. and more....
They work really well.

www.iskycams.com

The 3.08's are about as much fun on the street, as watching paint dry.

Last edited by F-BIRD'88; 10-27-2012 at 03:24 PM.
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Old 10-28-2012, 10:13 AM
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Cast iron Camshafts are induction hardened to a depth of .010". You indicate that the exhaust lobe on #2 is down by .042". The cam may last a hundred miles or a thousand miles before the valve quits opening, depending on type oil, cam lobe oiling and valve spring pressure.

Normally cam lobes will wear from .005" to .008" back in the days when valve spring pressure could be as high as 300 - 350 lb. over the nose and motor oil had ZDDP. In 1973, GM eliminated the "spit-hole" in the side of the rod caps in order to reduce oil spray on the cylinder walls in an effort to reduced pollution. Unfortuantely, that also reduced the oiling of the cam lobes. Also starting in 1973, zinc compound additives were being phased out. In an attempt to solve the problem of premature camshaft wear due to lack of oiling, the automakers first reduced the valve spring pressure to 240 lb. or less over the nose and in 1986 they finally introduced hydraulic roller camshafts. In 1986, the automakers and aftermarket camshaft grinders introduced a new camshaft heat treatment process called SADI (Selectively Austempered Ductile Iron) for the hydraulic roller cam lobes and the distributor drive gear. A melonized (case hardened) distributor driven gear was also introduced.

Unfortunately, the days of flat tappets and bone crushing valve spring pressure are over thanks to the EPA.

Last edited by MouseFink; 10-28-2012 at 10:32 AM.
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Old 10-28-2012, 02:50 PM
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Quote:
Originally Posted by JonnyRed View Post
I appreciate the advice guys. I checked and re-checked that lobe and it always came up short. I will replace the cam now versus later.
To accurately read the lobe lift on an assembled engine, you need a solid lifter or a tool that replaces the lifter and allows a direct measurement of the lobe lift (example below). Using a hydraulic lifter can skew the measurement if the lifter's plunger-to-body clearance is slightly excessive or if the check valve is allowing oil to escape.

You will get a more accurate measurement by eliminating the rocker arm from the equation, too. If you have a roller trunnion rocker, this is much less of a problem than if you are using stamped steel rockers- they can be all over the place, ratio-wise. But measuring the lift at the valve instead of off the lobe isn't as accurate, regardless.


Tool is assembled using the adapter for a roller lifter. The flat tappet adapter is to the left.
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Old 10-28-2012, 08:15 PM
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Pulled the cam today and found that it is a Elgin E1211P with the following lobe lifts:

Intake: .311
Exhaust. .325

The dial indicator method was very close in most readings.

Still going to replace the cam due to the lobe lift on #2 exhaust lobe.

Thanks for all the advice.
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