I've been wondering for a long time why the stock 2.8L HO cam specs that are posted various places on the web look wrong. Now I know. I've had an '87 V6 engine with almost zero miles (don't ask - it's a long story) in my garage for YEARS, and I finally got around to actually putting a degree wheel on it and measuring the cam. I found actual #1 cylinder TDC using a dial indicator on the piston top because I didn't want to just trust the harmonic balancer marks. Here's what I measured (3 times with all falling within 1 degree each time):

Measurements @ 0.050" lobe lift (measured at the lifter):
Intake duration: 196 deg.
Exhaust duration: 201 deg.
Intake opens @ 12 deg. ATDC
Exhaust opens @ 28 deg. BBDC
Intake closes @ 28 deg. ABDC
Exhaust closes @ 7 deg. BTDC
Intake centerline: 110 deg. ATDC
Exhaust centerline: 108 deg. BTDC
Lobe separation: 109 deg. (calculated)
Intake total lift: 0.263" at the lifter
Exhaust total lift: 0.272" at the lifter

At .005" lobe lift I measured the following durations (these should be similar to "advertised" durations, which some cam companies take at .004" and some at .006" lobe lift):
Intake 255 degrees
Exhaust 275 degrees
I calculated 55 degrees of overlap at .005" lobe lift.
Note: The .005" measurements were a little more difficult to repeat, so I wouldn't bet the farm on them.

I also happen to have a 3100 SFI V6 out of a '94 GP torn down in my garage, so I measured the roller cam while I was measuring stuff. I think this cam is the same used on the 3400 SFI, but can't be sure. I've never found cam specs on this cam on the web, so I thought this would be interesting. The results are below. Please be aware that I already removed the pistons from this engine, so I had to trust the harmonic balancer mark for setting up the initial #1 TDC mark on the degree wheel. There is a possibility that all of these are off by 1 - 2 degrees, but all would be in the same direction. I also repeated these measurements 3 times and they were very consistent. Anyway, here's what I got:

Measurements @ 0.050" lobe lift:
Intake duration: 196 deg.
Exhaust duration: 196 deg.
Intake opens @ 17 deg. ATDC
Exhaust opens @ 28 deg. BBDC
Intake closes @ 33 deg. ABDC
Exhaust closes @ 12 deg. BTDC
Intake centerline: 115 deg. ATDC
Exhaust centerline: 110 deg. BTDC
Lobe separation: 112.5 deg. (calculated)
Intake total lift: 0.271" at the lifter
Exhaust total lift: 0.270" at the lifter

At .005" lobe lift I measured the following durations:
Intake 260 degrees
Exhaust 259 degrees
I calculated 33 degrees of overlap at .005" lobe lift.

Note that the Fiero engine has 1.5 rockers, but the 3100 has 1.6 rockers, so the lift at the valve is much higher on the 3100. The overlap is also much lower on the 3100, so that at least partially explains why they idle so smooth compared to the Fiero V6.

FWIW!

John

I don't have my books handy, but I am pretty sure that the "big runner" 3x00s received a bigger camshaft. 99+ or something.

That could be. The 3100 I have is the small port version.

Thanks.

John

Also, in my experience roller cams have much steeper ramps so though the timing may be similar the actual "area under the curve" time that the valve is open is significantly higher. It's like opening a door and closing it slowly vs slamming it open and closed.

For reference, the published specs for the Fiero cam are 196/203° @ 0.050" and .394/.410 lift intake/exhaust @ valve.

JazzMan

[This message has been edited by JazzMan (edited 01-04-2008).]